Quality of Vision After LASIK

Although LASIK can correct lower order aberrations, i.e., spherocyclinders, with great precision and success, we have come to realize that higher order aberrations of the cornea may increase after surgery (12). The satisfaction level has been relatively high after LASIK in terms of uncorrected visual acuity (UCVA) and refractive predictability and stability (13–16). However, dry eyes, glare, ghost images, and night vision disturbance can reduce quality of vision and thus patient satisfaction following laser refractive surgery (17,18).

B. STUDIES OF PATIENT SATISFACTION

Several studies have examined patient satisfaction following photorefractive keratectomy (PRK) (19–31), but only a few studies examined patient satisfaction after LASIK (7–8,17,32–33). In the most recent study by Miller et al. (17) of a patient population ranged from 0.75 to 15.75 D sphere and 0 to 4.50 D cylinder, a high level of patient satisfaction was achieved following LASIK myopic and myopic astigmatic correction. A high level of overall patient satisfaction has also been reported in other studies. As high as 90–97.9% of patients following low to moderate myopic ( 10.00 D) (7,32–33) and 78–85% of high myopic correction ( 10.00 D) (7–8) with LASIK were satisfied with an improved quality of life according to other publications. These studies suggest a correlation between higher satisfaction and a lower spherical correction. As with the findings observed in PRK patients (21,24), Miller et al. (17) showed a correlation between satisfaction and amounts of preoperative astigmatism. A higher mean satisfaction score was achieved among the groups with less than 2.00 D of astigmatism, with a statistical significance between the 0 to 0.75 D and 2.00 to 2.75 D cylinder groups.

When comparing PRK to LASIK, patients tend to prefer the LASIK procedure even though both PRK and LASIK have been shown to be equal in terms of efficacy, predictability, stability, and final visual outcome in correcting myopia (34–36). In a prospective randomized study of spherical equivalent correction from 2.00 to 5.50 D, el Danasoury et al. compared satisfaction of patients treated with PRK on one eye and LASIK on the fellow eye. They showed that, one year after the procedure, 83% were very satisfied with the LASIK eye while only 63% were very satisfied with the PRK eye. In an another prospective, randomized study by el Maghraby et al., LASIK produced a higher percentage of eyes (26% more eyes at 2 years) with an uncorrected visual acuity of 20/20 or better. Similarly, at one year, almost twice as many patients were highly satisfied with the LASIKtreated eye as opposed to the PRK-treated eye (90% versus 52%), although this difference became much less significant at two years (81% versus 71%).

C. OPTICAL ABERRATIONS

A number of self-perceived optical disturbances such as glare and halo have been reported after laser refractive surgery (27,32). After corneal refractive surgery, higher order aberrations of the cornea typically increase (12). Increased higher order aberrations after corneal laser surgery is also correlated with a significant decrease in quality of vision, especially under scotopic conditions (12,41,44–45). Aspheric changes in the cornea also limit visual performance under decreased illumination as pupil size increases (43). Roberts et al. have also shown that there is a persistent increase in elevation, curvature, and pachymetry outside the ablation zone (44,45). Peripheral elevation increases were strongly correlated with central flattening in a series of eyes after LASIK, suggesting a structural change in the

cornea secondary to a biomechanical response over the entire cornea, independent of the ablation profile on the cornea. A 10-fold to 20-fold increase in ocular wavefront aberrations has also been reported in other studies (12,46,47).

The development of wavefront technology may help to minimize optical aberration of the eye and improve its visual quality and performance, especially under scotopic conditions. Using wavefront-guided LASIK, Seiler et al. (47) demonstrated that ocular aberrations are correctable in addition to myopia and astigmatism. An improved quality of the retinal image does not necessarily result in improved vision. Perhaps evolution has optimized the human eye to reach an optical quality that matches or exceeds the mosaic of the retinal photoreceptors (49). In addition, corneal healing after LASIK, though considered minimal, may be responsible for some regression of the refractive effect and thereby may influence spherical aberration afterwards. Mrochen and coauthors (50) conclude that wave- front-guided LASIK is not very predictable in reducing higher order optical aberrations. According to their study, only 22.5% have a significant reduction in the higher order optical aberrations, and on average there is an increase in optical aberrations by a factor of 1.44 after 3 months. Variation also exists in the effective correction among the types of aberrations, with a fair correction of coma and an insufficient correction of spherical aberrations.

