Vision Assessment

Dr Rajvin Samuel

1 st yr pg

• Vision assessment in adults• Visual assessment in children• Retinal function tests• Visual field examination

1. Examination of Vision

Assessment of visual function

• Forms of visual perception are form sense , the field of vision, the light sense and the colour sense .

• Visual Acuity• Visual field examination with confrontation

test, perimetry (kinetic and static)• Dark adaptation – measurement of least

luminance required to produce a visual sensation

• Contrast sensitivity – is measurement of the smallest distinguishable contrast ,it is assessment of quality of vision

• Colour vision –with lantern test (Edridge green lantern) and Isochromatic charts

Visual Acuity• The principal of assessment is measurement of spatial resolution of

the eye i.e. an estimation of ability of eye to discriminate between two points.

DISTANCE VISION

Two distance point can be visible as separate only when they subtend an angle of 1 minute at the nodal point of eye.

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Visual Acuity• Definition-

It is defined as the measure of the smallest retinal image which can be appreciated with reference to its shape and size .it is actually measure of form sense.Subjective examination of the function of eye

• Central or direct vision • Distance vision with Snellen test type • Near vision with Snellen test type or Jaeger’s

test type

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Snellen chart Principle

• Each individual letter subtends an angle of 5 minutes and each component of letter subtends an angle of 1 minute at the nodal point of eye from the distance in meters written as numerical.

• Snellen chart is having different number of letters in different rows and the letter at top line should be read clearly at distance of 60 m. similarly the letters at subsequent lines as are read at 36, 24,18,12,9,6,5mts respectively

• Numerical convention is used for recording visual acuity. In fraction, the numerator is the distance at which the patient is sitting from chart and the denominator is the distance at which person (with normal vision) should be able to read the last line that person is able to read.

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Trial frame

Occluder and Pin Hole

Snellen Chart

Procedure of testing

• Patient is seated at the distance of 6 meters from Snellen’s chart (distance of 6 mts is taken as at this distance it is assumed that the rays are almost parallel and patient exert minimum accommodation)

• The chart should be properly illuminated at minimum of 20 feet candles. Patient made to wear trial frame. It is adjusted according to patient inter pupillary distance. 9

Procedure of testing• Ask the patient to read with one eye from the top letter

while the contra lateral eye is closed gently with the patient arm or with occulder in the trial frame.

• Now patient is asked to reads the Snellen’s chart and depending upon the smallest line which the patient can read from distance of 6mts his vision is recorded as 6/6, 6/9 ,6/12,6/18, 6/24, 6/36, 6/60.

• But if patient is not able to see the top line from 6mts he is asked to come towards Snellen’s charts step by step and vision recorded at 5,4, 3, 2, 1 mts and noted as 5/60,4/60,3/60,2/60,1/60 respectively

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Procedure of testing

• If patient is not able to read top line even at the distance of 1 mts he is asked to count fingers of examiner and his vision is recorded as CF3FT, CF 2FT, CF1FT OR CF close to face .

• If patient not able to count examiner finger close to face then examiner waves or moves his hand and asks patient whether he is able to see hand movement or not. Visual acuity then recorded as HM+ 11

Procedure of testing• When patient cannot distinguish hand

movements the examiner notes whether the patient can perceive light (PL) or not. If he perceive light it is noted as PL +ve otherwise as PL-ve. Also examiner then throw the light from four directions (nasal, superior, temporal, inferior)

• and record accordingly. if present patient perceive light from all directions it is marked as PR (Projection of rays ) present or else mark as absent or defective. The test is repeated for the other eye in similar fashion

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Pin Hole TestInterpretation

• If patient vision is improved with pin hole it means the poor acuity is due to refractive error.

• If static acuity means may be due to structural or organic cause.

• If reduced the poor visual acuity may be due to corneal opacity or lenticular opacity occupying papillary area or macular pathology.  

Near vision Charts for testing near vision are

1) Snellen near vision chart -

2) Jaeger chart

3) Roman test type

• Ask the patient to sit with his back to the• light • If the patient is using glasses for distance• the same number will be put on the trial frame. Occlude one eye

with an occulder • Ask the patient to hold the near vision by his right hand at a distance

of 25 to 33 cms.• Note the near vision as per the letter read • Repeat the test for the other eye. 14

Method of recording Near vision

• Ask the patient to sit with his back to the light • If the patient is using glasses for distance the

same number will be put on the trial frame. Occlude one eye with an occulder

• Ask the patient to hold the near vision by his right hand at a distance of 25 to 33 cms.

