Macular Function tests

Abubaker Ahmed

M.Sc Ophthalmolgy

Macula is a round area at the posterior pole temporal to the optic disc 5.5mm in diameter

It is yellowish color derived from the

presence of xanthophyll pigment

Anatomical background

Densest concentration of cones

a one to one photoreceptor-ganglion

cell relationship

Cones more elongated and slender

Absence of rods at the foveola

RPE cells are taller, thinner and

deeply pigmented

Presence of xanthophyll pigment

Specific anatomic cofiguration of the Fovea

This special anatomy enable the fovea for:

highest discriminative ability(VA) colour perception

Diagnosis and Follow up of macular diseases

For evaluating the potential macular

function in eyes with opaque media such as cataract and dense vitreous hemorrhage

Uses of macular function tests

Symptoms

• Central vision impairment • Metamorphopsia• Micropsia• Macropsia

Clinical assessment of the macula

MFT With clear media

MFT With opaque media

Macular function tests classification

MFT with clear media Visual acuity

Contrast sensitivity

Slitlamp biomicroscopy

 Photostress test

Colour vision

Amsler grid

Microperimetry

FFA

OCT

Maddox rod test

Focal ERG

VEP

Laser interferometry

Potential visual acuity meter test

Entoptic phenomena

B scan

MFT with opaque media

V/A is measured by the visual resolution of a

letter, symbol or a pattern under conditions

of maximal contrast

In pts with macular disease VA is frequently

worse when the pt looks through a pin-hole

Visual acuity

Contrast sensitivity is a measure of the

minimum amount of contrast needed to

distinguish a test object

indirectly assesses the quality of vision

Can detect early/subtle visual loss when VA

is normal

Contrast sensitivity

To detect retinal conditions like DR, ARMD and

other retinal, macular and optic nerve diseases

Optical conditions like refractive error,

refractive surgery, cataract and intraocular

lens implantation and normal aging of the eye

Uses of contrast sensitivity

Contrast sensitivity grating

Spatial frequency is the number of

dark light cycles per visual angle

In macular diseases, there is a

marked impairment for the

intermediate and higher spatial

frequencies

Hamilton-Veale Contrast Sensitivity Chart

Is an effective test

for monitoring

potential decreases

in contrast

sensitivity function

over time. 

With a strong convex lens

affords excellent visualization

of the macula

Slitlamp biomicroscopy

PRINCIPLE : 

The test involves exposing the macula to a light

source bright enough to bleach a significant

proportion of the visual pigments.

Return of normal retinal function and

sensitivity depends on the regeneration of

the visual pigments

Photostress test

pathological states that affect the

photoreceptors,Bruchs membrane, chorio-

capillaries or choroid can prolong visual

recovery time.

no such prolongation is observed in

diseases affecting the neural conducting

pathways

Evaluates the 10 < of visual field

centered on fixation

Used in screening and

monitoring macular diseases

square 10*10 cm divided into

400 5*5 mm squares to be held

at 30 cm

Amsler grid

reading glasses, cover 1 eye

Pt asked to see the central spot

Presence of abnormalities like blurred areas,

holes, distortions, or blank spots

Pt with maculopathy reports that the lines

are wavy whereas pt with optic neuropathy

remarks some lines are missing or faint

Procedure

Colour vision is the function of three

populations of retinal cones

Blue ( tritan) 414-424 nm

Green ( deuteran) 522-539nm

Red (protan) 549-570nm

Normal person possess all these three

cones and called trichromat

Colour vision

Acquired macular diseases tends to produce

blue yellow defects and optic nerve lesions

red green defects

Deutran anomaly is the most common and

those subjects can not differentiate

between red and green colours

Colour confusion tests

Ishihara charts it is useful as screening test

Farnsworth-Munsell

100 Hue test is the

most sensitive but

seldom used

Hue discrimination tests

The principle of microperimetry rests on

the possibility to see —in real time— the

retina under examination (by infrared

light) and to project a defined light

stimulus over an individual, selected

location

Microperimetry

SLO microperimetry was the first technique

which allowed to obtain a fundus-related

sensitivity map

SLO uses a near infrared diode laser

(675nm)beam that rapidly scan the posterior

pole.

The reflected light is detected by a confocal

photodiode and the digitized image is stored in

a computer

Scanning Laser Ophthalmoscope microperimetry

SLO fundus perimeter did not allow to

perform fully automatic examination.

Moreover, automatic follow-up examination

to evaluate exactly the same retinal points

tested during baseline microperimetry was

not available with this instrument.

