Visual Field Loss — How the Disability Percentages Are Determined

The visual field is everything the eye takes in while the gaze is fixed on a single point. Visual acuity measures the centre; the field measures all the rest. A person can read the bottom line of the chart and still struggle to cross a road — and that is precisely the situation in which rating by acuity alone misses what actually happened.

For the broader picture of how rating works see Ophthalmic Expert Opinions for the National Insurance Institute, and for an initial numerical estimate the eye disability calculator, which carries both schedules.

Two systems, two schedules

Visual field loss is rated by the National Insurance Institute under clause 52(2), and by the Ministry of Defence under clause 52(b) of the Disabled Persons Regulations. These are not two phrasings of the same thing; they rest on different logic.

The Institute sorts first by the type of loss — quadrant, half, or concentric constriction. The Defence schedule opens instead with concentric constriction, gives it a finer scale, and adds a standalone item for bilateral homonymous defects that has no separate counterpart in the Institute’s table.

The practical consequence: the same visual field test can yield two different numbers, sometimes far apart, in the two systems. Anyone running both tracks in parallel should know this in advance.

How it is measured — and what counts as an admissible test

The Defence regulations require testing expressly on a Goldmann perimeter with a V/4 target, or on another accepted instrument. In practice most testing today is automated, which is fine — but the result has to be comparable.

The “diameter of the visual field” is defined as the average of the vertical and the horizontal diameter. The definition sounds technical and it determines outcomes: a field constricted mainly along the vertical axis gives a higher average than the chart appears to show, and the reverse.

And the point that decides more than any other: if the chart is unreliable on repeat testing as well, the rating is set from the clinical findings. Perimetry is a subjective test — it depends on cooperation, concentration, fatigue and steady fixation. The instrument reports fixation losses, false positives and false negatives, and a test with poor reliability indices will not carry weight. A large share of the disputes I see are not about the size of the defect but about whether the test is admissible at all.

Two practical conclusions follow: a single test is not enough where the finding is significant, and repeat tests showing a consistent pattern are worth far more than one impressive test.

National Insurance Institute — clause 52(2)

Quadrant loss (or less):

• Loss of less than a quadrant — 0% in one eye, 0% in both.
• Upper nasal quadrant — 0% and 0%.
• Upper temporal quadrant — 5% and 15%.
• Lower nasal quadrant — 5% and 15%.
• Lower temporal quadrant — 10% and 25%.
• Lower nasal in one eye and lower temporal in the other — 30%.

Half-field loss:

• Upper half — 10% and 30%.
• Inner half — 10% and 25%.
• Complete right or left homonymous half — 60%.
• Outer half — 20% and 50%.
• Lower half — 20% and 65%.

Concentric constriction by diameter:

• Above 80° — 0% and 0%.
• 61°–80° — 0% and 5%.
• 41°–60° — 5% and 20%.
• 20°–40° — 10% and 40%.
• Under 20° — 30% and 100%.

Note the asymmetry between upper and lower: a lower temporal quadrant is worth twice an upper temporal quadrant, and a lower half in both eyes is worth 65% against 30% for an upper half. This is not arbitrary — the lower field is the one used for walking, descending stairs and detecting obstacles on the ground.

Ministry of Defence — clause 52(b)

(1) Concentric constriction by average diameter:

• Up to 60° — 1% in one eye, 10% in both.
• 41°–59° — 5% and 20%.
• 31°–40° — 10% and 40%.
• 21°–30° — 25% and 60%.
• 20° or less — 30% and 100%.

(2)–(3) Loss of half the field from the periphery to 20° from centre or less:

• The inner half — 10% and 25%.
• The outer half — 20% and 60%.

(4) Bilateral homonymous defect:

• Homonymous hemianopsia — 50%.
• Upper homonymous quadrantanopsia — 10%.
• Lower homonymous quadrantanopsia — 40%.

