MACULAR FUNCTION

TEST

DR. PUSHPANJALI

macula

• The International ARM Epidemiological study group, defined macula as the posterior part of retina centered on the foveola.

• 5.5-6 mm diameter.• Comprises of fovea centralis(1.5mm),

foveola(0.35mm) and FAZ(0.4-0.6mm).

Fovea differs from retina in that it has only the following 6 layers :

• Retinal pigment epithelium,• Photoreceptors (cones only),• External limiting membrane, • Outer nuclear layer,• Outer plexiform (Henle) layer, & • Internal limiting membrane.

FUNCTIONAL DISTINCTION

• highest discriminative ability(VA),

• colour perception and • light plane polarity.

Specific anatomic configuration

• Densest concentration of cones and a one to one photoreceptor-ganglion cell relationship. Cones more elongated and slender.

• Absence of rods - fovea and foveola.• RPE more deeply pigmented.• Presence of xanthophyll.

Imparts certain properties …MFTs.

USES of macular function tests:

• Diagnosis; • Follow up of macular diseases &• For evaluating the potential macular

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

Macular function tests methods

• Psychophysical tests1. Visual acuity2. Contrast sensitivity 3. Photostress test4. Amsler grid5. Two point discrimination

test*6. Entoptic phenomenon7. Tests dependent on

macular pigment*8. Maddox rod test*9. Color vision10. Foveal flicker sensitivity11. Dark adaptation12. Perimetry/Scanning laser

ophthalmoscopy*13. LI, PAM*

• Electrophysiologic tests

15. Electroretinography (ERG)*

16. Electrooculography (EOG)*

17. Visually evoked response(VER)*

Visual Acuity

• A guide to the functioning of the entire visual pathway i.e. the visual axis, the macula and the optic pathways once the eye has been corrected for refractive errors.

• The best-corrected visual acuity is a measure of actual foveolar function.

• Visual acuity is measured by the visual resolution of a letter, symbol or a pattern under conditions of maximal contrast.

Visual acuity testing

The Snellen Chart• The Snellen score = test distance/size of the

smallest letter correctly identified.• The numerical value of the denominator is

the distance at which the height of this smallest identified

test letter subtends 5 minutes of visual angle

on the retina.• Each component of this letter subtends 1 min at this distance.LANDOLT C CHART : NAS-NRC recommended.SLOAN LETTERS

• Bailey-Lovie chart (ETDRS study)• Illiterate E chart (used with

illiterate patients)• Sheridan-Gardiner cards

(children>3 yrs)• Cat ford Drum - Based on

Oscillatory movements• Teller’s acuity cards (useful in

case of children from 6 months to 2 years).

• Cardiff vision chart ( useful for children from 2-3 years).

• Angular visual acuity cards (to avoid crowding phenomenon).• Near vision - by near vision

charts for each eye separately.

Teller’s Acuity Cards(with Black & White strips)

Caradiff vision charts (diminishing optotypes)

Pin-hole test• In pts with macular disease VA is frequently worse when pt looks

through a pin-hole. Pupillary reactions• The pupillary reactions are usually

normal in eyes with macular diseases.

• The defect usually indicates either a lesion of the optic nerve(APD) or extensive retinal disease.

Contrast sensitivity

• Contrast sensitivity is a measure of the minimum amount of contrast needed to distinguish a test object & indirectly assesses the quality of vision.

• Unlike VA, it is a measure of visual function under conditions of reduced contrast.

• Uses : 1. To detect early/subtle visual

loss esp when VA is Normal.2. To detect retinal conditions

like DR, ARMD and other retinal, macular and optic nerve diseases.

3. Optical conditions like refractive error, refractive surgery, cataract and intraocular lens implantation and normal aging of the eye.

• In macular diseases, there is a marked impairment for the intermediate and higher spatial frequencies.

Sinusoidal gratings

Functional acuity contrast test

CONTRAST SENSITIVITY GRATINGS

The Pelli Robson Chart developed in 1988 is the accepted gold standard for measuring contrast sensitivity.

The Hamilton-veale Contrast Sensitivity Chart

LETTER CONTRAST SENSITIVITY

Laser interferometer

• Useful subjective test of the resolving power of eye by using Laser generated interference fringes.

• Rodenstock interferometer.

• Dilated pupil.• Coarse to fine fringes,

change orientation.

Small helium-neon laser

collimated beam

optically divided

2 beams Overlap at/post. to

plane of lens Intersection of 2

beams Interference

fringes, imaged on

macula.

