ZEISS Technology A Collection of Studies and white papers.

// DISPENSING TOOLS & INSTRUMENTS MADE BY ZEISS

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Technology by ZEISS 3

// 1 Exam and Refraction

Most Strongly Recommended:Polatest Visual Testing Instrument Designed by Haase

Friedrich Lorch, M.D. Article published in the Magazine for Practical Ophthalmology (Zeitschrift für praktische Augenheilkunde) 13:399-400 (1992) 4

The Evolution of Refraction: i.Profi ler® plus with i.Scription® technology.

White paper by Darryl Meister, ABOM Carl Zeiss Vision and Larry Thibos, PhD Indiana University (2010) 6

i.Scription® Clinical Study

Report on the clinical study performed by Carmel Mountain Vision Care, published in the Review of Optometry (2013). 14

// 2 Lens Fitting and Consultation

Standard Spectacle Lens Fitting

Article written by Darryl Meister, ABOM Carl Zeiss Vision (2010) 18

// 3 Technical data

i.Polatest® 22

i.Profi ler® plus 22

i.Terminal® 2 23

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The advances in technology, data transfer and communication channels characterizing

our world today have transformed our daily lives, and the field of eyecare is no

exception.

ZEISS has found a way to make these technological advances accessible to eye care

professionals and their patients through state-of-the-art instruments, such as the

i.Polatest®, i.Profiler® plus and i.Terminal® 2.

Not only do these instruments deliver precise results to optimize your patient´s visual

performance, but they also allow you to experience faster and more reliable data

management throughout your practice.

ZEISS dispensing tools have been the subject of many different tests and studies,

which have yielded very good results on their innovative qualities and reliability. This is

a collection of articles and white papers published in a wide range of media, aimed at

providing more in-depth technical information on ZEISS instruments.

Discover how instruments such as i.Polatest®, i.Profiler® plus with i.Scription technology

along with i.Terminal® 2 deliver on our promise of excellence and superior value for

you and your patients.

As one of the pioneers in optical technology, ZEISS offers innovative systems for measuring and fitting in today’s fields of eyecare. Besides providing solutions for your practice, ZEISS instruments support you in delivering a fully remarkable consultation experience for your patient.

Technology by ZEISS

i.Polatest®i.Profiler® plus i.Terminal® 2

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// 1 Exam and RefractionMost Strongly Recommended:Polatest Visual testing Instrument Designed by HaaseFriedrich Lorch, M.D. Article published in the Magazine for Practical Ophthalmology (Zeitschrift für praktische Augenheilkunde) 13:399-400 (1992)

In his letter to the editor “Normosensory

late onset strabismus” (ZPA 13: 145-

146/1992) Professor Lang attacks the

Polatest lobby and calls it “blatant

therapeutic wishful thinking”. This

accusation prompted me to write my

own letter to the editor reporting the two

years of experience that I gained from

an unbiased exposure to the Polatest

Visual Testing Instrument manufactured

by ZEISS according to the correction

recommendations of H.J. Haase.

Early in 1990 I received an invitation to

the Congress of the International Union

for Binocular Full Correction (IVBV) in

Stuttgart. The subject of the conference,

dyslexia, interested me. Because I was

unfamiliar with some of the vocabulary,

I was unable to understand much of the

material that was reported. But the results

of the heterophoria corrections were so

impressive that I most certainly wanted to

become more involved with the method.

After all, in my practice I saw at least

3-4 patients every day for whom I had

the feeling that I could not explain their

asthenopic symptoms, let alone resolve

them. It was with a sense of failure that I

had abandoned the training therapy that

had been possible in a few appropriate

cases which I had undertaken in the fi rst

years of my practice.

As I studied the literature on the correction

method according to H.J. Haase, it became

clear to me that I would be needing some

introductory seminars on binocular full

correction. As a doctor predominantly

oriented towards natural science, in the

fall of 1990 I started with binocular full

correction using the Polatest Visual Testing

Instrument without any therapeutic wishful

thinking and was thoroughly skeptical. My

assistants were my fi rst “test subjects”.

As one of them had complained of

daily headaches since childhood which

could not be explained by any medical

discipline as an experiment I prescribed

the prismatic correction I had established,.

Only 2 weeks after she received her glasses,

the headaches had disappeared, much to

our surprise. But they always came back

whenever, as an experiment, the glasses

were not used.

With this as motivation, I started to

prescribe full prismatic corrections for

patients with asthenopic symptoms with

increasing frequency. The numerous

successes were so encouraging that I gladly

accepted the considerable extra workload.

Today I can no longer imagine my daily

practice without the Polatest Visual Test

Instrument.

I have recorded the statistics of my full

prismatic correction “cases”. Here are the

most important results:

cm/m (n = 166)

0 - 0.75 36%

1 - 2.25 40%

2.5 - 4.75 21%

5 - 7.25 3%

Table 2: Distribution of vertical phorias

Of 198 patients:

73.3% were vertical esophorias

19.1% were vertical exophorias

3.5% were vertical phorias

3.5% were esophorias

0.6% were exophorias

Table 3: Distribution of vertical phorias

cm/m (n = 166)

0 - 1.75 24%

2 - 4.75 28%

5 - 4.75 21%

10 - 14.75 10%

15 - 19.75 4%

20 - 24.75 4%

25 - 29.75 3%

30 - 39.75 1%

gr. 40 5%

Table 1: Distribution of horizontal phorias

The large portion of phorias over 10 cm/m

are noticeable (Tables 1 and 2). Frequently,

these are patients that show only a slight

deviation or none at all, with the classic

methods such as an alternating cover test.

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Furthermore, work with the Polatest Visual

Testing Instrument shows that also small

heterophorias that cannot be detected

using the classical methods often cause

signifi cant problems. Very few exophorias

are to be found using the Polatest Visual

Testing Instrument (Table 3). In at least

21% of the heterophorias corrected in

the Polatest, the Maddox or alternating

color test would have lead to the wrong

direction. This does not even include those

cases in which these tests would not have

provided any conclusion.

Measured against many therapies in

medicine, the success rate of prismatic full

correction is very gratifying (Table 4).

Although so many positive things are

reported on the work with binocular full

correction according to H.J. Haase, it must

also be said that it is a very time-consuming

method, when applied correctly: A

binocular measurement and correction

phase, which lasts on the average at

least 45-60 minutes, follows the exact

monocular refraction. At present I perform

full prismatic corrections on 3-4 patients

every day; this cannot be integrated into

an already excessively long practice day

without considerable additional overtime.

In addition, the fi nancial losses are also

considerable. Nonetheless, I consider

H.J. Haase’s Polatest procedure to be

so revealing that it is worth the effort.

Unlike the synoptophore, it offers not

only diagnostic insights but also provides

valuable correction values at the same

time. For the optometrist that likes to get

involved with problems of binocular sight

himself and does not want to delegate

these cases to his orthopist, work on

the Polatest is always interesting. When

forced to participate in intensive case

history discussion, it becomes obvious

that many patients suffer considerably

from binocular problems. Thus the good

results of binocular full correction are all

the more satisfying and compensate for

the considerable workload and fi nancial

losses, at least in theory.

In the last 12 years of my practice I have

never had so much enjoyment from

my work as I have since I started using

“Polatesting”. To all my colleagues who

are self-critical and willing to take on a

new way of thinking, to jump beyond

their shadows and prescribe prisms in

high values as well, to perform refractions

– especially using a trial frame – and

are willing to make considerable time

and fi nancial sacrifi ces, I most strongly

recommend working with the Polatest

Visual Testing Instrument.

However, a basic, theoretical and practical

training course, as offered in seminars by

the IVBV and others, is indispensible. Such

training courses are also recommended

for later. The successes will be self-

evident despite all skeptical reservations.

“Therapeutic wishful thinking” is not

necessary. This is needed only by the

therapeutically unsuccessful.

