Thin Corneas and Laser Eye Surgery

Corneal strength is, in part, due to its thickness. The laser ablation does result in some thinning; the higher the amount of short-sightedness treated, the greater the amount of cornea ablated and the greater the thinning. This thinning is still small in relative terms, typically less than 10 to 20 per cent of total corneal thickness. Although rare, this thinning of the cornea can result in ectasia.

Corneal thinning from the ablation is less significant when performed at a deeper level in the cornea. LASIK is performed under a flap of cornea, typically 110 to 120 micrometres thick. PRK, on the other hand, is performed at a more superficial level under the epithelium, which is only 50µm thick. The risk of ectasia, although very low, is slightly greater in relative terms after LASIK compared with PRK.

There are generally accepted safety margins regarding how much cornea should be ablated (or how much short-sightedness should be treated) for different corneal thicknesses. For thinner corneas, consideration should be given to PRK in preference to LASIK. For particularly thin corneas, PRK should be performed.

It is also worth noting that other factors are taken into account when considering whether PRK or LASIK is the best treatment for patients with thin corneas.