Two-incision radial keratotomy for low myopia with astigmatism

PURPOSE

To evaluate the effectiveness of two-incision radial keratotomy (RK) in correcting low-magnitude refractive myopic astigmatism.

SETTING

Two clinical study sites, one in St. Louis, Missouri, USA, the other in Caracas, Venezuela.

METHODS

Fifty-seven eyes of 43 patients with low-magnitude myopic astigmatism had two-incision RK at one of two clinical study sites. In the initial phase of this series, 10 eyes with amblyopia at the 20/30 level had surgery at one center. Refractive keratotomy was performed with the radial incision placed in the plus cylinder axis of refraction. This axis was verified as the meridian of greatest corneal curvature by standard keratometry and computer-assisted corneal topographic analysis. Two eyes received a second operation (enhancement).

RESULTS

Mean follow-up was 11.1 months (range 6 to 12 months). Mean preoperative and postoperative myopic spherical equivalent measured -1.42 diopters (D) +/- 0.51 (SD) and -0.14 +/- 0.39 D, respectively; the mean reduction was 1.28 +/- 0.59 D (P = .0001). Mean preoperative and postoperative refractive astigmatism was 1.41 +/- 0.45 D and 0.48 +/- 0.33 D, respectively (P = .0001). Mean preoperative and postoperative keratometric astigmatism was 1.26 +/- 0.54 D and 0.31 +/- 0.35 D, respectively, a mean reduction of 0.95 D (P = .0001). The surgical meridian was flattened by an average of 2.06 D by keratometry and the orthogonal meridian, by an average of 1.10 D. Preoperative uncorrected visual acuity (UCVA) was 20/40 or better in five (9%) eyes (range counting fingers to 20/40). Postoperative UCVA acuity was 20/40 or better in all eyes (mean acuity 20/25). In the nonamblyopic subgroup mean postoperative UCVA was 20/24.

CONCLUSIONS

A limited number of radial incisions placed in the topographically confirmed axis of greatest curvature are effective in the treatment of low-magnitude myopic astigmatism.

Refractive evaluation of astigmatic keratotomy procedures

We evaluated the efficacy of three transverse incision astigmatic keratotomy procedures using a vector analysis that enabled us to determine the magnitude of the effect and the axis in which it occurred. These procedures were used for low levels of astigmatism (0.5 diopter [D] to 3.75 D): (1) staggered, radial-touching transverse (T) incisions, (2) non-radial-touching T incisions, and (3) T incisions with interrupted radial. Most procedures were performed in conjunction with radial keratotomy for spherical correction of myopia. The non-radial-touching T procedure was the least effective method of reducing astigmatism. The staggered, radial-touching T and T with interrupted radial procedures were equally effective in reducing over 93% (on the average) of the preoperative astigmatism. Of these two procedures, the T with interrupted radial procedure was the most accurate, with the effect of the surgery deviating less than ten degrees from the desired axis in over 70% of the eyes.

Wound healing after astigmatic keratotomy in human eyes

The authors analyzed three full-thickness corneal buttons and two corneal scleral rims obtained 5 1/2 to 44 months after three trapezoidal keratotomies (Ruiz), one "L," and one "TL" procedure. The indications for the penetrating keratoplasty were photophobia, corneal edema, and loss of best-corrected vision after the astigmatic keratotomy procedures. Epithelial plugs were seen in all five specimens. Complete basal lamina lined the wounds in two cases. Tangential incisions of the Ruiz procedure were shallower and demonstrated more advanced wound healing than the corresponding semiradial incisions. Two of the three Ruiz procedures demonstrated peripheral separation of the semiradial incisions. Wound healing events after astigmatic keratotomy procedures appear similar to those reported previously after standard radial keratotomy with the exception that tangential incisions appear to heal faster than the semiradial incisions.