Visual Outcomes After Primary LASIK

A. EARLY STUDIES OF LASIK IN MODERATE AND HIGH MYOPIA

Several reports regarding LASIK in moderate and high myopia were published before January 1997 and are considered in the analysis. The total number of eyes reported in these papers was 1028.

a. Follow-Up

The follow-up ranged from 10 days to 24 months but was most often performed at 6 (1–8) or 12 months (9–13). In one study (14) it was ambiguous, and in others (15–18) only a mean follow-up was presented.

b. Preoperative Refraction

The preoperative refraction was generally in the range of moderate to high myopia. The lowest was 6.0 D and the highest (18), 37.0 D, with a mean of 12.59 D. Only Salah et al. (17) operated on a group with low myopia (2.0 to 6.0 D) in the series on which they reported clinical results. Arenas and Maglione (16) operated on four contact lens intolerant patients after PKP because of high residual myopia (mean 11.2 D) causing anisometropia.

1. Refractive Outcome and Predictability

a. Postoperative Refraction

An undercorrection was seen in most of the reviewed series. The postoperative result ranged from an overcorrection (1) of 6.63 to an undercorrection (3) of 9.5 D, with a mean of 1.1 D. Bas and Onnis (19) aimed at emmetropia in cases of low myopia and at overcorrection by 2.0 D in cases of high myopia because the myopia progresses over time and the cornea tends to bend its anterior surface slightly after surgery (stromal scar, molecular memory in collagen fibers, and intraocular pressure on the cornea). In the post-PKP study (16), the mean post-LASIK refraction was 2.37 D at a mean follow-up of 7 months. The scattergram in the series by Knorz et al. (3) showed that most eyes were somewhat undercorrected, with 22% beyond 3.0 D. Analysis of these cases showed that the cause of this undercorrection was not related to the ablation algorithm. Pérez-Santonja et al. (5) had a mean postoperative refraction of 0.18 D 1.6 (SD) at 6 months. They found that the mean postoperative spherical equivalent was significantly higher with the 5.0/5.5/6.0 mm ablation profile ( 0.47 1.5D) than that with the 4.0/4.5/5.0 mm profile ( 0.93 2.1 D). In another study (18), six eyes between 20.0 and 40.0 D were undercorrected due to the limitation that 30% of the preoperative corneal thickness must be left undisturbed beneath the ablated area to avoid subsequent corneal ectasia.

b. Percentage Within 1.0 D

The percentage of LASIK patients within 1.0 D of emmetropia was 46.5% (19) and 70.0% (14) at 3 months postoperatively; 47.0% (2,3), 74.2% (4), 60.0% (5), and 85.0% (moderate myopia group), and 41.0% (high myopia group) (6), 67.65% (7), 72.0% (17), and 47.8% (8) at 6 months; and 57.0% (9), 66.6% (10), and 85.7% (13) at 1 year, with an overall mean of 67.0%.

The studies indicate that the predictability of LASIK decreases when the preoperative myopia is high. In one study (17), the group with low myopia (2.0 to 6.0 D) had the highest predictability; 92.5% at a mean follow-up of 5.2 months; whereas the groups with moderate (6.0 to 12.0 D) and high (12.0 to 20.0 D) myopia had predictabilities of 65.0%

and 43.0%, respectively (17). Guell and Muller (6) found that 85.0% of eyes with moderate myopia and only 41.0% of eyes with high myopia were within 1.0 D. In their study, Pérez-Santonja et al. (5) reported 72.4% with 8.0 to 12.0 D of myopia were within 1.0 D at 6 months; this predictability was lower in the two groups with higher myopia.

2. Visual Outcome

In several studies, patients with reduced levels of preoperative corrected and uncorrected vision because of progressive myopic chorioretinal degeneration, anisometropic amblyopia, or both were included. To ensure that upcoming studies reflect the exact postoperative outcome, patients with a low preoperative best corrected visual acuity (BCVA) should be studied separately from those with a BCVA of 20/40 or better. Studies should specify the preoperative uncorrected visual acuity (UCVA), permitting comparisons between preoperative and postoperative acuities.

a. Postoperative UCVA of 20/40 or Better

The mean UCVA improved from 20/1000 preoperatively to 20/45 postoperatively at 6 months in one study (5). A UCVA of 20/40 or better was achieved by 49.9% (19) and 81.0% (14) at 3 months; by 66.0% (1,8), 81.0% (4), 71.4% (moderate myopia group), and 45.0% (high myopia group) (6), 71.0% (17), 29.2% (3), and 46.4% (5) at 6 months, and by 10.0% (9) and 75.0% (13) at 1 year, with an overall mean of 49.2%.

