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Photorefractive Keratectomy Retreatments for Regression
Photorefractive Keratectomy Retreatments for Regression One . . year Follow . . up Mihai Pop, MD, Marc Aras, BSc Purpose: Ninety eyes were retreated to correct myopic regression, with or without corneal haze, after primary photorefractive keratectomy (PRK); astigmatism ranging from -0.50 to -3 diopters (D) was present in 43 eyes. Results: The sphere (mean::!:: standard deviation) was -2.82 ::!::1.74 D before repeat surgery. At 6 months, the mean was +0.30 D; at 1 year, it was -0.17 D. Patients were divided into two groups: group 1 included 56 eyes with little or no haze (:51). The mean sphere value for this group was -2.13 D before retreatment; at 1 year, it was -0.20 ::!:: 0.76 D. At 6 months, 84% of sphere values were within ::!::1 D of the intended correction, with a mean haze value of less than 0.5, similar to that before repeat surgery; there was a mean gain of 0.25 Snellen line of best-corrected visual acuity. Astigmatism equal or greater than -0.5 D was present in 34 eyes (mean, -1.17 ::!:: 0.55 D). At 6 months, astigmatism was reduced to -0.45 ::!::0.48 D. The second group included 34 eyes with corneal haze greater than 1 (mean, 2.7). The mean sphere value was -3.95 D before photorefractive keratectomy and -0.12 ::!:: 1.48 D 1 year after treatment. Fifty percent of the mean sphere values were within::!:: 1 D at 6 months, with a mean haze value of 1. The gain in mean best-corrected visual acuity was 1.3 Snellen lines. The mean astigmatism in nine eyes was -1.75 ::!:: 0.75 D before photorefractive keratectomy and -0.72 ::!:: 0.78 D 6 months after treatment. Conclusion: There is a significant difference in the outcome predictability between the two groups. A second photo refractive keratectomy can be done 6 months after the primary treatment in patients with regression with or without trace haze. This group has a high predictability in achieving a good correction, with a low complication rate. When haze is present, retreatments are less predictable with 40% of patients overcorrected. Generally, however, these eyes have a statistically significant decrease in haze (Student's t test; P < 0.01) and an improvement in best-corrected visual acuity. Ophthalmology 1996; 103: 1979-1984
It is well known that a certain percentage of photorefrac-
tive keratectomy (PRK)-treated eyes will tend toward myopic regression. 1 In eyes with low myopia, this percentage is small, generally less than lO%, making PRK an effec-
Originally received: December 6, 1995. Revision accepted: July 12. 1996. From the Michel Pop Clinics, Montreal, Canada. Presented at the American Academy of Ophthalmology Annual Meeting, Atlanta,OctINov 1995. The authors have no proprietary interest in any of the materials used in this study. Reprint requests to Mihai Pop, MD, Michel Pop Clinics, 9001 de I' Acadie Blvd N, Suite 102, Montreal, PQ, Canada H4N 3H5.
tive treatment. 2 In higher degrees of myopia (> -6 diopters [D]), regression can be a limiting factor? Due to this increased incidence of regression and haze formation, some investigators discourage the use of PRK to correct high myopia. 4 In our experience, 30% of eyes with myopia greater than -lO D regressed more than -1 D, and 11 % had a haze grade of 1.5 to 2 at 6 months with the multizone/multipass surface PRK technique. s Sher et al,6 in a multicenter study, considered the correction of high myopia with the excimer laser a reasonably good technique even though they found a fair amount of regression, comparable to our results. However, if a second treatment can improve visual acuity without risking the quality of vision, then PRK may be
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Volume 103, Number 11, November 1996
considered a reliable technique in the vast majority of cases. Seiler7 reported that 63% of eyes were corrected within ± 1 D at 6 months after a first retreatment. He concluded that the technique is safe and effective, although he noted a significant amount of regression in the high myopia group after repeat surgery and more unpredictable results when scar tissue is present. Epstein et al8 reported an 80% success rate for retreatments on eyes that originally were treated for low myopia correction. This study reports all first retreatments done at our clinics on 90 eyes that regressed from the intended correction before January 31, 1995. Preoperative and postoperative refractions, haze, best-corrected visual acuity (BCV A), uncorrected visual acuity (UCV A), and loss of BCVA were analyzed.
