Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia

Improvement of Visual Acuity Following Refractive Surgery for Myopia and Myopic Anisometropia

PURPOSE

To test the hypothesis that anisometropic adults without significant amblyopia suffer from mild visual impairment probably due to aniseikonia, which might be improved by corneal refractive surgery.

METHODS

Fifty-seven patients presenting with myopic anisometropia > or = 3.25 diopters (D) and 174 myopic controls appropriate for refractive surgery were included. Photorefractive keratectomy (PRK) or LASIK was performed on 57 anisometropic eyes. As 43 of the 174 myopic control patients had bilateral surgery, PRK or LASIK was performed on 217 myopic control eyes. Best spectacle-corrected visual acuity (BSCVA), refraction, and refractive correction were measured preoperatively and at 1, 3, 5 to 7, 8 to 13, and 25 months following surgery.

RESULTS

Preoperative mean spherical equivalent was -7.20 +/- 2.40 D for anisometropic patients and -6.40 +/- 1.90 D for myopic patients. At 8 to 13 months postoperatively, when 23 (40%) anisometropic eyes and 94 (43%) myopic eyes were examined, the mean spherical equivalent refractions were -0.80 +/- 1.60 D and -0.30 +/- 0.60 D, respectively. Preoperatively, the mean BSCVA on a logMAR scale was -0.0143 +/- 0.0572 (Snellen 0.98 +/- 0.12) in the anisometropic group and 0.0136 +/- 0.0361 (Snellen 1.04 +/- 0.09) in the control group (P = .001). Eight to 13 months postoperatively, these values were 0.0076 +/- 0.0659 (Snellen 1.03 +/- 0.15) and 0.0495 +/- 0.0692 (Snellen 1.13 +/- 0.18) and this difference remained statistically significant (P = .012). For the myopic patients, the improvement in BSCVA reached almost maximum at 3 months, and this improvement was found to be highly significant 3 months after surgery (P = .001). The improvement in BSCVA was significantly slower for anisometropic patients and became statistically significant only after 8 to 13 months postoperatively (P = .041).

CONCLUSIONS

Anisometropia reduces visual acuity in the more myopic eye and can be at least partially reversed by refractive correction. The slower improvement in BSCVA for anisometropic patients suggests plastic changes in the visual cortex following refractive surgery.

Predictability and outcomes of photoastigmatic keratectomy using the Nidek EC-5000 excimer laser

PURPOSE

To evaluate the effect of astigmatic correction on the accuracy of the myopic and astigmatic correction in patients having photorefractive astigmatic keratectomy (PARK) and in those having photorefractive keratectomy (PRK).

SETTING

Specialist excimer laser refractive clinic.

METHODS

This prospective consecutive case series comprised 6097 eyes with a preoperative mean spherical equivalent (MSE) of -4.63 diopters (D) +/- 1.95 (SD) (range -0.75 to -13.00 D) and a mean cylinder of -1.13 +/- 0.73 D (range -0.50 to -6.00 D) having PARK with a Nidek EC-5000 excimer laser. Visual and refractive outcomes were assessed 12 months postoperatively and compared with those in 3004 eyes that had spherical PRK.

RESULTS

At 12 months, the MSE was -0.02 +/- 0.79 D and the mean cylinder was -0.49 +/- 0.47 D in the PARK group; the MSE was -0.07 +/- 0.66 D in the PRK group. An MSE within +/-0.05 D of emmetropia was achieved by 69.8% and within +/-1.00 D, by 87.9%. The uncorrected visual acuity (UCVA) was 20/20 or better in 42.6% and 20/40 or better in 91.2%. Statistical significance (P <.001, analysis of variance) was achieved for MSE, sphere, cylinder, haze, and visual acuity (best corrected [BCVA] and UCVA) based on the preoperative cylinder. The loss of BCVA varied from 1.1% to 5.8% depending on the degree of astigmatism treated. Accuracy varied with the attempted myopic correction and the attempted astigmatic correction.

CONCLUSIONS

Excimer laser PARK was an effective treatment for compound myopic astigmatism, but predictability decreased and complications increased as the attempted astigmatic correction increased.

Prospective Randomized Study of Corneal Aberrations 1 Year After Radial Keratotomy or Photorefractive Keratectomy

PURPOSE

To evaluate the optical properties of the cornea 1 year after either radial keratotomy (RK) or photorefractive keratectomy (PRK) in a randomized group of patients with low myopia.