D. REDUCED CONTRAST SENSITIVITY AFTER LASIK

A decrease in contrast sensitivity can deteriorate the quality of vision and impair visual function independent of Snellen visual acuity. Greater impairment in contrast sensitivity is on the other hand associated with difficulties with day and evening driving, and causes a higher number of at-fault motor vehicle accidents (48–51). After LASIK, patients may complain of reduced contrast sensitivity (52). Nakamura and coauthors (53) reported that patients with myopia ranging from 6.0 to 14.0 D experienced persistent decrease in intermediate and low CVA, while patients with 2 to 5.75 D experienced transient decreases (53).

Some authors report initial decreased contrast sensitivity, which recovers quickly with no significant change from the preoperative value at 3 months following LASIK (43). Mutyala et al. (54) report a slight decrease in contrast sensitivity at the higher frequencies (12 and 18 cycles/degree), which improves by 1 month after surgery at 18 cycles/degree, but remained depressed at 12 cycles/degree for at least 3 months after LASIK, which was within the normal range. Based on the results, they concluded that LASIK has little effect on contrast sensitivity for patients with up to 13.75 D of myopia and 5.25 of astigmatism.

E. EFFECT OF LASIK ON UNCORRECTED DAYTIME VISION

Miller et al. (17) noted that 96% of eyes treated with LASIK were able to enjoy freedom from corrective lenses. McGhee et al. (33) reported that 81% to 100% of patients had functional improvement and satisfaction across the spectrum of visual tasks assessed using a questionnaire-based cross-sectional study; 85.1% perceived improvement in reading without correction in natural light. Most patients also noted significant improvement in their ability to drive in daylight (94.0%), watch television (95.7%), or watch movie at a cinema (95.0%). Other functional tasks with a marked improvement after LASIK include the ability to play sports (97.5%), to swim (100%), and to shop (91.3%) without refractive aids. Only two patients expressed disappointment with the postoperative UCVA. However, both patients had had more than 5.00 D or anisometropia before LASIK, and only one eye was treated to balance the refraction with that in the untreated eye.

F. EFFECT OF LASIK ON NIGHT VISION

Reduced clarity with night vision was noted in 29% in the study by Miller et al. (17). McGhee et al. (33) identified 11.8% of patients with increased difficulty with nighttime driving with 8.8% reported being “much worse.” The authors note that none of these patients had a central ablation zone diameter of less than 5.0 mm and all of them had an ablation centration within 0.5 mm of the center of the pupil.

Similar problems with nighttime vision were also identified in eyes treated with PRK (20,22–23,26). In one study of patient satisfaction after bilateral PRK (25), over 60% noted reduced quality of vision in dim light relative to daylight, and as high as 50% reported night driving difficulties. Freitas et al. (29), using preand post-PRK questionnaires, identified a net subjective functional improvement in night driving. Brunette et al. (31) reported that 66.1% of patients perceived poorer night vision relative to daytime vision, 20.2% of patients thought that their night vision was poor or very poor, 68.3% of patients noted that night vision was either the same or better than before surgery, and 31.7% reported that it was worse or much worse.

These findings demonstrate that difficulties with nighttime vision and driving still pose a significant problem for a fair number of patients, thus reducing the overall quality of vision. It is a potential side effect of refractive surgery that should not be underestimated or understated to the patients seeking refractive surgery.

The visual disturbances associated with decreased night vision are not unique to patients who receive surgical refractive correction. Patients using spectacles or contact lenses also report similar visual problems with glare, halo, and reduced contrast sensitivity, especially at night. Nevertheless, given the unique demographics and psychological profile of most patients seeking refractive surgery, patient expectations are high; many patients want perfect UCVA to get rid of their spectacles or contact lenses but without unwanted visual aberrations. Future advances in laser technology, such as the active eye tracking system, variable spot scanning laser, and wavefront analysis, may minimize these aberrations. The journey to achieving an aberration-free refractive vision correction, or the so-called super vision, is long. Until then, it is important to realize that visual acuity alone is not an indicator of patient satisfaction and visual function. Careful patient selection, thorough evaluation, patient education, and informed consent about these potential side effects cannot be overemphasized.

