basic optics
DESCRIPTION
Lynn Lawrence, CPOT, ABOC. Basic Optics. Disclaimer. Please prepare for certification testing with materials from the organization in which you want your certification granted i.e.: AOA JCAHPO ABO NCLE OT. Outline. The Visual System Physiology Ametropias Ophthalmic Lenses - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/1.jpg)
Lynn Lawrence, CPOT, ABOC
![Page 2: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/2.jpg)
Please prepare for certification testing with materials from the organization in which you want your certification granted i.e.:
AOA JCAHPO ABO NCLE OT
![Page 3: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/3.jpg)
The Visual System Physiology Ametropias
Ophthalmic Lenses Properties of Light
▪ UV, Visible, and Infrared Spectrums▪ Reflection, Refraction, & Absorption▪ Aberrations
Lens Designs▪ Fitting
Basic Optical Formulas
![Page 4: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/4.jpg)
There are two main refractive bodies in the human eye...
Cornea
Crystalline Lens
![Page 5: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/5.jpg)
The cornea is the primary refractive element in the eye...
Cornea
... with a power of around +42-44 diopters
![Page 6: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/6.jpg)
The tear film maintains both the health and optics of the cornea...
Cornea
![Page 7: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/7.jpg)
The crystalline lens has a power of around +12-18 diopters...
Crystalline Lens
...it is primarily responsible for changing the eye’s focal point…a term referred to as accommodation
![Page 8: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/8.jpg)
The retina is the “film” or sensory body...
Retina
![Page 9: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/9.jpg)
Light is converted to electrical impulses which are sent through the optic nerve...
Retina
...the “blind spot” is the point at which the optic nerve connects
Fovea
Macula Optic Disc
![Page 10: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/10.jpg)
The eye is connected to the orbit by several muscles which control movement...
Eye Movement or ocular motility
Orbit
![Page 11: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/11.jpg)
Ametropias
In a “normal” eye, parallel light is brought to a focus on the retina...
...an eye free of refractive error is called “emmetropic”
![Page 12: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/12.jpg)
AmetropiasAn eye with excessive focal power for its length focuses light in front of the retina...
...this refractive error is known as “myopia”
![Page 13: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/13.jpg)
AmetropiasAn eye with insufficient focal power for its length focuses light in front of the retina...
...this refractive error is known as “hyperopia”
![Page 14: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/14.jpg)
AmetropiasAnother refractive error can occur if every axis is not refracted evenly...
...this refractive error is known as “astigmatism”
![Page 15: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/15.jpg)
AmetropiasAs the eye ages, the crystalline lens loses flexibility...
...this results in a condition known as “presbyopia”
![Page 16: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/16.jpg)
Presbyopia
The inability to focus on near objects becomes noticeable around age 40 and steadily worsens thereafter...
![Page 17: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/17.jpg)
Ophthalmic Lenses Properties of Light
▪ UV, Visible, and Infrared Spectrums
▪ Reflection, Refraction, & Absorption
Lens Designs Lens Materials
![Page 18: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/18.jpg)
Properties of Light
Like the artist’s paint, the eye requires light to see...
...what is “light,” and how does it work?
![Page 19: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/19.jpg)
particles in the form of a wave electromagnetic radiation with wavelengths
between 400 and 700 nanometers (a nanometer is 1/1,000,000th mm)
white light is composed of all wavelengths
Properties of Light
So what is light?
![Page 20: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/20.jpg)
visible light is a small portion of the spectrum EM surrounding the visible spectrum is
hazardous Ultra-Violet is <390nm Infrared is >720nm
Properties of Light
So what is light?
![Page 21: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/21.jpg)
Properties of Light
Ultra-Violet Radiation
UVA is less photobiologically active than UVB and consists of light just beyond the blue end of the visible spectrum...A
![Page 22: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/22.jpg)
Properties of Light
Ultra-Violet Radiation
UVB falls farther from the visible spectrum, is the most significant UV most of us experience, and is variably absorbed by ozone...
A B
![Page 23: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/23.jpg)
Properties of Light
Ultra-Violet Radiation
UVC light is farthest from the visible spectrum, and is almost completely absorbed by ozone (except at very high altitudes)....
A B C
![Page 24: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/24.jpg)
Properties of Light
Infrared
Infrared is >720nm- the most common source is blown glass...
![Page 25: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/25.jpg)
Properties of Light
Movement of Light
Light moves in wave form along a straight line...
...the distance between peaks determines wavelength
![Page 26: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/26.jpg)
Properties of Light
Movement of Light
As light spreads from a point, it forms a wavefront...
![Page 27: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/27.jpg)
Wavefronts interact with lenses in 3 ways Reflection Refraction
▪ prism▪ dispersion
Absorption
Properties of Light
Movement of Light
![Page 28: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/28.jpg)
Properties of Light
Reflection
Every lens has a “critical angle”...
...light striking the lens flatter than this angle will be reflected
![Page 29: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/29.jpg)
Properties of Light
Refraction
Light striking at an angle steeper than critical is refracted...
