Excimer laser photoastigmatic refractive keratectomy

Excimer Laser Photoastigmatic Keratectomy Eighteenmonth

Refractive

Follow~u~

David Zadok, MD, David Haviv, MD, Vicktoria Vishnevskia-Dai, David Krakowski, MD, Pinhas Nemet, MD

MD,

Yair Morad, MD,

Yair Levy, MD,

Objective: To study the efficacy of photoastigmatic refractive keratectomy (PARK) by the MEL 60 (AesculapMeditec, Jana, Germany) scanning excimer laser for the treatment of myopic astigmatism, with follow-up of 18 months. Patients and Methods: One hundred and twenty-eight eyes of 102 patients with different degrees of myopic astigmatism were treated by PARK and followed prospectively in an open study. Ablations were performed with an MEL 60 excimer laser using an astigmatic module. Results: Mean preoperative refractive cylinder improved from a preoperative value of -1.8 + 0.8 diopters (D; range, -1 .O to -6.0 D) to -0.3 t 0.5 D (range, f1.0 to -2.5 D) at 18 months. The mean reduction in cylindrical correction alone was 84 ? 37% in the low astigmatism group (- 1.O to - 1.5 D); 91 ? 21% in the moderate astigmatism group (-1.75 to -2.5 D); and 75 + 25% in the high astigmatism group (-2.75 to -6.0 D). One hundred and three eyes (80%) at 12 months and 100 eyes (85%) at 18 months were within +0.5 D of the intended astigmatic correction, with more eyes in the low astigmatic group. One hundred and nineteen eyes (93%) and 114 eyes (97%) at 12 and 18 months, respectively, were within +l .O D of the intended correction. Ninety-two percent to 95.7% of the eyes in the different groups had a postoperative axis less than 10 degrees of the preoperative and intended axis at 12 and 18 months after PARK. Uncorrected visual acuity (UCVA) of 20/40 or better was achieved in nearly 84% of the eyes 12 and 18 months after PARK. A UCVA of 20/20 was achieved in 49% of eyes 18 months after PARK. Ten eyes (8%) underwent reoperation at the end of 12 months. Conclusions: The data indicate that PARK is an effective surgical tool for correcting astigmatism, especially astigmatism of 1 .O to -2.5 D, with a success rate of approximately 70%. Ophthalmology 1998; 105:620-623

The evolving technology of excimer laser offers an alternative treatment for refractive defects previously corrected by spectacles and contact lenses and by incisional techniques.’ The few studies published on the correction of astigmatism by photoastigmatic refractive keratectomy

(PARK)253 report more predictable results than those obtained with incisional surgery, but follow-up in both of these studies was short. We report here the results of PARK in 128 eyes after 18 months and provide evidence of the efficacy of this procedure for correction of astigmatism.

Originally received: January 13, 1997. Revision accepted: September 19, 1997. From the Department of Ophthalmology, Assaf Harofeh Medical Center, Zerifin, Israel. Presented as a poster at the Annual Meeting of the American Academy of Ophthalmology, Chicago, October, 1996. Address correspondence to David Zadok, MD, Department of Ophthalmology, Assaf Harofeh Medical Center, Zerifin 70300, Israel.

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Patients and Methods Patientstreated by PARK for myopic astigmatismwere followed prospectively in an open study. Subjectsenrolledin the study were at least 18 years old and had stablerefraction for at least2 years.The subjectshadnoneof the following: clinical or topographicsignsof keratoconus,previous ocular surgery, cornea1infection, adnexapathology, or systemicdiseases that could affect cornea1healing. The final study sampleincluded 128eyesof 102patients,40 (39%) men and 62 (61%) women, 18 to 59 yearsold (mean,33 years). All patientsunderwentcompletepreoperativeocularexamination includingpachymetry,keratometry,andcornea1topography. Before beginningthe PARK procedure, care was taken to align the patient’s headand neck with the axial length of his or herbody andthe lasersystembed.Ablationswere performed with a MEL

60 (Aesculap-Meditec,

Jana, Germany)

excimer

laser,usinga l-mm scanningslit, following mechanicalremoval of the epithelium. The center of the ablation zone was determined by identifying the pupillary center in relatively high illumination, inducing miosis, and marking the pupillary center

with the blunt tip of a delicate hook. A vacuum suctionring was centeredusing a crosshairand applied to the limbus. A