Limitations of SLO microperimetry

The limitations of SLO have been

overcome by MP1 microperimetr a

recently developed automatic

fundus perimeter

MP1 microperimeter automatically

compensates for eye movements

during the examination via a

software module that tracks the

eye movements

MP1 microperimetry

Dark appearance of the fovea on FFA is caused by FAZ and blockage of the choroidal background by xanthophyll and dense RPE

FFA is a very useful tool in diagnosing macular disorders e.g. diabetic maculopathy, CSR , CNVM and can reveals the functionality of the lesion e.g. ischemic maculopathy

Fluorescien Angiography

OCT it is non invasive noncontact imaging

that produce high resolution cross sectional

image

Useful in diagnosing macular disorders and

to delineate retinal layers and detect subtle

anatomical changes

Optical Coherence Tomography

Maddox rod

Focal ERG

VEP

Laser interferometry

Potential visual acuity meter test

Entoptic phenomena

Preferential hyperacuity perimeter (PHP)

B scan

MFT with opaque media

Simple and reliable test and can

be used in semi opaque media

Pt is asked to fixate light at a

distance of 1/3m through M.R.

with opposite eye occluded

Any breaks/holes;

discoloration/distortion indicates

a macular lesion

Maddox rod test

ERG is only abnormal when a large area of retina is functionally impaired

Focal ERG needs a stimulus localized to one area without scattering of light to stimulate the rest of the retina

Focal Electroretinogram

It is a hand held foveal ERG

It employs a 3-4 degrees

whit flickering light focused

on the fovea with a 10

degrees annulus of constant

white light to desensitize

surrounding retina

Maxwell ophthalmoscope(foveal flickering sensitivity)

VEP Measure of the electrical potential

generated in response to a visual stimulus

it represents integrity of entire visual

pathway from retina to occipital lobe so can

not differentiate between macula ,ON and

cortical pathology

Visually Evoked Potential

Two types of stimulus either

by flash of light or by

patterned stimuli

If the issue is the V/A then

the amplitude is measured

If the issue is the lesion in

the visual pathway then the

latency is measured

Utilizes coherent white light or helium-neon

laser generated interference stripes or fringes

that are projected onto the retina through the

ocular media

Brightness increased in pts with dense cataracts

The laser interferometer resolving power

converted to standard V.A

Laser interferometery

1. subjective

2. Laser fringe vision>vision of letter acuity.

3. over predicts visual potential in amblyopes

Limitations

PAM introduced in1983

This is attached to a slit lamp and

projects a reduced Snellen’s chart via

narrow beam of light through a

pinhole clear area in the cataract

towards the macular region

The resulting potential acuity is the

smallest line where the patient was

able to read three characters

Potential visual acuity meter test

Subjective

methods that require an alert and cooperative patient and skilled compassionate examiner

But it is easier than laser interferometry

Limitation

It is refer to visual perceptions that have their

origin in the structure of an observer's eye

Three types are used for testing the macula in

opaque media

1/ PURKINJE VASCULAR E.P

2/ Flying spot( blue field entoptic phenomenon)

3/Haidinger’s Brushes

Entoptic phenomena

The Purkinje’s vascular

entoptic test is a simple

method which elicits the

response by placing a penlight

against a closed eyelid or the

globe and moving it back and

forth, creating images of the

patient’s retinal vascular tree

PURKINJE VASCULAR E.P

Blue field entoptoscopy relies on

the observation of leucocytes

flowing in the macular retinal

capillaries. The leucocytes

appear as ‘Flying Corpuscles’

when the retina is diffusely

illuminated with a bright blue

light.

Flying spots( blue field entoptic phenomenon)

Subject looks at a surface

illuminated with blue light

through a polarizer

hourglass shaped yellowish

brushes seen radiating from the

point of fixation. On rotating

polarizer, brushes rotate

Haidinger’s Brushes

Phenomenon caused by variations in

absorption of plane polarized light by

oriented molecules of xanthophyll

pigment in foveal retina

Used to sensitize the fovea in

amblyopic child with eccentric

fixation

limited by the patient’s subjective

interpretation

May yield false negatives if the retina

cannot be sufficiently illuminated through a

dense cataract

Limitations of EP

PHP relies on the concept of hyperacuity

which is the ability to discern a subtle

misalignment of an object.

This can be explained by the fact that an

extended edge will stimulate an array of

cones and when there is a break in this line

the fovea can perceive it.

Preferential hyperacuity perimeter

if the patient’s

photoreceptors are slightly

misaligned due to macular

lesion (e.g. drusen) then

this misalignment can be

perceived by the patient

and recorded by the PHP.

This gives a gross idea about the anatomic

normalcy of the eye, and rules out

pathologies like vitreous hemorrhage,

retinal detachment, optic nerve anomalies,

etc

Scanning does not offer any information on

macular function

Ultrasonography (Bscan)

Evaluation of the macular function of a

patient with opaque media is a challenging

problem commonly faced by us

No single test is infallible

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