• Brightness increased in pts with dense cataracts.

• The laser interferometer resolving power converted to standard V.A.

• Fringes not dependent on optical components of eye, except large r.e. uncorrected aphakia.

• Limitations : 1. subjective, 2. Laser fringe vision>>

vision of letter acuity. 3. overpredicts visual

potential in amblyopes, 4. requires atleast 2 clear

areas.• Greatest usefulness – 1. Moderate

cataracts, 2. Macular diseases.

Potential acuity meter• GUYTON and MINKOWSKI.• It consists of a slit lamp attachment that

can project an entire V.A. chart on the macula.

• Emits 0.1mm beam into windows of pt’s cataract.

• Focusing with a slide scale ranging from +13 to-10D.• Dilated pupil, relaxed pt.• Easier than laser interofer-metry, does not overpredictV.A. in macular diseases.

Amsler Grid TEST• Evaluates the 20* of visual field

centered on fixation.• Used in screening and monitoring

macular diseases like1. Maculopathy – congenital, stargardt,

ARMD.2. Retinopathy – diabetic, CSR,

chloroquine related.3. Macular holes and4. Optic neuropathies. GRID : square 10*10 cm dividedinto 400 5*5 mm squares to be heldat 28-30 cm. Chart subtends angleOf 20*,each small square 1*.

Amsler Grid Testing• Procedure : reading glasses, cover

1 eye.• SIX standard questions to be

asked :1. Ability to see the central spot.2. Ability to see the 4 corners and sides of the

grid.3. Presence of any interruptions in the network of

small squares by holes or blurry areas.4. Ability to see all the horizontal and vertical lines

straight and parallel to each other.5. Presence of abnormalities like blurred areas,

holes, distortions, movement of certain lines, vibrations or waning, something shining or an abnormal colour or tint.

6. Distance of above abnormalities from the fixation point and the presence of any intact square between the central point and the abnormal areas.

• Recently 7 different charts have been used for increasing the sensitivity.

CHART 1

CHART 3CHART 2 CHART 4

CHART 5 CHART 6 CHART 7

MetamorphopsiaMicropsiaMacropsia

Positive/Absolute Paracentral Scotoma Arcuate Scotoma Central Scotoma 

Colour vision• The central 30-60 degree of visual field

processes trichromatic color vision.• Hereditary dystrophies of posterior pole, non-

hereditary maculopathies & certain optic nerve conditions often result in acquired color defects.

• Congenital:not particularly rare, affect males, symmetric, involve red-green color & occur as isolated visual defect.

• Acquired: asymmetric, accompanied by other visual dysfunctions, most commonly show irregularity in color testing not usually seen in congenital variety. Eg.

• BLUE-YELLOW defect – CSR & RP, or• RED-GREEN defect – Acq cone

degeneration/optic neuritis.

COLOR CONFUSION TESTS

1. ISHIHARA CHART 2. Farnsworth panel D-15 3. The American Optical

Hardy-Rand-Rittler pseudoisochromatic plates.

4. Sloan Achromatopsia Test.

• HUE

DISCRIMINATION TEST :

Farnsworth-Munsell 100 Hue test.

• SPECTRAL TEST : Nagel Anomaloscope

: the best method for accurate classification of red-green defects.

Two Point DiscriminationTest

• The ability to distinguish two illuminated points of light suggests good retinal function.

• “Rule of 2” : Two illuminated points of 2 mm diameter size and 2 inches apart are placed 2 feet away from the patient’s eye. The patient is then asked to indicate whether he can perceive the two points separately.

Maddox rod test• Simplest, most reliable test(opaque med).• Rod consists of several cylinders of glassplaced side by side in a frame.• Pt is asked to fixate light at a distance of 1/3

m through M.R. with opposite eye occluded.• Image formed is a straight

line(vertical/horizontal streak) running perpendicular to the axis of rods.

• Any breaks/holes; discoloration/distortion indicates a macular lesion.

• RED: more sensitive, tells us about color perception.

• Test various meridians by rotating : may reveal a RD/ a glaucomatous field defect.

Photostress test:• Bailliart in 1954.• Methods of assessing macular function

by timing the recovery of visual acuity after adaptation to an intense light source have been called macular photostress tests.

• 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.

• This regeneration can be measured by the rate of recovery of visual acuity or of contrast sensitivity.

• As the rate and extent of this regeneration is determined by anatomical and physiological apposition of photoreceptors and RPE, pathological states that affect the photoreceptors, Bruchs membrane, chorio- capillaris or choroid can prolong visual recovery time.