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B. LASIK FOR HYPEROPIA

The early studies of the treatment of hyperopia with PRK were not encouraging. Maloney et al. (6) were unable to achieve a hyperopic correction using an erodible PMMA mask in experimental animals. Our group showed very limited success in reducing hyperopic shift after excimer PTK by attempting to steepen the peripheral corneal with an early prototype excimer laser (7). The use of automated lamellar keratoplasty (H-ALK) for hyperopia caused a deliberate corneal ectasia. The results of H-ALK were not satisfactory and produced irregular astigmatism as well as progressive ectasia in some patients (8). Other work showed significant regression and limited predictability. Ditzen and Nadimi demonstrated that it was possible to treat hyperopic refractive errors of more than 3 diopters. In a preliminary study, they reported more predictable results than with H-PRK (9). Condon reported another small series in 10 eyes ranging from 2 to 9 with an average correction at 6 months of 1.5 D (10). Other studies published at the same time also led investigators to modify and refine their techniques (11). The early encouraging results of myopic LASIK led surgeons to attempt LASIK for hyperopic errors. These initial studies pointed out that a number of technical challenges needed to be overcome before H-LASIK could be considered successful.

C. METHODS OF HYPEROPIC CORRECTION

In contrast to myopic correction, to achieve hyperopic change, one must permanently steepen the central cornea. A typical hyperopic profile, in this case from the VISX Star S2, is shown in Fig. 20.1. A comparison of the hyperopic profiles of ablation (2A) with those of myopic (2B) and astigmatic (2C and 2D) profiles is shown in Fig. 20.2.

Various laser systems accomplish this by different methods. The Summit Apex Plus laser utilizes an Axicon lens system to deliver most of the energy between 6.5 mm and out to 9.5 mm. The Axicon lens diverges the laser beam. The laser also uses an erodible disc, which absorbs laser energy so as to produce a smooth transition zone. The Chiron Technolas PlanoScan excimer laser (various models including the 117c and 217) delivers laser pulses (2 mm) at a relative high frequency (25 Hz) in a circular pattern over the cornea and optical zone of 6 to 9 mm (12). The VISX Star S2 laser utilizes a similar system, as pictured here (Figs. 20.3 and 20.4).

Figure 20.1 A typical hyperopic profile, in this case from the VISX Star S2 excimer laser. (Photo courtesy of Edward Manche, M.D., Palo Alto, CA.)

Table 1 summarizes some of the recent studies (9,13–18) and shows encouraging results with several different excimer lasers. The studies show that the procedure is safe, having similar complications to myopic LASIK. These studies show that predictability after hyperopic LASIK is only moderate and lags behind myopic LASIK in predictability. One of the problems in assessing results in hyperopic surgery is the measurement uncorrected visual acuity. Unlike myopia, this parameter is very age dependent.

In the studies, which reported results in this manner, 67% to 100% achieved corrections within 1 D of the intended. In a small series of 14 eyes, Buzard and Fundingsland (19) found that 85% of eyes achieved a correction within 1 diopter. The predictability falls off sharply for higher hyperopic corrections. H-LASIK however was much better than some of the predecessor procedures such as ALK. For example, Manche (20) reported that only 41% of eyes achieved outcomes within 1 diopter in eyes undergoing ALK for hyperopia. Regression of effect was seen in a number of the reported series. The higher the attempted

hyperopic correction, the higher the regression. The mechanism of regression may be epithelial thickening. This was demonstrated by Reinstein et al. using high frequency ultrasound (21). This thickening begins at a point precisely coincident with the beginning of the donut-shaped zone of stromal tissue removal. It reverses the contouring effect of the laser ablation.

D. HYPEROPIC ASTIGMATISM

1. Earlier Work

The treatment of astigmatism with hyperopia presents the surgeon with an additional challenge. In myopia, the treatment of astigmatism involves flattening the steep meridian (Fig. 2D). Early studies by C. Barraquer showed poor results when this approach was used (22). In a subsequent study, C. Barraquer et al. attempted to steepen the flatter meridian (23). Us-

ing the Schwind-Keratom laser with a MultiScan system and active tracking, 111 eyes were treated. In this series, 54.5% of eyes were within 0.5 D of emmetropia at 6 months for defects up to 9.75 D. The cylindrical component in steepening the flatter meridian was accurate to within 0.50 D and with 1.00 D in 90% of eyes.