Salah et al. (17) reported a UCVA of 20/40 or better in 92.8% of patients in the low myopia group (2.0 to 6.0 D), 62.3% in the moderate myopia group (6.0 to 12.0 D), and 36.8% in the high myopia group (12.0 to 20.0 D) at 5.2 months after LASIK. In Guell and Muller’s series (6), the postoperative UCVA in the moderate and high myopia groups was 71.4% and 45.0%, respectively. In the post-PKP study (16), no patient had a UCVA better than 20/40, but all four eyes improved to 20/150 or 20/100.

b. Postoperative UCVA of 20/20 or Better

A UCVA of 20/20 or better was achieved by 44.0% (15) and 50.0% (14) of patients at 2 to 3 months postoperatively; by 34.0% (1), 0% (6), 36.0% (17), and 7.8% (3) at 6 months; and by 0% (9) and 17.5% (13) at 1 year. The overall mean was 22.0%.

3. Astigmatism

Several studies do not mention correcting the astigmatic error (5,6,9,14,20). In the papers, the mean preoperative and postoperative astigmatism were 0.85 and 0.95 D, respectively.

Two studies (12,18) reported the attempted correction of the astigmatic error. In one, (18), the cylindrical component was reduced from a mean of 2.1 D ( 0.5 to 6.0) to a mean of 0.5 (0 to 3.25). Two other studies (6,13) reported that after LASIK, the percentage of patients experiencing an increase in astigmatism was lower than the percentage experiencing a decrease (6.0% and 27.5% increase; 17.2% and 42.3% decrease). In the post-PKP study (16), there was an increase in mean astigmatism after LASIK.

4. Loss of BCVA

A reduction in BCVA is consistently seen in some eyes having LASIK. It can be due to interface abnormalities (7,18,21), central islands (3,18), or induced irregular astigmatism (3,7). In one study (18), it was attributed to the learning curve associated with this tech-

nique, particularly while the flap was being fashioned. The percentage of eyes that lost two or more lines was 8.0 (22), 21.3 (1), 13.4 (19), 20.0 (12), 0 (4,6), 10.0 (15), 8.82 (7), 3.6 (17), 5.5 (2), 12.0 (3), and 1.4 (5), with a mean of 8.0.

B. OUTCOMES OF LASIK IN LOW MYOPIA ( 0.75 TO 4 D)

Reports about LASIK for low myopia have emerged in the recent 4 years. The concern during the first few years of LASIK practice was the treatment of moderate to high myopia; the range of myopia where PRK has increased the risk of scaring and complications. In recent years and after that LASIK proved to be a reliable and predictable procedure for moderate to high myopia, reports (23,24,25–27) on the treatment of low myopia with LASIK started to emerge in the literature showing similar results to those of the higher ranges of myopia (28).

The total number of eyes reported in these papers was 1125. The F/U ranged between 1 and 12 months with a mean of 4.5 months.

Preoperative Refraction

Articles reporting on series with a preoperative SE less than 4 D were included. The preoperative mean SE was 3.64 1.28 D (mean st. dev.).

1. Refractive Outcome and Predictability

a. Postoperative Refraction

Postoperatively, a minimal undercorrection was noticed in most of the reviewed series. The postoperative refraction ranged from an overcorrection (29) of 2 D to an undercorrection (30) of 2.25 with a mean spherical equivalent of 0.2 0.46 D.

b. Percentage Within 1.0 D

The percentage of LASIK patients within 1 D of emmetropia was 89 (23), 96.4 (29), 100 (24,27), 91 and 89 (26), 93 and 87 (30), with a mean of 92.3.

c. Percentage Within 0.5 D

The percentage of LASIK patients within 0.5% of emmetropia was 71 (23), 92.8 (29), 87.5 (24), 78, and 73 (26), and 94 (27), with a mean of 80.

