LASIK works by removing minute amounts of corneal tissue from the surface of the eye. By doing so, certain parts of the cornea can be flattened, and other parts steepened. For example, in shortsighted patients the central part of the cornea is flattened, the amount of flattening corresponding to the spectacle power of the patient.
Back to the question: Can spectacle power return after LASIK? The short answer is yes. This can happen for a few reasons:
1. The corneal shape slowly regresses towards its original shape (It can never regain its original shape, but the 'healing' process sometimes causes the corneal curvature to become a little more like how it was before the LASIK)
2. The eyeball changes in length, usually by becoming longer in very shortsighted people
3. Some other unrelated eye disease, such as cataract
The higher the spectacle power of the eye to begin with, the more likely this is to happen. However, overall the risk is low as has been shown in a number of studies.
Am J Ophthalmol 2008;145:46–54.
The above graph from an article in the American Journal of Ophthalmology shows that even after 10 years, the average spectacle power of the eyes of a group of patients was only about 50 degrees, or 0.50 dioptre of shortsightedness.
If the spectacle power returns, what next?
It depends on how much power has come back, how much cornea is left, and how keen the patient is on having a LASIK enhancement/adjustment.Generally speaking, an enhancement is not recommended if the residual spectacle power is 50 degrees or less than targeted. Some patients are also quite happy if the power is higher than that, and there is no need to repeat surgery for all these patients.
When the power gets to 75 degrees or higher though, more and more people find that it affects their daily activities. They may need glasses, for example, when driving. If so, the inconvenience may drive them to seek an enhancement. This can be considered if the remaining cornea is thick enough.
In recent times it has been found that a LASIK flap can be lifted again many years after the original surgery. As such, an enhancement surgery is very much 'half an original LASIK operation', since it does not involve making another flap. Using topography guided techniques, enhancements can be done not only to correct residual short/long sightedness and astigmatism, but also aberrations like spherical aberration and coma. The picture below shows topographies (corneal maps) of a patient who had coma and residual shortsightedness before (left most map) and the subsequent healing after enhancement. Note how the blue area has shifted from the right side (left map), over to the centre (right map).
If the cornea under a LASIK flap is already too thin for further treatments, alternative techniques would include PRK on the flap, or even ICL surgery if the anterior chamber of the eye is deep enough.