Argento et al. reported another series in which steepening the flattest meridian was attempted by utilizing a variety of techniques utilizing the Keracor 116/117 laser (24). This technique produced a steepening in the flattest meridian, with almost no effect on the opposite meridian (Fig. 2C). The results with mixed astigmatism were quite good and better than simple astigmatism and compound astigmatism, although the degree of hyperopia was high in the latter group.

2. More Recent Work

The VISX STAR S2 laser corrects hyperopia and astigmatism using seven scanning beams over the cornea and offsetting them to effect an ablation out to 9.0 mm. Doane et al. (25) recently presented data on 100 eyes with hyperopia from 0.5 to 6.0 D (mean 2.08) and a cylinder from 0.5 to 4.0 (mean 0.74 D). They utilized the Hansatome and a 9.5 mm ring and an external fixation device to reduce decentration. The results were satisfactory with an effective reduction in hyperopic sphere and cylinder. The vast majority of eyes maintained, gained, or lost one line of best corrected visual acuity. In another study by Manche (20) using the same laser, good results were obtained with a mean pre and post of cycloplegic spherical equivalent of 3.23 and 0.21 D, respectively. There was a 70% reduction in mean astigmatism as measured by vector analysis and no loss of BCVA.

In another recent study, Ruiz (26) performed a study on 60 hyperopic eyes ranging from 4.0 to 6.75 D. The preoperative mean refraction was 5.24 D and the postoperative mean refraction was 0.46 D. The preoperative cylinder was 2.38 D and postoperatively it was 0.90 D. At one year, there was no loss of contrast sensitivity and a loss of 2 lines of BCVA in 2.4% of patients.

Azar and Primack’s study of LASIK ablation profiles in hyperopic and mixed astigmatism showed that patients with compound hyperopic or mixed astigmatism may benefit from reduced ablation depths using hyperopic cylindrical and/or combined cylindrical treatments (27). In this study, the theoretical depths of tissue ablation during LASIK treatments of similar amounts of myopic spherical versus myopic cylindrical errors were compared. Similar comparisons of hyperopic spherical versus hyperopic cylindrical error were also performed. The depths of tissue ablation in the following four treatment approaches for both compound hyperopic astigmatism and mixed astigmatism were then compared. Figure 20.5 shows the patterns of ablation of correcting hyperopic with-the-rule astigmatism, and Fig. 20.6 shows the patterns of correcting mixed astigmatism.

In this study they demonstrate that the combined use of hyperopic spherical and myopic cylindrical corrections to treat hyperopic astigmatism or mixed astigmatism incurs the greatest amount of central and peripheral corneal tissue ablation and therefore may be the least optimal therapeutic alternative. Ironically, this treatment alternative was the only available laser surgical option for refractive surgeons in the United States to treat compound hyperopic or mixed astigmatism until October 2000. Although the final optical result may be the same, different strategies vary in the depth, profile, and amount of tissue ablation. Future studies comparing the visual outcomes of the above method of correcting hyperopic and mixed astigmatism should yield valuable clinical data that may strengthen these theoretical predictions.

Figure 20.5 (A) (Azar) Hyperopic WTR astigmatism corrected with a 5.00 D hyperopic spherical (green) and a 3.00 D myopic cylindrical (blue) laser ablation pattern applied to the LASIK bed (resulting in greatest central ablation and volume of tissue removed). (B) (Azar) Hyperopic WTR astigmatism corrected with a 2.00 D hyperopic spherical (dark green) and 3.00 D hyperopic cylindrical (green) laser ablation pattern applied to the LASIK bed. Note absent ablation in central cornea. (C) (Azar) Hyperopic WTR astigmatism corrected with a 2.00 D 180 (green) and 5.00 D 90 (dark green) combined hyperopic cylindrical laser ablation pattern applied to the LASIK bed. Note absent ablation in central cornea. (D) (Azar) Hyperopic WTR astigmatism corrected with a combined cross-cylin- der ( 1.50 D 90 [green] and 1.50 D 180 [blue]) and 3.50 D SE (dark green) laser ablation pattern applied to the LASIK bed. Note intermediate depth and volume of ablation. [Color in original.]

