Abstract
Purpose :
To examine the impact of various preoperative characteristics, mitomycin C 0.2 mg/ml (MMC) exposure time, and reduction in refractive correction (backoff) when using topical MMC on the outcome of photorefractive keratectomy (PRK) for myopia.
Methods :
In this retrospective analysis, data collected included demographics, pre and postop manifest refraction (MR), preop pachymetry, percent reduction in treatment (sphere reduced by 0 to >10% of SE), MMC exposure time, presence of post PRK haze, and postop uncorrected visual acuities. Outcome measures included uncorrected postop acuity, residual refractive error, and incidence of haze. Inclusion criteria were preoperative myopia defined as > -4.00 D with regular preoperative astigmatism < 5.00 D, with mean of -6.75, [-12.75, -0.50] in patients who underwent PRK with MMC. Patients presenting for enhancement surgery, patients with preexisting corneal disease or tear deficiency were excluded. Linear mixed model and generalized linear mixed model were used to assess the associations between MMC exposure time with 3-month log mar visual acuity and incidence of haze respectively.
Results :
A total of 91 eyes from 57 patients were included. The mean (standard deviation, SD) of 3-month log mar visual acuity was 0.06 (0.16). The incidence of haze was 28.6% (30). There was no significant difference in the development of corneal haze with increased MMC exposure time (odds ratio 1.22). There were 71 eyes with 20/25 vision or better defined as group 1, and 20 eyes with 20/30 or worse acuity (up to 20/70) in group 2.The mean (SD) back off in group 1 was 6.6% (4.5) of SE, mean preoperative MR -6.9 (2.3 [-11.75, -1], and mean postop MR -0.4 D (0.67 [-2.25,-0.25]). In group 2, the mean backoff was 9.7% (4.5), the mean preoperative MR -8.9 (2.4 [-12.75, -3.75]), and mean postoperative MR 1.2 D (0.69 [-3.25, 1.75]).
Conclusions :
Incidence of haze was higher than expected, but not visually significant. There was no significant difference in refractive outcome even when MMC exposure time was <20 seconds. Extending exposure time beyond 20 seconds was not necessary to prevent visually significant haze. A larger percent backoff of 10% or greater may contribute to undercorrection after PRK.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.