Journal of Refractive Surgery

Original Articles 

One-Year Results of Excimer Laser Photorefractive Keratectomy for Myopia

James J Salz, MD; Ezra Maguen, MD; Jonathan I Macy, MD; Thanassis Papaioannou; John Hofbauer, MD; Anthony B Nesburn, MD

Abstract

ABSTRACT

BACKGROUND: Excimer laser photorefractive keratectomy tor the correction of myopia is presently under investigation in the United States by the Food and Drug Administration (FDA). The Phase 1 1 -B FDA study is being conducted on 75 normally sighted myopic eyes utilizing three currently available excimer lasers. This report presents the 1 -year results on 12 myopic eyes treated with the VISX excimer laser system at the Ellis Eye Center at Cedars-Sinai Medical Center in Los Angeles under the Phase H-B FDA protocol.

METHODS: Twelve eyes of 12 patients with myopia between - 1.75 and -5.00 diopters underwent 193 nm argon/fluoride excimer laser photorefractive keratectomy. The epithelium was mechanically removed, and fixation was accomplished with a suction ring which provided nitrogen flow across the corneal surface. The computer controlled corneal ablations were 5.00 mm in diameter and were accomplished with an iris diaphragm closing from large to small.

RESULTS: The preoperative spherical equivalent myopia was -3.50 D (SD = 1.02) and the postoperative myopia was -0.25 (SD = 0.48). Eleven of the 12 patients achieved an uncorrected visual acuity of 20/30 or better and were corrected to within ±0.50 D of emmetropia. All corneas demonstrated a mild reticular subepithelial haze which was barely visible at 1 year. There were no visionthreatening complications and none of the eyes experienced a loss of best corrected visual acuity.

CONCLUSIONS: In this small trial, the excimer laser appears to be capable of accurately changing the refractive power of the cornea for the correction of myopia with minimal side effects. Only when larger numbers of patients undergo the procedure will we be able to determine the safety and efficacy of photorefractive keratectomy as a refractive surgical procedure Refract Corneal Surg 1992;8:269-273.)

RÉSUMÉ

INTRODUCTION. La kératectomie refractive lamellaire au laser excimer pour Ia correction de la myopie est maintenant un sujet d'investigation chez la Food and Drug Administration (FDA) aux Etats-Unis. On est en train de conduire la phase H-B de l'étude clinique chez 75 yeux myopes avec une potenìiaìiìé de vision de 10/10° en utilisant trois lasers maintenant disponibles. Cette communication présente les résultats de 12 yeux myopes traités aux VISX système de laser excimer chez The Ellis Eye Center au Cedars-Sinai Medical Center à Los Angefes, selon le protocole de la phase M-B de la FDA, et suivis depuis une année.

Abstract

ABSTRACT

BACKGROUND: Excimer laser photorefractive keratectomy tor the correction of myopia is presently under investigation in the United States by the Food and Drug Administration (FDA). The Phase 1 1 -B FDA study is being conducted on 75 normally sighted myopic eyes utilizing three currently available excimer lasers. This report presents the 1 -year results on 12 myopic eyes treated with the VISX excimer laser system at the Ellis Eye Center at Cedars-Sinai Medical Center in Los Angeles under the Phase H-B FDA protocol.

METHODS: Twelve eyes of 12 patients with myopia between - 1.75 and -5.00 diopters underwent 193 nm argon/fluoride excimer laser photorefractive keratectomy. The epithelium was mechanically removed, and fixation was accomplished with a suction ring which provided nitrogen flow across the corneal surface. The computer controlled corneal ablations were 5.00 mm in diameter and were accomplished with an iris diaphragm closing from large to small.

RESULTS: The preoperative spherical equivalent myopia was -3.50 D (SD = 1.02) and the postoperative myopia was -0.25 (SD = 0.48). Eleven of the 12 patients achieved an uncorrected visual acuity of 20/30 or better and were corrected to within ±0.50 D of emmetropia. All corneas demonstrated a mild reticular subepithelial haze which was barely visible at 1 year. There were no visionthreatening complications and none of the eyes experienced a loss of best corrected visual acuity.

