healed. Healing time depends on the size of the epithelial defect but in general takes between 4 and 7 days. A tight-fitting lens should be removed if there is evidence of corneal hypoxia (eg, corneal edema, folds in the Descemet membrane, or iritis).
Contact Lenses After LASIK
The indications for contact lens fitting after LASIK are similar to those following other types of refractive surgery. The corneal contour is usually stable by 3 months after LASIK for myopia; however, it may take up to 6 months for the cornea to stabilize after LASIK for hyperopia.
A soft contact lens may be used immediately after LASIK surgery to promote epithelialization and to prevent epithelial ingrowth. It is generally used for several days on an extended-wear basis and then removed by the surgeon. Daily-wear contact lenses for refractive purposes should not be considered until the surgeon believes the risk of flap displacement is low.
Glaucoma After Refractive Surgery
The force required for applanation of a Goldmann tonometer is proportional to the central corneal thickness. As a result, an eye that has a thin central cornea may have an artifactually low IOP as measured by Goldmann applanation tonometry (GAT). Patients with normal-tension glaucoma have significantly thinner corneas than do patients with primary open-angle glaucoma. When a correction factor based on corneal thickness is applied, more than 30% of glaucoma patients demonstrate abnormally high IOP. The correction factor needed may be lower for measurements taken with the Tono-Pen (Reichert Ophthalmic Instruments, Depew, NY) and the pneumotonometer.
For IOP measured with GAT, an artifactual IOP reduction occurs following surface ablation and LASIK for myopia, both of which reduce central corneal thickness. Similar inaccuracies in IOP measurement can occur after surface ablation and LASIK for hyperopia. After excimer laser refractive surgery, the mean reduction in IOP measurement is 0.63 mm Hg per diopter of correction, with a fairly wide variation. Postoperatively, some patients may demonstrate no change in IOP measurement, whereas others may exhibit an increase. In general, the reduction of measured IOP is greater after LASIK than after surface ablation. Surface ablation patients with a preoperative refractive error of <5.00 D may have a negligible decrease in IOP measurements.
Topical corticosteroids that are used after refractive surgery pose a serious risk of corticosteroidinduced IOP elevation, particularly because accurate IOP measurement is difficult to obtain. By 3 months postoperatively, up to 15% of surface ablation patients may have IOP above 22 mm Hg. If the elevated IOP is not recognized early enough, optic nerve damage and visual field loss can occur.
If topical corticosteroids are used postoperatively for an extended time, periodic, careful disc evaluation is essential. Optic nerve and nerve fiber layer imaging may facilitate the evaluation. Periodic visual field assessment may be more effective than IOP measurement for identifying at-risk patients before severe visual field loss occurs (see Chapter 10, Fig 10-4).
Refractive surgery patients who develop glaucoma are initially treated with IOP-lowering medications, and their IOP is carefully measured. If medication or laser treatment does not adequately reduce the IOP, glaucoma surgery may be recommended. Patients who have had refractive surgery should be warned prior to glaucoma surgery of the potential for transient vision loss from inflammation, hypotony, or change in refractive error. The glaucoma surgeon should be made aware of the patient’s previous LASIK in order to avoid trauma to the corneal flap. For additional information on glaucoma management, see BCSC Section 10, Glaucoma.
Belin MW, Hannush SB, Yau CW, Schultze RL. Elevated intraocular pressure–induced interlamellar stromal keratitis. Ophthalmology. 2002;109(10):1929– 1933.
Brandt JD, Beiser JA, Kass MA, Gordon MO. Central corneal thickness in the Ocular Hypertension Treatment Study (OHTS). Ophthalmology. 2001;108(10):1779–1788.
Chang DH, Stulting RD. Change in intraocular pressure measurements after LASIK: the effect of refractive correction and the lamellar flap. Ophthalmology. 2005;112(6):1009–1016.
Hamilton DR, Manche EE, Rich LF, Maloney RK. Steroid-induced glaucoma after laser in situ keratomileusis associated with interface fluid. Ophthalmology. 2002;109(4):659–665.
Kaufmann C, Bachmann LM, Thiel MA. Comparison of dynamic contour tonometry with Goldmann applanation tonometry. Invest Ophthalmol Vis Sci. 2004;45(9):3118–3121.
Yang CC, Wang IJ, Chang YC, Lin LL, Chen TH. A predictive model for postoperative intraocular pressure among patients undergoing laser in situ keratomileusis (LASIK). Am J Ophthalmol. 2006;141(3):530–536.