METHODS

Ninety-six patients with myopia between -0.75 and -5.00 D were randomized to either radial keratotomy (n = 46) or photorefractive keratectomy (n = 50). Topography maps were obtained 1 year after surgery and analyzed by computation of total corneal wavefront aberration and Zernike polynomial coefficients for pupil sizes of 2, 4, and 6 mm. The 4-mm pupil size was used for optimization of the model.

RESULTS

The total corneal wavefront aberrations after RK and PRK were similar and not statistically different. Wavefront aberrations arising from astigmatism or defocus accounted for approximately 70% of the total wavefront error at all pupil sizes in both groups. All types of aberrations, and in particular spherical aberration, increased significantly with increasing pupil size. Higher-order wavefront aberrations were almost twice as high after RK than after PRK at pupil sizes of 4 and 6 mm. Spherical aberration and coma were slightly higher after PRK than after RK.

CONCLUSIONS

Pupil size had a major effect on corneal aberrations after RK and PRK. The most important aberrations were sphero-cylindrical, in which eyes became significantly more myopic with increasing pupil size. The image forming properties of the cornea are better after PRK compared with RK due to the lesser amount of higher-order aberrations.

Results of bilateral photorefractive keratectomy

OBJECTIVE

To study the refraction and potential risks of bilateral photorefractive keratectomy for myopia.

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Four hundred eighteen consecutive patients (836 eyes) with myopia from -18 to -0.50 diopters (D) had bilateral simultaneous refractive surgery.

INTERVENTION

Refractive surgery was performed with the Nidek EC-5000 slit-scanning excimer laser (Nidek Co., Tokyo, Japan).

MAIN OUTCOME MEASURES

Manifest refraction, Snellen best spectacle-corrected visual acuity (BSCVA) and uncorrected visual acuity, haze, and halos were evaluated for 12 months after surgery. Both eyes of each patient were examined at the same follow-up after initial treatment.

RESULTS

At 12 months after surgery, 95% of eyes were within +/- 1D of emmetropia, and 0.4% of patients had residual anisometropia more than 2 D. Thirty-three eyes (3.9%) were retreated, whereas 5 patients (1.2%) had retreatments in both eyes. Odds ratios between unilateral versus bilateral postoperative events were evaluated for the retreatments (1:0.22; P = 0.001), undercorrections more than 1 D (1:0.17; P < 0.0001), overcorrections more than 1 D (1:0.23; P < 0.0001), loss of 1 line of BSCVA (1:0.44; P < or = 0.002), and loss of 2 lines of BSCVA (1:0.18; P = 0.013). At 12 months after surgery, one eye with a loss of 2 lines of BSCVA was treated for haze more than 1; the fellow eye had haze 0.75. No patient had bilateral haze more than 1. At 12 months after surgery, no patient lost 2 lines of BSCVA in both eyes. There was a higher incidence of halos in both eyes rather than in one eye only (odds ratio: 4.17; P < 0.0001). No postoperative infections occurred.

CONCLUSIONS

Bilateral events occurred approximately 2.5 to 4 times less often than unilateral events, except for the incidence of halos. The calculated odds ratio did not show an increased risk for the fellow eye while performing bilateral surgery, although not exempted from the risk of infection. It may be difficult to predict a complication in the fellow eye based on the results of the first operated eye.

Predictability of spherical photorefractive keratectomy for myopia

OBJECTIVE

This study aimed to examine the effects of purely spherical excimer laser photorefractive keratectomy (PRK) for myopia.

DESIGN

Consecutive case series.

PARTICIPANTS

A total of 3218 eyes with a mean preoperative mean spherical equivalent (MSE) of -3.75 diopters (D) +/- 1.73 D standard deviation (SD) (range, -1.00 D to -11.88 D) underwent PRK with a Nidek EC-5000 excimer laser. Eyes were divided into groups based on the degree of preoperative myopia in 1 D steps.

INTERVENTION

All eyes underwent PRK with a Nidek EC-5000 excimer laser.

MAIN OUTCOME MEASURE

Visual and refractive outcome of PRK treatment was measured.

