A Study of Central Islands after Excimer Laser phootorefractive Keratectomy

ABSTRACT

We analyzed computed corneal topography(EH-270,visioptics, Inc., USA) after excimer laser photorefractive keratectomy(PRK, Omnimed, Summit Technology, Inc., USA) to determine the prevalence f central islands, the factors having an influence on their occurrence, and the corneal ablation patterns. PRK was performed with single zone on 314 consecutive myopias(-1.0D~-11.25D) on which topographic analysis was done at least 3 months after surgery. Corneal ablation patterns were classified as uniform, keyhole, semicircular, and central island. Age, sex, amount of attempted correction, preoperative corneal thickness, and ablation zone(5.0mm vs 6.0mm) were studied whether they can affect on the prevalence of central islands. Topographic results showed a uniform ablation patterns in 213 eyes(67.7%), a keyhole ablation in 54 eyes(17.3%),a semicircular ablation in 18 eyes(5.7%), and a central islands in 29 eyes(9.3%). There was no association between prevalence of centralisland and age, sex, amount of attempted correction, or preoperative corneal thickness(P>0.05). Only one of 81 eye(1.0%) with smaller ablation diameter(5.0mm) presented central islands showing the highly statistical significance(P<0.005) while 28 of the 233 eyes(12%) with larger ablation diameter(6.0mm) presented central islands. In conclusion, we think that the ablation diameter is a risk factor in the prevalence of central island, and the further studies for the etiology of central island, which are based on the optical zone should be needed.