The visual field test: what is it for?

The visual field test, also known as perimetry, maps the full extent of what you perceive around the point you are fixing on, without moving your eyes. It is a painless examination carried out in the practice, essential for screening and monitoring glaucoma as well as many disorders of the optic nerve and the retina. It measures your peripheral vision, the vision that a simple visual acuity measurement is not enough to assess.

UNDERSTANDING

What is the visual field?

The visual field refers to the entire area that a stationary eye can perceive when it fixes on a point straight ahead. It includes central vision, precise, which is used for reading and recognising faces, and peripheral vision, coarser, which detects movement and helps you orient yourself in space.

In adults, one eye normally covers about 60° towards the nose, 90° towards the temple, 60° upwards and 70° downwards. The two eyes combined provide a wide binocular field, with a central overlap zone that enables depth perception.

Schematically, we distinguish:

• The central visual field: the 30° around the point of fixation, where fine vision is concentrated
• The peripheral visual field: beyond 30°, up to the outermost limits of perception
• The blind spot: an area naturally not perceived, corresponding to the head of the optic nerve, which is devoid of photoreceptors

DEFINITION

What is perimetry, the visual field test?

Perimetry is the technique used to measure the visual field. It consists of presenting, at different points in space, light stimuli of varying intensity while you fix on a central marker. By signalling each point you perceive, you allow the device to reconstruct a map of your retinal sensitivity, eye by eye.

Automated static perimetry

This is the most widely used method today. Fixed light points appear at predefined locations, with a brightness that increases gradually until you perceive them. The device thus determines the sensitivity threshold of each area. Automated perimeters of the Humphrey or Octopus type are based on this principle.

Kinetic perimetry (Goldmann)

Older, Goldmann-type kinetic perimetry moves a light point from the periphery towards the centre until you see it. It remains useful for exploring the far peripheral field, particularly in certain neuro-ophthalmological disorders or for assessing fitness to drive.

HOW IT WORKS

How does the visual field test take place?

The examination takes place in the practice, seated, one eye after the other, with the eye not being tested covered by a patch. You place your chin on a chin rest facing an illuminated bowl, you fix on a central marker, and you press a button each time you perceive a light point. The examination is not painful and does not require dilation.

Step by step

1. Your near vision is corrected first if needed (a suitable lens is fitted on the device)
2. You rest your head on the chin rest and the forehead support
3. You fix on the central point, never looking around for the points
4. You click the button as soon as a light point appears, even faintly
5. The device tests the other eye using the same protocol

Duration and comfort

Allow 5 to 10 minutes per eye depending on the programme chosen and your response pace. The examination requires concentration: it is normal not to see some points, this is not a mistake. Breaks are possible if fatigue sets in. No dilating eye drops are needed, and you leave with normal vision.

Advice before the examination — come rested and, if you wear glasses, bring your recent correction. Avoid straining to fixate: simply keep your eye resting on the central point and let the stimuli appear in the periphery. Tell the operator of any discomfort or urge to blink, as the examination can be paused.

INDICATIONS

In which cases is the visual field test prescribed?

The visual field test is prescribed whenever a disorder of peripheral vision is suspected or needs to be monitored. Its prime indication is glaucoma, but it also plays a part in diseases of the optic nerve, cerebral disorders and the assessment of fitness to drive. It complements, without replacing, the fundus examination and OCT.

Glaucoma, the main indication

Glaucoma progressively destroys the fibres of the optic nerve and creates characteristic defects in the visual field, often silent and long overlooked by the patient. Perimetry makes it possible to detect these defects, measure their extent and follow their progression over time, generally once or twice a year depending on severity.

Neuro-ophthalmological disorders

A lesion along the course of the visual pathways, from the optic nerve to the occipital cortex, leaves a typical signature in the visual field:

• Optic neuropathies (inflammatory, ischaemic, compressive)
• Hemianopia: loss of one half of the visual field, suggestive of a cerebral disorder (stroke, tumour)
• Quadrantanopia: loss of one quarter of the field
• Pituitary adenoma compressing the optic chiasm

Retinopathies and fitness to drive

Certain retinal diseases alter the peripheral visual field: retinitis pigmentosa, sequelae of vascular occlusion, or complications of advanced diabetic retinopathy. In addition, regulations require a minimum visual field for a driving licence: perimetry then serves as a medical certificate of fitness, particularly for professional drivers.

INTERPRETATION

How do you read visual field results?

The visual field report is presented as a map of points, more or less dark depending on your sensitivity at each location. The areas where you do not perceive the expected stimuli appear grey or black: these are the defects. Several numerical indices summarise the whole and allow one examination to be compared with another.

Defects and scotomas

A scotoma is an area of the visual field where perception is reduced or absent. Its shape guides the diagnosis: an arcuate scotoma, curving around the point of fixation, suggests glaucoma; a defect respecting a vertical midline points rather to a disorder of the cerebral visual pathways.

The MD and PSD indices

The automated report provides global indicators:

• MD (Mean Deviation): the mean deviation of your sensitivity compared with a reference population of the same age. The more negative it is, the more diffuse the involvement
• PSD (Pattern Standard Deviation): measures the irregularity of the field, useful for spotting localised defects
• Reliability indices: rates of false positives, false negatives and fixation losses, which indicate whether the examination is usable

A single abnormal examination is not enough to make a diagnosis. Reproducibility matters: it is the repetition of examinations over time, compared point by point, that distinguishes a genuine defect from an artefact linked to fatigue or to insufficient learning of the test.

PERFORMING THE TEST WELL

How can you perform your visual field test well?

The quality of a visual field test depends greatly on your concentration and cooperation. A well-performed examination provides sound reliability indices, which are essential for accurate interpretation. A few simple guidelines help to obtain a usable report, especially during the first examination, where the learning effect plays a far from negligible role.

• Always fix on the central point: never look around for the light points
• Click as soon as you perceive a point, even a very faint one, without waiting to be certain
• Do not worry about the silences: some points are deliberately too faint to be seen
• Blink normally between stimuli, but avoid keeping your eyes closed for long
• Report fatigue: a break is better than a rushed examination

FAQ

Frequently asked questions

Sources

1. Société Française d’Ophtalmologie (SFO). Glaucome primitif à angle ouvert. Rapport SFO 2014 (Renard J-P, Sellem E, dir.), chapitre 12 « Quel bilan à quel stade? ». em-consulte.com/em/SFO/2014
2. Collège des Ophtalmologistes Universitaires de France (COUF). Item 84: Glaucomes. Référentiel d’ophtalmologie, chapitre 14. couf.fr
3. Haute Autorité de Santé (HAS). Dépistage et diagnostic précoce du glaucome: problématique et perspectives en France. 2006. has-sante.fr/jcms/c_500229
4. Inserm. Glaucome: mieux dépister pour lutter contre une cause majeure de cécité. Dossier, 2013. inserm.fr/dossier/glaucome
5. Société Française d’Ophtalmologie (SFO). Neuro-ophtalmologie pratique. Rapport SFO 2020 (Vignal-Clermont C, dir.). sfo-online.fr

Further reading

• Glaucoma and diabetes: an association to screen for
• Diabetic retinopathy: screening and follow-up
• Book an appointment at the practice

Cachan practice · Tel. +33 1 45 47 08 11

Medical disclaimer

This article is intended for information purposes. A personalised ophthalmological opinion remains essential for any diagnostic or therapeutic decision.

This article is intended as general information and is not a substitute for a medical consultation. The interpretation of a visual field test requires a complete ophthalmological examination, set alongside the fundus, OCT and intraocular pressure. For any question concerning your vision, consult an ophthalmologist.

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