• In contrast no such prolongation is observed in diseases affecting the neural conducting pathways.

• USES : 1. to quantify subtle maculopathies,

2. discriminate between optic neuropathy & maculopathy,

3. to plot the recovery or progression of macular disease.

Often the photostress test will show changes where other more standard clinical tests may fail to show any change.

TECHNIQUE• The patient's pre-stress BCVA is noted. • The patient is asked to cover or occlude one

eye while the other eye is subjected to a bright light from fully charged ophthalmoscope directed onto the macula for 15 seconds/indirect ophthalmoscope light held 3cm away for 10 seconds.

• Photostress recovery time (PSRT) is the time it takes for the patient to read the line just above its pre-test best acuity line backwards.

• Normal PSRT ranges from 8-70 seconds.

CONDITIONS WITH PROLONGED PSRT

• Central serous retinopathy,• Age related maculopathy,• Macular edema, • Retinal detachment,• Diabetic retinopathy,• Systemic hypertension,• Retinal pigmentary degeneration, • Chloroquine retinopathy,• Alcohol or marijuana ingestion.

Dark adaptation• Dark adaptation refers to the ability of the

visual system,(both rods and cones mechanisms) to recover sensitivity following exposure to light.

• Most primitive model-photometer of Richard Forster.

• Hemispherical adaptometers are used nowadays (Goldman-Weekes by Haag Streit).

• Useful in pts presenting with c/o night blindness as in hereditary macular degenerations.

• Normally the whole process of dark adaptation requires 15-30 minutes.

• When performed at 5* a typical biphasic curve is obtained.

• PROCEDURE: 1. Subject exposed to intense light that

bleaches photoreceptors.2. Then Suddenly placed in dark.3. Threshold at which sub just perceives light

is plotted.4. Flashes repeated at regular intervals;

sensitivity of eye to light gradually increases.

5. By taking a threshold reading every min a curve of changing threshold Vs time of dark adaptation is obtained.

• Sensitivity curve : a. cone branch b. rod-cone break c. rod branch

Dark Adaptation Curve

Clinical applications1. Disorders of pigment degenerationa. Vitamin A deficiency; b. Fundus

albipunctatus2. Disorders of neural adaptationa. Oguchi’s diseaseb. Congenital stationary night blindness

(CSNB)3. Chloroquine toxicity,4. Retinitis pigmentosa Type II,5. Tapetoretinal degenerations,6. High myopia,7. Glaucoma.

The entoptic phenomenon (or Scheerer's phenomenon)

• visual perceptions that are produced or influenced by the native structures of one’s own eye.

• Structures producing – N anatomic parts/Media opacities.

1. PURKINJE VASCULAR E.P. :Visual elements underlying bld vsls become

adapted to this pattern of illumination.Focal source(at an unusual angle),pressed firmly against globe, retinalblood vessel pattern transiently.-Useful in pts with media opacities.-Limitation : intelligent & perceptive patients.

2. The blue field Entoptic Phenomenon

(Flying spots)• series of fast moving, luminous points or

spots seen on looking at a bright and diffuselyilluminated surface with no contrastingfeatures.• Best seen in background illuminated by blue light in spectral region of 350-450nm.• Capillaries full of RBCs too close to each

other, too far away from retina; so normally invisible. WBCs large act like gaps.

• White blood cells passing through the snake like retinal capillaries executes a sinusoidal wiggle motion.

• 5/> - normal.• Abnormal: (a) failure to see any, (b) partial loss in 1 part

of the field, (c) less no., (d) slow movement.• More accurate than : Two light discrimination, color perception & purkinje vascular

entoptic phen. • Disadvantage : subjective, poorly quantifiable.• Little use in significant vitreous opacity.• D/d : FLOATERS : variable appearance, almost

stationary or drift slowly, dont follow well-defined paths & are due to debris floating in vireous.

Haidinger’s Brushes• Subject looks at a surface illuminated with blue light

through a polarizer.• N – hourglass shaped yellowish brushes seen

radiating from the pt of fixation. On rotating polarizer, brushes rotate.

• Phenomenon - caused by variations in absorption of plane polarized light by oriented molecules of xanthophyll pigment in foveal retina.

• Screening test for retinal or macular pathology in strabismus patients with amblyopia.

Maxwell’s Spot• Subject looks at a brightly illuminated white

surface through blue filter.• N - dark/greyish spot in the visual field

corresponding to fovea surrounded by a dark ring is seen that gradually fades with time.

