Excimer laser photorefractive keratectomy with tapered transition zone for high myopia

Abstract

To improve the stability of refraction after photorefractive keratectomy (PRK) to correct myopia, we developed a new ablation profile with a 1.5 mm wide tapered transition zone bordering the refractive zone. The treated area's total diameter was 7 mm, the diameter of the refractive zone, 4 mm. The effect of the tapered transition zone on refraction stability was investigated in a 12-month follow-up study of six eyes of six patients. All eyes were partially sighted, with corresponding fundus changes and myopia of between -12.0 diopters (D) and -24.0 D. The therapeutic goal was to reduce myopia by 10.0 D to 13.0 D. All patients were treated unilaterally. The change in refraction in five eyes 12 months after surgery was < or = 1.0 D as compared with the first month postoperatively. In one case the change after 12 months was 2.75 D. There was less regression after PRK with the transition zone than with a conventional ablation profile (i.e., stability was improved). However, epithelial healing took longer.

Goldmann applanation tonometry after myopic photorefractive keratectomy

“…This diaphragm starts from 6 mm in diameter for treatments of less than 6.5 diopters, and 7 mm in diameter for treatments Ø7D. In addition to the standard Munnerlyn algorithm used centrally, a transition zone outside this area is used (Dausch et al 1993). At the end of the procedure preservative free gentamycin eyedrops were applied and the eye was patched.…”

“…Excimer laser changes the central corneal power according to the degree of treatment. There is a corneal thinning of about 10 microns for each diopter of treatment (Dausch et al 1991).…”

Role of epithelial hyperplasia in regression following photorefractive keratectomy.

“…The aetiology of myopic regression is still unclear.2' It has been widely suggested that there is a relation between regression and epithelial hyperplasia and/or stromal remodelling. 2 [4][5][6][7][8] Epithelial hyperplasia has been reported histologically9"4 and clinically.25 However, the relation between epithelial hyperplasia and refractive changes has not been investigated.…”

Laser intrastromal keratomileusis for high myopia and myopic astigmatism

“…Of course, contrast sensitivity testing would perhaps uncover others who are asymptomatic, but to date, contrast sensitivity has not been examined in LASIK patients. Regression associated with high myopic PRK may be somewhat ameliorated by utilising a multizone technique8 13 or tapered transition zones,4 25 but further research in these areas is warranted. Regression after LASIK is not a significant problem—we found that while the mean regression peaked at the 1–3 month period for all groups except group 3 of the ML series, the amount is insignificant, especially for this latter group, if one considers the range of myopia corrected.…”