If the laser removes too little tissue from the eye during a LASIK procedure, it can result in an undercorrection. This means that the patient won't get the clearest vision results they expected. Undercorrections are more common in people who are nearsighted. In some cases, a second LASIK procedure may be necessary to remove more tissue and achieve the desired results.
On the other hand, overcorrection occurs when too much tissue is removed during LASIK. This can usually be corrected with an improvement procedure, but in certain cases it can cause keratoconus, a thinning of the cornea that makes it unstable and irregular, resulting in significant vision problems. To treat this condition, topographic guided ablation combined with corneal cross-linking may be necessary to restore vision and correct the problem. In most cases, both overcorrection and undercorrection can be treated with an enhancement or retreatment procedure.
If this is not possible, eyeglasses or contact lenses can be used to correct the excessive or insufficient correction. In cases of significant undercorrection or regression, additional laser vision correction may be necessary after the surgeon confirms that the residual refractive error is stable.