• Now used clinically to detect eccentric fixation by placing a fixation pt in the diffusely illuminated field.

• Perception is related to the arrangement of the yellow pigment in the inner retinal layers of the macula.

• Thus, both these tests utilise the phenomenon of the entoptic imagery of the fovea.

erg• The clinical ERG is the

recording of the electrical potential waveform generated by the total (pre-ganglionic) retina in response to a diffuse light stimulus.

• Test-performed in dark adaptation using a corneal contact lens(active) electrode which records changes in the corneo-retinal potential with each light stimulus. Reference electrode is attached to forehead.

• Negative ‘a wave’ – activities of rods & cones.

• Positive (composite)‘b-wave’ – from Muller cells in the bipolar region(inner retinal layers).

• c-wave – retinal metabolism (RPE).

• Peak amplitudes and latencies as well as waveform shape are considered in the interpretation of the ERG.

• Monitors preganglionic retinal activity so optic atrophy – N ERG.

• ERG - mass retinal response; an isolated lesion of the macula would not be expected to affect this test as it contains only 7% of total retinal cone population.

The Multifocal ERG• Produces topographical maps

of retinal function.• Stimulus is scaled for variation

in photoreceptor density across the retina; at fovea where receptor density is high smaller stimulus element is used than in periphery.

• The information can be summarised in form of a 3-D plot, resembling hill of vision.

• Use : Any disorder that affects retinal function.

Clinical applications

1. Vitamin A deficiency & xerosis.2. Retinitis pigmentosa & allied diseases e.g.(a) Congenital Night Blindness. (b) Oguchi's Disease. (c) Retinitis punctate albicans.3. Prognosis in Cataract.4. Prognosis in Glaucoma.5. Detachment of retina.6. Systemic & retinal vascular conditions.7. Macular diseases.

8. Malingering

Eog• Measures changes in corneo-retinal potential of the eye undervarying conditions of illumination.• 2 electrodes are placed on the skin,1 at lateral canthus & other at medialcanthus. Pt is asked to shift fixation back

&forth between 2 red lights that turn on &

offsequentially in an alternating fashion. • Several measurements are taken every

min for total of 15 min in darkness & then 15 min in light.

• Plot of average amplitude value for each min against time normally shows a min trough value during dark period & a max peak value in light.

• Dark trough - integrity of pigment epithelial outer segment region.

• Light rise - function of mid-retinal layers + outer retina-pigment epithelial complex.

• Light peak/dark trough ratio - reliable parameter of retinal function.

• N - >185%.• Arden ratio : calculated by taking ratio of(max light adapted to

min dark adapted response)*100. • EOG is a reflection of generalized retinal responsiveness. So,

abnormal in most of those conditions in which ERG is abnormal.• Except Best’s Vitelliform macular dystrophy, Butterfly

dystrophy, fundus flavimaculatus & generalized drusen. Here, ERG -N, EOG -abnormal.

v.e.r.• Measure of the

electrical potential generated in response to a visual stimulus.

• It is recorded with scalp electrodes placed over occipital lobe region, a cortical area with primarily a macular representation.

• Diffuse light stimulus flashes intermittently-in suspected monocular pathology.

• Patterned stimulus-alternating dark and light bars in form of a sinusoidal grating.

• Checkerboard pattern stimulator with alternation of dark and light checks.

• Then average potential is calculated by a computer.• USES: monitoring of visual function in babies, macular

pathway function & inv of optic neuropathy(demyelination).

• Though VER is predominantly a foveal response, it represents integrity of entire visual pathway from retina to occipital lobe.

• Limitation : cant differentiate macular from an optic n/cortical pathology.

Foveal Flicker Sensitivity

• A small flickering test light (0.5-2*) is superimposed on a constant background luminance.

• The luminance of the flickering test light is so modulated; that the mean luminance of the test light is equal to that of the surround.

• For a given frequency value, minimum modulation depth at which test spot is barely perceived to be flickering is defined as threshold modulation, reciprocal of which is sensitivity.

• Comparison with normal patients yields information about presence of macular pathology.

Flicker sensitivity curve is then plotted for a given point on retina as a function of flicker frequency.

perimetry• Perimetry can also test the

retinal function.• N useful for defects of

peripheral visual fields careful STATIC of central 2-4* - early maculopathy.

• FLICKER PERIMETRY.• Scanning Laser

ophthalmoscope.• Macular disease is

sometimes part of a generalized pathologic process & in such cases peripheral field may also show abnormalities.

SCANNING LASER OPHTHALMOSCOPE

Thank you!