Diagnosis of visual impairment

If visual problems are suspected an ophthalmologist usually examines the eyes.

An ophthalmologists specializes in diagnosing, and treating eyes and their diseases.

Diagnosis of visual impairment in children

An ophthalmologist, optometrist, paediatrician or other specialist may examine a child between birth and 3 months, between 6 months to 1 year, around 3 years or 5 years of age.

This is especially important if there is someone in the family with vision problems. (1-4)

Signs of vision problems in children

Signs of vision problems in children include (3) –

• The child closes or covers one eye
• The child squints the eyes or frowns
• He or she complains that things are blurry or difficult to see
• He or she has trouble reading or doing other close-focussed work, or holds objects close to eyes
• The child blinks more than usual or seems frustrated when doing close-up work (such as looking at books)
• Eyes could be watery, and eyelids could look red-rimmed, swollen or crusted with secretions

Process of diagnosis

Diagnosis begins with complete history and family history of visual impairment in the patient.

External examination of the eye including lids, conjunctiva, cornea, iris, lens, etc. are the next step.

Tests for visual impairment

The tests that are used to diagnose visual acuity and visual impairment include the Snellen test, visual field test and so forth. (1-4)

Snellen test

The Snellen test is also known as the visual acuity test.

Usually a chart called the Snellen’s chart is used. It contains progressively shortening random letters and numbers and is placed 6 meters away from the patient.

The patient is asked to read the letters with each eye separately and both together. Ability to read the letters at each size determines the visual acuity.

After the test a score is obtained. It is made up of two numbers.

The first number represent how far away from the chart the patient was when he or she was able to successfully read the letters on the chart.

The second number represents how far away a person with healthy vision should be able to read the chart.

Healthy vision scores 6/6. If the score is 6/60, it means that the patient can only read something 6 metres away what a person with healthy eyesight can read 60 metres away.

Being partially sighted, or sight impaired means if level of sight loss is moderate and blindness, or severe sight impairment means when level of vision loss is so severe that a person is unable to complete any activities that require eyesight.

Partial sight or sight impairment is defined as 3/60 to 6/60 vision or having a combination of moderate visual acuity (up to 6/24) and a reduced field of vision.

Blindness is defined as having poor visual acuity (less than 3/60) but having a full field of vision or having poor visual acuity (between 3/60 and 6/60) and a severe reduction in the vision field or having average visual acuity (6/60 or above) and an severely reduced field of vision.

Visual field test

Visual field is the range of vision that a person can see without tilting or turning one’s head. This measures the peripheral vision of the eyes.

The test uses a device strapped over the patient’s eyes. Lights are flashed on and off in the patient’s peripheral vision.

He or she is then asked to press a button every time they see a light. Any gap of field of vision is detected.

Tonometry test

This test uses specialized instruments to determine fluid pressure inside the eye to evaluate for glaucoma.

Ocular Motility Assessment

This tests if there is squint of other problems in the movement of the eyeballs.

Other tests

Other tests like Visually evoked potential (VEP), Electroretinogram (ERG), Electro-oculogram (EOG) are sometimes prescribed to test if the signals from the eye are travelling adequately to the brain.

These may help if the patient is very young and clinical examination is difficult or if there are multiple handicaps that make diagnosis difficult.

Further Reading

• All Visual Impairment Content
• What is visual impairment?
• Visual impairment Types
• Visual impairment Causes
• Visual impairment Treatment

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.