• Note the near vision as per the letter read • Repeat the test for the other eye.

Contrast sensitivty• Ability of eye to perceive slight changes in

luminance between regions not separated by definite borders.

Uses : 1. To assess for problems that could be faced [Driving in night /Cloudy day 2. To quantify accurately loss of vision [in cataracts, Corneal edema]

Letter contrast Contrast sensitivity sensitivity grating [Pelli Robson Chart] [Sine wave gratings]

• Spatial frequency : High sensitivity Narrower, frequent bands Low sensitivity Wider ,less frequent bands

Visual Assessment in Children• Preliminary Tests :

• Preliminary Tests Begin with general observation of the child. • Hirschberg’s Test: Gross check of ocular alignment.• Pupils: size, shape, reaction.• Ocular motility. • Fixation pattern.

Classification : • Infants: < age 1 yr• Toddlers: 1 yr – 4 yrs • Children: 5 yrs – 14 yrs• Adolescence: 15 yrs – 17 yrs• Adults: 18 yrs and above

Resolution acuity tests

• Optokinetic Nystagmus: • Nystagmus is elicited by passing a drum with black and white

stripes. If normal vision is present, rail-road nystagmus will be seen.

• Preferential Looking Test: Child is presented with two adjacent stimulus fields, one is

striped and the other is a plain background. The child will look at the striped pattern for a longer time. The location of the stripes is shifted randomly from right to left. Fineness of the stripes is reduced till the infant can no longer differentiate the stripes and the background.

• Visually Evoked Response: Useful in assessing visual function in infants. It is the electroencephalographic recording made from the occipital lobe in response to visual stimuli. It measures acuity by assessing the response of the brain to finest alternating black and white stripes or checks.

Optokinetic Nystagmus Preferential looking test Visual evoked potential

• Indirect assessment of VA: • Blink reflex in response to sound. • Menace reflex : i.e. closure of eyes on approaching of object if vision is

normal. • Fixation Reflex : i.e. Central / Steady / Maintained. Monocular behaviour:

resists occlusion on covering good eye.

• VA measurements (1-2 yrs) : • Marble game test: Child is asked to place marbles in the holes of the box.

Not intended to measure the visual acuity, but the monocular visual functioning. Vision is noted being ‘useful’ or ‘less useful’.

• Sheridan’s ball test: Series of balls of progressively smaller sizes used. Balls rolled on grey or white background, smallest size which the child picks gives the estimation of vision

• VA measurements (3-5 yrs) : Tumbling E test: Consists of different sizes of E with 4 directions. Child

asked to identify the correct direction. Sjogren’s hand test: Similar to Tumbling E test. Consists of picture of hand

in 4 different directions. Landolt’s C test / Broken wheel test: Pair of cars of progressively smaller

sizes, one of it with a broken wheel is shown. Child asked to identify the one with broken wheel.

Broken wheel test

Landolt’s C test Tumbling E Test

• VA measurements (3-5 yrs) : • Sheridan-Gardiner HOTV test: Child is handed a card of HOTV. Asked to

match the letters on the chart. Snellen's equivalent 6/60 – 6/6 can be estimated.

• Boek candy bead test: Child asked to match beads at 40 cms. Snellen’s VA of 20/200 can be estimated.

• Light home picture cards: Performed at 10 feet distance. Contains apple, house and umbrella arranged in Snellen's equivalent 20/200 – 20/10. Child asked to identify pictures in each line.

• Kay picture tests : Child is given set of pictures in hand. Similar pictures shown at 10 feet distance on a log MAR chart. Snellen’s equivalent 20/200 – 20/20 can be measured.

Sheridan-Gardiner HOTV test Kay picture tests

Retinal function tests• Amsler’s grid• Light perception test• Projection of rays• Photostress test• Two light discrimination• Maddox rod test• Entopic visualisation• Laser inerferometry• Potential acuity meter• Colour perception

Amsler’s grid

Colour vision

Pseudo isochromic charts

Farnsworth D 15 Test

Anomaloscope

• Maddox rod test

• Entopic visualisation

• Potential acuity meter

• Laser interferometry

Visual field testing