Purpose
To analyze the effect of laser in situ keratomileusis to correct high myopic astigmatism in patients with suboptimal best spectacle-corrected visual acuity (BSCVA).
Design
Retrospective, interventional series of consecutive cases.
Methods
setting: Vissum Madrid, Madrid, Spain. patients: Two hundred five eyes of consecutive patients with suboptimal BSCVA and high myopic astigmatism of −3 diopters or more. intervention: Laser in situ keratomileusis surgery. main outcome measures: BSCVA.
Results
The BSCVA (decimal Snellen fraction notation) improved significantly ( P = .0001) from a mean preoperative 0.77 ± 0.18 (range, 0.05 to 0.90) to 0.81 ± 0.19 (range, 0.05 to 1.25) 3 months after surgery. The mean change in lines of BSCVA (decimal Snellen fraction notation) was 0.04 ± 0.11 (range, −0.25 to 0.4). A significant inverse relationship ( P = .001) was found between the preoperative BSCVA and the improvement in BSCVA.
Conclusions
In eyes with high myopic astigmatism and suboptimal preoperative BSCVA, laser in situ keratomileusis may result in a significant improvement in BSCVA.
Some degree of astigmatism is present in 90% of the world’s population, and up to 20% of the population has astigmatism of 1.5 diopters (D) or more. Uncorrected astigmatism results in blurred vision, diplopia, glare, ghosting, and asthenopia in adults and is a common cause of meridional amblyopia in children. Strategies to prevent amblyopia in children apply aggressive interventions to improve and recover as much best spectacle-corrected visual acuity (BSCVA) as possible during the critical period of visual acuity (VA) development. However, the results also indicated that after 1 year of optical treatment, astigmatic children still had significantly poorer BSCVA than nonastigmatic children. It is unclear whether the persistently decreased VA in astigmatic children after 1 year of treatment is the result of reduced plasticity in this age range, poor treatment compliance in some subjects, or other factors, such as uncorrected spherical aberration or coma.
Several techniques have been developed for surgical correction of astigmatic errors, including transverse or arcuate incisions: simple, combined, or in conjunction with radial incisions. Excimer laser corneal refractive surgery is safe and efficient for correcting high astigmatism errors in adults. In pediatric patients, excimer laser photorefractive keratectomy and laser in situ keratomileusis (LASIK) have been suggested as potential treatments for highly asymmetric ametropias when contact lens wear is not safe or feasible to prevent development of amblyopia. Photorefractive keratectomy seems to be a safe procedure in children, at least in the short term, although studies dealing with the long-term results are still lacking.
Some authors have found minimal VA improvement in adult amblyopic eyes in patients who underwent refractive surgery for high myopia. This finding is probably related to the change in the minification that the myopic optical correction induces, which is known to be smaller when the correction is located closer to the nodal point of the eye. Other authors have reported a significant improvement in the BSCVA in adult amblyopic eyes resulting from any refractive error, including astigmatism. Thus, it may well be that some cases believed to have refractive amblyopia really have a suboptimal BSCVA just because the optical correction of high astigmatism with glasses is difficult, and it induces some degree of distortion, and therefore suboptimal image quality.
A recent study, designed to evaluate efficacy and safety of bitoric LASIK ablation to treat astigmatism, disclosed an improvement in BSCVA in patients with high astigmatism. The fact that this study included only 34 eyes and that half of them had normal preoperative BSCVA prompted us to study the refractive and visual results obtained after LASIK performed to correct high myopic astigmatism (HMA) in patients with BSCVA lower that 20/20.
Methods
This was a retrospective interventional study that included 205 eyes of consecutive patients who fulfilled the inclusion criteria. The inclusion criteria were adults with HMA, defined as an astigmatism of at least −3 D or more, and suboptimal BSCVA higher than 0 logarithm of the minimal angle of resolution (logMAR) units. When both eyes of the same patient fulfilled the inclusion criteria, both eyes were included for analysis. The exclusion criteria included a history of glaucoma or retinal detachment, corneal disease, previous corneal or intraocular surgery, abnormal iris, pupil deformation, macular degeneration or retinopathy, neuro-ophthalmic diseases, surgical complications or postoperative macular edema, or a history of ocular inflammation.