Materials and Methods First retreatments were initiated in 90 eyes of 86 patients for regression from January 8, 1993, to January 31, 1995, by one of us (MP), using two VIS X 20/20 excimer lasers in two clinics. Their primary PRKs had been done with the same lasers between May 1992 and June 1994. To be included in this study, eyes had to have a sphere of at least -0.75 D at the time of retreatment. The decision to have a retreatment was left to the patient, so that the number of repeat surgeries is not equivalent to the population that had a correctable regression after a first PRK. Forty-three eyes had astigmatism between -0.50 and -3.00 D. Three eyes were retreated principally for their astigmatism, with each having a sphere at -0.75 D and astigmatism ranging from -1.00 to -1.50 D. The retreatment protocol included an astigmatism correction when necessary. Thirty-four eyes had an original refraction equal to or less than -6 D (range, -0.25 to - .6.0 D), 42 were between -6 and -10 D (range, -6.25 to -9.75 D), and 14 were higher than -10 D (range, -10.25 D to -17.5 D). Before the second surgery, the sphere (mean ± standard deviation) was -2.82 ± 1.74 D (range, -0.75 to -10.00 D). Regression can occur with or without haze. We divided the population into two groups; a no haze (NH) group, 56 eyes with little or no haze (0-1); and a prior haze (PH) group, 34 eyes with definite haze (1.5-4). These two groups were different initially (P < 0.01): the original mean refraction was -6.35 ± 3.15 D in the NH group and -8.72 ± 3.83 D in the PH group (Table 1). These figures are consistent with the increase in haze production in higher myopic corrections, as described in the literature?,4,6 Of the 86 patients (90 eyes), 51% were femal~ and 49% were male. In the NH group, 64% were female and 36% were male, whereas in the PH group 25% were female and 75% were male. Repeat surgeries were done when refractions stabilized; it is defined as a difference in refraction of 0.5 D or less when taken at I-month intervals with no medication other than artificial tears, Surgery was performed 6 to 14 months after the primary PRK. When haze is present, the epithelium is removed with the laser. First, a 6-mm photo therapeutic keratectomy is 1980
performed. Ablation is stopped when the peripheral epithelial surface, corresponding to a third of the diameter, has been removed completely. The remaining epithelium is removed by a PRK to a maximum of 1.75 D in a one-step 6-mm procedure. If necessary, the remaining centrally located epithelium is removed mechanically with a Paton spatula. The myopic correction (mean ± standard deviation) attempted is 96% ± 26% and the astigmatic correction is 125% of the refraction error. Three eyes have received a treatment equal to 50% of the myopic error. When haze is not present, the epithelium is removed mechanically in 20 to 35 seconds with a random 6- to 12o'clock movement using a Paton spatula. The treatment is similar to that performed for a virgin eye. The postoperative regimen consisted of ciprofloxacin hydrochloride in the first 72 hours and kerotolac trimethamine four times daily for 24 hours, then every 12 hours for 48 hours. A soft contact lens is placed on the surgical eye until completion of re-epithelialization. Long-term care includes corticosteroids: 0.1 % fluorometholone acetate is started after completion of re-epithelization and is instilled twice daily for 1 to 3 months. In cases of postoperative scarring or regression, corticosteroids may be prescribed and modulated to the healing process; in all patients, medication had been stopped for 2 to 4 months between the regular follow-up. Fourteen eyes in the PH group and nine in the NH group were taking fluorometholone once daily when the 6-month follow-up examinations were done. Five eyes in the PH group and two in the NH group received corticosteroids once daily at the 12-month follow-up. Artificial tears (Tears Naturale II, Alcon) are instilled twice daily for 1 month and as needed afterward. Postoperative examinations included retinoscopic refraction, Snellen visual acuity, videokeratography, slitlamp microscopy, and tonometry. Haze was evaluated using the same subjective grading scale from 0 (clear cornea) to 4 (obscures completely any details of the iris) proposed by several refractive surgeons. 9 Patients were evaluated at 1, 2, 3, 6, 12, and 24 months. All eyes reached the 12-month postoperative period, except for eight that were retreated. To this date, second retreatments were performed in 12 eyes 6 to 14 months after their previous PRK: 8 (24%) in the PH group and 4 (7%) in the NH group. Statistical analysis was performed using Simstat V.3.5. statistical analysis (PROV ALIS Research, Montreal, Canada) of differences between the NH and the PH groups and patients receiving or not receiving medication were done by using Student's t distribution test. When astigmatism was present, a vector analysis was performed by using a software. developed by Julian Stevens called Refract Tools V.1.38. To estimate the quality of asti§matic correction, Alpins' success index was calculated.I
Results The refraction was -2.82 ± 1.74 D before retreatment for the entire population. The sphere was + 1.19 D at 1 month; +0.30 D at 6 months; and -0.17 Dafter 1 year.
Pop and Aras . PRK Retreatments for Regression Table 1. Mean Sph~re Values: Original, before, and after Retreatment NH (with haze
Time Period (mos)
-6.35 -2.13 0.70 0.27 0.00 -0.20 -0.27
= no haze;
PH (with haze
1)
Mean ± SD
Original Before 1 3 6 12 24 NH
:5
PH
= prior haze;
± ± ± ± ± ± ±
SO
No.
3.15 1.19 0.98 0.86 0.87 0.76 0.71
56 56 50 50 51 44 13
Mean ± SD -8.72 -3.95 1.97 1.29 0.80 -0.12 -0.18
± ± ± ± ± ± ±
3.83 1.92 1.65 1.63 1.66 1,48 1.46
> 1) No.
34 34 31 33 30 29 7
= standard deviation.
In the group of 56 eyes with a haze value of 1 or less and a mean sphere of -2.13 D before retreatment, the mean sphere was 0.70 D at 1 month. This value slowly decreased to 0.00 D at 6 months and to -0.20 D at 1 year (Table 1) (Fig 1). In the group of 34 eyes with a haze higher than 1, the mean sphere was -3.95 D before retreatment, and + 1.97 at 1 month, +0.80 at 6 months, and -0.44 D at 1 year after retreatment (Table 1) (Fig 1). The results are statistically different at 6 months (P < 0.01), but not at 12 months (P = 0.75). One eye in the PH group that received a treatment equal to 50% of the myopic error was included in the statistics at 6 months (-0.25 D). A scattergram of the refraction at 6 months shows the large difference in the number of patients in the NH group who achieved the intended correction compared with the PH group (Figs 2a and 2B). Of the 51 eyes with no prior haze, 84% are within ± 1 D, and 98% are within ±2 D of the intended correction; overcorrections of 1.25 to 2.00 D were present in 8% of the population (Table 2). When these results are compared with the 30 eyes with a prior presence of haze, only 50% are within ± 1 D, and 77% are within ±2 D of the intended correction. Overcorrections of 1.25 to 3.00 D were present in 40% of eyes (Table 2). At 12 months, overcorrection was present in 9% of the NH group and 20% of the PH group. The percentage of eyes within ± 1 D in the NH group stayed
the same at 12 months (84%), whereas it increased in the PH group to 62% because of a higher percentage of second retreatments which left more eyes in the target zone. When refractions of patients receiving corticosteroids at 6 months are compared with those of patients not receiving them, the mean results are not statistically different in the NH group (P = 0.56) and the PH group (P = 0.57). Before retreatment mean cylinder of the 34 eyes with an astigmatism of at least -0.50 D was -1.17 D (standard deviation ± 0.55 D) in the NH group (range, -0.50 to -3.00 D) and -1.75 D ± 0.75 in the nine eyes of the PH group (range, -0.75 to -3.00 D); these data were
Sphere before retreatment
4 3 2 1
o
-1 -2 -3 -4 -5 -6
............................... I · No
Haze I!!IlPriorHaze
I... •.... .............. ..... ..... .