2. Visual Outcome

a. Postoperative UCVA of 20/40 or Better

A UCVA of 20/40 or better was achieved in 91% (23,30,31), 100% (24,27,29), and 93% (25,26), with a mean of 93.5%.

b. Postoperative UCVA of 20/20 or Better

A UCVA of 20/20 or better was achieved in 83% (23), 52% (29), 79.2% (24), 39% and 46% (26), 81% (27), 43% (31), and 60% and 37% (30), with a mean of 55.1%.

3. Loss of BCVA

The loss of two lines or more was reported as 1% (23), 10.7% (29), and 0% (24,26,27,30, 31), with a mean of 0.39%.

C.OUTCOMES OF LASIK IN THE MODERATE ( 4 TO 9 D) TO HIGH ( 9 TO 13 D) MYOPIA RANGE

The results of Knorz et al. (32) indicate that LASIK provides stability of manifest refraction and adequate UCVA as well as a high degree of patient satisfaction without significant visual loss in patients with myopia up to 10 D. Results still may be acceptable in patients with myopia up to 15D, but the rate of visual loss is higher and patient satisfaction is lower. For myopia greater than 15 D, accuracy and patient satisfaction were sufficiently poor to advise against the use of LASIK. Furthermore, patients with astigmatism correction were less pleased with the results than were patients who received spherical corrections only (32). The total number of eyes was 1373 in the moderate myopia group and 289 in the high myopia group.

a. Follow-Up

The follow-up ranged from 1 month to 25 months but was most often performed at 6 (29,33–37) or 12 months (32,38,39). In two studies (31,40), it was ambiguous and in another two (41,42), a mean follow-up was presented.

b. Preoperative Refraction

The preoperative refraction was in the range of moderate to high myopia. We arbitrarily chose to include in this group articles reporting on preoperative spherical equivalents between 4 and 13 diopters. We chose 13 as the highest limit because when using the Munnerlyn formula, and keeping in mind that a residual stromal bed thickness of 250 should be left, only 13 diopters of myopia can be treated with LASIK in a normal thickness cornea (550 ) with a 150 thick flap. We divided this group into the moderate myopia group (spherical equivalent between 4 and 9 D) and the high myopia group (spherical equivalent between 9 and 13 D).

The mean preoperative spherical equivalent in the combined group was 8.12 D. It was 7.25 D in the moderate myopia group, and 11.36 D in the high myopia group.

1. Refractive Outcome and Predictability

a. Postoperative Refraction

An undercorrection was seen in most of the reviewed series. The postoperative spherical equivalent ranged from an overcorrection (34) of 1.62 to an undercorrection (35) of 5 D, with a mean of 0.31 D. It was 0.17 D in the moderate myopia group and 0.84 D in the high myopia group.

Most of the nomograms used took into consideration the age of the patient and the difference in ablation between deep and superficial stroma.

b. Percentage Within 1.0 D

The percentage of eyes after LASIK within 1.0 D of emmetropia was 83% (41) and 73% and 54.1% (26) at 3 months postoperatively; 78% (33), 80% (34), 40.7% (35), 90.7% (36), 83% (37), 72% and 100% (42), and 72.7% and 61.5% (29) at 6 months; and 85% and 72.75% (32), 54% (38), and 96% and 91% (39) at 1 year, with an overall mean of 71.6% for the combined group. It was 75% for the moderate myopia group and 56.3% for the high myopia group.

c. Percentage Within 0.5 D

The percentage of LASIK patients within 0.5 D of emmetropia was 56% (41) and 52.5% and 39% (26) at 3 months postoperatively; 67% (33), 26% (34), 27% (35), 72% (36), 67% (37), 20% and 43.75% (42), and 50% and 53.8% (29) at 6 months; and 50% and 57.6% (32), 23% (38), and 68% and 75% (39) at 1 year, with an overall mean of 52.92% for the combined group. It was 55.8% for the moderate myopia group and 38.8% for the high myopia group.