Zadoket al . Excimer Laser PARK Percent of eyes

Post-PARK

80%

q q

20120

20/25-20/30

12 months 18 months

30

58 (92%) 4 (6.4%) 1 (1.6%)

46 (90.1%)

13 (92.9%) 1 (7.1%) -

55 (91.6%) 5 (8.4%) -

44 (95.7%) 2 (4.3%) -

11 (91.7%)

McDonnell and coauthors2,5reported promising results in a series of nine eyes operated by PARK for myopic astigmatism,’ and good results in another series of four eyes that had astigmatism.2Kremer et al6found the VISX 20/20 laser to be an efficient tool for correcting myopic astigmatism over 1 D. To the best of our knowledge, ours is the first study evaluating long-term results (18 months) of PARK with the Meditec laser, one of the most popular lasers in Europe. The differences in astigmatic reduction at 12 months between the high (86%), moderate (87%), and low (79%) astigmatism group were not statistically significant (P < 0.05). However, at 18 months the mean percentage of astigmatic reduction was 75% in the high astigmatism group comparedwith 84% and 91% in the low and moderate groups, respectively. Yet, eyes with an initial high cylinder had a significant amount of residual astigmatism. For example, a 25% residual astigmatism is larger for a higher preoperative cylinder. In our study, 80% of all eyes and only 57% in the high astigmatism group achieved cylinder within 0.5 D of intended correction 12 months after PARK. Our residual cylinder postoperative is lower than results presented by Kremer,6 Kim,7 and others’,’ who used the VISX 20/20 excimer laser, but is less than we had hoped for. Severalfactors may contribute

to the poorer than expected outcome: irregular epithelial thickening, epithelial hyperplasia, or stromal tissue regeneration, which differ from eye to eye. Results can also vary with the precision of the laser machinery. The surgeon has no way of monitoring the actual ablation during the procedure, and an imprecise instrument can lead to undercorrection or overcorrection. One of the most important findings in our study is the lack of significant change in the residual refractive cylindrical axis before and after PARK. Only 32% had manifest refractive astigmatism, and 79% of them (93% of all eyes) were within 10 degreesaround the preoperative astigmatic axis. Optical experimentation and calculation show a direct relationship between axis error and undercorrection in astigmatism, showing a 50% effect with a 15-degree error.” The deviation of the residual cylindrical axis after PARK compared to the axis before PARK depends on the following factors: (1) axial positioning of the patient’s head during treatment; (2) the eyeball rotation of up to 15 degreesthat can occur when the patient goes from sitting to a prone position;” (3) accuracyof the subjective evaluation of the residual cylinder before and after PARK; and (4) a discrepancybetween the axis determined by manifest refraction and by cycloplegic refraction, with uncertainly about which value

m pre-PARK (63 eyes) q 12 months post-PARK (63 eyes)

q

Percent of eyes ,w/., ._._ ,

18 months post-PARK (60 eyes)

q

pre-PARK (51 eyes)

/J

12 months post-PARK (51 eyes)

[7 18 months post-PARK (46 eyes)

Percent of eyes 70%

1 60%

60%

0% -1.75 to - 6.0

-0.6 to -1.5

Spherical Equivalent

Figure 2. Sphertcal equivalent at 12 and 18 months after exclmer laser photoasttgmatic refractwe keratectomy in the low astIgmatIsm group (-1.0 CO+1.5 D). Three eyes were reoperated after 12 months.

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1 (8.3%)

n=4 -10.0 to -12.0

"31 "4 -6.1 to - 9.9

I I I n=,s "4 n-3 -1.75to - 6.0

I I I n=s n-7 -0.6 lo -1.5

I'll "433 "32

0 to -0.5

1.il "A "=4 +0.2510 +2.0

Spherical Equivalent

Figure 3. Spherical equivalent at 12 and 18 months after excimer laser photoastigmatic refractive keratectomy in the moderate astigmatism group (-1.75 to -2.5 D). Five eyes were reoperated after 12 months.

Zcdok et al * Excimer Laser PARK

Percent of eyes

m

pre-PARK (14 eyes)

q q

12 months post-PARK (14 eyes) 18 months post-PARK (12 eyes)

60% 50% !.

