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 ey es, which showed a certain level of subepithelial scarring, were exami ned 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 subepitheli al 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 mon ths following PRK with the 50-80 MHz transducer of a Zeiss-Humphrey Mo del 840 ultrasound biomicroscope, A control UBM examination was carrie d out in each patient 3 months after the initial assessment. The sever ity of subepithelial haze correlated with the previous photo-ablation depth. Below and including Haze Grade 2.0, UBM showed loss of the Bowm an's membrane and a slight thinning of the central 5.5 mm diameter cor nea. Above Grade 2.0, the reflectivity of the anterior stromal parts b egan to increase. Between Grades 3.0 and 4.0, a hyper-reflective one-t hird of the anterior stroma with irregular borders was observed. In co nclusion, haze graded below 2.0 was not observable with UBM, Haze grad ed more than 2.0 caused increased anterior stromal reflectivity in the central cornea. Ultrasound biomicroscopy was found to be a suitable m ethod for presenting and following data over time for each patient wit h serious haze phenomena after excimer laser photo-ablation.