...the amount of refraction depends on the amount of prism
![Page 30: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/30.jpg)
Properties of Light
Refraction - Prism
Prism bends light towards its base...
...but displaces images towards its apex base
apex
![Page 31: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/31.jpg)
Properties of Light
Refraction - Prism
Light Rays
Plus lenses are prisms placed base to base...
...resulting in convergence
![Page 32: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/32.jpg)
Properties of LightRefraction - Prism
Light Rays
Minus lenses are prisms placed apex to apex...
...resulting in divergence
![Page 33: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/33.jpg)
When light is not focused on the retina, an ametropia is present...
E
for example, a myopic eye focuses light in front of the retina...
![Page 34: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/34.jpg)
E...a minus powered (diverging) lens shifts the focus back to the retina
E(unaided focal length of eye)
(focal length of eye + lens)
![Page 35: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/35.jpg)
E
A hyperopic eye focuses light behind the retina...
![Page 36: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/36.jpg)
E...a plus powered (converging) lens shifts the focus up to the retina
E
(unaided focal length of eye)
(focal length of eye + lens)
![Page 37: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/37.jpg)
E E
Astigmatism causes light along different axes to focus at different planes...
![Page 38: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/38.jpg)
E E
...a cylindrical lens is prescribed to compensate for astigmatism in the eye- creating a common focal point on the retina...
(multiple focal lengths in unaided eye)(common focal lengths of eye + lens)
![Page 39: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/39.jpg)
E E
As previously mentioned, the crystalline lens enables the eye to focus on near objects...
accommodation
![Page 40: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/40.jpg)
E E
...as the crystalline lens ages, it loses its flexibility- and its ability to adjust focus...this condition is called presbyopia and typically becomes noticeable around age 40
![Page 41: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/41.jpg)
E E
To restore near vision, the required convergence is supplied by a plus powered lens...
Single Vision lens (NVO)
single point of focus
![Page 42: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/42.jpg)
...this plus lens may stand alone (NVO) or may work with distance correction (ADD)
E EADDDistance Rx
![Page 43: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/43.jpg)
Properties of Light
Refraction - Dispersion
All prisms break white light into its component colors...
...this is called dispersion and results in chromatic aberration
W h i t e L i g h t
Dispersed Light
![Page 44: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/44.jpg)
Properties of Light
Refraction - Dispersion
Blue waves are more compact than red waves...
...therefore, they are refracted to a greater degree
![Page 45: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/45.jpg)
Properties of Light
Refraction - Dispersion
Blue waves are more compact than red waves...
...therefore, they are refracted to a greater degree
![Page 46: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/46.jpg)
Properties of Light
Refraction - Dispersion
Abbe value is used to describe the amount of dispersion a material will create...
...ranges are from 59 (CR-39) to 30 (polycarbonate)
Chromatic Aberration
![Page 47: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/47.jpg)
Properties of Light
Absorption
A dark lens absorbs light...
![Page 48: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/48.jpg)
Neutral grey filters are the most difficult to achieve (as thousands of red-grey lenses can attest)…
…why?
Properties of Light
Absorption
![Page 49: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/49.jpg)
White light is composed of all colors in the rainbow- but all colors can be formed using a combination of three “primary colors:”
RedYellowBlue
Properties of Light
Absorption
![Page 50: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/50.jpg)
Filters absorb light. Chemical compounds are used to selectively filter single colors.
To create a green filter, only red light must be absorbed. The appropriate chemicals are applied, and a green filter is created.
Properties of Light
Absorption
![Page 51: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/51.jpg)
Properties of Light
Absorption
To create a perfectly neutral- or gray- filter, energy from all three primary points in the spectrum must be absorbed to the same degree.
When creating a filter by absorbing dye into resin, this process is further complicated by the inconsistent nature of the chemicals involved.
![Page 52: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/52.jpg)
Properties of Light
Aberrations
The most common aberrations found in ophthalmic lenses are:
Power Error Distortion Marginal
Astigmatism Chromatic
Aberration Unwanted Prism*
![Page 53: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/53.jpg)
Properties of Light
Aberrations
Aberrations occur due to various factors:
Refractive power Off-axis viewing of objects
lens tilt peripheral objects
Vertex distance Lens material
![Page 54: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/54.jpg)
Properties of Light
Aberrations – Power Error
Spherical lenses are stronger in the periphery...
![Page 55: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/55.jpg)
Properties of Light
Aberrations – Distortion
The result is barrel distortion...
...the periphery of an object will be minimized to a greater degree than the center
![Page 56: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/56.jpg)
Properties of Light
Aberrations – Distortion
Plus lenses create the opposite effect...pincushion effect
...the periphery of an object will be magnified to a greater degree than the center
Aspheric lenses reduce distortion
![Page 57: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/57.jpg)
Properties of Light
Aberrations – Distortion
Compare a spherical lens to an aspheric lens of equal power...
...notice the central curve & thickness
![Page 58: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/58.jpg)
Properties of Light
Aberrations – Marginal Astigmatism
Light striking the lens at an oblique axis do not refract evenly...
