Learn · Practical questions

Is my prescription bad?

Short answer: for almost everyone, no — and "bad" is the wrong axis anyway. A prescription describes a shape, not a health verdict. What is worth paying attention to is not how big the number is, but which direction it has been moving.

Rough bands, and what they actually mean day to day

There is no official threshold, but these are the ranges optometry works with. They apply to the sphere, mirrored on the plus side:

Under 3.00 D — mild

You get around a room unaided. What you lose is detail at distance: signs, faces, a screen across the office. The overwhelming majority of prescriptions sit here.

3.00 to 6.00 D — moderate

Correction becomes the default rather than a tool for specific tasks. Lens thickness starts to be worth discussing, and high-index materials become useful.

Above 6.00 D — high

Still very correctable. But a highly myopic eye is a structurally longer eye, and that carries a raised lifetime risk of retinal detachment, glaucoma and maculopathy — independent of how sharp your corrected vision is. It justifies regular dilated retinal checks, not worry.

The steps are small. Lenses come in quarter-dioptre increments, so −2.25 and −2.50 are neighbours, not a jump. A single-step change between two visits is usually within normal measurement variation — including how tired you were on the day.

The other numbers, briefly

Cylinder — under −0.75 is mild and extremely common; beyond −1.50 makes a clear difference uncorrected. High cylinder that is rising in a young person is the one pattern worth raising with a clinician.
Axis — not a strength at all. 175 is not worse than 12.
ADD — rises with age and then stops. Expected, not a decline.

What actually deserves attention

Almost every genuinely useful signal in a prescription is a change, not a value:

Myopia increasing quickly, especially in a child — the whole basis of myopia management
Astigmatism rising and its axis rotating together, in a young adult
A difference between the two eyes that is widening
A sudden shift in an adult whose prescription had been stable for years

Not one of those is visible on the paper in your hand. They are only visible against the previous ones — which is the entire argument for keeping them.

None of this is a diagnosis. If something about your vision has changed noticeably or suddenly, that is a reason to see an optometrist or ophthalmologist, whatever the numbers say.

Decode your own prescription Keep every prescription free