THE EFFECT OF ALTITUDE ON RADIAL KERATOTOMY

The authors analyzed refractive results of patients who underwent radi al keratotomy (RK) at sea level and high altitude and evaluated the ef fects of the altitude. A total of 102 eyes undergoing RK procedures pe rformed in two clinical centers having different altitude were analyze d. The results compared between subjects who had undergone RK at sea l evel (Istanbul/Turkey) and at an altitude of 5750 feet (Van/Turkey) we re compared. Subjects were 19-42 years old with myopia from -4.00 to - 12.00 diopters (D). The average preoperative spherical equivalent cycl oplegic refractions (SECR) were -8.01 +/- 1.86 D and -6.99 +/- 2.15 D in the istanbul and Van groups, respectively. These were divided into subgroups according to myopia degree and number of incisions and optic zone size. The RK procedures were performed by the same surgeon with diamond blade in standard Russian style. The average changes in SECR w ere 5.09 +/- 1.29 D and 6.50 +/- 2.24 D in subjects who had undergone RK at sea level and at 5750 feet, respectively. There was a significan t difference between the subgroups (P < 0.0002). This difference was e specially higher in the high myopia subgroups. Additionally, we obtain ed a partial relation between increase of RK incision number and SECR change at high altitude but not at sea level. No notable regression an d progression were seen in the 3 months of follow up at high altitude. These results support hy potheses suggesting both corneal hypoxic exp ansion in the area of RK incisions, which may lead to central corneal flattening, and barometric pressure directly altering corneal shape, w hich is responsible for the hyperopic shift induced by altitude. Ophth almologists performing RK surgery at high altitude had better consider redesigning their RK nomograms in light of these findings. However, w hen the nomogram used at sea level was used at high altitude, the subj ects became hyperopic. (C) 1998 Japanese Ophthalmological Society.