Examination of subepithelial scarring with ultrasound biomicroscopy following photorefractive keratectomy

Subepithelial haze and concomittant refractive regression are the most important complications of photorefractive keratectomies (PRK) in the higher diopter range. Twenty previously photokeratectomized myopic eyes, which showed a certain level of subepithelial scarring, were examined in the present study. The range of PRK treatment varied between — 4.0 and - 12.0 D (on average - 7.4 ± 3.88 D). Subsequent subepithelial haze was graded between 0.5 and 4.0, according to Hanna et al. The first ultrasound biomicroscopy (UBM) was performed between 1 and 3 months following PRK with the 50–80 MHz transducer of a Zeiss-Humphrey Model 840 ultrasound biomicroscope. A control UBM examination was carried out in each patient 3 months after the initial assessment. The severity of subepithelial haze correlated with the previous photo-ablation depth. Below and including Haze Grade 2.0, UBM showed loss of the Bowman’s membrane and a slight thinning of the central 5.5 mm diameter cornea. Above Grade 2.0, the reflectivity of the anterior stromal parts began to increase. Between Grades 3.0 and 4.0, a hyper-reflective one-third of the anterior stroma with irregular borders was observed. In conclusion, haze graded below 2.0 was not observable with UBM. Haze graded more than 2.0 caused increased anterior stromal reflectivity in the central cornea. Ultrasound biomicroscopy was found to be a suitable method for presenting and following data over time for each patient with serious haze phenomena after excimer laser photo-ablation.