What are the tests for glaucoma?

Following initial tests and their purpose are summarized below


A Snellen chart is used to measure distance vision with your distance glasses.

It is helpful to bring your current glasses and prescription if available.

Colour vision

A specialized chart called Ishihara chart is used to check the colour vision. This is useful to differentiate causes of vision loss due to glaucoma and other optic nerve diseases. In glaucoma colour vision is preserved till late in the course of the disease.

Visual fields

This tests the periphery of the vision. Head is placed inside a large bowl and lights are flashed in the periphery. You then press a button when you see the lights while looking at the central fixation light. The same process is repeated with the other eye.

Slit lamp examination

This is the microscope like instrument that is used in all routine eye examinations. It shines a light in to the eye and the doctor looks at the front and the back of the eye through it. This gives a magnified image of the eye.


To measure eye pressure (IOP- intraocular pressure)

IOP is measured after making the eye numb with an anaesthetic/dye drop. An instrument called Goldmann tonometer mounted on the slit lamp is used to measure this.

The instrument comes close to the eye and measures the eye pressure. There is no sudden puff of air like you get at the opticians.


To examine the angle of the eye.

A special contact lens is put on the surface of the eye to look inside the eye and decide whether the ‘door’ or the angle of the eye is open or closed. This is a fundamental and important test as it helps to differentiate between open angle and closed angle type of glaucoma. This distinction is important, as the initial treatment for the two conditions is different.


To measure the central corneal thickness by an instrument called ultrasound pachymeter.

The instrument comes close to the eye and makes a noise. It does not hurt as the eyes are already numb due to the anaesthetic drops.

Dilated eye examination

Eye drops are instilled to dilate the pupils. These take about 10-20 minutes to work and make the vision blurred for a few hours. It is advisable not to drive till your sight returns to normal.

Dilatation helps to examine the lens and the back of the eye in detail.

Disc assessment/retinal nerve fiber layer assessment

This is the most important part of the examination where the optic nerve head (called disc) and the nerve fibres around it are assessed for changes due to glaucoma.

This is a specialized assessment as there are variations between normal and abnormal that can be hard to distinguish.

A glaucoma specialist is best able to find out if the optic nerve head is normal or suspicious for early glaucoma or has changes that are normal for you (physiological) but may look like glaucoma.

Disc photos

Pictures of the back of the eye are taken to serve as a baseline to look for any changes in future.

Disc/RNFL (retinal nerve fiber layer) OCT scan

A specialized scan of the back of the eye is done that measures the optic nerve head and retinal nerve fibre layer to compare it with normal database of similar age.

Once all these tests are done your specialist will be able to guide you about your diagnosis and appropriate management.

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October 06, 2019 10:09:19 AM, Mr IND, Bexley, Kent
I was very satisfied throughout with Mr Goyal’s clear explanations, patience, calm and reassuring approach during my procedure and with the outcome. Blind in my left eye – and a glaucoma sufferer – it was hugely important to me that my right eye functioned as well as was possible for a 83 year old. As a result, DVLA have sanctioned a 3-year driving licence in place of the previous annual renewal application … Excellent!!
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October 05, 2019 10:01:19 AM, Mrs J J, Kent
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