Lasik correction - what conditions can it help?

In the early days of Lasik correction there were promises of complete freedom from corrective lenses, either eyeglasses or contacts.  These days a much narrower range of eye problems is treated.   What you should actually expect is less dependence on corrective lenses, not their elimination.

The three major conditions that Lasik can treat successfully are myopia (nearsightedness), hyperopia (farsightedness) and astigmatism.

If you are nearsighted, light from somethimg some distance away is focused in front of the retina (the back "screen" of the eye), rather than on the retina itself.   This means you can easily see something that is close, but have problems with things that are further away.

Hyperopia

The reverse happens with hyperopia.  The light is focussed behind the retina instead of on it, so you can clearly see objects some distance away, but have problems with closer ones.

With astigmatism, there are problems either with the shape of the cornea (the very front portion of the eye)or the lens itself.   Light reaches two focal points on the retina instead of one.   The result - blurred vision.

There is a fourth condition, called presbyopia, which is a natural process and really is a function of aging.   It mostly affects people over 40, when the cornea and the lens become less flexible and can't properly focus light rays on the retina.

The result is problems focusing on nearby objects, and the usual solution is bifocals.

One possible answer is the monovision route, in which one eye is corrected for distance vision and one for closeup work.   However not everyone is comfortable with this solution, and later opt to have both eyes made the same in a second treatment.

Myopia success rate

Lasik correction is generally very successful with myopia and somewhat less so when dealing with hyperopia.   Astigmatism lasik surgery can also be very successful.  Presbyopia is more difficult and generally can't be corrected by laser eye surgery without going the monovision route.

There are some limits that eye surgeons generally stick to. 

For myopia the limits are -0.75 to -11 diopters; for hyperopia the limits are +0.75 to +4; and for astigmatism the figures are +0.75 and +4.

In addition, your pupil diameter must be less than 8.5 millimetres, and the cornea must be at least 500 microns thick (a micron is one millionth of a meter).

Within those limits, surgeons are generally happy to undertake a lasik correction.