Dr.med.Dipl.-Biochem. Friedrich Lorch:

“Wärmstens zu empfehlen:

Polatest-Sehprüfgerät nach Haase”

Zeitschrift für praktische Augenheilkunde

13:399-400 (1992)

Symptoms

n disappeared

% still seldom

% better

% unchanged

% worse

%

Visual problems up close 60% (81) 73 17 5 5 0

Forehead and periorbital headaches 48% (64) 73 16 6 5 0

Visual problems at a distance 22% (29) 72 17 4 7 0

Other headaches 18% (24) 54 33 8 5 0

Blinking, burning, foreign body sensation 10% (13) 62 23 8 8 0

Night driving problems 8% (10) 60 20 0 20 0

Near/far adjustment 5% (7) 28 57 0 15 0

Tears with visual strain 4% (6) 83 0 17 0 0

Neck pains 2% (3) 100 0 0 0 0

Sensitivity to glare during the day 2% (3) 33 67 0 0 0

Sensitivity to glare at night 0,7% (1) 100 0 0 0 0

Reduced amplitude of accommodation 0.7% (1) 100 0 0 0 0

Dizziness 0.7% (1) 100 0 0 0 0

Table 4: Symptoms of 134 patients undergoing full prismatic correction and changes in symptoms 8 weeks later

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Traditionally, the fi nal or manifest

refraction that serves as the basis for an

eyeglass prescription is the result of a two-

part process: The refractive errors of the

eye are fi rst estimated objectively, using

either retinoscopy or an autorefractor,

and then the prescription is subjectively

refi ned by comparing the vision of the

patient through trial lenses, using either

a refractor head or trial frame. Many

of the tools and techniques commonly

used during refraction procedures have

remained largely unchanged for over a

century, since the pioneering work of

Donders, Jackson, Copeland, and others.

Even today, with the widespread use

of sophisticated autorefractors and

photorefractors, manual subjective

refraction is still considered the “gold

standard” by clinicians. Nevertheless,

traditional subjective refraction techniques

suffer from certain inherent limitations. In

particular, subjective refraction procedures

often attempt to simulate ideal viewing

conditions by using a brightly-illuminated,

high-contrast visual acuity chart under

normal room lighting, which causes the

pupil of the eye to remain relatively small

in diameter. Because a small pupil size

restricts focusing to the central “paraxial”

region of the eye, the infl uence of ocular

aberrations upon vision is decreased,

while variation in subjective responses

from the patient due to the depth of

focus of the eye is increased.

// 1 Exam and RefractionThe Evolution of Refraction: i.Profi ler® plus with i.Scription® technology.White paper by Darryl Meister, ABOM Carl Zeiss Vision and Larry Thibos, PhD, Indiana University (2010)

Now, with the recent advent of

commercially-available aberrometers,

which measure the “wavefront”

aberrations of the eye, new enabling

technologies may fi nally elevate the

standard of refractive eyecare for

the fi rst time in decades. Evaluating

the wavefront aberrations of an

optical system has already become

commonplace in high-performance

optical fi elds such as astronomy.

There has been increasing interest in

the ophthalmic applications of this

technology, driven by advances in laser

refractive surgery.

Figure 1.

i.Profi ler® plus by ZEISS is

a “3-in-1” instrument

that incorporates the

functionality of an

aberrometer, corneal

topographer, and

autorefractor in a fast,

compact, and easy-to-use

system.

Refractive surgeons can now reduce

more of the wavefront aberrations of

the eye, in addition to the traditional

spherical and cylindrical refractive errors,

in an effort to achieve supernormal vision

with better than average visual acuity.

Although the “high-order” wavefront

aberrations of the eye cannot be

eliminated with a spectacle lens, without

introducing even greater aberrations

when the eye rotates behind the lens,

instruments such as i.Profi ler® plus by ZEISS

have made possible a new generation

of vision correction solutions that

should yield improved clinical outcomes

(Figure 1).

Aberrometry is elevating the standard of refractive eyecare by allowing clinicians to evaluate the optical characteristics of the eye more thoroughly, includi ng both low-order and high-order wavefront aberrations.

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OBJE

CT P

OINT

AT I

NFIN

ITY

IDEALWAVEFRONT

SINGLEPOINTFOCUS

ABERRATEDWAVEFRONT

ERROR

SPREADOF

FOCUS

OBJE

CT P

OINT

AT I

NFIN

ITY

B

A

Wavefront Aberrations

The propagation of “light” has been

described as a rapid movement of energy

particles – or photons – that travel in

a wave-like manner. The propagation

of light from an object point can be

represented conceptually using either

rays or waves emanating outward from

the light source. Just as rays of light

diverge from an object point, waves

of light spread out like ripples of water

traveling away from a stone that has

been dropped into a pond. At any given

distance from the original object point,

a wavefront exists that represents the

envelope bounding waves of light that

have traveled an equal distance from the

object.

As the distance from the object

increases, the curvature of these

wavefronts becomes progressively

fl atter, eventually appearing fl at beyond

“optical infi nity” (6 meters). The object

point serves as the common center

of curvature of these wavefronts.

Conversely, light converging to a point

focus can be described using spherical

wavefronts that become progressively

smaller, converging to the image point.

Further, a ray of light from the same

object point remains perpendicular to

the corresponding wavefront as both

propagate away from the object or

toward the image (Figure 2).

An aberration is essentially an error

in focus. There are several ways to

characterize the aberrations produced by

a lens or optical system. In geometrical

optics, ray tracing is often utilized to

calculate the path of a bundle of rays

from an object point as the rays are

refracted at the various surfaces of each

lens or optical element. Aberrations

are then determined by calculating the

distance of these refracted rays from

the intended focal point. Alternatively,

the deformation of the corresponding

wavefront of light as it passes through

the optical system may be also

determined.

In a perfect optical system, wavefronts

of light from an object point should

converge to a single point focus at

the desired image location, such as

the retina of the eye, after refraction

through the system. In the presence of

focusing errors or aberrations, however,

these wavefronts become either too

steep, too fl at, or distorted from their

ideal shape. Accordingly, the rays of light

corresponding to these wavefronts are

spread out at the plane of the desired

focus, instead of intersecting at a single,

sharp point. Consequently, optical

aberrations may be represented using

rays, wavefronts, or even the spread

of light intensity at the image plane

(Figure 3).

At any point across the aperture of

the optical system, such as the pupil

of the eye, the wavefront error is the

effective optical separation between

the actual wavefront and the ideal

spherical wavefront centered on the

desired focal point. Wavefront errors

are usually expressed in micrometers or

microns (mm), which are equal to one-

thousandth of a millimeter (0.001 mm).

For simple wavefront aberrations,

differences in curvature between the

aberrated and ideal wavefronts may

also be used to quantify the aberration.

The curvature of a wavefront, expressed

in diopters, is simply equal to the

reciprocal of its radius of curvature, in

meters. The sphere and cylinder powers

of a prescription actually indicate the

differences in curvature between the

aberrated and ideal wavefronts of

the eye. For more complex wavefront

aberrations, curvature, alone, does not

suffi ciently characterize the aberration.

Figure 2. Light diverging from an object point or

converging to an image point can be represented

using either rays or wavefronts representing the

envelope that bounds waves of light that have

traveled in unison or phase.

Figure 3. An optical system should produce

wavefronts of light that eventually converge to

the intended point focus (A), although wavefronts

of light do not converge to a sharp focus at the

desired point in the presence of aberrations (B).

WAVEFRONT

DISTANCE FROM OBJECT OR IMAGE POINTEQUALS RADIUS OF WAVEFRONT CURVATURE

WAVERAY

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Zenike Polynomial Series

Quantifying more complex wavefront

aberrations often relies on more

descriptive mathematics. Once the

wavefront errors have been measured

across the aperture (or pupil) of an

optical system, these measurements

can be “modeled” mathematically

for easier analysis and manipulation.

Most commonly, the shape of an

aberrated wavefront is modeled by

“fi tting”– or closely approximating –

the measurements with a series of

polynomial functions using mathematical

curve fi tting techniques. This allows

even complex wavefront aberrations

to be represented as a combination of

more basic shapes, often associated with

traditional optical aberrations.

The Zernike polynomial series is

commonly used to fi t wavefront

measurements. This is a set of functions

that each represent individual optical

aberrations, known as modes. Zernike

polynomials are typically grouped by

their radial order, which indicates how

rapidly the aberration increases with

pupil size (Figure 4):

• Low-order aberrations include

defocus and astigmatism, broken into

components at axis 45/135 (oblique)

and at axis 180/90 (WTR/ATR), which

are associated with the spherical and

cylindrical refractive errors of the eye,

respectively.

• High-order aberrations include

third-order aberrations, such as coma

and trefoil, fourth-order aberrations,

such as spherical aberration, and

aberrations of successively higher

radial orders, which increase more

rapidly as the pupil size increases.

