Topographic comparison of monozone, multipass and multizone ablations for myopic photorefractive keratectomy

Multizone and multipass ablation techniques have been developed in an attempt to improve results over monozone photorefractive keratectomy (PRK). This study was conducted to evaluate the results obtained in the treatment of myopia with multizone PRK in comparison with monozone ablation in low myopia, and with multipass ablation in high myopia.

Sixty-two eyes with low myopia (-1.90 to -6.25 diopters [D]) were divided into two groups: 42 eyes were treated with a 5.0 mm monozone ablation and compared with 20 eyes treated with a multizone software using 5.0-5.7-6.5 mm optical ones and a 100-60-40% algorithm. Thirty-four eyes with high myopia (-6.50 to -12.00 D) were also divided into two groups: 17 eyes were treated with a multipass technique dividing the attempted correction in three successive treatments with 5.0-6.0-6.5 mm optical zones and 50-30-20% of the total correction, and compared with 17 eyes treated with the multizone software using the same parameters as in the low myopia group.

Multizone treatment induced less initial hyperopic shift than monozone or multipass techniques, with significant differences at 15 days and 1 month. At 6 months after surgery 100% of low myopes and 88.24% of high myopes treated with the multizone software were within +/- 1.00 D of emmetropia as compared with 90.5% of the monozone eyes and 52.9% of the multipass patients.

In low myopes this improvement seems to be related only to the increase in ablation diameter, but in high myopes we found a great improvement in the ablation profile and a shortening of the procedure as the likely factors of the better results obtained with multizone ablation.