CONCLUSIONS: In this small trial, the excimer laser appears to be capable of accurately changing the refractive power of the cornea for the correction of myopia with minimal side effects. Only when larger numbers of patients undergo the procedure will we be able to determine the safety and efficacy of photorefractive keratectomy as a refractive surgical procedure Refract Corneal Surg 1992;8:269-273.)

RÉSUMÉ

INTRODUCTION. La kératectomie refractive lamellaire au laser excimer pour Ia correction de la myopie est maintenant un sujet d'investigation chez la Food and Drug Administration (FDA) aux Etats-Unis. On est en train de conduire la phase H-B de l'étude clinique chez 75 yeux myopes avec une potenìiaìiìé de vision de 10/10° en utilisant trois lasers maintenant disponibles. Cette communication présente les résultats de 12 yeux myopes traités aux VISX système de laser excimer chez The Ellis Eye Center au Cedars-Sinai Medical Center à Los Angefes, selon le protocole de la phase M-B de la FDA, et suivis depuis une année.

One-year results of excimer laser photorefractive keratectomy in sighted eyes have recently been reported by McDonald et al,1 Seiler and Wollensak,2 and Sher et al.3 This report summarizes our experience with the WSX excimer laser in 12 sighted eyes treated with photorefractive keratectomy and followed for 1 year at Cedars-Sinai Medical Center in Los Angeles.

PATIENTS AND METHODS

Patient selection was accomplished according to the US Food and Drug Administration (FDA) criteria under an Investigational Device Exemption for the Phase IIB clinical trial of photorefractive keratectomy. Each patient received a detailed oral and written informed consent. Patient age ranged from 21 to 42 (8 males and 4 females). All patients had normal slit-lamp examinations and had spherical equivalent myopic refractive errors from - 1.75 D to -5.12 D with no more than 1.50 D of astigmatism. Only one eye of each patient was treated.

All eyes were treated with the VISX excimer laser which produces a 193-nanometer wavelength from an argon-fluorine gas mixture at 5 Hz and a fluence of 160 mJ/cm2. The delivery system includes an iris diaphragm capable of producing up to 240 steps. All eyes received a 5.00-millimeter diameter treatment zone.

The laser parameters were confirmed for each treatment by cutting a test block of polymethylmethacrylate to the dioptric power of the target ablation and confirming the power on a lensometer. The appropriate parameters to obtain the target dioptric correction at the corneal plane were then entered in the computer controlling the laser.

Anesthesia was obtained by applying several drops of tetracaine prior to surgery. With the patient fixating on a coaxial light, the surgeon marked the center of the pupil with a blunt hook. A 6-millimeter dull trephine was then centered over this mark, creating a demarcation circle for mechanical epithelial removal. A suction fixation ring was then applied to the eye. This ring includes three small openings, permitting nitrogen flow across the cornea. A reticule in the ocular representing the laser beam was then centered over the pupil and the ablation was completed without interruption in 20 to 40 seconds.

Chloramphenicol, polymyxin B sulfate and hydrocortisone acetate ointment, 5% homatropine drops, and a pressure path were applied after completion of the ablation. The hydrocortisone acetate (Ophthocort) ointment and pressure patch were applied for 2 to 4 days until the epithelium covered the ablation zone. Fluorometholone (FML) drops were applied every 2 waking hours for the 1st week and then 4 times daily for 4 months. Patients were examined monthly for the first 4 months, then at 6 months, 10 months, and 1 year postoperatively.

Examinations included uncorrected visual acuity, manifest refraction (cycloplegic refraction at 6 months and 1 year), tonometry, fundus examination, visual field examination, pachymetry, and computerized corneal topography.

RESULTS

All patients experienced moderate to severe pain, especially during the first 8 to 10 postoperative hours. Oral analgesics such as codeine phosphate, oxycodone and acetaminophen, and meperidine hydrochloride were relatively ineffective in controlling the pain, but most patients were fairly comfortable by the morning of their first postoperative visit. The eyes were patched with chloramphenicol polymyxin B sulfate and hydrocortisone acetate ointment until epithelial healing was complete. This occurred in 3 to 4 days in all cases.