Low-order aberrations are detrimental

to vision quality at both small and

large pupil sizes. These aberrations

are typically corrected by eliminating

the refractive errors of the eye using

sphero-cylindrical lenses. High-order

aberrations become more detrimental

to vision quality when the pupil size is

large. Although often less severe than

the low-order aberrations of an eye,

these aberrations can also degrade

visual acuity and reduce image contrast

(Figure 5).

Figure 5. Low-order aberrations degrade vision

quality even at smaller pupil sizes, whereas

high-order aberrations become more detrimental

at larger pupil sizes.

LARGE (6 MM) PUPIL SIZESMALL (3 MM) PUPIL SIZE

LOW

-ORD

ERAB

ERRA

TION

HIGH

-ORD

ERAB

ERRA

TION

Figure 4. Complex wavefront aberrations can be represented as a combination

of Zernike polynomial functions or “modes”:

• Each mode has a coeffi cient that specifi es the magnitude of the aberration in the wavefront.

• A wavefront is reconstructed by adding together quantities of the various modes.

• Modes are grouped by their radial order, which indicates the “power” of the function.

• Radial orders are whole numbers that begin with the zeroth order and continue indefi nitely.

• The total number of modes in each subsequent radial order increases by one mode.

• Modes in the second order are associated with spherical and cylindrical refractive errors.

• Modes in zeroth and fi rst radial orders are typically ignored in calculations of image quality.

NORMAL QUATREFOILOBLIQUE QUATREFOIL SPHERICAL ABERRATIONOBLIQUE SECONDARY ASTIG WTR/ATR SECONDARY ASTIG

VERTICAL COMA HORIZONTAL COMAOBLIQUE TREFOIL WTR/ATR TREFOIL

OBLIQUE ASTIGMATISM DEFOCUS WTR/ATR ASTIGMATISM

VERTICAL TILT OR PRISM HORIZONTAL TILT OR PRISM

RADI

AL O

RDER

Z 11Z -1

1

TRADITIONALEYEGLASS

PRESCRIPTION

1ST

2ND

3RD

4TH

Z -22 Z 2

2Z 02

Z 13Z -1

3Z -33 Z 3

3

Z -44 Z -2

4 Z 04 Z 2

4 Z 44

LOW

ORD

ERHI

GH O

RDER

IGNORED INIMAGE QUALITYCALCULATIONS

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Limits of Subjective Refraction

Subjective refraction is a clinical

procedure that determines the optimal

prescription for correcting the refractive

errors of an eye by having the patient

compare vision quality through different

spectacle lens powers, after establishing

an estimate of the refractive status of the

eye using objective refraction. Although

the subjective refraction is considered

the “gold standard” for judging the

accuracy and precision of objective

methods for performing refraction, the

outcome can vary between different

clinicians and between repeated

measurements by the same clinician.1

On average, refractions performed

by different clinicians agree to within

±0.12 D, but for individual patients the

discrepancies can be much larger (95%

limits of agreement = -0.90 to +0.65 D).2

This variability is due to a variety of

factors. The patient may use different

perceptual criteria when choosing

between lenses, such as sharpness,

contrast, or legibility. The depth of focus

of the eye may make it diffi cult for the

patient to discriminate between small

changes in image quality. The ideal

refraction will often vary with pupil size

and, therefore, luminance levels in the

presence of high-order aberrations. With

irregular corneas, sphere and cylinder

powers can vary by up to 1.00 D or

more between 3 mm and 7 mm pupil

sizes.3 Rounding errors due to the use of

trial lenses in 0.25-diopter steps limit the

precision of the refraction to ±0.12 D.

Moreover, high-order aberrations may

result in irregular astigmatism or multiple

combinations of cylinder power and axis

that yield relatively good vision quality.

Although the Jackson cross-cylinder

technique will isolate one of these local

maxima of vision quality, the technique

may not necessarily converge to the

combination of cylinder power and axis

that yields the best vision quality or global

maximum (Figure 6). Thus, the variability

of subjective refraction undermines any

attempt to validate objective refraction

techniques, because the “gold standard”

is, in effect, a “moving target.”

Although conventional vision corrections

are intended to correct only the low-

order aberrations of the eye, the optimal

sphere and cylinder powers for these

corrections are infl uenced by higher-

order aberrations. In the presence

of ocular high-order aberrations, the

vision correction that maximizes the

focus of paraxial rays of light passing

through the central region of the pupil

will differ from the vision correction

that maximizes the focus of marginal

rays passing through the periphery

of the pupil. Further, both vision

corrections will suffer from residual

blur (Figure 7). Maximum retinal image

quality will actually be achieved when

blur is minimized using a balanced vision

correction that represents a compromise

between the defocus of the paraxial rays

and the marginal rays.

In fact, experiments have shown that

patients typically judge the optimal focus

as lying somewhere between the paraxial

focus and the marginal focus.4 Because

subjective refraction often involves

viewing conditions that serve to restrict

the pupil size, however, this procedure

favors the paraxial focus. Additional

information regarding the high-order

aberrations of the eye should be applied

in order to compute a sphero-cylindrical

vision correction that optimizes image

quality for the entire pupil. Determining

the size of the patch of blur produced on

the retina is one such method, but there

are many ways to quantify image quality,

each emphasizing a different aspect of

the optical system and resulting image.

Because the patient ultimately decides

whether one retinal image is better than

another, the best metric of image quality

should refl ect the image processing

characteristics of the human visual

system.

Figure 6. In the presence of high-order aberrations,

a polar plot of retinal image quality as a function

of cylinder power may reveal multiple combinations

of cylinder power and axis that yield “good”

vision quality, although the Jackson cross-cylinder

technique may not necessarily converge to the

“best” vision correction.

Figure 7. Because ocular high-order aberrations,

such as spherical aberration, cause the best vision

correction for focusing the paraxial rays (A) to differ

from the best correction for focusing the marginal

rays (B), the ideal vision correction for the entire

pupil typically represents a compromise between

these two extreme cases.

PARAXIALFOCUS

OBJE

CT P

OINT

AT I

NFIN

ITY

MARGINALFOCUS

OBJE

CT P

OINT

AT I

NFIN

ITY

SPHERICALABERRATION

WEAKERMINUS LENS

STRONGERMINUS LENS B

A

045°

135°

180°090°

BESTVISION

WORSTVISION

2D

2D

060°

150°

075°

165°

030°

120°

015°

105°

1D

LOCALMAXIMUM

GLOBALMAXIMUM

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Wavefront-guided Objective Refraction

An aberrometer measures the wavefront

aberrations of the eye. Just as topographers

now provide more detail regarding the

surface characteristics of the cornea than

conventional keratometers, aberrometers

now capture more detail regarding the

refractive characteristics of the eye than

conventional autorefractors. Autorefractors

typically measure only the low-order

aberrations of the eye over a small region of

the pupil, roughly 3 mm in diameter, which

essentially restricts light to the paraxial

region of the eye. Aberrometers, on the

other hand, measure both the low-order

and high-order aberrations of the eye over

the entire pupil.

Many aberrometers utilize a Shack-

Hartmann wavefront sensor. A point source

of light – representing a distant object – is

projected onto the retina. The retinal

image of this point source then serves as

the object point for measurement. After

leaving the eye, light from this object point

passes through an array of small lenslets

that sample the optics of the eye over the

entire pupil. Each lenslet brings light to a

focus on a CCD sensor. Ideally, light from

the retina should produce a plane (fl at)

wavefront after passing back through

the optics of the eye. Any differences

between the plane wavefront and the

actual wavefront exiting the eye will cause

light to deviate as it passes through the

lenslets. The displacement of each focus

is then measured and used to model the

wavefront errors (Figure 8).

Once the wavefront errors have been

modeled, often using the Zernike

polynomial series, a vision correction can

be determined. Because the eye remains

in a constant state of movement, it is

not feasible to correct the high-order

aberrations of the eye with a spectacle

lens. A conventional sphero-cylindrical

vision correction eliminates the low-order

aberrations of the eye. Nevertheless, it is

possible to determine a wavefront-guided

vision correction using a combination of

conventional sphere power and cylinder

power that minimizes the blur that results

from the interaction between the low-

order and high-order aberrations.

