To find a novel method for calculation of the initial trial spherical rigid gas-permeable contact lens fitting in pellucid marginal corneal degeneration (PMCD) to reduce the number of trial fitting required to achieve a best fit.
A retrospective data of 16 subjects (8 men and 8 women) who were diagnosed to have PMCD and under went contact lens trial were selected after reviewing the medical records of the patients who visited medical research foundation over a period of year. The demographic details, refractive error, details of lens trial, dispensed lens parameters, fluorescein pattern achieved, and simulated keratometry (Sim-K) reading were noted.
Of the 32 eyes (16 subjects), 6 eyes (4 subjects) continued with glasses. Three eyes were advised deep anterior lamellar keratoplasty (DALK). Twenty-three eyes were fitted successfully with gas-permeable lens and achieved vision between 6/9 and 6/6. The base curve of the final lens achieved was compared with the calculated appropriate base curve by stability factor method, flat keratometry readings, and average keratometry readings. Analysis showed no significant difference between the final lens base curve and the calculated appropriate base curve by stability factor method, with a P value of 0.71 and correlation coefficient of 0.77. The average lens diameter was 9.02 mm, with average optic zone of 7.5 mm.
Calculation of appropriate base curve of the lens by stability factor method is found to be the best method to start with a trial in PMCD.