~---------------------------------~
Before
1
3
6
12
24
months Figure 1. Comparison of mean refraction values before and after retreatment between the no haze group (NH) and the presence of haze group (PH). Vertical bars = standard deviation.
Sphere before retreatment
Figure 2. A, scattergram shows the value of the sphere before retreatment compared with the sphere 6 months after retreatment for the no haze regression group (NH). B, scattergram shows the value of the sphere before retreatment compared with the sphere 6 months after retreatment for the presence of haze group (PH).
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Ophthalmology
Table 2. Percentages of Eyes within the Intended Correction 6 Months after Retreatment Group
±2D
±lD
± 0.5 D
No. of Eyes
NH
98 77
84 50
63 30
51 30
PH
o=
100 (%)
60 40
diopters; NH = no haze; PH = prior haze.
20 0
significantly different (P = 0.01). At 6 months, the mean cylinder values were at -0.45 ± 0.48 D in the NH group and at -0.72 ± 0.78 D in the PH group and not significantly different (P = 0.23). Vector analysis of the astigmatism at 6 months shows a small undercorrection, with a minimal rotation of the axis. The mean change in the cylinder was 0.84 D and a mean magnitude of cylinder error was -0.2 ± 0.47 D, with 3 overcorrected and l3 undercorrected eyes in the NH group, whereas the change was 1.33 D and an error of -0.32 ± 0.63 D, with one overcorrected and three undercorrected eyes in the PH group. Alpins' success index was 0.47 ± 0.42 for the NH and 0.35 ± 0.34 for the PH group. The mean haze value before retreatment was less than 0.5 in the NH group and remained constant at 6 months. None of the eyes had more than grade 1 haze throughout the follow-up examinations (Table 3). The mean haze value was 2.7 in the PH group before retreatment and decreased to less than 1 by 1 month postoperatively, remaining at that value throughout the 12-month follow-up (Table 3). Of the 31 eyes for which we have refraction results, 8 still had a haze of at least 2 at 6 months. In one eye, the haze increased, resulting in a loss of BCVA (a loss of 3 Snellen lines). Best-corrected visual acuity was not affected by retreatment in the NH group. Ninety-eight percent of these eyes had 20/40 or better visual acuity before surgery and remained at this level throughout the 12-month follow-up; BCVA of 20/25 or better was 80% before surgery and 82% at 12 months. Best-corrected visual acuity improved in the PH group: those with 20/40 or better visual acuity increased from 76% before surgery to 93% at 12 months. More dramatically, BCVA of 20/25 or better improVed from 49% to 76% for 29 eyes examined at 6 months (Fig 3). Table 3. Mean Haze Values: Before and after Retreatment Time Period (mos) Before
1 3 6 12 24
NH (haze
:5
1)
Mean ± SD
No.
± ± ± ± ± ±
56 47 48 46 41
0.3 0.6 0.4 0.3 0.2 0.1
0.4 0.4 0.4 0.4 0.3 0.1
13
PH (haze Mean ± SD
± ± ± ± 1.1 ± 0.6 ± 2.7 0.9 0.9 1.0
0.8 0.5 0.6 0.8 1.0 0.4
NH = no haze; PH = prior haze; SO = standard deviation.
1982
IIilINH 20/40 .NH 20125 DPH 20/40 .PH 20/25
80
<-. 1) No.
34 30 32 29 28 6
Original
0
3
months
6
12
Figure 3. Percentages of eyes with 20/40 or better and 20/25 or better best-corrected visual acuity before any photorefractive keratectomy, before retreatment, and in the months after treatment for the no haze regression (NH) and presence of haze (PH) groups.
Uncorrected visual acuity of 20/40 or better was achieved in 92% of NH eyes at 1 month and in 93% at 6 months, and decreased in 84% at 12 months. The rate of eyes with UCV A of 20125 or better changed from 66% at 1 month to 56% at 12 months. In the PH group, the rate of eyes with UCV A of 20/40 or better rose from 71 % at 1 month to 76% at 12 months, whereas the rate of eyes with UCVA of 20125 or better increased from 36% at 1 month to 56% at 12 months (Fig 4). The two groups differ remarkably in terms of change in BCVA. In the NH group, no eye lost more than one line at 6 months: 9% lost one line, 66% had no change, 17% gained one line, and 9% gained two lines. In the PH group, one eye (5%) lost three lines due to a change in haze from arciform (which affects minimally vision) before surgery to hemispheric at 6 months after retreatment. This patient has undergone retreatment for a second time. She was taking topical Prednisone forte for 8 months after her second retreatment. Fifteen months after the second retreatment, she is at the same level of BCVA as she was before her first PRK. The remaining eyes had varying results; 7% lost one line, 32% had no change, 14% gained one line, and 43% gained two or more lines (Table 4). When gain or loss of BCVA is compared on virgin eyes and the results obtained 6 months after a first retreatment, the two popUlations are significantly distinct (Student's t test; P < 0.01). In the NH group, 11% lost one line, 70% had no change, 19% gained one or more lines, and 4% gained two lines. In the PH group, 11 % lost two or more lines, 29% lost one line, 54% had no change, and 8% gained one or more lines (Table 4). Central islands appear occasionally after PRK and are defined as central bulges of more than 1 D on topographic examination. 6 In the NH group, the central islands were seen in 16% of the patients at 1 month; however, at 12 months, none were seen, showing the transitory nature of the phenomenon. In the PH group, the highest incidence was seen at 2 months in 8% of eyes; at 6 months, one eye (4%) still had a central island (Table 5).