...unwanted astigmatism occurs
![Page 59: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/59.jpg)
Properties of Light
Aberrations – Chromatic Aberration
As previously discussed, chromatic aberration is the dispersion of white light into its component colors......large amounts of prism are necessary for chromatic aberration to affect vision
![Page 60: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/60.jpg)
Properties of Light
Prism
Although prism is not technically an aberration, unwanted prism does affect quality of vision...
...the optical center of a lens usually has no prism
![Page 61: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/61.jpg)
Properties of Light
Prism
The eye does not always view objects through the optical center...
...what will the eye perceive?
![Page 62: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/62.jpg)
Lens Types
Single Vision Distance Vision Near & Intermediate Vision
Bifocals Flat Tops Executive
Trifocals Progressive Addition Lenses
There are many types of lenses designed to meet specific patient needs...
![Page 63: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/63.jpg)
Lens Types – Single Vision
Single Vision lenses have only one focal length...
...single vision lenses can be used to provide clear distance, intermediate, or near vision for presbyopes
![Page 64: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/64.jpg)
Lens Types – Single Vision
The myopic eye focuses light in front of the retina...
...using a minus powered single vision lens, light is focused on the retina
![Page 65: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/65.jpg)
Lens Types – Single Vision
“Reading glasses” are also single vision lenses...
...a plus powered single vision lens restores near vision
![Page 66: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/66.jpg)
Lens Types – Single Vision
Single vision readers only provide clear vision at one working distance...
![Page 67: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/67.jpg)
Lens Types – Single Vision
Single vision lenses require measurement of pupillary distance, and occasionally fitting height...
![Page 68: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/68.jpg)
Lens Types – Bifocals
Bifocal lenses have two focal lengths...
Distance
Near
![Page 69: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/69.jpg)
Lens Types – Bifocals
For distance vision, the lens contains a “carrier” similar to a single vision lens...
![Page 70: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/70.jpg)
Lens Types – Bifocals
For near vision, an extra “reading” segment is added...
![Page 71: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/71.jpg)
Lens Types – Bifocals
to lower limbus (seg line @ lower lid) decentered 1.5mm in from Far PD
Flat-top bifocals are usually fit:
![Page 72: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/72.jpg)
Lens Types – Bifocals
Flat Tops FT28 FT35 FT45 Smart Seg*
Curve Top (Cosmolit) Executive (E-Line) Round Seg (Kryptok) Blended
There are several types of bifocals suited to different needs...
![Page 73: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/73.jpg)
Lens Types – Trifocals
Trifocal lenses have three focal lengths...
Distance
Near
Intermediate
...generally, the intermediate ADD is 50% of the near ADD
![Page 74: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/74.jpg)
Lens Types – Trifocals
Objects at the focal length of either the near or intermediate segments are focused on the retina...
![Page 75: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/75.jpg)
Lens Types – Trifocals
to lower edge of the pupil decentered 1.5mm in from Far PD
Flat-top trifocals are usually fit:
![Page 76: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/76.jpg)
Lens Types – Trifocals
Flat Tops FTT 7/28 FTT 8/35 Smart Seg*
Executive (E-Line) Occupational*
There are several types of trifocals suited to different needs...
![Page 77: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/77.jpg)
Lens Types – Progressives
Progressive Addition Lenses (PALs) have an infinite number of focal lengths across a range... Distance
Near
Intermediates
![Page 78: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/78.jpg)
Lens Types – Progressives
PALs contain a reading ADD that progressively gets stronger- providing many, many focal lengths...
![Page 79: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/79.jpg)
Lens Types – Progressives
at pupil center
Progressives are usually fit:
![Page 80: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/80.jpg)
Lens Types – Progressives
Monocular pupillary distances Verification of fitting height Proper frame adjustment
PALs require precise fitting if the lens is to perform to its potential, this necessitates:
![Page 81: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/81.jpg)
Lens Types – Progressives
Traditional hard design soft design monodesign multidesign
Short Corridor Customized Task Specific
There are literally hundreds of PAL designs available- each with unique characteristics...
![Page 82: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/82.jpg)
Calculations
Prentice’s Rule Box Measurements
There are perhaps two calculations every person who works with eyewear MUST know...
![Page 83: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/83.jpg)
Box Measurements
Measurements of the frames- and the eye’s relationship to them- should be specified...
![Page 84: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/84.jpg)
Box Measurements
Datum Line
“A” Measurement
“B” M
easu
rem
ent
“Effec
tive D
iamete
r” (ED)
“DBL”
“FPD”
![Page 85: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/85.jpg)
Box Measurements B = 56Datum (56/2) = 28Seg Ht = 2228-22 = 6 down
A = 58DBL = 20FPD = 78NPD = 60(78-60)/2 = 9 in
![Page 86: Basic Optics](https://reader036.vdocuments.us/reader036/viewer/2022081502/56815d93550346895dcbaf9d/html5/thumbnails/86.jpg)
Lynn Lawrence, CPOT, ABOC [email protected]
Information assistance provided by Essilor (Pete Hanlin)
http://lynnslecturehelp.wordpress.com