The effect of redeepening incisions on radial keratotomy outcome.

BACKGROUND: Patients scheduled to undergo radial keratotomy in both eyes received redeepening incisions in one eye and single pass incisions in the other. Eye and order of surgery were assigned randomly and surgical parameters were otherwise identical in the two eyes. METHODS: This study was designed to measured the improvements in myopia obtained by radial keratotomy, with and without redeepening incisions. RESULTS: There was a greater decrease in spherical equivalent manifest refraction in the redeepening group than in the control group at 1 week (0.41 D) and 1 month (0.36 D) after surgery, as measured by keratometry. The difference in change between groups was 0.41 D at one week, 0.36 D at 1 month, and 0.26 D at 3 months. Change in spherical equivalent was significantly more in the redeepened group at 3 months after surgery (0.37 D); however, the improvement constituted only 8.8 percent of the decrease in myopia achieved by radial keratotomy without redeepening (3.87 D). CONCLUSIONS: Although redeepening yields an incremental effect in the correction of myopia, the technical difficulties of redeepening and the increased chance of perforation of the cornea with redeepening outweigh the benefits of the procedure.

Effect of incision direction on radial keratotomy outcome.

The goal of maximizing radial keratotomy results by using optical-zone-directed (centrally directed) incisions rather than limbus-directed (peripherally directed) incisions is evaluated in this prospective study. Five patients had bilateral radial keratotomy, with optical-zone-directed incisions in one eye and limbus-directed incisions in the other. The order of surgery and eye was randomly assigned. Patients were evaluated preoperatively, at one week, and at one month. There were no significant differences preoperatively between the two groups of eyes in spherical equivalent or keratometry. At one week postoperatively, however, there were significant group differences in spherical equivalent changes (P less than .010). Eyes with limbus-directed incisions were -2.2 diopters (D) myopic, on average, while eyes with optical-zone-directed incisions were near emmetropic, with a mean spherical equivalent of 0.10 D. Because of these results, we stopped randomizing cases at this point. The difference in surgical effect was still significant at three months (P less than .01); eyes with limbus-directed incisions had an average of 3.5 D less surgical effect than eyes with optical-zone-directed incisions.

Rigid lens base curve stability upon hydrogen peroxide disinfection.

Because of the possibility of transmitting communicable diseases, in particular the HIV virus, it has been recommended that all diagnostic contact lenses, including rigid lenses, be disinfected after each use. Hydrogen peroxide is a recommended disinfection agent, but its effect on rigid lens polymers is relatively unknown. We soaked 50 lenses of 5 different polymers in 3% hydrogen peroxide for 10 min and measured the base curves to determine if any changes occurred. Our results showed no statistically significant change in base curve for the lenses measured, but 22% of the lenses did exhibit a small amount of warpage (mean 0.0382 mm) of the base curve. We were not able to determine what caused these lenses, and not all the lenses, to warp. Under the conditions of this study, hydrogen peroxide does not appear to cause clinically significant parameter changes, but lenses should be checked for warpage before use.