Discussion Early in the history of PRK treatments, researchers discovered that a significant segment of the PRK population
Pop and Aras . PRK Retreatments for Regression Table 5. Percentage of Eyes Showing a Central Island on Topographies
100
80 (%)
eNH 20/40 .NH 20/25 DPH 20/40 .PH 20/25
60 40
Time Period (mos) 1 2 3 6 12
20 o~----------==~======~======
3
6
12
months
Figure 4. Percentages of eyes with 20/40 or better and 20/25 or better uncorrected visual acuity before any photorefractive keratectomy, before retreatment, and in the months after retreatment for the no haze regression (NH) and presence of haze (PH) groups.
did not attain the desired correction due to undercorrection, regression, and/or the presence of haze. I •9 Even though most PRK surgeons chose to retreat eyes when the initial outcome is unsatisfactory, many others have cautioned that high myopia should not be treated with PRK due to an increased risk of potential complications that will require retreatments. 5 Seiler et alII found the presence of scar tissue in 1% of eyes that did not exceed -6 D, whereas it was noted in 17% of eyes with myopia higher than -6 D. The outcomes of a first retreatment are very different for each of the groups. In eyes with little or no haze, success in attaining emmetropia is greatly increased, with 84% within ± 1 D 6 months after retreatment and little or no risk of inducing haze. None of the eyes had more than grade 1 haze throughout all follow-up examinations. None of the retreated eyes in the NH group lost more than one line of BeVA 6 months after retreatment, compared with their virgin BeVA or their BeVA after the initial PRK. These figures are consistent with those of Epstein et al,12 who reported on 17 retreated eyes that had no increase in haze after retreatment; 58.8% were within ± 1 D of the intended correction. These authors concluded that the majority of regression can be successfully retreated.
Table
4.
Gain or Loss of Best-corrected Visual Acuity Snellen Lines Before and after Retreatment (%)
Original and after Retreatment (%)
Snellen Lines
NH
PH
NH
PH
Gain of ~ 2 lines Gain of 1 line No change Loss of 1 line Loss of ~ 2 lines
9 17 66 9 0
43 14 32 7 4
4 15 70
4 4 54 29 11
NH
=
no haze; PH
=
prior haze.
11 0
NH (haze
NH
= no haze;
16
PH
:5
1)
PH (haze> 1) 4
11
8
2 2 0
7 4 0
= prior haze.
Repeat surgery on eyes with scar tissue has seldom been reported in the literature. Seiler et al, 7 reporting on 21 eyes, described a phototherapeutic keratectomy - PRK approach. Their protocol adds 1 D to the refractive error before retreatment. These authors found scar recurrence in 4 (19%) of 21 eyes of the eyes. Loewnstein et al l3 have proposed a nonlaser approach: epithelial scraping. They obtained a mean spherical equivalent of -2.63 at 3 months on 21 eyes, but reported a high standard deviation of ±4.04 D. Thirteen of these eyes had a BeVA less than 20/40. In the PH group, a full correction within ± 1 D is more difficult to attain, with only 50% within this range. There is a tendency toward overcorrection, with a mean sphere of 0.80 D compared with 0.00 D in the NH group. It is, however, the standard deviation that provides a good picture of the more scattered response. The PH group was ± 1.66 D compared with ±0.87 D for the NH group at 6 months. We propose two possible factors contributing to the more scattered response: (1) the amount of ablation per laser pulse might be different in scar tissue because of changes in the structure and the physiology of the stroma, and (2) the change in the epithelium structure and thickness is another hypothesis. In light of the overcorrection tendency, a conservative approach is advised for eyes in which haze develops: a correction limited to 50% of the myopic error to avert severe overcorrections is proposed, even if it means a second treatment in case of an undercorrection. Vector analysis of the astigmatism correction shows a statistically significant change in both groups with a tendency to undercorrect, whereas the change of axis is minimal. Potential loss of BeVA must be addressed. One of 34 eyes lost three Snellen lines due to increased haze in the central part of the ablation; two eyes lost one line. A second retreatment was performed on the eye that lost three lines. Fifteen months postoperatively, this patient completely has regained his original BeVA of 20/40. Overall, the PH population gained BevA due to the decrease in haze. Forty-eight percent gained two or more lines of BeVA after retreatment. However, caution is still the rule: even after retreatment, 11 % of the population with marked haze will lose two or more lines of BeVA when compared with their original value before any PRK. Because of the potential loss of BevA, we suggest
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that retreatment in the presence of haze be limited to patients with BCVA less than 20/40 before surgery. For other patients, repeat surgery may be postponed until the haze has resolved naturally to grade 1 or less. However, if haze is visually debilitating, patients may undergo repeat surgery after a thorough explanation and understanding of the expected outcome. This study has not only confirmed the importance of haze in regression, but also its impact on retreatment outcomes. Limiting haze formation during primary PRK is crucial in improving retreatment outcomes. Such advances in the technical approach to PRK as the multizonel multipass technique, which has been shown to limit haze formation,S and better medication regimens are two promising areas of research.
5. 6. 7.
8.
9.
References 1. Seiler T, Wollensak J. Myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1991;98:1156-63. 2. Maguen E, Salz JJ, Nesbum AB, et al. Results of excimer laser photorefractive keratectomy for the correction of myopia. Ophthalmology 1994; 101:1548-57. 3. Heitzmann J, Binder PS, Kassar BS, Nordan LT. The correction of high myopia using the excimer laser. Arch Ophthalmol 1993; 111: 1627 -34. 4. Menezo JL, Martinez-Costa R, Navea A, et al. Excimer
10. 11. 12. 13.