For instance, approximating a map of the

vergence errors over the pupil of the eye

with the best-fi tting sphero-cylindrical

map is a simple way to determine an

ocular wavefront refraction.5 Alternatively,

diffraction and interference effects can

be taken into account by approximating

a map of the wavefront errors over the

pupil.6 Other methods are available

to determine the optimal wavefront

refraction as well. The refraction can

be determined by iteratively optimizing

the optical quality of either the retinal

image of a point source using the point

spread function or the image of sinusoidal

gratings using the modulation transfer

function.

These functions can be manipulated in a

variety of ways to develop novel measures

of optical quality. Some especially useful

metrics, such as the Strehl ratio, have

even been modifi ed to account for

the early stages of visual processing.

Furthermore, other criteria may also prove

benefi cial when optimizing a wavefront-

guided vision correction. For instance,

experiments have shown that observers

prefer a vision correction that maximizes

the area of the pupil for which the

vergence errors or the wavefront errors

are negligible.7

Although refractive errors are determined

clinically for distant objects, in everyday

life the eye must form the retinal image

for objects at a variety of distances,

simultaneously. Thus, providing a large

depth of focus is arguably more important

than optimizing the focus for any single

viewing distance. This is why the ZEISS

VoluMetric merit function was developed

to optimize the three-dimensional image

intensity produced in the vicinity of the

focus of the lens-and-eye combination.

Rather than limiting attention to a single

focal plane, this function integrates

the beam intensity along the depth

of the focus in addition to the cross-

sectional area in order to minimize

the volume of blur. The VoluMetric

function therefore provides a superior

wavefront refraction that is less sensitive

to the frequent fl uctuations in viewing

distance, accommodation, and pupil

size encountered throughout the day

(Figure 9).

POINT ONRETINA

ERRO

R

ABERRATIONS OF EYEDISTORT WAVEFRONT

CCDSENSOR

LENSLET FOCUSDISPLACED ON CCD

LENSLETARRAY

MINIMUMBLUR VOLUME

WAVEFRONTWITH SPHERICAL

ABERRATION

OPTIMUMFOCUS

WAVEFRONT-GUIDEDVISION CORRECTION

Figure 8. Many commercial aberrometers, like

i.Profi ler® plus by ZEISS, use a wavefront sensor that

is based on the Shack-Hartmann principle, which

measures the focusing errors of an array of small

lenslets caused by the distorted wavefront originating

from a point on the retina at the back of the eye (not

to scale).

Figure 9. The ZEISS VoluMetric merit function utilized

to calculate a wavefront-guided i.Scription® seeks

a combination of sphere and cylinder power that

minimizes the three-dimensional “volume” of a

focus distorted by high-order aberrations in order to

maximize vision quality as well as the depth of focus

of the eye.

10 29.08.2013 04:49:15

11

i.Scription® Technology by ZEISS

Traditional subjective refractions

are often performed under viewing

conditions involving luminance levels

that result in relatively small pupil sizes.

Ambient light levels vary considerably,

however, between photopic (or daytime),

mesopic (or twilight), and scotopic (or

nighttime) viewing conditions. Although

most light adaptation occurs within

the retina, the size of the pupil varies

inversely as a function of luminance,

becoming smaller as luminance increases

in order to control retinal illumination

and to maximize retinal image quality.

The pupil size varies from a minimum

of roughly 2 during photopic vision to

a maximum of roughly 8 mm during

scotopic vision (Figure 10).8 Because of

the increasing dependence on pupil size

of the aberration modes in higher orders,

the infl uence of high-order aberrations

upon the ideal vision correction increases

at low luminance levels when the pupil

size is large.

Although the low-order, sphero-

cylindrical refractive errors will remain

relatively constant in the absence of

high-order aberrations, regardless of

pupil size, all eyes suffer from at least

some high-order aberrations. Normal

eyes have on average a root-mean-

square error (RMS) of 0.33 mm for

high-order aberrations at a pupil size of

6 mm, which is roughly equivalent to

0.25 diopters of defocus.9 Determining

the endpoint of refraction by taking

into account the effects of high-order

aberrations on retinal image quality

may therefore result in superior sphero-

cylindrical vision corrections that deliver

optimal vision over a broader range of

luminance levels.

Using wavefront aberrometry data

captured by i.Profi ler® plus, the ZEISS

VoluMetric merit function calculates a

wavefront refraction with sphere and

cylinder powers that deliver the most

optimal vision quality over a range of

viewing conditions (Figure 11). The

clinician must then conduct a standard

subjective refraction as usual for

assessing binocular vision, performing

binocular balancing, and determining

the near addition. Lastly, the wavefront

refraction is reconciled against the

subjective refraction using a unique

subjective refi nement algorithm in order

to ensure that the spherical equivalent

of the fi nal refraction does not deviate

excessively from the subjective fi ndings.

The result of this patented process is

the patient’s i.Scription®: a precise,

wavefront-guided vision correction.

Because the VoluMetric merit function

maximizes depth of focus of the eye

based on the interaction between the

low-order and high-order aberrations,

i.Scription® should improve visual

performance under more demanding

viewing conditions. Wearers may

experience improvements in contrast

sensitivity, low-light vision, and

night driving due to a reduction in

“night myopia” caused by high-order

aberrations and the Purkinje shift in

ocular color sensitivity. Additionally,

wearers may experience a reduction in

the apparent effects of ocular chromatic

aberration.

Every i.Scription® spectacle refraction

comprises a sphere power, cylinder

power, and cylinder axis. Unlike traditional

eyeglass prescriptions, however, the

i.Scription® sphere and cylinder powers

are calculated to the nearest 0.01-diopter

step. Thus, i.Scription® is more precise

than a conventional prescription, which

can result in rounding errors of up to

±0.12 D due to the use of trial lenses

in 0.25-diopter steps. The use of more

precise prescription values further

enhances the optimized wavefront

refraction of i.Scription®.

LUMINANCE

PUPIL SIZE

10-6 10+6 10+810-4 10-2 100 10+410+2

7.9 2.0 2.07.5 6.1 3.9 2.12.5

STARLIGHT MOONLIGHT OFFICE LIGHT SUNLIGHT

MESOPIC PHOTOPICSCOTOPIC

CD/M2

MM

Figure 10. The pupil of

the human eye varies

from a minimum of

roughly 2 mm during

photopic vision to a

maximum of roughly

8 mm during scotopic

vision.

Figure 11. Conventional vision corrections

often provide optimal performance under ideal

viewing conditions (A), but may provide reduced

performance under more demanding conditions

due to high-order aberrations (B), whereas

i.Scription maximizes visual performance over a

broad range of viewing conditions (C).

OBJE

CT P

OINT

AT I

NFIN

ITYOB

JECT

POI

NT A

T INF

INITY

OBJE

CT P

OINT

AT I

NFIN

ITY

PUPIL BLOCKS HIGH-ORDER ABERRATIONS

REFRACTION AFFECTEDBY H-O ABERRATIONS

REFRACTION OPTIMIZEDFOR H-O ABERRATIONS

i.SCRIPTIONMODIFICATION

B

A

C

LOW-LIGHT VISION

EXAM ROOM VISION

11 29.08.2013 04:49:17

12

Precision Customized Lenses

Once an i.Scription® vision correction has

been determined, a spectacle lens must

be fabricated to the desired prescription

powers. Unfortunately, traditional

spectacle lenses often introduce

additional wavefront aberrations that

can compromise optical performance

and vision quality for the wearer

compared to the vision achieved during

the eye exam (Figure 12):

• Residual low-order aberrations occur

in traditional spectacle lenses because

of oblique astigmatism as a result of

either the tilt of the fitted lens (that is,

position of wear) or the angle that the

line of sight makes to the lens during

peripheral vision.

• Residual low-order aberrations also

occur in spectacle lenses due to the

power rounding errors inherent in

traditional lens surfacing, which

typically relies on hard “lap” tools

that are stocked in only 0.12-diopter

increments of surface power.

Traditional, semi-fi nished lens blanks

are typically available in only a handful

of unique base curves or lens designs,

which are factory-molded in mass

quantity. Changes to the basic design of

traditional spectacle lenses are limited to

subtle variations in optical design across

a small number of base curves that must

work suffi ciently well for relatively broad

prescription ranges. Traditional spectacle

lenses are therefore specifi cally designed

for a few “average” prescription powers,

using either “average” fi tting parameters

for progressive lenses or assuming a

fi tting condition free of lens tilt for

single vision lenses. The use of average

assumptions for each lens design results

in uncorrected low-order aberrations for

many wearers that can restrict, distort,

and blur the fi elds of clear vision.

