| Background and ObjectiveLaser in situ keratomileusis is widely accepted as a safe, predictable and effective refractive surgical procedure for the correction of myopia. However, Refractive regression is liable to occur to a few high myopic eyes undergone laser in situ keratomileusis-The mechanism of myopic regression is complicated and is not understood fully. It hasn't had an effective method to prevent refractive regression of high myopia after laser in situ keratomileusis. It have been shown by previous studies that forward shift of the cornea is one of the important factors for refractive regression after laser in situ keratomileusis because of intraocular pressure acting on thinner cornea. This study included these high myopia eyes that are more likely to occur refractive regression after laser in situ keratomileusis. Ocular hypotensive medication was administered to the eyes, to assess preventive effect on the forward shift of the posterior surface of cornea and the refractive regression.Materials and MethodsThis prospective, randomized study included 50 patients (78 eyes) that had undergone laser in situ keratomileusis for high myopia from January 2010 to October 2010 in our hospital, and Spherical equivalent refraction ranged from 0 to -0.75D at 1 day after operation. They were divided into two groups according to medication—plan (control group and study group). Control group (26 patients,42 eyes) received antibiotic eyedrops 10 days and corticosteroid eyedrops 1 month after operation. Study group (24 patients,36 eyes) received antibiotic and corticosteroid eyedrops in the same procedure as that of control group, in addition, Timolol 0.5% was administered topically twice daily after operation for 1 month. All of the eyes were examined after operation, and we obtained the refraction (spherical equivalent), intraocular pressure (IOP), difference value and radius of posterior corneal curvature at 10 day,1 month and 3 months after operation separatelly. The amount of forward shift of the posterior corneal surface (difference-diff) was determined at the center of the difference map generated from preoperative and postoperative elevation maps. For surface alignment in the difference map, the 3-mm wide peripheral annular fit-zone was used. We compared the intraocular pressure (IOP), difference-diff value, radius of posterior corneal curvature and the refraction (spherical equivalent) between two groups at 10 days,1 month and 3 months after operation separately by t-test. Results were considered significant at P<0.05.Results1. Intraocular pressure of study group (9.61±2.90) mmHg, (9.97±2.45) mmHg was lower than control group(11.7±2.6)mmHg,(11.99±3.07mmHg) at 10 days and 1 month after operation, respectively. The difference was statistically significant. (t =2.37, P=0.023; t=2.22, P=0.533). There was no statistical difference of Intraocular pressure between two groups at 3 months after operation(t=0.35, P= 0.73).2. Difference-diff value of study group (9.56±6.66)μm, (10.72±6.70)μm and (14.11±4.66)μm was lower than control group (19.57±7.76)μm, (20.24±.37)μm and (20.10±6.98)μm at 10 days,1 month and 3 months after operation, respectively. The difference was statistically significant(t=3.08, P=0.04; t=2.25, P=0.03t=4.19, P=0.004).3. Radius of posterior corneal curvature of study group (6.43±0.20) mm,(6.40±.25)mm and(6.35±0.13)mm was higher than control group(6.25±0.30) mm, (6.25±0.25)mm and(6.21±0.18)mm at 10 days,1 month and 3 months after operation, respectively. The difference was statistically significant(t=2.52, P =0.016;t=3.45, P=0.001;t=3.60, P=0.001)4. There was no statistical difference of refraction (spherical equivalent) between two groups at 1 day after operation (t=0.53,p=0.579). The refraction (spherical equivalent) of study group (-0.46±0.28) D, (-0.61±0.34) D and (-0.75±0.21) D was lower than control group(-0.67±0.23) D, (-0.93±0.23) D and (-1.05±0.29) D at 10 days and 1 month and 3 months after operation, respectively. The difference was statistically significant(t=2.52, P=0.016; t=3.45, P=0.001; t=3.60, P=0.001)ConclusionsAdministering Timolol eye drops to high myopia undergone laser in situ keratomileusis early postoperatively can reduce the forward shift distance of the posterior corneal surface and myopia refraction. It is a better way to prevent refractive regression of high myopia after laser in situ keratomileusis. |
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