Corbett M C, Prydal J I, Verma S, Oliver K M, Pande M, Marshall J
Department of Ophthalmology, St. Thomas' Hospital, London, England, UK.
Ophthalmology. 1996 Sep;103(9):1366-80. doi: 10.1016/s0161-6420(96)30495-8.
To make serial measurements of corneal haze and microscopic anatomy after photorefractive keratectomy (PRK) and compare the results with visual function measured at the same time points in the same single group of human subjects.
Ten patients underwent -6.00-diopter, 6-mm PRK. The patients were reviewed frequently for 12 months. Corneal haze was measured objectively in two ways: (1) an opacification index was determined from the variance in digitized retroillumination images; and (2) light reflected and scattered back from the cornea was assessed by gray-scale analysis of video slit images. In vivo confocal microscopy recorded the anatomic changes occurring in the cornea, and computer analysis of the images quantified the keratocytes and subepithelial deposit. Visual performance was assessed by Snellen visual acuity, contrast sensitivity, and glare-induced visual dysfunction.
In the first week, epithelial irregularity resulted in a transient reduction in all aspects of visual function. In the first month, keratocyte disturbances reduced contrast sensitivity at high frequencies and produced glare. Over the next couple of months, the subepithelial deposit resulted in a more prolonged loss of contrast sensitivity at low frequencies and glare-induced visual dysfunction due to the scattering of light. In several patients, these visual defects persisted after 1 year.
Epithelial and keratocyte disturbances only transiently affect visual function. The subepithelial deposit is more persistent and can have a lasting effect on visual performance. Therefore, attempts to improve the visual outcome of PRK must be aimed at controlling the synthesis of subepithelial material.