RESULTS

After a mean follow-up period of 52.6 weeks (range, 26-150 weeks), the final MSE was -0.07 D (+/-0.68 D) (range, -5.50 D to +4.50 D). Of the 3218 eyes, 2919 (90.7%) were within 1.00 D of emmetropia, and 3038 (94.4%) of eyes had an uncorrected visual acuity of 20/40 or better, with 1886 (58.6%) achieving 20/20 or better visual acuity. Eyes in the lower preoperative myopia groups had a greater chance of attaining 20/40 unaided visual acuity than those in the higher groups (e.g., 98.3% of the -2D group and 53.6% of the -9D group achieved 20/40 unaided visual acuity). Overall, mean postoperative haze was 0.29+/-0.39 SD (scale, 0-3), and 29 eyes (0.9%) lost 0.3 or more logarithm of the minimum angle of resolution (LogMAR) unit of best-corrected visual acuity.

CONCLUSIONS

Excimer laser PRK is an effective treatment for myopia of up to -9.00 D. The outcome parameters are less predictable for eyes with greater than -9.00 D of myopia.

Risk of retinal detachment in myopic eyes after intraocular lens implantation: a 7 year study

PURPOSE

To evaluate the benefits and risks of lens removal using extracapsular cataract extraction (ECCE), primarily phacoemulsification, to correct high myopia.

SETTING

A Medicare accredited surgical center, Bakersfield, California, USA.

METHODS

Five hundred eighty-one lens extractions were performed in 311 patients from 1989 to 1996. Surgeries were performed by the same surgeon (C.D.F.). The incidence of capsule rupture, vitreous loss, and retinal detachment, as well as preoperative and postoperative visual acuities, were studied.

RESULTS

Phacoemulsification was performed in 73.4% of cases, planned ECCE in 24.8%, and unplanned ECCE in 1.8%. Capsule rupture occurred in 1.5% and vitreous loss in 0.8% of cases. Two cases of retinal detachment occurred 1 to 2 years postoperatively. In 76.2% of patients, uncorrected visual acuity was 20/40 or better.

CONCLUSION

Carefully selected patients with high myopia may benefit from cataract extraction and posterior chamber intraocular lens placement. This study suggests an acceptable level of safety.

Surgical correction of moderate myopia: which method should you choose? I. Radial keratotomy will always have a place

This set of "Viewpoints" articles examines the relative merits of radial keratotomy (RK), photorefractive keratectomy (PRK), and laser assisted in-situ keratomileusis (LASIK). Drs. Rowsey and Morley review advances in RK techniques, long-term results, and complications, and explain why RK will remain a viable method for correction of moderate myopia, notably its minimal cost. Drs. Steinert and Bafna review both PRK and LASIK, discussing techniques and results and comparing their advantages and disadvantages with each other and with RK. Dr. Dutton, as "Viewpoints" section editor, summarizes clinical, technologic, and economic aspects of all three techniques, concluding that all will find a place among refractive surgeons for some time to come.

The Suction Bridge for Radial Keratotomy May Avoid Late Hyperopic Shift

BACKGROUND

Radial keratotomy may induce late hyperopic shift. We present data on 140 consecutive eyes with a follow-up of up to 3 years that underwent radial keratotomy with the RK suction bridge.

METHODS

We conducted a retrospective study of 140 consecutive eyes that had radial keratotomy between 1987 and 1994. Mean preoperative spherical equivalent was -5.21 D (range -2.00 to -9.75 D). All operations were performed by one surgeon (JHK) with the RK suction bridge. A suction ring maintaining physiological intraocular pressure immobilized the eye and left a peripheral rim of uncut cornea. The ring incorporated an eccentric bridge that guided the radial keratotomy knife. The knife setting was 90% of the central corneal thickness, measured by pachymetry. Spherical equivalent refraction and spectacle corrected visual acuity were measured at 1 week, 1, 3, 6 months, 1 year, and 3 years after radial keratotomy.

RESULTS

The mean preoperative spherical equivalent refraction of -5.21 D dropped to -0.43 D at 1 week (n = 136), -0.71D at 1 month (n = 120), -0.85 D at 3 months (n = 95), -0.74 D at 6 months (n = 73), -0.77 D at 12 months (n = 79), and -0.85 D at 3 years (n = 67). Compared to 1 month spherical equivalent, at 3 years three eyes (4.4%) had moved > = or 1.00 D toward hyperopia. One eye (1.4%) shifted by 1.25 D. Paired t-tests of mean spherical equivalent refraction did not reveal significant shifts toward hyperopia. Mean preoperative spectacle-corrected visual acuity was slightly diminished at 1 week and was equal or better thereafter.

CONCLUSIONS

Our 3-year data suggest that a late hyperopic shift following radial keratotomy may be prevented if an intact peripheral rim is maintained and cutting depth does not exceed 90% of the lowest corneal thickness.