laser photorefractive keratectomy for high myopia. J Cataract Refract Surg 1995;21:393-7. Pop M, Aras M. Multizone/multipass photorefractive keratectomy: six month results. J Cataract Refract Surg 1995; 21:633-42. Sher NA, Hardten DR, Fundingsland B, et al. 193-nm excimer photorefractive keratectomy in high myopia. Ophthalmology 1994; 101:1575-82. Seiler T, Schmidt-Peterson H, Wollensak J. Complications after myopic photorefractive keratectomy, primarily with the Summit excimer laser. In: Salz JJ, McDonnell PJ, McDonald MB, eds. Corneal Laser Surgery. St Louis: MosbyYear Book, Inc, 1995; 131. Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Reoperations. In: Salz JJ, McDonnell PJ, McDonald MB, eds. Corneal Laser Surgery. St Louis: Mosby-Year Book, Inc, 1995; 159. Fantes F, Hanna D, Waring GO III, et al. Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmol 1990; 108:665-75. Alpins NA. A new method of analyzing vectors for change in astigmatism. J Cataract Refract Surg 1993; 19:524-33. Seiler T, Holschbach A, Derse M, et al. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153-60. Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Excimer retreatment of regression after photorefractive keratectomy. Am J Ophthalmol 1994; 117:456-61. Lowenstein A, Lipshitz I, Lazar M. Scraping of epithelium for treatment of undercorrection and haze after photorefractive keratectomy. J Refract Corneal Surg 1994; IO:S274-6.
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1984
It is well known that a certain percentage of photorefrac-
tive keratectomy (PRK)-treated eyes will tend toward myopic regression. 1 In eyes with low myopia, this percentage is small, generally less than lO%, making PRK an effec-
Originally received: December 6, 1995. Revision accepted: July 12. 1996. From the Michel Pop Clinics, Montreal, Canada. Presented at the American Academy of Ophthalmology Annual Meeting, Atlanta,OctINov 1995. The authors have no proprietary interest in any of the materials used in this study. Reprint requests to Mihai Pop, MD, Michel Pop Clinics, 9001 de I' Acadie Blvd N, Suite 102, Montreal, PQ, Canada H4N 3H5.
tive treatment. 2 In higher degrees of myopia (> -6 diopters [D]), regression can be a limiting factor? Due to this increased incidence of regression and haze formation, some investigators discourage the use of PRK to correct high myopia. 4 In our experience, 30% of eyes with myopia greater than -lO D regressed more than -1 D, and 11 % had a haze grade of 1.5 to 2 at 6 months with the multizone/multipass surface PRK technique. s Sher et al,6 in a multicenter study, considered the correction of high myopia with the excimer laser a reasonably good technique even though they found a fair amount of regression, comparable to our results. However, if a second treatment can improve visual acuity without risking the quality of vision, then PRK may be
1979
Ophthalmology
Volume 103, Number 11, November 1996
considered a reliable technique in the vast majority of cases. Seiler7 reported that 63% of eyes were corrected within ± 1 D at 6 months after a first retreatment. He concluded that the technique is safe and effective, although he noted a significant amount of regression in the high myopia group after repeat surgery and more unpredictable results when scar tissue is present. Epstein et al8 reported an 80% success rate for retreatments on eyes that originally were treated for low myopia correction. This study reports all first retreatments done at our clinics on 90 eyes that regressed from the intended correction before January 31, 1995. Preoperative and postoperative refractions, haze, best-corrected visual acuity (BCV A), uncorrected visual acuity (UCV A), and loss of BCVA were analyzed.
Materials and Methods First retreatments were initiated in 90 eyes of 86 patients for regression from January 8, 1993, to January 31, 1995, by one of us (MP), using two VIS X 20/20 excimer lasers in two clinics. Their primary PRKs had been done with the same lasers between May 1992 and June 1994. To be included in this study, eyes had to have a sphere of at least -0.75 D at the time of retreatment. The decision to have a retreatment was left to the patient, so that the number of repeat surgeries is not equivalent to the population that had a correctable regression after a first PRK. Forty-three eyes had astigmatism between -0.50 and -3.00 D. Three eyes were retreated principally for their astigmatism, with each having a sphere at -0.75 D and astigmatism ranging from -1.00 to -1.50 D. The retreatment protocol included an astigmatism correction when necessary. Thirty-four eyes had an original refraction equal to or less than -6 D (range, -0.25 to - .6.0 D), 42 were between -6 and -10 D (range, -6.25 to -9.75 D), and 14 were higher than -10 D (range, -10.25 D to -17.5 D). Before the second surgery, the sphere (mean ± standard deviation) was -2.82 ± 1.74 D (range, -0.75 to -10.00 D). Regression can occur with or without haze. We divided the population into two groups; a no haze (NH) group, 56 eyes with little or no haze (0-1); and a prior haze (PH) group, 34 eyes with definite haze (1.5-4). These two groups were different initially (P < 0.01): the original mean refraction was -6.35 ± 3.15 D in the NH group and -8.72 ± 3.83 D in the PH group (Table 1). These figures are consistent with the increase in haze production in higher myopic corrections, as described in the literature?,4,6 Of the 86 patients (90 eyes), 51% were femal~ and 49% were male. In the NH group, 64% were female and 36% were male, whereas in the PH group 25% were female and 75% were male. Repeat surgeries were done when refractions stabilized; it is defined as a difference in refraction of 0.5 D or less when taken at I-month intervals with no medication other than artificial tears, Surgery was performed 6 to 14 months after the primary PRK. When haze is present, the epithelium is removed with the laser. First, a 6-mm photo therapeutic keratectomy is 1980
