This single-center, retrospective study evaluated the incidence and risk factors for corneal breakthrough haze following photorefractive keratectomy (PRK) with mitomycin c (MMC).
The cohort comprised 3854 patients (7535 eyes) who underwent PRK with intraoperative MMC (0.02%). Eyes were grouped by preoperative refraction, intraoperative time and MMC application time.
The main outcome measures were incidence, onset time, and severity of corneal haze.
The incidence of haze was almost 2-times higher in eyes with high vs. low-to-moderate myopia (P=0.002), 3.5-times higher in eyes with high vs. low astigmatism (P<0.05), and over 8-times higher among eyes treated for hyperopia vs. myopia (P=0.0001).
In moderate and high myopes, as well as in hyperopes, the incidence of haze was significantly lower when the MMC application time was greater than 40 seconds. Haze incidence was also higher when the epithelium was removed with alcohol compared with patients that underwent trans-epithelial PRK.
After surgery, mild early haze incidence peaked at 69 days, whereas severe late haze peaked at 115 days.
This study was limited by its retrospective nature and unmasked design. Bilateral eyes of the same patient were included, which might have skewed the results as responses to treatment might be correlated in contralateral eyes. Additionally, since visual outcomes were not assessed, the clinical significance of haze level was not directly established.
While risk factors for development of corneal haze after PRK have been discussed in the past, this study provides more evidence that patients who have hyperopia, high myopia or astigmatism carry a higher risk of breakthrough haze despite MMC use. The findings suggest that longer MMC application times might be beneficial in those high-risk subgroups.