Fortunately, the advent of free-form or

digital surfacing technology has freed

many lens designers from the constraints

of traditional, mass-produced spectacle

lenses. This modern manufacturing

platform relies on computer-controlled

generators that can precisely grind

surface curves of extremely high

complexity, including aspheric and

progressive designs, directly onto a semi-

fi nished lens blank.

Figure 12. Although vision through refractor-head

or trial-frame lenses may be clear (A), low-order

aberrations due to oblique astigmatism can occur

in fi tted spectacle lenses that will blur vision when

viewing through a lens that is tilted in front of the

eye (B) or when viewing through the periphery of

the lens (C).

Figure 13. Contour plots of ray-traced astigmatism demonstrate that the optics of traditional progressive

lens designs may be signifi cantly infl uenced by the position of wear, resulting in residual low-order

aberrations that can restrict, distort, and blur the zones of clear vision, whereas the fully-customized

lens designs utilized for i.Scription® lenses maintain the desired optical performance, regardless of the

prescription or position of wear.

LINE OF SIGHT AT ANGLETO LENS PERIPHERY

LENS AT ANGLETO LINE OF SIGHT B

C

A

+25+20+15+10+50–5–10–15–20–25

+25+20+15+10+50–5–10–15–20–25

+25+20+15+10+50–5–10–15–20–25

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

0.5 0.5

1.0 1.0

1.5 1.52.0

2.0

2.52.5

0.5 0.51.0

1.01.5

1.52.0

2.02.5

2.5

TRADITIONAL LENS DESIGNWITH SIGNIFICANT LENS TILT

+3.00 SPH RX: 15° PANTO & 15° WRAP +3.00 SPH RX: 15° PANTO & 15° WRAP

CUSTOMIZED LENS DESIGNWITH SIGNIFICANT LENS TILT

+3.00 SPH RX: NEGLIGIBLE LENS TILT

TRADITIONAL LENS DESIGNWITH “TRIAL FRAME” FITTING

EFFECTIVE RX:+3.00 SPH

EFFECTIVE RX:+3.51 –0.43 × 044

EFFECTIVE RX:+3.00 SPH

When combined with advanced optical

design software, free-form lens designs

can be calculated in “real time,” using

the wearer’s specifi c prescription and

fi tting parameters, immediately prior

to fabrication. Progressive and single

vision lens designs with i.Scription® by

ZEISS can therefore be fully customized

to the unique visual requirements of

the individual wearer. Customized

lenses preserve the intended optical

performance of the lens design by

minimizing residual low-order wavefront

aberrations, while ensuring that every

wearer enjoys the visual benefi ts of the

i.Scription® vision correction, regardless

of his or her prescription requirements

or position of wear (Figure 13).

Additionally, free-form surfacing is not

subject to the power rounding errors of

traditional lens surfacing.

12 29.08.2013 04:49:17

13

Clinical Proven Performance

Several clinical studies have demonstrated

the effi cacy of i.Scription® for improving

vision at night, color perception,

and contrast sensitivity, without

compromising visual performance

during normal viewing conditions.10 A

randomized, double-masked clinical study

comparing i.Scription® to conventional

spectacle refractions was conducted

at InSight Eyecare, an independent

optometric clinical research facility near

Kansas City, Missouri. This wearer trial

utilized a crossover design in which each

of 40 subjects wore a pair of ZEISS single

vision lenses with i.Scription® and a

pair of conventional single vision lenses

for one week each, in random order. A

variety of objective measures of visual

performance and subjective measures

of wearer preference demonstrated

improved results for vision quality under

demanding viewing conditions:

• Subjects rated ZEISS lenses with

i.Scription® higher for distance vision,

night vision, and color perception.

• ZEISS lenses with i.Scription® also

performed better on average than

conventional spectacle lenses in

measures of mesopic visual acuity and

contrast sensitivity.

A similar clinical study was also

conducted by investigators at the

prestigious Clinical Research Center of

the School of Optometry at the University

of California at Berkeley. Each of 30

subjects compared ZEISS single vision

lenses with i.Scription® to conventional

single vision lenses in a randomized,

double-masked wearer trial utilizing a

crossover design. Once again, a variety of

objective measures of visual performance

and subjective measures of wearer

preference demonstrated several positive

outcomes:

• Subjects with low- to moderate-

prescription powers preferred ZEISS

lenses with i.Scription® more often

for distance vision, active vision,

sharpness, changing focus, and overall

vision.

• Subjects preferred ZEISS lenses with

i.Scription® more often for night

vision, vividness of colors, and having

less glare.

• ZEISS lenses with i.Scription® also

performed better than conventional

spectacle lenses in measures of low-

contrast, mesopic visual acuity – by

approximately half a line of acuity.

Each i.Scription® vision correction

represents a synergy between a

thorough wavefront refraction, a skillful

subjective refraction, and a customized

lens design. The product of this patented

integration of optical science and clinical

art is a uniquely calculated wavefront

refraction, subjectively refi ned based

on the judgment of the clinician,

and precisely fabricated using digital

surfacing technology. ZEISS lenses with

i.Scription® will deliver excellent vision,

day or night, with improved contrast

sensitivity compared to conventional

spectacle lenses (Figure 14).

Automated refraction has not yet

replaced subjective refraction. Many

factors infl uence the fi nal manifest

refraction, including patient history,

binocular balancing, and cosmetic

appearance. Nevertheless, wavefront

refraction technology can determine a

starting point of refraction more quickly

and reliably by optimizing retinal image

quality more accurately. Subjective

refi nements can then be applied as

needed based on the professional

judgment of the clinician, in consultation

with the patient. Because aberrometers

characterize the optics of the eye so

thoroughly, the expectations are high

that this technology will yield improved

clinical outcomes.

Figure 14. Calculations

of the contrast

sensitivity of a

typical wearer for a

conventional spectacle

correction and an

i.Scription® wavefront-

guided vision

correction demonstrate

the improvement in

visual performance

with i.Scription®.

1000

100

10

1

0.11 10 100

IMPROVEDACUITY

IMPROVEDCONTRAST

CONT

RAST

SEN

SITI

VITY

SPATIAL FREQUENCY (CYCLES PER DEGREE)

CONTRAST SENSITIVITY COMPARISON FOR A TYPICAL EYE

i.SCRIPTIONSTANDARD

13 29.08.2013 04:49:19

14

// 1 Exam and Refractioni.Scription® Clinical StudyReport on the clinical study performed by Carmel Mountain Vision Care, published in the Review of Optometry (2013).

Our Study Design

We have served as clinical investigators

on scores of contact lens and

pharmaceutical studies and knew we

could execute a study to determine

if new technology was right for our

practice. We wished to avoid the pitfall

of very small experiences, and we

wanted to see if there was an indication

that we could do a better job. We used

a design similar to contact lens studies

we had conducted. A randomized,

single-masked, cross-over clinical study

comparing the effi cacy of customized

ZEISS Individual® Single Vision (SV)

lenses with i.Scription® technology to

customized ZEISS Individual® SV lenses

without i.Scription® technology was

selected for our practice, Carmel

Mountain Vision Care in San Diego. A

direct comparison of the visual quality

of 37 subjects was made between the

two single vision lenses, under mesopic

and photopic conditions. Each subject

was measured with the i.Profi ler® plus

and received a comprehensive eye

examination, including our customary

subjective manifest refraction. Objective

measurements were taken of the

wavefront aberrations of the eye with

the i.Profi ler® plus and combined with

our subjective manifest refractions

by use of the proprietary ZEISS Volu-

Metric merit function algorithm to

create customized ZEISS Individual®

SV lenses with i.Scription® technology

(Figure 3). A second pair of customized

ZEISS Individual® SV lenses without

i.Scription®, using only the conventional

subjective refraction, were manufactured

as the control lenses. The control and

test lenses were fi tted into two identical

frames, with the same position of

wear, measured with the i.Terminal®

by ZEISS. A refractive index of 1.6 was

used, as the lens material and lenses

were manufactured according to the

standard customization parameters of

ZEISS Individual® SV lenses. The study

spectacles were randomized for wearing

order and labeled to mask the type. The

subjects were compensated at their fi nal

visit with the study pair that they felt

gave them the best overall visual quality

and comfort.