performed. Ablation is stopped when the peripheral epithelial surface, corresponding to a third of the diameter, has been removed completely. The remaining epithelium is removed by a PRK to a maximum of 1.75 D in a one-step 6-mm procedure. If necessary, the remaining centrally located epithelium is removed mechanically with a Paton spatula. The myopic correction (mean ± standard deviation) attempted is 96% ± 26% and the astigmatic correction is 125% of the refraction error. Three eyes have received a treatment equal to 50% of the myopic error. When haze is not present, the epithelium is removed mechanically in 20 to 35 seconds with a random 6- to 12o'clock movement using a Paton spatula. The treatment is similar to that performed for a virgin eye. The postoperative regimen consisted of ciprofloxacin hydrochloride in the first 72 hours and kerotolac trimethamine four times daily for 24 hours, then every 12 hours for 48 hours. A soft contact lens is placed on the surgical eye until completion of re-epithelialization. Long-term care includes corticosteroids: 0.1 % fluorometholone acetate is started after completion of re-epithelization and is instilled twice daily for 1 to 3 months. In cases of postoperative scarring or regression, corticosteroids may be prescribed and modulated to the healing process; in all patients, medication had been stopped for 2 to 4 months between the regular follow-up. Fourteen eyes in the PH group and nine in the NH group were taking fluorometholone once daily when the 6-month follow-up examinations were done. Five eyes in the PH group and two in the NH group received corticosteroids once daily at the 12-month follow-up. Artificial tears (Tears Naturale II, Alcon) are instilled twice daily for 1 month and as needed afterward. Postoperative examinations included retinoscopic refraction, Snellen visual acuity, videokeratography, slitlamp microscopy, and tonometry. Haze was evaluated using the same subjective grading scale from 0 (clear cornea) to 4 (obscures completely any details of the iris) proposed by several refractive surgeons. 9 Patients were evaluated at 1, 2, 3, 6, 12, and 24 months. All eyes reached the 12-month postoperative period, except for eight that were retreated. To this date, second retreatments were performed in 12 eyes 6 to 14 months after their previous PRK: 8 (24%) in the PH group and 4 (7%) in the NH group. Statistical analysis was performed using Simstat V.3.5. statistical analysis (PROV ALIS Research, Montreal, Canada) of differences between the NH and the PH groups and patients receiving or not receiving medication were done by using Student's t distribution test. When astigmatism was present, a vector analysis was performed by using a software. developed by Julian Stevens called Refract Tools V.1.38. To estimate the quality of asti§matic correction, Alpins' success index was calculated.I
Results The refraction was -2.82 ± 1.74 D before retreatment for the entire population. The sphere was + 1.19 D at 1 month; +0.30 D at 6 months; and -0.17 Dafter 1 year.
Pop and Aras . PRK Retreatments for Regression Table 1. Mean Sph~re Values: Original, before, and after Retreatment NH (with haze
Time Period (mos)
-6.35 -2.13 0.70 0.27 0.00 -0.20 -0.27
= no haze;
PH (with haze
1)
Mean ± SD
Original Before 1 3 6 12 24 NH
:5
PH
= prior haze;
± ± ± ± ± ± ±
SO
No.
3.15 1.19 0.98 0.86 0.87 0.76 0.71
56 56 50 50 51 44 13
Mean ± SD -8.72 -3.95 1.97 1.29 0.80 -0.12 -0.18
± ± ± ± ± ± ±
3.83 1.92 1.65 1.63 1.66 1,48 1.46
> 1) No.
34 34 31 33 30 29 7
= standard deviation.
In the group of 56 eyes with a haze value of 1 or less and a mean sphere of -2.13 D before retreatment, the mean sphere was 0.70 D at 1 month. This value slowly decreased to 0.00 D at 6 months and to -0.20 D at 1 year (Table 1) (Fig 1). In the group of 34 eyes with a haze higher than 1, the mean sphere was -3.95 D before retreatment, and + 1.97 at 1 month, +0.80 at 6 months, and -0.44 D at 1 year after retreatment (Table 1) (Fig 1). The results are statistically different at 6 months (P < 0.01), but not at 12 months (P = 0.75). One eye in the PH group that received a treatment equal to 50% of the myopic error was included in the statistics at 6 months (-0.25 D). A scattergram of the refraction at 6 months shows the large difference in the number of patients in the NH group who achieved the intended correction compared with the PH group (Figs 2a and 2B). Of the 51 eyes with no prior haze, 84% are within ± 1 D, and 98% are within ±2 D of the intended correction; overcorrections of 1.25 to 2.00 D were present in 8% of the population (Table 2). When these results are compared with the 30 eyes with a prior presence of haze, only 50% are within ± 1 D, and 77% are within ±2 D of the intended correction. Overcorrections of 1.25 to 3.00 D were present in 40% of eyes (Table 2). At 12 months, overcorrection was present in 9% of the NH group and 20% of the PH group. The percentage of eyes within ± 1 D in the NH group stayed
the same at 12 months (84%), whereas it increased in the PH group to 62% because of a higher percentage of second retreatments which left more eyes in the target zone. When refractions of patients receiving corticosteroids at 6 months are compared with those of patients not receiving them, the mean results are not statistically different in the NH group (P = 0.56) and the PH group (P = 0.57). Before retreatment mean cylinder of the 34 eyes with an astigmatism of at least -0.50 D was -1.17 D (standard deviation ± 0.55 D) in the NH group (range, -0.50 to -3.00 D) and -1.75 D ± 0.75 in the nine eyes of the PH group (range, -0.75 to -3.00 D); these data were
Sphere before retreatment
4 3 2 1
o
-1 -2 -3 -4 -5 -6
............................... I · No
Haze I!!IlPriorHaze
I... •.... .............. ..... ..... .
~---------------------------------~
Before
1
3
6
12
24
months Figure 1. Comparison of mean refraction values before and after retreatment between the no haze group (NH) and the presence of haze group (PH). Vertical bars = standard deviation.
Sphere before retreatment
Figure 2. A, scattergram shows the value of the sphere before retreatment compared with the sphere 6 months after retreatment for the no haze regression group (NH). B, scattergram shows the value of the sphere before retreatment compared with the sphere 6 months after retreatment for the presence of haze group (PH).
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Volume 103, Number 11, November 1996
Ophthalmology
Table 2. Percentages of Eyes within the Intended Correction 6 Months after Retreatment Group
±2D
±lD
± 0.5 D
No. of Eyes
NH
98 77
84 50
63 30
51 30
PH
o=
100 (%)
60 40
diopters; NH = no haze; PH = prior haze.
