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Combined laser in situ keratomileusis and radial keratotomy for the treatment of moderate to high myopia

Damiano, Richard E. MDa,*; Kouyoumdjian, Gregory A. MDa; Forstot, Lance S. MDa; Kasen, Wesley B. MDa; Moore, Charles R. MDb

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Journal of Cataract & Refractive Surgery: May 2003 - Volume 29 - Issue 5 - p 908-911
doi: 10.1016/S0886-3350(03)00117-2
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Abstract

For years, patients with high myopia and those with thin corneas who wish to stop wearing spectacles or contact lenses have had few options. In a report by the American Academy of Ophthalmology, the safety and efficacy of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for the treatment of high myopia was addressed.1 However, a recent study reports that the amount of residual corneal stroma after ablation is critical to the development of postoperative keratectasia.2 Previous experience with lamellar techniques suggests that at least 250 μm of central residual stromal tissue should be preserved to maintain long-term corneal integrity and prevent corneal ectasia.3

Clear lens extraction, phakic intraocular lens (IOL), and implantable contact lens (ICL) procedures are being performed increasingly in patients with high myopia.4 Unfortunately, these procedures present the inherent risks of intraocular surgery such as retinal detachment,5 loss of accommodation, endothelial cell loss, pupillary block,6 cataract formation,7,8 endophthalmitis, and cystoid macular edema.

A review article describes the complications following radial keratotomy (RK) for high myopia.9 Rowsey and Morley,10 however, argue that RK is a safe and effective method for the correction of low to moderate myopia. Several articles11–13 note the reliability of treating PRK undercorrection with RK.

To our knowledge, no study has addressed the treatment of moderate to high spherocylindrical myopia using LASIK followed by RK. We report the outcomes in vision, refractive stability, and complications in a consecutive series of eyes treated with this technique.

Patients and Methods

This retrospective study comprised 63 eyes of 44 consecutive patients who had LASIK followed by RK to correct refractive errors. Three eyes of 3 patients were not included because the patients could not be followed beyond 6 months. Analysis therefore included 60 eyes of 41 patients. All patients provided informed consent.

The mean age of the 15 men and 26 women at the time of LASIK was 40.1 years ± 9.76 (SD) (range 20 to 63 years). Procedures were performed in 35 right eyes and 25 left eyes. The mean follow-up after RK was 15.4 ± 4.42 months (range 9 to 25 months). All procedures were performed by 2 surgeons (R.E.D., C.R.M.). Bilateral simultaneous LASIK was performed in 36 patients (88%) and bilateral simultaneous RK, in 13 patients (32%).

Some patients lacked sufficient stromal thickness to perform the entire refractive correction with LASIK alone. These patients had a planned 2-stage procedure leaving −2.0 to −5.0 D of myopia to be corrected by RK. The remaining patients fell into 2 groups. In 1 group, the residual corneal stromal bed was calculated to be less than 250 μm and RK enhancement was performed. In the other group, the surgeon and patient agreed to an RK enhancement even though the residual stromal bed allowed LASIK enhancement. In the latter group, 3 eyes remained undercorrected after RK and had LASIK enhancement.

Preoperative examinations including manifest and cycloplegic refractions, slitlamp examination, dilated fundus examination, and corneal topography (Humphrey Corneal Topography System) were performed by the surgeons with the help of experienced technicians. Patients wearing gas-permeable contact lenses were asked to discontinue use 4 weeks before the examination. Those wearing soft contact lenses discontinued use 2 weeks before.

The patients were given topical proparacaine 0.5% in the operative eye immediately before the procedure. A plastic drape and lid speculum were placed, and an additional drop of proparacaine was instilled. An 8.5 mm keratectomy flap was created using the Hansatome® microkeratome (Bausch & Lomb Surgical) and lifted using a LASIK spatula.

Laser in situ keratomileusis was performed with the Visx Star S2 or Summit Apex Plus® laser using a 6.0 mm ablation zone. The flap was then repositioned and the interface irrigated with a balanced salt solution. The flap was allowed to adhere for 2 minutes, after which ofloxacin 0.3% and prednisolone acetate 1% were administered and prescribed 4 times daily for 1 week.

The mean time between the LASIK and RK procedures was 7.3 ± 6.5 months (range 3 to 33 months). The blade depth was determined using 90% of paracentral pachymetry measurements with the DGH pachymeter. The cornea was anesthetized with proparacaine, and 4, 6, or 8 centrifugal RK incisions were made with a 3.0 to 6.0 mm optical zone. Figure 1 is the 6-incision RK nomogram used to correct −1.0 to −6.0 D of myopia using optical zones of 3.0 to 5.5 mm. The incision terminated 1.0 mm from the limbus. Astigmatic keratotomy was performed if astigmatism greater than 1.0 D was noted. Ofloxacin 0.3% and prednisolone acetate 1% were prescribed 4 times daily for 1 week.

Figure 1.
Figure 1.:
(Damiano) Optical zones (millimeters) for the 6-incision RK nomogram.

