Central islands are like mountains on the cornea, usually occuring due to non-homogenity of the laser beam or fluid accumulation during ablation preventing smooth lasering. Lasers need a lot of maintenance, one part of which is keeping the lens clean so that none of the beam is blocked. Other problems can also cause problems with the beam. The worst part about central islands is that those of us who have them are in no-man's land right now, as we wait for technology to advance enough to fix this nasty complication.
Haw, W.W. and E.E. Manche, Large optical ablation zone using the VISX S2 smoothscan excimer laser. J Cataract Refract Surg, 2000. 26(12): p. 1742-7.
PURPOSE: To prospectively evaluate the safety and efficacy of the new large-zone (6.5 mm) photoablation technology using the VISX S2 Smoothscan excimer laser. SETTING: University-based hospital, Stanford, California, USA. METHODS: Forty-two eyes of 21 patients with a mean preoperative spherical equivalent (SE) of-5.55 diopters (D)+/- 2.24 (SD) (range-2.13 to-10.75 D) had laser in situ keratomileusis (LASIK) using the VISX Smoothscan S2 excimer laser for simple myopia or compound myopic astigmatism. A 6.5 mm optical zone was used in all eyes. Patients were prospectively followed 1 day and 1 and 3 months postoperatively. RESULTS: At 3 months, the mean SE was reduced 94% to- 0. 31+/- 0.55 D. Ninety-one percent of eyes had an uncorrected visual acuity of 20/40 or better. Eighty-eight percent were within+/-1.00 D of attempted correction and 84%, within +/-0.50 D. Stability within+/-0.50 D occurred after the first postoperative month. Vector analysis of eyes that had toric ablations demonstrated a difference vector within+/-1.00 D in 100% of eyes. The mean angle of error was-0.04+/- 6.37 degrees. Visually significant steep central islands associated with loss of best spectacle-corrected visual acuity was observed in 7.5% of eyes at 1 month. No eyes experienced significant glare or halos. CONCLUSIONS: The new large-zone (6.5 mm) photoablation technology with the VISX S2 Smoothscan resulted in effective reduction of simple myopia and compound myopic astigmatism. However, with the 6.5 mm zone, there may be an increased risk of developing symptomatic steep central islands in the early post-LASIK period compared with the standard 6.0 mm treatment zone.