Subject Selection

Our eligibility criteria for subjects

required normal, healthy eyes; patient

age between 18-40 years; best corrected

monocular distance visual acuity

(logMAR) of 0.10 (20/25) or better; and

subjects who were full-time eyeglass

wearers for all distances. Subjects were

classifi ed according to three different

prescription power categories. The

classifi cation was made according to the

eye with the highest Manifest Refraction

Spherical Equivalent (MRSE). Subjects

with an MRSE greater than or equal to

-4.00D were classifi ed as Subjects with

High Myopia; between -3.75D and

A group of Doctors of Optometry at Carmel Mountain Vision Care in San Diego conducted a randomized, singlemasked, cross-over clinical study comparing the effi cacy of customized ZEISS Individual® Single Vision (SV) lenses with i.Scription® technology to customized ZEISS

-0.25D inclusive, as Subjects with Mid-

Myopia and more plus or equal to plano,

as Subjects with Hyperopia. The study

concluded with 11 subjects with high

myopia; 21 subjects with mid-myopia

and fi ve subjects with hyperopia.

Clinical Measurements

Clinical measurements were conducted

under mesopic (30 lux) and photopic

(300 lux) conditions. The i.Profi ler® plus

measurement, Subjective Refraction and

Point-Spread-Function (PSF) test were

performed under mesopic conditions.

The PSF test was designed with a single

green LED light source, the same size as

a .0.1 LogMAR letter, that was mounted

against a matte black blackground

and placed at the same distance from

the patient as the visual acuity char.

Monocular und binocular high (100%)

and low (10%) contrast distance visual

acuities were measured in a straight-

ahead gaze position with the M&S Smart

System II 20/20™ 2010. Monocular

and binocular high-contrast near visual

acuities were measured in a straight

ahead gaze position, with ZEISS near

VA chart. Independent mesopic and

photopic pupil sizes were measured with

a Colvard Pupilometer.

Control and Test eyeglasses were worn

independently for a 10-day period

each, followed by a one-week direct

comparison period. Clinical measurement

14 29.08.2013 04:49:20

15

evaluations and patient-reported

outcomes were performed on days 10,

20 and 27, respectively. Results were

analysed using the following methods:

Percentage Analysis; Descriptive

Statistical Analysis; P-Test Analysis; Bland-

Altman Plots and ANOVA calculations. A

Visual Analog Scale response valuation

was used in all questionnaires (Figure 4).

Subjects were required to fi ll out a daily

study journal commenting on their

visual experiences under specifi c visual

conditions that were outlined in the

journal.

Results

Comparison to Habitual Rx. We asked

the subjects to compare the two pairs

of study eyewear to eyewear with

their habitual prescription prior to the

study. Subjects were asked to rate the

i.Scription® Rx and manifest refraction

Rx to their habitual Rx after they wore

each pair independently for a minimum

of 10 days. The overall preference for

the i.Scription® Rx vs. the Habitual Rx

was 95%. The overall preference for

the Manifest Rx vs. the Habitual Rx

was 92%. This outcome indicates that

both study prescriptions were preferred

over the habitual Rx and there was an

apparent need for prescription change.

Overall Preference Final Choice.

Subjects were asked which study

spectacles they preferred overall as their

fi nal choice for visual quality and visual

comfort, and to rate that choice. Answers

were recorded on a 1 to 6 numerical

scale and analyzed. A mean difference

of 0.514 higher for the Test lenses

resulted. Percentage analysis revealed

that 59.5% of subjects preferred the

Test lenses as their fi nal choice for visual

quality and visual comfort, compared to

the Control. This differenc was driven

mainly by the subjects with high myopia

and mid-myopia: 67% of subjects with

high myopia and 59% of subjects with

mid-myopia preferred the Test lenses and

subjects with Hyperopia had an equal

preference for the Test and Control lenses.

Mid Myopes High Myopes

The i.Scription® Rx was the prescription of choice overall for Visual Quality and Visual Comfort.

The overall preference for the i.Scription® Rx was mainly driven

by the High Myopes and Mid Myopes.

33%

67%

41%

59%

40,5%

59,5%

Final choice i.Scription Rx

Final choice Manifest RX

Final choice i.Scription Rx

Final choice Manifest RX

Final choice i.Scription Rx

Final choice Manifest RX

59.5% of subjects preferred the

i.Scription® Rx to the Manifest Rx.

15 29.08.2013 04:49:20

16

Visual Acuity: The Test lenses provided

better mean visual acuity in mesopic

conditions when compared to the Control

lenses. All visual acuity measurement

conditions resulted in no statistically

signifi cant mean logMAR acuity

differences with the Test and Control

lenses. In each case, the difference was

less than one line of vision improvement.

A difference of one line or more is

required to conclude that the diffrnce is

clinically signifi cant.5

Preference Under Lighting Conditions.

Our subjects wore each pair solely for

10 days, and then were allowed to make

a direct comparison with both study Test

and Control spectacles for one week

prior to their fi nal visit where clinical

measurements were also conducted with

direct comparison. The comparison is

reported in Figure 4. Overall, the Test

lenses were preferred for fi ve of the

seven visual conditions; for one visual

condition the Test lenses were preferred

equally to the Control and for the other

visual condition the Control lenses were

preferred over the Test. Adaptation Time.

Our subjects were asked how quickly they

adapted to the study spectacles after

having worn each pair independently for

a minimum of 10 days. Answers were

recorded on a 1 to 5 numerical scale

and analyzed. A mean difference of

0.027 resulted, indicating no signifi cant

difference and that the Test rated slightly

higher than the Control. There were no

cases of non-adaptation for either the

Test or Control.

Visual Conditions Questionnaire

Our subjects were asked which study

spectacles they preferred overall for

17 different visual conditions (Figure 5).

The Test lenses rated higher than the

Control lenses for all 17 different visual

conditions: distance vision; mid-range

vision; near vision; active vision;

brightness; brightness of environment;

colors more vivid; edges sharper;

less glare; peripheral vision; depth

perception; adaptation; visual comfort

for distance vision; visual comfort for

near vision; quicker to change focus;

night vision; natural vision. They were

asked which statement(s), out of eight,

best described their study spectacles.

They were allowed to select either or

both study spectacles for each statement

when applicable. The Test lenses rated

higher than the Control for all eight

statements as follows: Provides more

comfortable vision; provides fewer

headaches; provides good near vision;

provides good intermediate vision;

provides good distance vision; provides

a feeling of more relaxed vision; provides

less tiredness; provides less strain.

Likelihood to Recommend Lenses. Our

subjects were asked to rate on a scale

from 1 (very unlikely) to 10 (very likely)

how likely they would recommend the

study spectacles to family or friends.

A mean difference of 0.135 resulted,

which indicates that the Test lenses rated

higher than the Control. Percentage

analysis of the number subjects who

gave the highest rating (10) revealed

that 41% of subjects would “very likely”

recommend the Test lenses and 27% of

subjects would “very likely” recommend

the Control.

Our Conclusions

As clinicians and practice managers,

we try to make quantitative decisions

for constant product and service

improvements to meet our mission of

providing the highest quality of care in

our region. While we appreciate that our

in-offi ce studies may not have statistical

power for 95% confi dence, we endeavor

to execute our studies to allow us to

have more than anecdotal evidence.

In this study, we found that the blended

or optimized prescription of the lenses

with i.Scription® technology prevailed

in every category over the same ZEISS

Individual® lenses made according to

our subjective refractions only. The

overall preference rating was higher

with the Test spectacles than with the

Control spectacles. This difference was

driven mainly by the subjects with high

myopia and mid-myopia. While not

statistically our clinically signifi cant, the

preponderance of the evidence supports

a trend for enhanced performance and

patient satisfaction with the Test lenses.

The fi nding that the visual acuity was

better for the Test lenses under mesopic

lighting conditions was consistent with a

clear area where we wanted to improve

our patients(?) visual performance.

The preference for the Test lenses for

the Point Spread Function test also

supported our desire to improve visual

comfort in the presence of point sources

of light under dim light conditions.