2. Visual Outcome

a. Postoperative UCVA of 20/40 or Better

A UCVA of 20/40 or better was achieved by 77% (41) and 86% and 68% (26) at 3 months postoperatively; 73% (33), 69% (34), 55.7% (35), 79% (36), 91% (37), 84% and 100% (42), and 75% and 53.8% (29) at 6 months; and 77.7% and 84% (32), 85% (38), and 88% and 94.7% (39), at 1 year, with an overall mean of 77.6% for the combined group. It was 81% for the moderate myopia group and 61.3% for the high myopia group.

b. Postoperative UCVA of 20/20 or Better

A UCVA of 20/20 or better was achieved by 22% (41) at 3 months postoperatively; 20% (33), 26% (35), 35% (36), 56% (37), 16% and 68.75% (42), and 29.2% and 15.4% (29) at 6 months; and 36% (38), and 76% and 55.4% (39), at 1 year, with an overall mean of 29% for the combined group. It was 32.9% for the moderate myopia group and 16% for the high myopia group.

3. Loss of BCVA

A reduction in BCVA is consistently seen in some eyes having LASIK. It can be due to interface abnormalities, central islands, or induced irregular astigmatism. Loss of BCVA is reported in 1.2% (41) and 0% (26) at 3 months postoperatively; 4% (33,34), 3.2% (35), 2.32% (36), 3% (37), and 10.7% and 15.4% (29) at 6 months; and 6.3% and 0% (32), 2% (38), and 0% (39) at 1 year, with an overall mean of 2.65% for the combined group. It was 2% for the moderate myopia group and 6% for the high myopia group.

D.OUTCOMES OF LASIK IN THE EXTREMELY HIGH MYOPIA RANGE (BEYOND 13 D)

a. Follow-Up

The follow-up ranged from 1 month to 25 months with a mean follow-up of 10.5 months. The total number of eyes was 114.

b. Preoperative Refraction

The preoperative spherical equivalent refraction was in the range of extremely high myopia ( 13 D). Beyond 13 D the residual stromal bed thickness is less than 250 , which was found in several studies (44–48) to be associated with progressive keratectasia and loss of BCVA. The mean spherical equivalent in this group was 17.7 D.

1. Refractive Outcome and Predictability

a. Postoperative Refraction

An undercorrection was seen in most of the reviewed series. The mean postoperative SE was 1.13 D.

b. Percentage Within 1.0 D

The percentage of LASIK patients within 1.0 D of emmetropia was 83% (41) and 73% and 54.1% (26) at 3 months postoperatively; 78% (33), 80% (34), 40.7% (35), 90.7% (36), 83% (37), 72% and 100% (42), and 72.7% and 61.5% (33) at 6 months; and 85% and 72.75% (32), 54% (38), and 96% and 91% (39) at 1 year, with an overall mean of 36.44%.

c. Percentage Within 0.5 D

The percentage of LASIK patients within 0.5 D of emmetropia was 56% (41) and 52.5% and 39% (26) at 3 months postoperatively; 67% (33), 26% (34), 27% (35), 72% (36), 67% (37), 20% and 43.75% (42), and 50% and 53.8% (29) at 6 months; and 50% and 57.6% (32), 23% (38), and 68% and 75% (39) at 1 year, with an overall mean of 23.18%.

2. Visual Outcome

a. Postoperative UCVA of 20/40 or Better

A UCVA of 20/40 or better was achieved by 77% (41) and 86% and 68% (26) at 3 months postoperatively; 73% (33), 69% (34), 55.7% (35), 79% (36), 91% (37), 84% and 100% (42), and 75% and 53.8% (29) at 6 months; and 77.7% and 84% (32), 85% (38), and 88% and 94.7% (39) at 1 year, with an overall mean of 34.53%.

b. Postoperative UCVA of 20/20 or Better

A UCVA of 20/20 or better was achieved by 22% (41) at 3 months postoperatively; 20% (33), 26% (35), 35% (36), 56% (37), 16% and 68.75% (42), and 29.2% and 15.4% (29) at 6 months; and 36% (38), and 76% and 55.4% (39) at 1 year, with an overall mean of 4.85%.

3. Loss of BCVA

A reduction in BCVA is consistently seen in some eyes having LASIK. It can be due to interface abnormalities, central islands, or induced irregular astigmatism. Loss of BCVA is reported in 1.2% (41) and 0% (26) at 3 months postoperatively; 4% (33,34), 3.2% (35), 2.32% (36), 3% (37), and 10.7% and 15.4% (29) at 6 months; and 6.3% and 0% (32), 2% (38), and 0% (39) at 1 year, with an overall mean of 4.55%.