The outcome measures included manifest refraction, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and complications. Postoperative examinations were done at 1 day, 2 months, and approximately 1 year. Statistical analysis with Microsoft Excel 2000 was performed using the paired t test. A P value less than 0.05 was considered statistically significant.

Results

The mean spherical equivalent refraction was –8.09 ± 2.60 D (range –4.00 to –15.25 D) preoperatively, –2.02 ± 1.02 D (range –0.50 to –5.50 D) after LASIK, and –0.43 ± 0.61 D (range –2.00 to +0.75 D) after RK at the last follow-up examination.

Table 1 shows the preoperative BSCVA in all eyes divided into 3 groups. The number of eyes and percentage of total eyes in each preoperative group were compared to the postoperative UCVA (20/20, ≥20/25, or ≥20/40). Of the 54 eyes, regardless of the preoperative BSCVA, 36 eyes (67%) had a UCVA of 20/25 or better. No eye lost 2 or more lines of BSCVA, and all eyes had a BSCVA of 20/30 or better.

Table 1
Table 1:
Visual acuity results after LASIK and RK

Of the 6 eyes corrected for monovision, 4 (66%) had a preoperative BSCVA of 20/20 and of these, 3 (75%) had a UCVA at near of J1 and 1 (25%), of J2. One eye had a BSCVA of 20/25 preoperatively and was J1 postoperatively. One eye had a BSCVA of 20/30 preoperatively and was J2 postoperatively.

The mean keratometry was reduced from 44.90 ± 1.27 D (range 42.08 to 48.00 D) preoperatively to 38.87 ± 2.16 D (range 34.00 to 42.35 D) (t=27.9, P<0.001) at the final follow-up examination.

Three patients (4%) desired LASIK enhancement following RK, and pachymetry noted adequate stromal thickness to safely complete the ablation. Laser in situ keratomileusis was performed by lifting the original flap. These 3 eyes were analyzed before the LASIK enhancement. All had a UCVA of 20/20 at the final examination after the second LASIK.

There were no intraoperative complications with LASIK or RK. Postoperative complaints noted at the last examination included mild glare and halos around lights, 11 patients (23%); diurnal fluctuation in vision, 5 patients (10%); and distorted vision, 2 patients (4%). In the chart review, it could not be determined whether these complaints were present after LASIK but before RK or whether RK influenced the symptoms.

Discussion

The results of combining LASIK and RK to correct moderate to high spherocylindrical myopia indicate that this technique is safe and effective. It is an excellent combination of the positive aspects of both procedures. Laser in situ keratomileusis is the refractive procedure most ophthalmologists choose for the correction of low, moderate, and high myopia. This is likely due to the refractive predictability, stability, and ease of the procedure. Radial keratotomy is safe and effective for the treatment of low to moderate myopia. It is also an inexpensive and simple procedure to perform.

Thus far, the safety of phakic posterior chamber IOLs and ICLs has been reported to be comparable to that of LASIK and RK.7 Unfortunately, many potential complications with intraocular refractive techniques can be more serious.5–8 We found no intraoperative or postoperative complications with LASIK or RK. This is in contrast to the need for additional intraocular surgery if a cataract forms or a retinal detachment occurs as a result of intraocular refractive surgery.

Our outcome measures included a comparison of preoperative BSCVA and postoperative UCVA. Although only 22 eyes (41%) had a UCVA of 20/20 at the final examination, 9 eyes (17%) had a BSCVA of less than 20/20 preoperatively. Twenty-seven eyes (50%) had a UCVA equal to or better than the preoperative BSCVA.

Ectasia is a concern after LASIK for high myopia. Patients in this study known to have insufficient stromal thickness for complete myopic correction with LASIK were left with residual myopia of −2.0 to −5.0 D. This provided greater than 250 μm of residual stromal thickness. It was felt that this would maintain stronger corneal integrity.

Initially, when this combined technique was considered, there were concerns about postoperative haze where the RK incisions crossed the flap incision. To date, no patient has developed haze.

Concern about progressive flattening of the cornea will always exist with radial incisions. In the experience of the surgeons, flattening was sometimes noted within the first year after RK alone. The PERK Study noted a hyperopic shift of +1.00 D or more over 10 years in 43% of eyes.14 The study also showed that the rate of shift was greatest during the first 2 years.

With more than 1 year follow-up after LASIK–RK surgery, there have been no refractive or keratometric changes. In the 9 eyes that had a 2-year follow-up examination, no keratometric flattening or changes in refraction were noted. The progressive flattening caused by the peripheral weakening of the RK incisions may be countered by the mild central ectasia associated with LASIK.15 These findings may also indicate that the healing at the flap–RK incision junction may provide increased strength to the cornea and prevent curvature change. Another explanation may be that the paracentral depth measured post LASIK in this combined technique would be thinner than with typical RK alone. Therefore, the peripheral RK incision depth in our patients is shallower, further minimizing the hyperopic shift. Only long-term follow-up of these patients will resolve the issue of stability.

References

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© 2003 by Lippincott Williams & Wilkins, Inc.