Perimetry or Visual Field Test: How It's Done

By Cristiano Antonino On Jan 3, 2023

Perimetry is an eye test that measures the size of the visual space perceived around the eye by observing a fixed point

It is a non-invasive test that requires no medication and causes no discomfort, but only requires some attention. Here is how it is performed.

Perimetry, how the visual field test is performed

The perimetry test uses a computerised device, the campimeter, to assess the peripheral margins of vision and draw up real visual field maps.

The campimeter consists of a dome with a white background onto which a light stimulus of varying shape and intensity is projected. The patient has to press a button each time they perceive the stimulus.

The test involves assessing the visual field of one eye at a time: one of the two eyes is then covered and the test subject fixes a central point in front of him or her, marking the moment when he or she perceives the light stimulus in his or her visual field.

The test is then repeated for the other eye.

At the end, a map is produced that highlights

any points of reduced sensitivity
areas of visual field narrowing.

Visual field assessment performed with computerised equipment (computerised perimetry) can even detect losses in the patient’s concentration that reduce the reliability of the test.

What is the purpose of the visual field test?

Perimetry is used to study the sensitivity of the retina – quantifying any alterations or deficits – and the integrity of the nerve pathways that originate from it.

This test is used to monitor certain eye diseases characterised by loss of peripheral or central vision, such as glaucoma, optic neuritis and maculopathies.

Glaucoma and perimetric testing

The visual field test plays a critical role in the diagnosis of glaucoma and in monitoring its progression; glaucoma, in fact, is an optic neuropathy that causes a progressive narrowing of the visual field, which begins in the peripheral areas, until it leads – in the most advanced forms – to so-called ‘telescope vision’.

Perimetry, together with measurement of eye pressure and evaluation of the optic papilla, are the essential elements for the diagnosis of glaucoma, which, in its most common form, initially develops in a subtle form and only becomes evident when more than 50% of the optic nerve fibres have been lost, so much so that it is called ‘the silent thief of sight’.