E.OUTCOMES OF LASIK IN LOW ( 0.5 TO 4 D) AND MODERATE HYPEROPIA ( 4 TO 8D)

a. Follow-Up

The follow-up ranged from 1 month to 24 months with a mean follow-up of 7.5 months. The total number of eyes reported was 638.

b. Preoperative Refraction

The preoperative refraction was in the range of low to moderate hyperopia ( 0.5 to 8.0 D), with a mean spherical equivalent of 3.79 D for the combined group. The range was between 0.5 to 4 D (mean 2.37 D) for the low hyperopia group and between 4 to8.5 D (mean 5.52 D) for the moderate hyperopia group.

1. Refractive Outcome and Predictability

a. Postoperative Refraction

An undercorrection was seen in most of the reviewed series. The postoperative spherical equivalent ranged from an overcorrection (49) of 1.13 to an undercorrection (50) of 1.5 D, with a mean spherical equivalent of 0.69 D. It was 0.34 D in the low hyperopia group and 0.88 D in the moderate hyperopia group. Most of the nomograms overcorrected the intended correction taking into account the regression of effect after hyperopic ablations.

b. Percentage Within 1.0 D

The percentage of LASIK patients within 1.0 D of emmetropia was 86% (49), 75.9% (51), 85% and 58% (50), 72.7% and 56.5%, (52) 100, 95.3, and 71.4% (53) and 67% (54), with a mean of 83.4% for the combined group. It was 93.3% for the low hyperopia group and 69.9% for the moderate hyperopia group.

c. Percentage Within 0.5 D

The percentage of LASIK patients within 0.5 D of emmetropia was 39% (51), 36.5% and 30.8% (52), and 42% (54), with an overall mean of 37% for the combined group. It was 38% for the low hyperopia group and 36.5% for the moderate hyperopia group.

2. Visual Outcome

a. Postoperative UCVA of 20/40 or Better

A UCVA of 20/40 or better was achieved by 93% (49), 66.7% (51), 95% and 90% (50), 70.6% and 78% (52), 94%, 100%, and 87.8% (53), and 91% (54), with an overall mean of 89.5% for the combined group. It was 94.4% for the low hyperopia group and 83% for the moderate hyperopia group.

b. Postoperative UCVA of 20/20 or Better

A UCVA of 20/20 or better was achieved by 21% (49), 14.8% (51), 6.7% and 0% (52), 70.3%, 75%, and 45.3% (53), and 41% (54), with an overall mean of 51.5% for the combined group. It was 63.6% for the low hyperopia group and 34.4% for the moderate hyperopia group.

3. Loss of BCVA

A reduction in BCVA is consistently seen in some eyes having LASIK. It can be due to interface abnormalities, decentration, or induced irregular astigmatism. Loss of BCVA is reported in 0% (49), 6.8% (51), 5% and 4.3% (50), 0% (52–54), and 2% (53), with an overall mean of 1.37% for the combined group. It was 1.1% in the low hyperopia group and 1.72% for the moderate hyperopia group.

F. OUTCOMES OF LASER ASTIGMATIC TREATMENT

In the myopic astigmatism group the total eye number was 610, and the mean preoperative and postoperative astigmatisms were 1.76 and 0.51 D, respectively. In the hyperopic astigmatism group, the total eye number was 181, and the mean preoperative and postoperative astigmatism were 2.75 and 0.29 D, respectively.

Several methods are used to analyze the outcome of astigmatic treatment, such as the vector analysis method (29,36,55) (Holladay’s, Naeser’s, or Alpins’), the ratio of the postoperative to the preoperative cylinder (39), and the analysis of the visual and refractive outcomes (29,31,37,55–57), The nomograms used targeted the full amount of cylinder in the majority of the studies (31,36,39). In others (29,56,58), the targeted cylinder was more than the refractive cylinder. To correct hyperopic astigmatism, Argento et al. (56) added 70% to the cylindrical correction in cylinders less or equal to 1 D; from 60% to 70% for cylinders between 1 and 2 D; and 50% for cylinders greater than 2 D. Salchow et al. (29) added 10% to the myopic cylindrical correction.