Adaptation time was faster with the

Test spectacles than with the Control

spectacles. There were no cases of non-

adaptation for either the Test or Control

spectacles. We were impressed that the

Subjective ratings were higher with the

Test spectacles than with the Control

spectacles for all 17 visual conditions.

This complements the discovery that

the Test spectacles were more likely

to be recommended that the Control

spectacles. Under direct comparison, the

Test spectacles were preferred for visual

quality over the Control spectacles under

fi ve of seven lighting and contrast acuity

conditions. Further, the Test spectacles

16 29.08.2013 04:49:20

17

provided more comfortable vision;

fewer headaches; good near vision;

good intermediate vision; good distance

vision; a feeling of more relaxed vision;

less tiredness and less strain.

References1. Goss D, Grosvenor T. Rliability of refraction – a literature review. J Am Optom Assoc, 1996; Vol. 67, No. 10, pp619-630.2. Zadnik K, Mutti D, Adams A. The repeatability of measurement of the ocular components. Investigative Ophthalmology & Visual Science, June 1992;

Vol. 33, No. 7, p 23-29.3. Simms C, Durham D, The Jackson Cross Cylinder Disproved. T(?) Am. Ophth. Soc. 1986, vol. LXXXIV, pp 355-386.4. Bullimore M., Fusaro R., Adams C. The repeatability of automated and clinician refraction. Optom Vis Sci, 1998; Vol 75, No. 8, pp 617-622.5. ZEISS instrument guide.

Individual®, i.Scription® and i.Profi ler® plus are registered trademarks of Carl Zeiss Vision International GmbH. The authors wish to acknowledge the assistance of Jerome A. Legerton, OD, MS, MBA, and Barbara H. Bytomski, OD, in the preparation of this manuscript and the research from which it was derived.

Overall, our consideration of all the

investigational categories supports a

trend that i.Scription® by ZEISS provides

better visual quality and comfort for our

patients, and our patients are more likely

to recommend these lenses; thereby

adding to the growth of our practice.

We expect the use of this technology,

combined with our other study-based

decisions, will continue to support our

valuable fi nal product for the practice:

enthusiastic, satisfi ed patients.

27%

38% 35%24%

41%

35% 24%

38% 38%

51%

8%

41%

22%

19%59%

Mesopic High Contrast: i.Scription Rx Preference

Mesopic High Contrast: Manifest Rx Preference

Mesopic HighContrast: No Preference

Mesopic Neari.Scription Rx Preference

Mesopic NearManifest Rx Preference

Mesopic NearNo Preference

Mesopic PSFi.Scription Rx Preference

Mesopic PSFManifest Rx Preference

Mesopic PSFNo Preference

Mesopic Low Contrasti.Scription Rx Preference

Mesopic Low ContrastManifest Rx Preference

Mesopic Low ContrastNo Preference

Photopic Hight Contrasti.Scription Rx Preference

Photopic Hight ContrastManifest Rx Preference

Photopic Hight ContrastNo Preference

• Results: The i.Scription® prescription

was preferred by direct comparison

under Mesopic conditions.

i.Scription® was preferred under

Photopic High Contrast conditions

by direct comparison.

• Photopic Low Contrast: The

i.Scription® & Manifest Rx were

preferred equally, 57% of subjects saw

“No Difference”

• Photopic Near Vision: The Manifest

Rx was preferred by only 7% more

subjects. 59% of subjects saw

“No Difference”

KEY FACTS Study Spectacles: ZEISS Individual™ SV with i.Scription® vs. ZEISS Individual™ SV without i.Scription®

Study Subjects: 20 Males; 17 Females / 11 Subjects with High Myopia; 21 Subjects with Mid-Myopia; 5 Subjects with Hyperopia

Eligibility criteria: Normal healthy eyes 18 to 40 years / Full time spectacle lens wearers for all distances / Best corrected monocular distance VA 20/25 or better

Carmel Mountain Vision Care Optometry in San Diego, California, conducted a clinical study over the course

of eleven months. The aim of such study was to improve vision under mesopic conditions without compromising

vision under photopic conditions with i.Scription® by ZEISS.

17 29.08.2013 04:49:21

18

// 2 Lens Fitting and ConsultationStandard Spectacle Lens FittingArticle written by Darryl Meister, ABOM Carl Zeiss Vision (2010)

Traditional lens fi tting measurements are

limited in terms of both accuracy and

precision. Accuracy is the closeness of the

average measurement result to the actual

value. Random and systematic errors

introduced by parallax, or unwanted

head turn, and unwanted head tilt reduce

measurement accuracy. Errors introduced

by improper measurement techniques

or use of poorly maintained tools are

other causes for measurement errors.

Precision is the size of the smallest reliable

measurement or the overall spread of

the individual measurement results.

The standard “PD ruler” can be used to

measure reliably only to within ±½ mm

of the actual value, limiting measurement

precision. Random errors can also

reduce measurement precision, since

the repeatability of the measurement is

reduced. For any individual measurement,

limitations in either the accuracy or the

precision of a measurement technology

can result in a measurement error from

the true value (Figure 1).

Parallax error is the apparent change in the

location of the wearer’s pupil at the plane

of the lens when observed from different

positions. It is one common source of

High PrecisionHigh Accuracy

Low PrecisionLow Accuracy

Low PrecisionHigh Accuracy

High PrecisionLow Accuracy

Figure 1 Accuracy and precision measurement errors

Figure 3. Unwanted head tilt in vertical centrationFigure 2 Parallax errors in measurement

Eye Level Difference

Parallax Error

measurement error for both fi tting height

measurements and manual measurements

of interpupillary distance using a

pupilometer (Figure 2). For a head turn

of 12°, a 1.4 mm error in measurement

would occur for a binocular PD of

64 mm. Differences in eye level between

the dispenser and the eyeglass wearer

introduce signifi cant parallax errors.

Every 1 inch difference in eye level height

can result in an error in fi tting height

measurement of roughly 1.7 mm. In the

absence of a habitual head turn, the

wearer should be measured while facing

straight-ahead with his or her face parallel

to the dispenser’s face. Another signifcant

source of error derives from unwanted

head tilt. Every 1° of unwanted vertical

head tilt will result in an error in fi tting

height measurement of roughtly 0.5 mm.

In order to avoid erroneous vertical

centration, wearers should be measured

while maintaining a natural posture at the

same eye level as the dispenser (Figure 3).

Modern progressive lenses offer wearers better optical performance than ever, although the performance of these lenses is still limited by the accuracy and precision of the fi tting process.

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Lens centration errors reduce the width

of the binocular viewing zones, which

in turn degrades visual performance

and comfort. Every 1 mm of error in

monocular PD measurement will reduce

the width of the binocular viewing

zone by 2 mm (Figure 4). A 2 mm

error in centration from inaccurate

measurements can reduce the wearer’s

binocular fi eld of view by up to 25% or

more

This is especially critical for the

intermediate and near zones, which are

relatively narrow, or in lenses with high

add powers

Figure 4 Error in monocular PD

Pupilometers are not as accurate and

precise as eyecare professionals generally

assume. Repositioning of the dispenser’s

viewing eye and slight movements of the

device occur as the dispenser switches

fi xation from eye to eye, resulting in

random measurement errors. Inexact

calibration can result in systematic

measurement faults that are seldom

detected, while poor mechanical action

or friction can result in additional inexact

measurement.

Wesemann, Bartz, and Arnolds (1997)

showed that the standard deviations of

measurements taken with two popular

pupilometers by 30 observers were

0.52 and 0.55 mm. Obstfeld and Chou

(1998) showed that many pupilometers

suffer from systematic errors as high as

2 mm when the interpupillary distance

was signifi cantly larger or smaller than

60 mm.

Figure 5. Monocular interpupillary distances measured from center of the frame.

PD-R > PD-L

PD-R PD-L

Total PD

Example:PD-R = 31PD-L = 29Total = 60

Overlap = 18 mm

0 mm 2 mm

Overlap = 18 mm

Pupillometers do not always fi t the

wearer´s face like the chosen spectacle

frame. These may sit differently on the

bridge of the nose compared to the

positioning of pupillometers. Horizontal

centration for PD should be based

upon the center of the bridge of the

fi tted frame, not the bridge of the nose

(Figure 5).

This ensures that the fi tting point of each

lens remains aligned with the pupil center

of each eye in the mounted frame. This

may actually result in different monocular

interpupillary distances for the same

wearer in different frames.

