Photoastigmatic refractive keratectomy for primary treatment and revision of myopic astigmatism

Cyclotorsion: a possible cause of residual astigmatism in refractive surgery

PURPOSE

To determine whether cyclotorsion occurs when a subject changes from binocular to monocular fixation and to assess positionally induced cyclotorsion.

SETTING

Clinics of the Rotterdam Eye Hospital, Rotterdam, The Netherlands.

METHODS

The axis of astigmatism was measured with the Nidek handheld keratometer in 15 normal subjects under monocular and binocular fixation and in seated and supine positions. The limits of agreement for the repeatability of measurements with the Nidek keratometer were used to identify subjects with statistically significant cyclotorsion.

RESULTS

Two subjects (13%) showed statistically significant excyclotorsion when changing from binocular to monocular fixation in a seated position. In a supine position, 3 subjects (20%) showed excyclotorsion when the fixation changed. Body position itself had no influence on ocular torsion.

CONCLUSIONS

Significant cyclotorsion may occur under monocular viewing conditions. If monocular photorefractive keratectomy procedures are based on binocular keratometry readings, an undercorrection of myopic astigmatism may result. Individuals at risk should be identified before refractive keratectomy is performed.

Laser in situ keratomileusis for the correction of myopia and myopic astigmatism

PURPOSE

To evaluate the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of laser in situ keratomileusis (LASIK) for the correction of myopia and myopic astigmatism.

SETTING

Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.

METHODS

This retrospective study comprised 69 eyes that had LASIK to correct myopia and 74 eyes that had LASIK to correct myopic astigmatism. The excimer laser keratectomy was performed using a Summit Apex Plus machine. Refraction, visual acuity, and computerized corneal videokeratography data from the preoperative and postoperative examinations were collected. The astigmatic change was calculated by the Alpins vector analysis method.

RESULTS

The preoperative spherical equivalent at the glasses plane in the myopia and myopic astigmatism groups was -8.08 diopters (D) and -9.73 D, respectively. At 6 months, the spherical equivalent and residual corneal astigmatism were -0.25 D and 0.85 D, respectively, in the myopia group and -0.71 D and 0.82 D, respectively, in the myopic astigmatism group. In the myopia group, 88% of eyes were within +/-1.0 D of the intended myopia correction and in the myopic astigmatism group, 85% were within +/-1.0 D of the targeted spherical equivalent and 90% were within +/-1.0 D of the intended astigmatism correction. The uncorrected visual acuity was 20/40 or better in 94.1% of eyes in the myopia group and 92.5% of eyes in the myopic astigmatism group. The SIA magnitude was 0.66 D with the axis randomly distributed in the myopia group. The mean astigmatism correction index was 0.97, the mean magnitude of error was 0.13 D +/- 0.62 (SD), and the mean angle of error was -3.70 +/- 13.73 degrees in the myopic astigmatism group.

CONCLUSION

Laser in situ keratomileusis had similar predictability, safety, and efficacy in the treatment of myopia and myopic astigmatism. The astigmatism correction was effective, but the results suggest that subjective astigmatism of less than 1.0 D need not be treated with the Summit Apex Plus laser.

Outcome of corneal and laser astigmatic axis alignment in photoastigmatic refractive keratectomy

PURPOSE

To compare the refractive results of laser astigmatic treatment in eyes in which the astigmatic axes of the eye and laser are aligned by limbal marking at the 6 o'clock position and in eyes that are not marked.

SETTING

University Hospital and Clinics, Madison, Wisconsin, USA.

METHODS

This retrospective study comprised 143 eyes that had photoastigmatic refractive keratectomy with the VISX Star excimer laser. The eyes were divided into marked (G1) and unmarked (G2) groups. Based on the preoperative astigmatism, each group was subdivided into low astigmatism (</=1.00 diopter [D]) and high astigmatism (>/=1.25 D). Early postoperative manifest refractions (1.0 to 2.5 months) were analyzed. The Alpins vector analysis method was used to calculate the target induced astigmatism, surgically induced astigmatism, difference vector (DV), magnitude of error (ME), angle of error (AE), and index of success (IS).