I

40% 30% 20% 10% 6%

"=a

"3 n=*n=,

-10.0 to -13.0

-6.1 to - 9.9

-1.75 to - 6.0

n=3 "a -0.6 to -1.5

"2

"2

0 to -0.5

n=* n=, +0.25to +1.75

Spherical Equivalent

Figure 4. Spherrcal equwalent at 12 and 18 months after excnner laser photoasttgmatlc refractwe keratectomy m the htgh astlgmatlsm group (-2.75 to -6.0 D). Two eyes were reoperated after 12 months.

to enter in the computer for correction. We had two patients with large axis deviation that might be due to the reasons mentioned above, or perhaps because inaccurate numbers were entered into the laser’s computer for these two patients. The importance of correct axis alignment cannot be overemphasized in PARK. Another outcome of interest after excimer surgery is visual acuity, a major incentive for individuals to choose

Dost-PAR)< m 12 months

q

Cylinder reduction 100%

-1.0

to -1.5D

Moderate -1.75 to -2.5 D

18 months

Hmh -2.75t;-6.0

D

Degree of Cylinder

Figure 5. Mean astigmatic reduction 12 and 18 months after excimer laser photoasrigmatic refractive keratectomy in the three astigmatism groups.

elective excimer laser surgery. Treatment in the group with astigmatism of - 1.0 to -2.5 D gave, after 12 months, a UCVA of 20/20-20/40 in 84% of the eyes, which is satisfactory compared with the rates reported in the literature.6’7 Although a portion of our patients was left with residual astigmatism, the visual acuity was not significantly different from those of patients with simple myopia who underwent photorefractive keratectomy.‘* The post-PARK SE values are also encouraging, with almost 65% of the eyes with low and moderate astigmatism within plan0 to -0.5 D. All reoperated patients had SE of -6.0 D or higher and higher cylinder values. Our data indicate that PARK offers an effective and predictable surgical tool for correcting astigmatism, especially astigmatism of 1.0 to 2.5 D.

References 1. Duke-Elder S, ed. System of Ophthalmology. London: Kimpton, 1970; v. 5. 2. McDonnell PJ, Moreira H, Clapham TN, et al. Photorefractive keratectomy for astigmatism. Initial clinical results. Arch Ophthalmol 1991;109:1370-3. 3. Taylor HR, Guest CS, Kelly P, Alpins NA. Comparison of excimer laser treatment of astigmatism and myopia. Arch Ophthalmol 1993; 111: 1621-6. 4. Holladay JT, Cravy TV, Koch DD. Calculating the surgically induced refractive change following ocular surgery. J Cataract Refract Surg 1992; 18:429-43. 5. McDonnell PJ, Campos M, Hertzog L, Garbus JJ. Photorefraktive Keratektomy zur Korrektur von myopem Astigmatus. Klin Monatsbl Augenheilkd 1993;202:238-44. 6. Kremer I, Gabbay U, Blumenthal M. One-year follow-up results of photorefractive keratectomy for low, moderate, and high primary astigmatism. Ophthalmology 1996; 103:741-8. 7. Kim YJ, Sohn J, Tchah H, Lee CO. Photoastigmatic refractive keratectomy in 168 eyes: six-month results. J Cataract Refract Surg 1994;20:387-91. 8. Snibson GR, Carson CA, Aldred GF, Taylor HR. One-year evaluation of excimer laser photorefractive keratectomy for myopia and myopic astigmatism. Arch Ophthalmol 1995; 113:994- 1000. 9. Gallinaro C, Toulemont PJ, Cochener B, Colin J. Excimer laser photorefractive keratectomy to correct astigmatism. J Cataract Refract Surg 1996;22:557-63. 10. Stevens JD, Ficker LA, Gartry DS, Steele ADM, Rosen P, Ritten S. Results of VISX excimer laser photoastigmatic keratectomy. Ophthalmology 1996; 103(Suppl):129. 11. Pietrini D, Ganem-Albou C, Assaraf M, Andrade M. Chirurgie de liastigmatisme. Gestes simples pour une plus grande precision. Coup diOei1 1993;9: 12- 14. 12. McCarty CA, Aldred GF, Taylor HR. Comparison of results of excimer laser correction of all degrees of myopia at 12 months postoperatively. Am J Ophthalmol 1996; 121: 372-83.

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