Visual fields after refractive surgery

Purpose Laser correction of ametropias is achieved by changing the radius of curvature of a central portion of the cornea. Although current refractive laser technology allows relative uniform correction across an optical zone larger than the scotopic pupil it must be kept in mind that centration of the ablation pattern pertains only to objects on the line of sight. Off-axis objects are imaged not only through the corrected portion of the cornea but additionally through a meniscus of paracentral cornea involving the transition zone as well as untreated cornea. It was the purpose of this study to investigate the role of this optical effect in the peripheral visual fields in patients undergoing photorefractive keratectomy. Methods Twenty one eyes of thirteen patients were evaluated before and 3 months following PRK for the correction of myopia (average: -3.4D, SD:2.4D) at an optical zone of 6.5mm with the Allegretto 400 Excimer laser. Evaluation of the optical fields was made using the MEDMOND M700 visual fields analyzer using a full threshold procedure. Measurements were performed under cycloplegia while in all cases the subjects were corrected for the distance of the stimulus (+3 D) Results The detection threshold exhibited a decrease ranging from 0.5 to 9 dB (mean:1.5 dB, SD:2.5) for the periphery of the optical field (30 to 40 degrees). This change was statistically significant (p=0.00628). No statistically significant difference was observed for the central visual field (0-22 degrees). Conclusion The loss of peripheral visual fields following refractive surgery may be attributed to the deteriorated retinal image quality in the peripheral visual field. A mathematical model of this reduction is proposed