Excimer laser correction of astigmatism using erodible masks

The latest development in the erodible mask technology is an excimer laser containing the mask in the laser optical pathway. This paper reports the results of the first human series of consecutive treatments performed for the correction of compound myopic astigmatism.

We have treated 83 eyes. Spherical equivalent attempted correction ranged between -1.75 and -11.75 D (mean -7.07 +/- 2.45 D), astigmatic attempted correction ranged between -1.00 and -5.00 D (mean -2.42 +/- 1.02 D). The sphere correction was made by diaphragm using a multi-zone software with three ablation zones: 100% of the total attempted correction for the central 5.0 mm zone, 70% for the second 6.0 mm zone, 30% for the outer 6.5 mm zone. Cylinder correction was made sequentially after myopic correction using the appropriate mask.

One month after treatment, mean refractive error was +1.07 +/- 1.24 D (range +4.50/-1.75 D) for spherical equivalent, and -0.49 +/- 0.57 D (range +0.75/-2.00 D) for astigmatism. Forty-eight eyes (57.8%) had uncorrected visual acuity of 20/40 or better. At six months, mean refractive error was +0.42 +/- 0.97 D (range +3.75/-1.00 D) for spherical equivalent, and -0.44 +/- 0.51 D (range +0.25/-3.00 D) for astigmatism. Vector analysis showed that 57 eyes (68.7%) had 5 or less degrees rotation. Seventy-two (86.7%) and 54 eyes (65.1%) had uncorrected visual acuity equal or better than 20.40 and 20/25 respectively. One eye (1.2%) showed a best corrected visual acuity loss of more than one line, but 8 eyes (9.6%) had a gain of more than one line. One-year results on a smaller series (33 eyes) overlap the six-month results.

The mask in-the-rail excimer laser delivery system appears to be effective and predictable in the correction of compound myopic astigmatism. We observed no significant regression of the astigmatic correction over time. Longer follow-up on larger series is necessary to draw final conclusions.