Table

Table 1Pre- and Postoperative Cycloplegic Refraction and Visual Acuity at 1 YearTable 2Pre- and Postoperative Refraction (Spherical Equivalent) and Visual Acuity (Without Correction)

Table 1

Pre- and Postoperative Cycloplegic Refraction and Visual Acuity at 1 Year

Table 2

Pre- and Postoperative Refraction (Spherical Equivalent) and Visual Acuity (Without Correction)

Table 1 details the patient initials, age and sex, preoperative refraction, postoperative refraction, and visual acuity at 1 year for all 12 eyes. The mean preoperative spherical equivalent myopia was -3.50 (SD = 1.02) D and the mean postoperative spherical equivalent myopia was -0.25 (SD = 0.48) D at 1 year. Table 2 summarizes the preoperative spherical equivalent and postoperative manifest refraction data at 1 month, 3 months, 6 months, and 1 year.

Figure 1 is a scattergram of the attempted correction versus the achieved correction at 1 year, and Figure 2 is a 1-year postoperative regression analysis. Eleven of the 12 eyes (92%) were corrected to within ± 0.50 D of emmetropia (Rp 2 = 0.8) and had an uncorrected visual acuity of 20/25 or better at 1 year. One eye was significantly undercorrected by 1.75 D. There was no loss of best corrected visual acuity.

The procedure was essentially astigmatism neutral in that Il of the 12 eyes had a postoperative refractive astigmatism within 0.50 D of the preoperative value. Figure 3 details the postoperativeinduced astigmatism and shows that 3 eyes were unchanged, 6 eyes had an increased astigmatism of 0.50 D or less, and 3 eyes had a decreased astigmatism of 0.50 D or less. The remaining eye had 1.00 D of induced refractive astigmatism.

Reticular corneal haze in the area of the ablation was noted by all examiners. This was graded between 0.5 and 1.5 (on a scale of 4 where 4 prevents visualization of anterior chamber details and 1 is easily visible to the examiner at the slit-lamp, but does not interfere with refraction) for all eyes during the 1st 3 months and decreased to between 0.5 and 1.0 at 1 year.

Figure 1: Photorefractive keratectomy for myopia. Scattergram of intended versus achieved correction at 1 year in Phase HB FDA VISX study (SE = spherical equivalent, D = diopters).Figure 2: Photorefractive keratectomy for myopia. Regression analysis of intended versus achieved correction at 1 year in Phase HB FDA VISX study (SE = spherical equivalent, D = diopters).

Figure 1: Photorefractive keratectomy for myopia. Scattergram of intended versus achieved correction at 1 year in Phase HB FDA VISX study (SE = spherical equivalent, D = diopters).

Figure 2: Photorefractive keratectomy for myopia. Regression analysis of intended versus achieved correction at 1 year in Phase HB FDA VISX study (SE = spherical equivalent, D = diopters).

In most cases, the patients were unaware of this haze even in the early stages when it was most noticeable to the examiners. Although no patients voluntarily complained about the haze interfering with their visual function, when questioned about this, three patients admitted to a faint haziness to their night vision which disappeared after 6 months. Glare and contrast sensitivity testing were not studied.

DISCUSSION

The 1-year results of photorefractive keratectomy reported in this small series compare favorably with the reports by McDonald et al,1 Seiler and Wollensak,2 and Sher et al.3 The coefficient of determination (Rp 2) obtained by regression analysis (ANOVA) is 0.80.

The McDonald series included seven normally sighted patients with preoperative spherical equivalent myopia between - 2.25 and - 5.00 D; four (57%) were corrected to within 1.00 D of emmetropia and six (86%) achieved an uncorrected visual acuity of 20/40 or better. The remaining 11 normally sighted eyes had a preoperative spherical equivalent myopia between -5.50 and -8.00 D. In this group, only two (18%) were corrected to within 1.00 D of emmetropia and achieved an uncorrected visual acuity of 20/40 or better.

