Understanding Common Vision Problems

Four words cover most of what a prescription describes. They get used loosely, and the loose use makes them harder to understand than they need to be.

Myopia — short-sightedness

The eye focuses light in front of the retina rather than on it, usually because the eye is slightly longer than its optics suit. Distance is blurred; near is clear. It typically appears in childhood and often changes through the teenage years before settling.

Hyperopia — long-sightedness

Light focuses behind the retina. A young eye can often compensate by focusing harder, which is why hyperopia sometimes shows up as tired eyes and headaches after close work rather than as blur. As focusing reserve falls with age, the blur appears.

Astigmatism

The eye’s surface is curved more steeply in one direction than another, so light does not come to a single point. The result is a smearing rather than a simple blur, at all distances, and it very often occurs alongside one of the two above.

Astigmatism is common and unremarkable. It is not a disease and, in most eyes, it is stable.

Presbyopia

From the mid-forties onwards the lens inside the eye becomes less flexible and near focus becomes harder to hold. This happens to everyone. It is why reading glasses, bifocals and progressive lenses exist, and why a prescription that was stable for twenty years starts changing again.

What a prescription is not

A prescription is a description of how your eye focuses light. It is not a score, and a “strong” prescription is not a sign of an unhealthy eye. Two people with identical prescriptions can have very different eyes, which is the reason the health part of the examination exists at all.

If a change comes on suddenly, affects one eye only, or arrives with pain, flashes or new floaters, that is not a refractive change and it should be seen promptly rather than booked in for a routine test.