20 0
significantly different (P = 0.01). At 6 months, the mean cylinder values were at -0.45 ± 0.48 D in the NH group and at -0.72 ± 0.78 D in the PH group and not significantly different (P = 0.23). Vector analysis of the astigmatism at 6 months shows a small undercorrection, with a minimal rotation of the axis. The mean change in the cylinder was 0.84 D and a mean magnitude of cylinder error was -0.2 ± 0.47 D, with 3 overcorrected and l3 undercorrected eyes in the NH group, whereas the change was 1.33 D and an error of -0.32 ± 0.63 D, with one overcorrected and three undercorrected eyes in the PH group. Alpins' success index was 0.47 ± 0.42 for the NH and 0.35 ± 0.34 for the PH group. The mean haze value before retreatment was less than 0.5 in the NH group and remained constant at 6 months. None of the eyes had more than grade 1 haze throughout the follow-up examinations (Table 3). The mean haze value was 2.7 in the PH group before retreatment and decreased to less than 1 by 1 month postoperatively, remaining at that value throughout the 12-month follow-up (Table 3). Of the 31 eyes for which we have refraction results, 8 still had a haze of at least 2 at 6 months. In one eye, the haze increased, resulting in a loss of BCVA (a loss of 3 Snellen lines). Best-corrected visual acuity was not affected by retreatment in the NH group. Ninety-eight percent of these eyes had 20/40 or better visual acuity before surgery and remained at this level throughout the 12-month follow-up; BCVA of 20/25 or better was 80% before surgery and 82% at 12 months. Best-corrected visual acuity improved in the PH group: those with 20/40 or better visual acuity increased from 76% before surgery to 93% at 12 months. More dramatically, BCVA of 20/25 or better improVed from 49% to 76% for 29 eyes examined at 6 months (Fig 3). Table 3. Mean Haze Values: Before and after Retreatment Time Period (mos) Before
1 3 6 12 24
NH (haze
:5
1)
Mean ± SD
No.
± ± ± ± ± ±
56 47 48 46 41
0.3 0.6 0.4 0.3 0.2 0.1
0.4 0.4 0.4 0.4 0.3 0.1
13
PH (haze Mean ± SD
± ± ± ± 1.1 ± 0.6 ± 2.7 0.9 0.9 1.0
0.8 0.5 0.6 0.8 1.0 0.4
NH = no haze; PH = prior haze; SO = standard deviation.
1982
IIilINH 20/40 .NH 20125 DPH 20/40 .PH 20/25
80
<-. 1) No.
34 30 32 29 28 6
Original
0
3
months
6
12
Figure 3. Percentages of eyes with 20/40 or better and 20/25 or better best-corrected visual acuity before any photorefractive keratectomy, before retreatment, and in the months after treatment for the no haze regression (NH) and presence of haze (PH) groups.
Uncorrected visual acuity of 20/40 or better was achieved in 92% of NH eyes at 1 month and in 93% at 6 months, and decreased in 84% at 12 months. The rate of eyes with UCV A of 20125 or better changed from 66% at 1 month to 56% at 12 months. In the PH group, the rate of eyes with UCV A of 20/40 or better rose from 71 % at 1 month to 76% at 12 months, whereas the rate of eyes with UCVA of 20125 or better increased from 36% at 1 month to 56% at 12 months (Fig 4). The two groups differ remarkably in terms of change in BCVA. In the NH group, no eye lost more than one line at 6 months: 9% lost one line, 66% had no change, 17% gained one line, and 9% gained two lines. In the PH group, one eye (5%) lost three lines due to a change in haze from arciform (which affects minimally vision) before surgery to hemispheric at 6 months after retreatment. This patient has undergone retreatment for a second time. She was taking topical Prednisone forte for 8 months after her second retreatment. Fifteen months after the second retreatment, she is at the same level of BCVA as she was before her first PRK. The remaining eyes had varying results; 7% lost one line, 32% had no change, 14% gained one line, and 43% gained two or more lines (Table 4). When gain or loss of BCVA is compared on virgin eyes and the results obtained 6 months after a first retreatment, the two popUlations are significantly distinct (Student's t test; P < 0.01). In the NH group, 11% lost one line, 70% had no change, 19% gained one or more lines, and 4% gained two lines. In the PH group, 11 % lost two or more lines, 29% lost one line, 54% had no change, and 8% gained one or more lines (Table 4). Central islands appear occasionally after PRK and are defined as central bulges of more than 1 D on topographic examination. 6 In the NH group, the central islands were seen in 16% of the patients at 1 month; however, at 12 months, none were seen, showing the transitory nature of the phenomenon. In the PH group, the highest incidence was seen at 2 months in 8% of eyes; at 6 months, one eye (4%) still had a central island (Table 5).
Discussion Early in the history of PRK treatments, researchers discovered that a significant segment of the PRK population
Pop and Aras . PRK Retreatments for Regression Table 5. Percentage of Eyes Showing a Central Island on Topographies
100
80 (%)
eNH 20/40 .NH 20/25 DPH 20/40 .PH 20/25
60 40
Time Period (mos) 1 2 3 6 12
20 o~----------==~======~======
3
6
12
months
Figure 4. Percentages of eyes with 20/40 or better and 20/25 or better uncorrected visual acuity before any photorefractive keratectomy, before retreatment, and in the months after retreatment for the no haze regression (NH) and presence of haze (PH) groups.
did not attain the desired correction due to undercorrection, regression, and/or the presence of haze. I •9 Even though most PRK surgeons chose to retreat eyes when the initial outcome is unsatisfactory, many others have cautioned that high myopia should not be treated with PRK due to an increased risk of potential complications that will require retreatments. 5 Seiler et alII found the presence of scar tissue in 1% of eyes that did not exceed -6 D, whereas it was noted in 17% of eyes with myopia higher than -6 D. The outcomes of a first retreatment are very different for each of the groups. In eyes with little or no haze, success in attaining emmetropia is greatly increased, with 84% within ± 1 D 6 months after retreatment and little or no risk of inducing haze. None of the eyes had more than grade 1 haze throughout all follow-up examinations. None of the retreated eyes in the NH group lost more than one line of BeVA 6 months after retreatment, compared with their virgin BeVA or their BeVA after the initial PRK. These figures are consistent with those of Epstein et al,12 who reported on 17 retreated eyes that had no increase in haze after retreatment; 58.8% were within ± 1 D of the intended correction. These authors concluded that the majority of regression can be successfully retreated.
