Moderator : Dr. Vivek Kumar

Macular Function Tests

Macula is a round area at the posterior pole temporal to the optic disc

5.5mm in diameter Comprises of fovea

centralis(1.5mm), foveola(0.35mm) and FAZ(0.4-0.6mm).

MACULA

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

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

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

MACULAR FUNCTION TESTS

PSYCHOPHYSICAL ELECTROPHYSIOLOGIC

PSYCHOPHYSICAL TESTS

Visual acuity

Contrast sensitivity

 Photostress test

Amsler Grid

Two Point Discrimination

Entoptic Phenomenon

Maddox Rod test

PSYCHOPHYSICAL TESTS

Colour Vision

Foveal Flicker Sensitivity

Dark Adaptation

Perimetry / Scanning Laser Ophthalmoscopy

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

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

Pin-hole test

In pts with macular disease VA

is frequently worse when pt looks through a pin-hole

Usually normal in eyes with macular diseases

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

Pupillary Reactions

CONTRAST SENSITIVITY

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

The Hamilton-veale Contrast Sensitivity Chart

The pelli - robson Contrast Sensitivity Chart

Laser InterferometerCataract, Macular

Diseases

Rodenstock interferometer

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

Coarse to fine fringes, change orientation

• Dilated Pupils• Light Beam in the centre of pupil at

the plane of iris

• Pupil scanned until fringe pattern percieved

• Asked to indicate the orientation of light

• Gratings gradually diminished• V.A. measured from the width of

gratings

• 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

• Limitations : 1. Subjective 2. Laser fringe vision>> vision of

letter acuity 3. Overpredicts visual potential in amblyopes 4. Requires atleast 2 clear areas

Potential Acuity Meter (PAM)

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 patient’s cataract

Easier than laser interoferometry, does not overpredict V.A. in macular diseases

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

TECHNIQUE

The patient's pre-stress BCVA is noted

Occlude one eye while the other eye is subjected to a bright light from indirect ophthalmoscope light held 3cm away for 10 seconds

Photostress recovery time (PSRT) estimated

Normal PSRT ranges from 8-70 seconds

1. To quantify subtle maculopathies

2. To 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

USES

AMSLER GRID TESTEvaluates the 20* of visual field

centered on fixation.

Used in screening and monitoring macular diseases

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

MetamorphopsiaMicropsia

Macropsia

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 – Acquired cone degeneration/optic neuritis.

COLOUR VISION

COLOUR CONFUSION TESTS

1. Ishihara Chart 2. Farnsworth panel D-15

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.

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

Visual elements underlying blood vessels become adapted to this pattern of illumination

Focal source (at an unusual angle),pressed firmly against globe, retinal blood vessel pattern transiently

Useful in patients with media opacities

Limitation : intelligent & perceptive patients.

PURKINJE VASCULAR E.P.

Series of fast moving, luminous points or spots seen on looking at a bright and diffusely illuminated surface with no contrasting features

Best seen in background illuminated by blue light in spectral region of 350-450nm

>5 normal

THE BLUE FIELD ENTOPTIC PHENOMENON(FLYING SPOTS)

Abnormal: (a) failure to see any (b) partial loss in 1 part

of the field, (c) less no.

• More accurate than : Two light discrimination, color perception & purkinje vascular

entoptic phen.

• Disadvantage : subjective, poorly quantifiable

• D/d : FLOATERS : variable appearance, almost stationary or drift slowly, dont follow well-defined paths

MADDOX ROD TEST

Simplest

Most reliable test(opaque med)

Rod consists of several cylinders of glass placed 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

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

MADDOX ROD TEST

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.

Dark adaptationDark 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

PROCEDURE:

1. Subject exposed to intense light that bleaches photoreceptors

2. Then Suddenly placed in dark3. Threshold at which sub just perceives light is plotted4. Flashes repeated at regular intervals; sensitivity of eye

to light gradually increases5. 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 albipunctatus

2. Disorders of neural adaptation3. Chloroquine toxicity4. Retinitis pigmentosa Type II5. Tapetoretinal degenerations6. High myopia7. Glaucoma

PERIMETRYPerimetry can also test the

retinal function

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

ELECTRO-RETINOGRAM (E.R.G)

ELECTRO-OCULOGRAM (E.O.G)

VISUAL EVOKED POTENTIAL (V.E.P)

ELECTRO PHYSIOLOGICAL TESTS

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.

Performed in dark adaptation

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 ERGProduces 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 Cataract4. Prognosis in Glaucoma5. Detachment of retina6. Systemic & retinal vascular conditions7. Macular diseases

8. Malingering

EOG

Measures changes in corneo-retinal potential of the eye under varying conditions of illumination

Procedure

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

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

EOG

VEPMeasure of the electrical

potential generated in response to a visual stimulus

• 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

Then average potential is calculated by a computerUSES: 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