Most eye conditions reach a disability percentage through a single axis: the visual acuity table. Cataract, glaucoma, keratoconus — all are ultimately measured by what they did to acuity or to the visual field. Ptosis is one of the few exceptions. It has a clause of its own, clause 55, and it is rated by lid position — how far the lid has dropped and how much it hides the pupil — not by what the patient reads on the chart. And it is precisely here, in this clause, that Israel’s two disability systems measure the same thing in two entirely different ways.
What ptosis is, and why it matters
Ptosis is a descent of the upper eyelid from its normal position. It may be congenital, or acquired with age as the tendon holding the levator muscle stretches (aponeurotic ptosis), or the result of a neural problem — third-nerve palsy, Horner’s syndrome — or of a muscle disease such as myasthenia gravis, in which the droop worsens with fatigue and varies through the day.
Beyond appearance, the droop has a real functional cost: the lid blocks the upper visual field, and the patient compensates by tilting the head back to see beneath it. When the droop is bilateral and severe, that tilt becomes constant. This is why the schedule rates ptosis by how far it covers the pupil — because that is what decides whether it is merely cosmetic or already impairs function.
At the National Insurance Institute: clause 55(a), measured by MRD
The National Insurance Institute measures the droop on straight-ahead gaze by MRD — the distance from the light reflex on the centre of the cornea to the upper lid margin. The more the lid droops, the smaller the MRD. The scale:
| Finding | One eye | Both eyes |
|---|---|---|
| MRD greater than 2.5 mm | 0% | 0% |
| MRD 2.5 mm or less, but not covering the pupil | 10% | 10% |
| A difference of ≥2 mm in lid-margin height between the eyes | — | 10% |
| The pupil covered to its centre — vision by head tilt | 15% | 30% |
| Full droop — vision only by manually lifting the lid | 25% | 50% |
Two rows here deserve attention. The first: the 10% row is one of the very few in the entire eye schedule where the value for both eyes is no higher than the value for one — 10% in both cases. The second: a difference of 2 mm or more in lid height between the eyes gives 10%, but only as a comparative two-eye criterion — it has no one-eye form, because by its nature it measures the relation between the two eyes.
At the Ministry of Defence: clause 55(a), measured in millimetres of droop
Here the definition inverts. The Disabled Persons Regulations state explicitly that the droop is measured in millimetres — not by MRD as at the National Insurance Institute. That is, not the distance that remains visible, but the number of millimetres the lid has fallen. The scale:
| Finding | One eye | Both eyes |
|---|---|---|
| A droop of 1 to 1.5 mm | 1% | 2% |
| A droop of 1.6 to 5 mm | 10% | 20% |
| The lid covers the pupil on forward gaze | 15% | 30% |
And two further provisions outside the table. A full droop is not a row in the clause: the affected eye is deemed 3/60 on the visual acuity table, and the percentage is derived from there against the fellow eye — one eye at 3/60 against a normal eye comes out at 25%. In addition, ptosis remaining as a cosmetic defect in an eye already rated 30% gives an added 5% on a cumulative calculation.
Note the 1% in the first row: a mild one-millimetre droop, which at the National Insurance Institute would be absorbed into 0%, earns a percentage at the Ministry of Defence. This is part of the general principle of the Disabled Persons Regulations, under which a minimal finding is not zeroed.
The same lid, two numbers moving in opposite directions
This is the point easy to trip on. The National Insurance Institute measures MRD — a number that shrinks as the droop worsens. The Ministry of Defence measures millimetres of droop — a number that grows as the droop worsens. The very same lid will give a “small number” in one book and a “large number” in the other, and both describe the same eye.
The practical meaning: a result measured for one system cannot be submitted to the other. A document stating “an MRD of 2 mm” satisfies the National Insurance definition but tells the Ministry of Defence assessor nothing about how many millimetres the lid dropped, and vice versa. An examination prepared for a committee must document both measures explicitly.
What should be documented before the committee
- MRD and millimetres of droop, both. Each system requires a different measure, and documentation carrying only one loses percentages in the other.
- A straight-ahead photograph showing the lid position and its coverage of the pupil — the criterion that separates cosmetic from functional.
- A visual field test demonstrating the upper obstruction, especially where the pupil is covered — it illustrates the functional loss that the number alone does not show.
- A cause workup — aponeurotic, congenital, neural or muscular. In myasthenia, where the droop varies with fatigue, it is worth documenting the variation through the day rather than a single measurement.
- A stable measurement, on more than one occasion, especially after levator surgery or treatment — to show a final state rather than an intermediate point.
Anyone preparing for a committee in either system will find the full framework on eye disability assessment, which also explains how the visual acuity table works — relevant here especially because of the way the Ministry of Defence rates a full droop.
Bottom line
Ptosis is the reminder that not every eye disability passes through the visual acuity table. It has a clause of its own, measuring lid position — but the National Insurance Institute measures it by MRD and the Ministry of Defence by millimetres of droop, and the two numbers move in opposite directions. And only at the extreme, in the full droop, does the Ministry of Defence return the eye to the acuity table. Whoever walks into a committee with both measures in the file — not just one — knows the number that comes out will reflect the eye, and not the book it happened to be measured in.
Frequently asked questions
How many disability percentages does ptosis carry?
It depends on the degree of droop and on the system. At the National Insurance Institute, clause 55(a) rates by MRD: a mild droop that does not cover the pupil gives 10% for one eye, a pupil covered to its centre gives 15% for one eye or 30% for both, and a full droop gives 25% for one eye or 50% for both. At the Ministry of Defence measurement is by millimetres of droop, and the numbers differ: 1% for a droop of 1–1.5 mm, 10% for 1.6–5 mm, and 15% where the lid covers the pupil. The same eye can come out at a different number in each system.
Why does the same droop get a different percentage in the two schedules?
Because they measure different things. The National Insurance Institute measures MRD — the distance from the light reflex on the cornea to the upper lid margin on straight-ahead gaze — a number that grows as the droop is milder. The Ministry of Defence measures the number of millimetres of the droop itself — a number that grows as the droop is more severe. The two numbers move in opposite directions, so a result cannot be carried from one system to the other without re-measuring by the correct definition.
How is a full droop covering the whole pupil rated?
At the National Insurance Institute a full droop — one that allows vision only by manually lifting the lid — is rated 25% for one eye or 50% for both, as a standalone row in clause 55. At the Ministry of Defence there is no clause row for it: the affected eye is deemed 3/60 on the visual acuity table, and the percentage is derived from there against the fellow eye. One eye at 3/60 against a normal eye is rated 25%. So the top of the scale actually returns to the acuity table — the very axis ptosis usually bypasses.
A very mild droop — is it worth anything?
Here there is a characteristic gap between the systems. At the National Insurance Institute an MRD greater than 2.5 mm is still considered normal and rated 0%. At the Ministry of Defence a droop of 1 to 1.5 mm already gives 1% for one eye or 2% for both. This is part of a wider pattern: minimal findings at the Ministry of Defence yield 1% rather than 0%.