Undercorrection of the cylinder was the rule in most of the series reported (29,31,36, 37,39,55–59). This may be due to the inadequate nomograms and laser algorithms used and/or to the regression of effect (37,56,59).

In Zaldivar et al. series (58), 57% achieved the target refractive cylinder of 0.5 D, 27% had an undercorrection, and 4% had an overcorrection of the cylinder. In El Danasoury et al. series (39), the mean percent of cylindrical correction was 73% (range between 41.7% and 100%). The mean magnitude of the vectoral change in astigmatism was 1.23 D (range between 0.25 and 2.93 D), and the mean axis of the vectoral change was 0.37 degrees (range between 3.72 and 13.07 degrees) (39). In Chayet et al. series (55), 76% of eyes were within 0.5 D and 95% were within 1 D of the intended cylinder correction. Five eyes (12%) showed a cylinder overcorrection, from which only one eye was overcorrected for more than 1 D (55). At 6 months, Argento et al. (56) reported a reduction in the mean refractive cylinder from 3.37 to 0.58 D in the simple hyperopic astigmatism group, from 3.34 to0.12 D in the compound hyperopic group, and from 3.45 to 0.11 D in the mixed astigmatism group. UCVA were 20/20 in 66.7%, 60.4%, and 76.5% of the groups, respectively.

Several variables may decrease the astigmatic laser treatment outcome. Among others, decentration of the treatment, the discrepancy between topographic and refractive axes, the misalignment of the corneal and laser beam astigmatic axes, posterior corneal surface astigmatism, wound healing, inaccurate laser nomograms, and regression of effect.

CONCLUSIONS

The LASIK procedure was originally practiced for the moderate to high myopia cases, but it slowly invaded the low myopia range due to its quicker and more stable visual rehabilitation than PRK. With current techniques and third-generation machinery, LASIK has proven to be a good procedure for all ranges of myopia (29–31).

The studies indicate that the predictability of LASIK decreases when the preoperative refractive error increases.

REFERENCES

1.SF Brint, DM Ostrick, C Fisher, SG Slade, RK Maloney, R Epstein, RD Stulting, KP Thompson. Six-months results of the Multicenter Phase I Study of excimer laser myopic keratomileusis. J Cataract Refract Surg 1994;20:610–615.

2.H-M Kim, HR Jung. Laser assisted in situ keratomileusis for high myopia. Ophthalmic Surg Lasers 1996;27(suppl):S508–S511.

3.MC Knorz, A Liermann, V Seiberth, H Steiner, B Wiesinger. Laser in situ keratomileusis to correct myopia of 6.00 to 29.00 diopters. J Refract Surg 1996;12:575–584.

4.FB Kremer, M Dufek. Excimer laser in situ keratomileusis. J Refract Surg 1995;11(suppl): S244–S247.

5.JJ Pérez-Santonja, J Bellot, P Claramonte, MM Ismail, JL Alio. Laser in situ keratomileusis to correct high myopia. J Cataract Refract Surg 1997;23:372–385.

6.JL Guell, A Muller. Laser in situ keratomileusis (LASIK) for myopia from 7 to 18 diopters. J Refract Surg 1996;12:222–228.

7.A Marinho, MC Pinto, R Pinto, F Vaz, MC Neves. LASIK for high myopia: one year experience. Ophthalmic Surg Lasers 1996;27(suppl):S517–S520.

8.SG Slade, SF Brint, SA Updegraff. Excimer laser myopic keratomileusis: United States experience. In: JJ Salz, ed. Corneal Laser Surgery. St Louis, MO, Mosby, 1995;195–196.

9.L Buratto, M Ferrari, C Genisi. Myopic keratomileusis with the excimer laser: one year follow up. Refract Corneal Surg 1993;9:12–19.

10.IG Pallikaris, DS Siganos. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg 1994;10:498–510.

11.IG Pallikaris, DS Siganos. Laser in situ keratomileusis to treat myopia: early experience. J Cataract Refract Surg 1997;23:39–49.

12.I Kremer, M Blumenthal. Myopic keratomileusis in situ combined with VISX 20/20 photorefractive keratectomy. J Cataract Refract Surg 1995;21:508–511.