(5) Other constriction:

• Loss of less than one quadrant — 1% and 2%.
• Upper temporal quadrant — 5% and 15%.
• Upper half — 10% and 20%.
• Lower temporal quadrant — 10% and 30%.
• Lower half — 20% and 65%.
• Upper nasal quadrant — 1% and 10%.
• Lower nasal quadrant — 10% and 20%.

The most visible difference between the schedules is at the mild end: constriction to a diameter of 60° attracts 1% at the Ministry of Defence (10% in both eyes), whereas at the Institute the same diameter falls within the 41°–60° band and attracts 5% and 20%. At the severe end the two systems converge on 30% and 100%.

What causes field loss — and what that means for rating

• Glaucoma. The most common cause of progressive field loss. It begins in the periphery and the paracentral region and moves inward, and the patient notices it late. At the Institute glaucoma itself attracts no percentage — clause 58 refers the rating to the visual field and visual acuity. At the Ministry of Defence it is rated in its own right (5% in one eye, 10% in both) in addition to the field and acuity impairment.
• Brain injury — stroke, head trauma, tumour. The characteristic cause of a homonymous defect: the same half-field missing in both eyes. Here the rating may jump straight into the tens of percent.
• Retinal detachment and other retinal injuries. After successful treatment the rating follows what remains in acuity and field, not the event itself.
• Optic atrophy and optic neuropathies. Usually affect the central field or one half.
• Retinitis pigmentosa and retinal dystrophies. The classic pattern of progressive concentric constriction, up to tunnel vision — and precisely the situation in which acuity may remain 6/6 while the field is under 20°.
• Extensive peripheral laser treatment (PRP) in severe diabetic retinopathy — constricts the peripheral field as a side effect of sight-saving treatment.

A general principle in both systems: a retinal finding with no dedicated clause — a scar, atrophy, a coloboma — is not rated as a standalone item but according to its effect on visual acuity and on the visual field.

Combining field with acuity, and with other impairments

Field and acuity are two separate axes, and both can be impaired in the same eye. Where several separate impairments exist they are weighted from the remainder rather than added: 10% plus 10% is 19%, and 20% plus 10% is 28%. This is the most frequent calculation error in eye files.

And a further rule worth knowing: the same impairment must not be rated twice. Where the field defect is itself the expression of a disease already rated, the two clauses are not applied in parallel.

An aspect outside the schedule — fitness to drive

Visual field loss also bears on driving licensure, which is a separate matter from disability rating and is not decided by the medical committee. Functionally, a homonymous defect or significant peripheral constriction affects the detection of pedestrians and vehicles approaching from the side — sometimes more than it affects the percentage. In Ministry of Defence files and in work-accident files this is also what lies behind claims of an inability to return to the previous occupation.

What an ophthalmic opinion adds in a visual field file

• Examines the reliability of the tests — fixation indices and false responses — and explains which test reflects the true state.
• Measures the diameter as the schedule defines it, as a vertical–horizontal average, rather than by the impression the chart gives.
• Maps the finding to the correct clause in each system relevant to the file.
• Separates damage caused by the event from a pre-existing condition or an age-related change.
• Applies the weighting rules and ceilings correctly.
• Considers whether the condition is genuinely stable, or whether a temporary degree reflects it more faithfully.

And what an opinion does not do: it does not replace the committee’s examination, does not bind it and does not guarantee an outcome.

For civil proceedings running in parallel see Ophthalmic Expert Opinions for Civil Damages Claims, and for injuries arising at work, Eye Injury at Work.

How to get in touch

Examinations and assessments take place in Haifa and Herzliya, by prior arrangement. There is no need to send a full medical file with the first enquiry — a brief description of the finding, the stage the process has reached and what has been determined so far is enough to establish whether the case is suited to an assessment within this field of expertise. Every enquiry is considered on its own merits, with no undertaking as to a conclusion or to the outcome of the proceedings.

Get in touch to check suitability for an assessment