Public cataract surgery only from 0.6 acuity – why the Snellen chart alone is not enough

“You have a cataract, but you still see too well to be operated on” – many patients hear this sentence. It does not come from the doctor’s judgement but from a criterion that applies to operations funded by the Polish public health fund (NFZ): a patient qualifies when distance visual acuity with best correction is 0.6 or worse (roughly 6/10 or 20/32), measured on a Snellen chart. The threshold keeps waiting lists in order, but from the patient’s point of view it can cause real problems. Here is why.

What 0.6 actually means

An acuity of 0.6 is roughly the sixth row of the chart. It means that from six metres you read characters a healthy eye recognises from ten. The test is performed in a well-lit room, on black letters against a white background, in the best glasses that can be prescribed. These are ideal conditions – and that is exactly the problem.

Vision is more than acuity

The Snellen chart measures one thing: the ability to recognise small, maximally contrasting characters. A cataract, however, degrades vision in several other ways the chart does not show:

• Contrast. The world is rarely black and white. The face of the person you are talking to, the edge of a step, a kerb at dusk, a grey car on a grey road – these are low-contrast objects. A patient may read the 0.8 row and yet not see the step they are walking down.
• Glare. A cloudy lens scatters light. Oncoming headlights, low sun or a wet road can completely “flood” the image. In a darkened consulting room this phenomenon simply does not occur.
• Light and pupil size. In posterior subcapsular cataract the opacity lies exactly in the visual axis. In the dim light of the consulting room the pupil is wide and the patient reads the chart quite well; on a bright day the pupil constricts and vision collapses.
• Colours. A yellowing lens acts like a filter – colours fade and merge, which patients often do not notice until they compare the operated eye with the unoperated one.
• Doubling and “ghosting”. Uneven opacities can produce doubled outlines of letters and lights in one eye.
• A shifting prescription. Nuclear cataract shifts refraction towards myopia – glasses have to be changed every few months and still “are never right”.

This is why two people with the same result of 0.7 can function completely differently: one without any trouble, the other giving up driving after dark, struggling to read and afraid of stairs. Under a rigid threshold, neither qualifies for surgery.

The second-eye problem

Cataract usually develops in both eyes, but at different rates. A common scenario: the first eye meets the criterion and is operated on, while the second – with an acuity of 0.7 or 0.8 – does not. The patient is left “in between”:

• Anisometropia. The operated eye sees at distance without glasses, while the other still has its old refractive error, for example −4 or +3 dioptres. Glasses usually cannot comfortably balance such a difference: the images in the two eyes differ in size, the brain cannot fuse them, and double vision, headaches, and problems with balance and judging distance appear.
• Binocular vision. One eye sharp, bright and “cool” in colour, the other hazy and yellowish – this is not a sum but a conflict. Many patients say that only after the first operation did they realise how badly they see with the other eye.
• Multifocal lenses. With EDOF and trifocal lenses the brain adapts best when both eyes work the same way. A gap of many months between the eyes makes this adaptation harder.

The regulations provide exceptions to the 0.6 threshold – including significant anisometropia after surgery on the first eye (above 3 dioptres) – but a smaller difference, which in practice can also be very troublesome, is no longer an exception.

Pre-operative diagnostics: corneal topography is not required

There is one more difference patients are usually unaware of. The standard qualification for publicly funded cataract surgery does not require corneal topography. Lens power is calculated from biometry and a measurement of corneal curvature at its centre – without a map of the whole surface.

This matters above all in astigmatism. Without topography it is easy to miss irregular astigmatism, underestimate its magnitude or determine the axis inaccurately. And a toric lens is unforgiving in this respect: every degree of axis error means roughly 3% of the correction lost, so a lens selected or positioned on the basis of incomplete measurements may correct astigmatism only partially – or add new astigmatism. That is why, even when a patient does receive a toric lens, the result is sometimes worse than it could be. We explain where post-operative astigmatism comes from in the article Why a toric lens must be considered in every cataract operation.

What this means for the patient

• If, despite a “good” chart result, the cataract interferes with daily life – driving, work, reading – there are two options: wait until acuity falls to the threshold, or consider private surgery, where the indication is real symptoms and examination findings rather than a single number.
• Both eyes are best planned as a whole from the start: which lens, what target refraction and what interval between the operations.

This does not mean a cataract should be operated on as early as possible. Every operation carries risk and must be justified. The point is that timing should be decided by how the patient really sees and functions – not solely by a row of letters read in ideal conditions.

How we assess vision at OKUMED

During qualification we ask about specific situations: night driving, reading, glare, stairs, computer work. We assess the type and position of the lens opacities at the slit lamp, perform macular OCT, biometry and corneal topography, and plan for both eyes from the outset. We write more about the differences between public and private surgery in the article How much does cataract surgery cost in Gdynia.

Book a cataract qualification visit at OKUMED – Świętojańska 135/2, Gdynia, phone +48 882 650 299 or book online.

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This article is for information only and does not replace a medical consultation. The description of the public scheme’s criteria reflects the rules as of September 2026; regulations may change.