13.SA Helmy, A Salah, T Badawy, AN Sidky. Photorefractive keratectomy and laser in situ keratomileusis for myopia between 6.00 and 10.00 diopters. J Refract Surg 1996;12:417–421.

14.DC Fiander, F Tayfour. Excimer laser in situ keratomileusis in 124 myopic eyes. J Refract Surg 1995;11(suppl):S234–S238.

15.T Salah, GO Waring III, A El Maghraby. Excimer laser keratomileusis in the corneal bed under a hinged flap: results in Saudi Arabia at the El-Maghrabi Eye Hospital. In: JJ Salz, ed. Corneal Laser Surgery. St Louis, MO, Mosby, 1995;187–195.

16.E Arneas, A Maglione. Laser in situ keratomileusis for astigmatism and myopia after penetrating keratoplasty. J Refract Surg 1997;13:27–32.

17.T Salah, GO Waring III, A El-Maghraby, K Moadel, SB Grimm. Excimer laser in situ keratomileusis under a corneal flap for myopia of 2 to 20 diopters. Am J Ophthalmol 1996;121: 143–155.

18.PI Condon, M Mulhern, T Fulcher, A Foley-Nolan, M O’Keefe. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol 1997;81:199–206.

19.AM Bas, R Onnis. Excimer laser in situ keratomileusis for myopia. J Refract Surg 1995;11(suppl):S229–S233.

20.HV Gimbel, S Basti, GB Kaye, M Ferensowicz. Experience during the learning curve of laser in situ keratomileusis. J Cataract Refract Surg 1996;22:542–550.

21.IG Pallikaris, ME Papatzanki, DS Siganos, MK Tsilimbaris. A corneal flap technique for laser in situ keratomileusis; human studies. Arch Ophthalmol 1991;109:1699–1702.

22.L Buratto, M Ferrari, C Genisi. Keratomileusis for myopia with the excimer laser (Buratto technique): short term results. Refract Corneal Surg 1993:9(suppl):S130–S133.

23.Z Wang, J Chen, B Yang. Comparison of laser in situ keratomileusis and photorefractive keratectomy to correct myopia from 1.25 to 6 diopters. J Refract Surg 1997;13:528–534.

24.MA El Danasoury, A El Maghraby, SD Klyce, K Mehrez. Comparison of photorefractive keratectomy with excimer laser in situ keratomileusis in correcting low myopia (from 2 to 5.5 diopters). Ophthalmology 1999;106:411–421.

25.WA Pirzada, H Kalaawry. Laser in situ keratomileusis for myopia of 1 to 3.5 diopters. J Refract Surg 1997;13(suppl):S425–S426.

26.JC Casebeer, GM Kezirian. Outcomes of spherocylinder treatments in the comprehensive refractive surgery LASIK study. Semin Ophthalmol 1998;13(2):71–78.

27.M Montes, A Chayet, L Gomez, R Magallanes, N Robledo. Laser in situ keratomileusis for myopia of 1.5 to 6 diopters. J Refract Surg 1999;15:106–110.

28.SG Farah, DT Azar, C Gurdal, J Wong. Laser in situ keratomileusis: literature review of a developing technique. J Cataract Refract Surg 1998;24:989–1006.

29.DJ Salchow, ME Zirm, C Stieldorf, A Parisi. Laser in situ keratomileusis for myopia and myopic astigmatism. J Cataract Refract Surg 1998;24:175–182.

30.RL Lindstrom, DR Hardten, YR Chu. Laser in situ keratomileusis for the treatment of low, moderate, and high myopia. Trans Am Ophthalmol Soc 1997;XCV:285–306.

31.JM Davidorf, R Zaldivar, S Oscherow. Results and complications of laser in situ keratomileusis by experienced surgeons. J Refract Surg 1998;14:114–122.

32.MC Knorz, B Wiesinger, A Lierman, V Seiberth, H Liesenhoff. Laser in situ keratomileusis for moderate and high myopia and myopic astigmatism. Ophthalmology 1998;105:932–940.

33.F Lavery. Laser in situ keratomileusis for myopia. J Refract Surg 1998;14:S177–S178.

34.A Ozdamar, B Sener, C Aras, R Aktunc. Laser in situ keratomileusis after photorefractive keratectomy for myopic regression. J Cataract Refract Surg 1998;24:1208–1211.