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Maximum Fitting Errors with

ZEISS Centration Technology

Accurate and precise fitting

measurements are critical to the visual

performance and wearer satisfaction,

especially for progressive lenses.

ZEISS centration technology, implemented

in i.Terminal® 2, employs a precision

camera to eliminate potential

measurement erros due to parallax or

the location of the dispenser relative

to the wearer. A patented laser speckle

fixation target ensures that the wearer

maintains a fixation to optical infinity.

The device automatically compensates

for any unwanted head turn or head

tilt to avoid parallax errors (Figure 6).

Additionally, “Auto-X” functionality

compensates the monocular interpupillary

distance measurements for any unwanted

horizontal head turn.

Studies have confi rmed the accuracy,

precision and repeatability of i.Terminal®

(Figure 7). Winter showed an average

variance of 0.04 mm and a range of

0.4 mm with i.Terminal®, compared to 0.7

and 1.8 mm for pupilometers.

Wesemann (2010) also showed a

standard deviation of only 0.13 mm with

i.Terminal®, compared to 0.35 mm for

several pupilometers.

Figure 6. Patented laser speckle target

Collimating Optics

Laser Speckle

Beam Splitter

Figure 7. Comparison of measurement variance for i.Terminal®

Variance Range

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Customized Spectacle Lens Fitting

Traditional progressive lenses are often

designed for a focimeter, not the patient.

These must assume a fi xed position of

wear, often replicating how a focimeter

measures optics.

The position of wear represents the

position of the fi tted spectacle lens on

the patient, including tilt, wrap, and

vertex (Figure 1). Conventional, semi-

fi nished progressive lens design must

assume a single, average position of wear

while ray tracing the lens-eye system

during the optical design process. In

practice, however, the actual position of

wear varies signifi cantly among eyeglass

wearers, which results in errors from the

intended optical performance of the lens

design.

The position of wear introduces greater

wavefront aberrations than the high-

order aberrations of either the eye or

spectacle lens. The average high-order

wavefront error of human eyes is less

than 0.35 mm, which is comparable

to roughly 0.29 D of spherical error

(Figure 2).

Customized lenses like ZEISS Individual®

and Individual® Single Vision can utilize

additional fi tting measurements to

maximize the optical performance of the

lens design for each wearer.

Prescription changes are introduced

by variations in the position of wearer

that will blur vision through the central

viewing zones. Deviations from the

“standard” position of wear utilized

during optical design result in lens

aberrations due to lens tilt. These optical

aberrations blur vision through the

central viewing zones of the lens and

restrict the fi elds of clear vision.

Customization for the position of

wear fi ne-tunes the optics of the lens

design using the patient’s exact fi tting

geometry. Customized lenses will deliver

the intended optics with crystal clear

viewing zones to patients, regardless of

fi tting geometry (Figure 3).

Figure 2. Wavefront aberrations

derived from the position of wear

Figure 3. Customized progressive lenses

Figure 4. Wearer satisfaction comparison

Clinical studies have demonstrated

improved optical performance with

customized lenses. A study conducted at

the prestigious Clinical Research Center

at UC Berkeley, fi tted ZEISS Individual®

lenses using i.Terminal®. Han, Graham,

and Lin (2011) showed greater wearer

satisfaction with progressive lenses

customized for the position of wear

(Figure 4). By compensating for how

lenses are actually worn, customized

lenses deliver the intended optical

powers across the entire lens.

Figure 1. Position of wear

Reading Distance

Vertex

Tilt

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// 3 Technical Data

i.Polatest®

Line voltage 100 V to 240 V AC ± 10 %

Frequency 50 to 60 Hz

Power consumption 70 VA

Ambient conditions for intended use Temperature: +10 °C to +35 °C

Relative humidity: 30% to 85 % (no condensation)

Transport and storage conditions (in original packing)

Temperature: -15 °C to +60 °C

Relative humidity: 10% to 85% (no condenation)

Protection class I

Test area size (width x height) 299.5 mm x 223.5 mm

Testing distance 1 m to 8 m

Polarization direction for analyzers Image for right eye: 45°

Image for left eye: 135°

Dimensions (H x W x D) 608 mm x 570 mm x 85 mm

Weight incl. wall mounting bracket 12.75 kg

IR remote control unit 3 V, 100 μA

Spare parts Line fuse: 2x T 2.0 AE/250V

Battery for IR remote control unit: 2x Micro AAA 1.5 V

i.Profiler® plus

Measuring range sphere: –20 D to +20 D

Axis 0° – 180°

Measuring surface 2.0 mm to 7.0 mm (3 zones)

No. of measuring points 2.0 mm to 7.0 mm (3 zones)

Method Hartmann-Shack

Reference wavelength 1 555 nm (ISO 24157)

No. of rings 22 (18 complete rings)

No. of measuring points 3,425

Detected corneal surface at 42.125 D Dia. 0.75 mm to 9.4 mm

Diopters Measurement range 25 to 65 D

Accuracy ± 0.05 D (± 0.01 mm)

Reproducibility ± 0.10 D (± 0.02 mm)

Type A Complies with 19980

General dimensions 420 mm x 600 mm

Weight 30 kilograms

Power connection 100 V~ to 240 V~

Supply frequency 50 Hz to 60 Hz

Power consumption ≤ 200 VA

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i.Terminal® 2Line voltage 100 V to 240 V AC

Supply frequency 50 Hz to 60 Hz

Line fuses F1, F2 T2.0A/E 250V 5x20 IEC 60127-2/3

Protection class I I

Overvoltage category II

Pollution degree II

Laser class I according to CFR and IEC 60825-1

Ambient conditions for intended use Temperature: +10°C to +40°C

Rel. humidity: 30%…85% (no condensation) condensation)

Max. height (MSL): 2000 m

Transport and storage conditions(in original packaging)

Temperature: 40°C to +70°C

Rel. humidity: 10%…85% (no condensation)

Max. height (MSL): 2000 m

Dimensions of base 60 cm x 60 cm

Instrument (height x width x depth) 1250–2100 mm x 600 mm x 600 mm

Weight approx. 47 kg

Min. ceiling height 2.1 m

Range of movement Minimum eye height: 110 cm (corresponds to approx. 120 cm body height)

Maximum eye height: 195 cm (corresponds to approx. 208 cm body height)

Lifting range: 85 cm

1. Goss D. and Grosvenor T. “Reliability of refraction – a literature review.” J Am Optom Assoc, 1996; Vol. 67, No. 10, pp 619-630.2. Bullimore M., Fusaro R., and Adams C. “The repeatability of automated and clinician refraction.” Optom Vis Sci, 1998; Vol 75, No. 8, pp 617-622.3. Collins M., Shaw A., Menkens E., Davis B., and Franklin R. “The Effect of Pupil Size on Subjective Refraction with Irregular Corneas.” Invest Opthalmol Vis Sci, 2002; Vol. 43: E-Abstract 20584. Cheng X., Bradley A., and Thibos L. “Predicting subjective judgment of best focus with objective image quality metrics.” J Vis, 2004; Vol. 4, No. 4, pp 310-321.5. Nam J., Thibos L., and Iskander D. “Describing ocular aberrations with wavefront vergence maps.” Clin Exp Optom, 2009; Vol. 92, No. 3, pp 194-205.6. Thibos L. “Principles of Hartmann-Shack aberrometry.” J Refract Surg, 2000; Vol. 16, No. 5, pp S563-565.7. Thibos L., Hong X., Bradley A., and Applegate R. “Accuracy and precision of objective refraction from wavefront aberrations.” J Vis, 2004; Vol. 4, No. 4, pp 329-351.8. Stockman A. and Sharpe L. “Into the twilight zone: the complexities of mesopic vision and luminous effi ciency.” Ophthal Physiol Opt, 2006; Vol. 26, No. 3, pp 225-239.9. Salmon S. and Van de Pol C. “Normal-eye Zernike coeffi cients and root-mean-square wavefront errors.” J Cataract Surg, 2006; Vol. 32, No. 12, pp 2064-2074.10. Clinical study data on fi le with Carl Zeiss Vision.

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Carl Zeiss Vision GmbHTurnstrasse 2773430 AalenGermany

Phone: +49 (0) 7361 598 5000 Fax: +49 (0) 7361 591 480 Email: info-de@vision.zeiss.comwww.zeiss.de/vision

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