Correction of myopia and astigmatism using an ablatable mask

Most excimer laser refractive procedures use a computer driven mechanical diaphragm to shape the laser beam. Studies are currently underway using an ablatable polymethylmethacrylate (PMMA) mask to transfer a new spherical or toric curve to the cornea for the correction of myopia and astigmatism; it may leave a smoother corneal surface than diaphragm procedures.

As part of a Phase IIb FDA clinical study, 25 eyes of 25 patients underwent excimer laser photorefractive keratectomy using a hand held ablatable mask. Fifteen eyes had attempted spherical corrections of up to 6.00 diopters (D) and 10 had toric corrections of up to 6.00 D of sphere and 2.75 D of astigmatism.

Seventy-four percent of all eyes achieved uncorrected visual acuity of 20/40 or better--86% in the spherical group and 63% in the astigmatism group. Sixty-nine percent of eyes were within +/- 1 D of the attempted correction. In eyes treated for astigmatism, mean astigmatism decreased from 1.48 D preoperatively to 0.86 D postoperatively. Approximately one half of the eyes treated for astigmatism had a decrease in cylinder of more than 0.5 D. One eye lost 2 Snellen lines of best spherical corrected visual acuity. Video keratography showed toric ablations to result in an elliptical optical zone. Analysis of centration of the procedure showed 66% of ablations centered within 1.0 mm of the center of the pupil aperture.

The ablatable mask represents a promising modality for the treatment of eyes with both myopia and myopic astigmatism.