35.PS Hersh, SF Brint, RK Maloney, DS Durrie, M Gordon, MA Michelson, VM Thompson, RB Berkeley, OD Schein, RF Steinert. Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia. Ophthalmology 1998;105:1512–1523.

36.GE Fraenkel, SK Webber, GL Sutton, MA Lawless, CM Rogers. Toric laser in situ keratomileusis for myopic astigmatism using an ablatable mask. J Refract Surg 1999;15:111–117.

37.DD Dulaney, RW Barnet, SA Perkins, GM Kezirian. Laser in situ keratomileusis for myopia and astigmatism: 6 month results. J Cataract Refract Surg 1998;24:758–764.

38.RF Steinert, PS Hersh. Spherical and aspherical photorefractive keratectomy and laser in situ keratomileusis for moderate to high myopia: two prospective randomized clinical trials. Trans Am Ophthalmol Soc 1998:96:197–221.

39.MA el Danasoury, GO Waring III, A El Maghraby, K Mehrez. Excimer laser in situ keratomileusis to correct compound myopic astigmatism. J Refract Surg 1997;13:511–520.

40.A Maldonado-Bass, R Onnis. Results of laser in situ keratomileusis in different degrees of myopia. Ophthalmology 1998;105:606–611.

41.R Zaldivar, JM Davidorf, S Oscherow. Laser in situ keratomileusis for myopia from 5.5 to11.5 diopters with astigmatism. J Refract Surg 1998;14:19–25.

42.PM Pesando, MP Ghiringhello, P Tagliavacche. Excimer laser in situ keratomileusis for myopia. J Refract Surg 1997;13:521–527.

43.RJF Tsai. Laser in situ keratomileusis for myopia of 2 to 25 diopters. J Refract Surg 1997;13:S427–S429.

44.T Seiler, K Koufala, G Richter. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg 1998;14:312–317.

45.T Seiler, AW Quurke. Iatrogenic keratectasia after LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg 1998;24:1007–1009.

46.Z Wang, J Chen, B Yang. Posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness. Ophthalmology 1999;106:406–410.

47.HS Geggel, AR Talley. Delayed onset keratectasia following laser in situ keratomileusis. J Cataract Refract Surg 1999;25:582–586.

48.FW Price Jr, DL Koller, MO Price. Central corneal pachymetry in patients undergoing laser in situ keratomileusis. Ophthalmology 1999;106(11):2216–2220.

49.KA Buzard, BR Fundingsland. Excimer laser assisted in situ keratomileusis for hyperopia. J Cataract Refract Surg 1999;25:197–204.

50.K Ditzen, H Huschka, S Pieger. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg 1998;24:42–47.

51.S Goker, H Er, C Kahvecioglu. Laser in situ keratomileusis to correct hyperopia from 4.25 to8 diopters. J Refract Surg 1998;14:26–30.

52.MC Knorz, A Lierman, B Jendritza, P Hugger. LASIK for hyperopia and hyperopic astigmatism. Semin Ophthalmol 1998;13:83–87.

53.CJ Argento, MJ Cosentino. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg 1998;24:1050–1058.

54.W Portellinha, K Nakano, M Olivieira, R Simoceli. Laser in situ keratomileusis for hyperopia after thermal keratoplasty. J Refract Surg 1999;15:S218–S220.

55.AS Chayet, R Magallanes, M Montes, S Chavez, M Robledo. Laser in situ keratomileusis for simple myopic, mixed, and simple hyperopic astigmatism. J Refract Surg 1998;14:S175–S176.

56.CJ Argento, MJ Cosentino, A Biondini. Treatment of hyperopic astigmatism. J Cataract Refract Surg 1997;23:1480–1490.

57.CC Barraquer, AM Gutierrez. Results of laser in situ keratomileusis in hyperopic compound astigmatism. J Cataract Refract Surg 1999;25:1198–1204.

58.R Zaldivar, JM Davidorf, MC Shultz, S Oscherow. Laser in situ keratomileusis for low myopia and astigmatism with a scanning spot excimer laser. J Refract Surg 1997;13:614–619.

59.O Ibrahim. Laser in situ keratomileusis for hyperopia and hyperopic astigmatism. J Refract Surg 1998;14:S179–S182.