RESULTS

There was no significant difference between the groups in DV, ME, and IS. When the subgroups were analyzed, the DV and ME were comparable; the IS in the G1 high astigmatism subgroup was significantly better than that in the G2 high astigmatism subgroup (0.22 +/- 0.08 and 0.29 +/- 0.04, respectively; P <.0001). There was comparable scatter of AE values; 30% and 36% in G1 and G2, respectively, had an AE of 0. Similar scatter was observed in the subgroups. Of the eyes that had an AE of 0, 90% and 43% in the high astigmatism subgroups of G1 and G2, respectively (P <.05), had full correction of astigmatism.

CONCLUSION

Limbal marking and subsequent eye and laser astigmatic axis alignment improved the refractive outcome of laser astigmatic treatment of >/=1.25 D. A preliminary report of an ongoing prospective randomized study of eyes that had laser in situ keratomileusis is included.

Photorefractive keratectomy for compound myopic astigmatism

PURPOSE

To evaluate the safety and efficacy of photorefractive keratectomy for the treatment of primary compound myopic astigmatism.

METHODS

In a prospective study, 93 eyes from 56 patients with a mean spherical equivalent of -4.98 +/- 1.80 diopters (range, -1.75 to -8.5) underwent photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser using erodible mask technology and were followed for 2 years. Primary outcome measures included an assessment of astigmatic correction through vector analysis, manifest refraction, uncorrected visual acuity, corneal clarity, and the presence of adverse symptoms.

RESULTS

Eighty-five eyes (91.4%) were available for analysis at 6 months. Mean spherical equivalent refraction was reduced 85% (mean, -0.75 +/- 0.85 diopter) and the target-induced astigmatism was reduced 70% (mean, 0.98 +/- 1.88 diopters). Forty-eight eyes (56%) had an uncorrected visual acuity of 20/20 or greater, whereas 70 eyes (82%) had an uncorrected visual acuity of 20/40 or greater. Twenty-four eyes (26% ) required re-treatment because of undercorrection of the spherical equivalent and astigmatic components after the 6-month follow-up. Fifty-nine of the remaining eyes were available at the 24-month visit. Mean spherical equivalent refraction was reduced to -0.39 +/- 0.72 diopter (91.8%). The target-induced astigmatism was reduced 64% from 1.74 diopters. Forty-one eyes (81.3%) were within +/-1.0 diopter of attempted spherical equivalent correction. Stability within a spherical equivalent of +/-0.5 diopter occurred after the first postoperative month. Fifty-six eyes (94.9%) had an uncorrected visual acuity of 20/40 or greater, whereas 34 eyes (57.6 %) demonstrated an uncorrected visual acuity of 20/20 or greater. One eye (1.7%) lost 2 or more lines of best spectacle-corrected visual acuity.

CONCLUSION

Photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser is a safe and effective method of reducing compound myopic astigmatism. However, higher re-treatment rates may result from significant undercorrections because of current laser algorithms and variability in the mean angle of error.

Photoastigmatic Refractive Keratectomy in Myopes

PURPOSE

Photoastigmatic refractive keratectomy (PARK) was studied in a multi-center clinical trial. The Nidek EC-5000 excimer laser was evaluated for its effect on refraction, visual acuity, and safety measures as part of a U.S. Food and Drug Administration (FDA) regulated study.

METHODS

Eight U.S. centers enrolled adults with eyes having refractive astigmatism up to 4.00 D and a myopic spherical equivalent refraction up to -8.00 D. Results are reported for 749 eyes of 486 patients with at least 6 months follow-up. The rectangular beam scanning Nidek EC-5000 used a 5.5-mm-diameter treatment zone, a 7.0-mm-diameter peripheral blend zone, and a 40 Hz pulse rate for surface treatment of myopic astigmatism. Nomogram corrections to machine settings were required to achieve the desired results.

RESULTS

Preoperative average spherical equivalent refraction of -4.90+/-1.74 D was reduced to -0.02+/-0.79 D at 6 months. Refractive stability was established at 3 months. Over 62% of eyes were within +/-0.50 D of desired correction at 6 months, with over 86% within +/-1.00 D. Uncorrected visual acuity improved by an average of 10 Snellen lines; over 64% of eyes saw 20/20 or better uncorrected and over 93% saw 20/40 or better uncorrected at 6 and 12 months. PARK treatment effectively reduced astigmatism with little average axis error or magnitude error. Corneal haze and safety concerns were minimal.

CONCLUSIONS

Photoastigmatic refractive keratectomy using the Nidek EC-5000 excimer laser provided significant reduction of myopia and astigmatism, with minimal complications.