E. H-LASIK IN APHAKIA

Ruiz also treated a series of aphakic patients (26) who could not undergo intraocular lens implantation. In 12 aphakic eyes, the preoperative average MR was 10.90 D and after surgery, at one year, it was 0.87 D. Centration and axis alignment are critical on these higher hyperopic cases, and Ruiz decenters the center of his ablation by 0.5 mm nasally.

F. LASIK AFTER PRIOR REFRACTIVE SURGERY

H-LASIK has been used for the treatment of consecutive hyperopia after RK, PRK, LTK, and myopic LASIK. Manche in the above series treated 29 eyes (12 post RK, 13 post

Figure 20.6 (A) (Azar) Mixed WTR astigmatism corrected with a 200 D hyperopic spherical (green) and a 3.00 D myopic cylindrical (blue) laser ablation pattern applied to the LASIK bed. Note greatest volume and depth of ablation. (B) (Azar) Mixed WTR astigmatism corrected with a1.00 D myopic spherical (blue) and a 3.00 D hyperopic cylindrical (green) laser ablation pattern applied to the LASIK bed. (C) (Azar) Mixed WTR astigmatism corrected with combined 1.00 D myopic cylindrical (blue) and 2.00 D hyperopic cylindrical (green) laser ablation patterns applied to the LASIK bed. (D) (Azar) Mixed WTR astigmatism corrected with a combined cross-cylinder ( 1.50 D 90 [green] and 1.50 D 180 [blue] and 0.50 D SE (dark green) laser ablation pattern applied to the LASIK bed. Note intermediate depth and volume of ablation. [Color in original.]

LASIK, 4 post PRK) for consecutive hyperopia with no difference in outcomes from the congenital hyperopia (astigmatism) group. A successful treatment for the growing number of consecutive hyperopia after RK has been elusive. Compression sutures, hyperopic PRK, and LTK have all been tried but not have had a high degree of success. Linebarger (28) has reported good success with LASIK post RK in 16 eyes with no increase in haze or loss of BCVA. There was one eye with epithelial ingrowth; see Figure 20.7). Portellinha et al. (29) and Attia et al. (30) reported good success after undercorrected hyperopia after LTK. The predictability was less than for primary H-LASIK.

G. COMPLICATIONS

In the early studies, the complication rates were relatively high, indicating a learning curve for the new LASIK procedure and keratomes that were not as reliable as the ones now available.

Figure 20.7 Epithelial ingrowth following H-LASIK for consecutive hyperopia after radial keratotomy. (Photo courtesy of Eric Linebarger, M.D., San Diego, CA.)

There were some complications that seemed to be higher in H-LASIK than in myopic LASIK. This included higher rates of decentration than in myopia. This resulted in loss of best corrected spectacle acuity. Probst et al. (31) and Ozdamar et al. (32) reported an epithelial pigmentation ring pattern, which they called a pseudo-Fleischer ring, after H- LASIK. A case of acute angle closure glaucoma after H-LASIK has been reported (33). Otherwise, the complications in H-LASIK were similar to those in myopia.

H. PRESBYOPIC LASIK FOR PRESBYOPIA

With over 100,000,000 presbyopic individuals in the U.S. alone, the search for a successful correction of presbyopia has become the holy grail of refractive surgery. Research has centered on LASIK as well as scleral expansion techniques. The first description of presbyopic correction using the excimer laser was made by Anschutz in the early 1990s (34–36). Patients who are emmetropes or low hyperopes have the best results, while those with greater degrees of refractive error regress more. The principal problems experienced by most patients are a slight loss of uncorrected distance acuity and ghosting or double contours on images. This ghosting was typically worse at distance.

More recently, Bauerberg (37) described his results with an off-center ablation after LASIK to correct hyperopia and presbyopia. In a series of 16 eyes, all patients had a centered ablation in one eye and an inferior decentered ablation (1 mm) in the other eye. The patients with hyperopia that underwent inferior decentered ablation were able to read for a prolonged period of time, compared with eyes that had the conventional centered excimer laser ablation. Patients with steepened corneas in the inferior and eccentric zone ended up with better distance and near vision. There was no loss of best corrected spectacle acuity.

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