Seiler and Wollensak2 corrected 24 of 26 normally sighted eyes (92%) to within 1.00 D of emmetropia and 25 of 26 of these eyes (96%) achieved an uncorrected visual acuity of 20/40 or better. Although these results are similar to our results, the Seiler series is particularly impressive because it includes nine eyes with attempted corrections between -5.25 and -7.25 D.

Comparison with Sher et al's3 series is not appropriate because of significant differences in patient selection. Their patients had higher amounts of preoperative myopia (mean, - 6.50 D; range, 4.00 to - 12.00 D) with up to 6.00 D of astigmatism and included eyes that had previous refractive surgical procedures. Furthermore, some of their cases were later found to have undergone surgery with an improperly calibrated laser. Liu et al4 have previously reported less satisfactory results from photorefractive keratectomy when the preoperative myopia is greater than - 5.00 D.

Although it is premature to compare the results in these small series of photorefractive keratectomy patients to the many published reports on radial keratotomy, a few general comments seem appropriate. Both procedures, when properly performed, seem to have a low incidence of vision-threatening complications, and loss of more than one line of best corrected visual acuity is uncommon.

The results in both procedures seem to be most satisfactory for patients with less than 6.00 D of myopia. At 1 year postoperative, the PERK5 and SaIz et al6 studies reported that 84% and 96% of eyes with 3.00 D of myopia or less were corrected to within 1.00 D of emmetropia and 92% and 100% achieved an uncorrected visual acuity of 20/40 or better. For eyes with 3.10 to 6.00 D of myopia, 55% and 80% were corrected to within 1.00 D of emmetropia and 76% and 74% achieved an uncorrected visual acuity of 20/40 or better.

Although the PERK 1-year results were achieved by a single operation, 15% of the eyes in the SaIz series underwent at least one additional procedure. Many of the radial keratotomy reports in the literature include eyes that have had additional "touch up" surgeries. All of the reports on photorefractive keratectomy thus far are based on a single procedure, so it is quite likely that the final results will be even better when additional procedures are performed for undercorrections.

Figure 3: Photorefractive keratectomy for myopia. Induced astigmatism at 1 year in Phase HB of the FDA VlSX study (N = 12).

Figure 3: Photorefractive keratectomy for myopia. Induced astigmatism at 1 year in Phase HB of the FDA VlSX study (N = 12).

The progressive hyperopic shift observed in both the SaIz and PERK patients will hopefully be rare in photorefractive keratectomy patients since the procedure does not cause a structural weakening of the cornea. This could turn out to be one of the major advantages of photorefractive keratectomy over radial keratotomy.

Although the excimer laser is capable of unprecedented accuracy in terms of tissue removal, it is apparent that individual biologic variability will continue to play a role in determining the final outcome of photorefractive keratectomy. The ongoing FDA trials will eventually clarify this issue with appropriate long-term follow-up.

REFERENCES

1. McDonald MB, Liu JC, Byrd TJ, et al. Central photorefractive keratectomy for myopia. Ophthalmology. 1991;98:1327-1337.

2. Seiler T, Wollensak J. Myopic photorefractive keratectomy with the excimer laser. Ophthalmology. 1991;98:1156-1163.

3. Sher NA, Chen V, Bowers BA, et al. The use of the 193-nm excimer laser for myopic photorefractive keratectomy in sighted eyes. Arch Ophthalmol. 1991;109:1525-1530.

4. Liu JC, McDonald MB, Varnell R, Andrade HA. Myopic excimer laser photorefractive keratectomy: an analysis of clinical correlations. Refract Corneal Surg. 1990;6:321-328.

5. Waring GO, Lynn MJ, Gelender H, et al. Results of the prospective evaluation of radial keratotomy (PERK) study one year after surgery. Ophthalmology. 1985;92:177-199.

6. SaLz JJ, SaIz JM, SaIz MS, Jones D. Ten years experience with a conservative approach to radial keratotomy. Refract Corneal Surg. 1991;7:12-22.

Table 1

Pre- and Postoperative Cycloplegic Refraction and Visual Acuity at 1 Year

Table 2

Pre- and Postoperative Refraction (Spherical Equivalent) and Visual Acuity (Without Correction)

10.3928/1081-597X-19920701-05

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