Table
4.
Gain or Loss of Best-corrected Visual Acuity Snellen Lines Before and after Retreatment (%)
Original and after Retreatment (%)
Snellen Lines
NH
PH
NH
PH
Gain of ~ 2 lines Gain of 1 line No change Loss of 1 line Loss of ~ 2 lines
9 17 66 9 0
43 14 32 7 4
4 15 70
4 4 54 29 11
NH
=
no haze; PH
=
prior haze.
11 0
NH (haze
NH
= no haze;
16
PH
:5
1)
PH (haze> 1) 4
11
8
2 2 0
7 4 0
= prior haze.
Repeat surgery on eyes with scar tissue has seldom been reported in the literature. Seiler et al, 7 reporting on 21 eyes, described a phototherapeutic keratectomy - PRK approach. Their protocol adds 1 D to the refractive error before retreatment. These authors found scar recurrence in 4 (19%) of 21 eyes of the eyes. Loewnstein et al l3 have proposed a nonlaser approach: epithelial scraping. They obtained a mean spherical equivalent of -2.63 at 3 months on 21 eyes, but reported a high standard deviation of ±4.04 D. Thirteen of these eyes had a BeVA less than 20/40. In the PH group, a full correction within ± 1 D is more difficult to attain, with only 50% within this range. There is a tendency toward overcorrection, with a mean sphere of 0.80 D compared with 0.00 D in the NH group. It is, however, the standard deviation that provides a good picture of the more scattered response. The PH group was ± 1.66 D compared with ±0.87 D for the NH group at 6 months. We propose two possible factors contributing to the more scattered response: (1) the amount of ablation per laser pulse might be different in scar tissue because of changes in the structure and the physiology of the stroma, and (2) the change in the epithelium structure and thickness is another hypothesis. In light of the overcorrection tendency, a conservative approach is advised for eyes in which haze develops: a correction limited to 50% of the myopic error to avert severe overcorrections is proposed, even if it means a second treatment in case of an undercorrection. Vector analysis of the astigmatism correction shows a statistically significant change in both groups with a tendency to undercorrect, whereas the change of axis is minimal. Potential loss of BeVA must be addressed. One of 34 eyes lost three Snellen lines due to increased haze in the central part of the ablation; two eyes lost one line. A second retreatment was performed on the eye that lost three lines. Fifteen months postoperatively, this patient completely has regained his original BeVA of 20/40. Overall, the PH population gained BevA due to the decrease in haze. Forty-eight percent gained two or more lines of BeVA after retreatment. However, caution is still the rule: even after retreatment, 11 % of the population with marked haze will lose two or more lines of BeVA when compared with their original value before any PRK. Because of the potential loss of BevA, we suggest
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Ophthalmology
Volume 103 , Number 11, November 1996
that retreatment in the presence of haze be limited to patients with BCVA less than 20/40 before surgery. For other patients, repeat surgery may be postponed until the haze has resolved naturally to grade 1 or less. However, if haze is visually debilitating, patients may undergo repeat surgery after a thorough explanation and understanding of the expected outcome. This study has not only confirmed the importance of haze in regression, but also its impact on retreatment outcomes. Limiting haze formation during primary PRK is crucial in improving retreatment outcomes. Such advances in the technical approach to PRK as the multizonel multipass technique, which has been shown to limit haze formation,S and better medication regimens are two promising areas of research.
5. 6. 7.
8.
9.
References 1. Seiler T, Wollensak J. Myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1991;98:1156-63. 2. Maguen E, Salz JJ, Nesbum AB, et al. Results of excimer laser photorefractive keratectomy for the correction of myopia. Ophthalmology 1994; 101:1548-57. 3. Heitzmann J, Binder PS, Kassar BS, Nordan LT. The correction of high myopia using the excimer laser. Arch Ophthalmol 1993; 111: 1627 -34. 4. Menezo JL, Martinez-Costa R, Navea A, et al. Excimer
10. 11. 12. 13.
laser photorefractive keratectomy for high myopia. J Cataract Refract Surg 1995;21:393-7. Pop M, Aras M. Multizone/multipass photorefractive keratectomy: six month results. J Cataract Refract Surg 1995; 21:633-42. Sher NA, Hardten DR, Fundingsland B, et al. 193-nm excimer photorefractive keratectomy in high myopia. Ophthalmology 1994; 101:1575-82. Seiler T, Schmidt-Peterson H, Wollensak J. Complications after myopic photorefractive keratectomy, primarily with the Summit excimer laser. In: Salz JJ, McDonnell PJ, McDonald MB, eds. Corneal Laser Surgery. St Louis: MosbyYear Book, Inc, 1995; 131. Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Reoperations. In: Salz JJ, McDonnell PJ, McDonald MB, eds. Corneal Laser Surgery. St Louis: Mosby-Year Book, Inc, 1995; 159. Fantes F, Hanna D, Waring GO III, et al. Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys. Arch Ophthalmol 1990; 108:665-75. Alpins NA. A new method of analyzing vectors for change in astigmatism. J Cataract Refract Surg 1993; 19:524-33. Seiler T, Holschbach A, Derse M, et al. Complications of myopic photorefractive keratectomy with the excimer laser. Ophthalmology 1994; 101:153-60. Epstein D, Tengroth B, Fagerholm P, Hamberg-Nystrom H. Excimer retreatment of regression after photorefractive keratectomy. Am J Ophthalmol 1994; 117:456-61. Lowenstein A, Lipshitz I, Lazar M. Scraping of epithelium for treatment of undercorrection and haze after photorefractive keratectomy. J Refract Corneal Surg 1994; IO:S274-6.
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