The same experienced surgeon (M.A.T.) performed all LASIK procedures using the Moria 2 microkeratome (Moria, Anthony, France). The ablation was performed with an Esiris excimer laser (Schwind, Kleinostheim, Germany) in all cases. The postoperative follow-up included visits at 1 day and 1, 4, and 12 weeks in all cases.
At the baseline preoperative visit, an optometrist and the surgeon performed a complete ophthalmologic examination that included measurement of the manifest refraction and VA (Autochart projector CP-670; Nidek, Gamagori, Japan), keratometry (autokeratorefractometer KR-800; Topcon, Tokyo, Japan), slit-lamp biomicroscopy, Goldmann applanation tonometry, corneal topography (CSO; Compagnia Strumenti Oftalmici, Florence, Italy), and binocular indirect ophthalmoscopy through a dilated pupil. The same examiners performed a complete ophthalmologic examination at the 3-month postoperative visit. The VA was measured with Snellen optotypes expressed in decimal notation and converted to logMAR notation for statistical analysis. The cumulative average VAs were calculated using the logMAR notation. The refractive astigmatism was expressed as a negative value.
Refractive measurements were obtained objectively using the autokeratorefractometer. Subjective refractions were performed using the phoropter at a nominal vertex distance of 13.75 mm when the corneal vertex is located at the large mark on the calibration scale.
To study the possible effect of the astigmatism angle in the BSCVA change, we separated oblique astigmatism cases and those with either with-the-rule (WTR) or against-the-rule (ATR) astigmatism. We used the Rosenfield criteria for this subclassification. We defined WTR astigmatism as negative cylinder with axes between 160 and 20 degrees (positive cylinder, 70 to 110 degrees) and ATR astigmatism as negative cylinder with axes between 70 and 110 degrees (positive cylinder, 160 to 20 degrees). The astigmatism was considered to be oblique if the cylinder axes were between 20 and 70 degrees and between 110 and 160 degrees.
The relationships between the improvement in BSCVA and the preoperative BSCVA, spherical error, and astigmatism were assessed using linear regression analysis and the Pearson correlation coefficient. For other comparisons, the unpaired, 2-tailed Student t test was used. P values less than .05 were considered significant. The data were analyzed using Statview SE+Graphics (Abacus Concepts, Inc, Berkeley, California, USA) and a personal computer Macintosh PowerBook 1400cs/117 (Apple Computer, Inc, Cupertino, California, USA).
Results
A total of 205 eyes with suboptimal BSCVA resulting from HMA error were included. The mean patient age was 35.09 ± 7.9 years (range, 20 to 57 years). The preoperative subjective sphere and cylinder were −3.96 ± 3.23 D (range, 0 to −12.00 D) and −3.93 ± 0.81 D (range, −7.50 to −3.00 D), respectively. The mean optical zone was 6.01 ± 0.44 mm (range, 6.50 to 7.50 mm).
The UCVA at the 3-month postoperative visit was 0.19 + 0.18 logMAR (0.67 + 0.23 decimal Snellen fraction notation). The BSCVA (decimal Snellen fraction notation) changed from the mean preoperative level of 0.77 ± 0.18 (range, 0.05 to 0.9.0) to 0.81 ± 0.19 (range, 0.05 to 1.25) at 3 months, indicating a significant ( P = .0001) improvement in lines of BSCVA (decimal Snellen fraction notation) of 0.04 ± 0.11 (range, −0.25 to 0.4). Using logMAR notation, the significant improvement ( P = .001) in BSCVA at 3 months was −0.02 ± 0.007 (range, −0.2 to 0.3).
The mean postoperative refractive sphere and subjective cylinder values were 0.09 ± 0.83 D (range, −6.7 to 1.75 D) and −0.82 ± 0.81 D (range, 0 to −3.5 D), respectively, indicating a significant ( P = .001) postoperative decrease in both cases. The changes in VA lines are shown in Figure 1 .
A significant ( P = .001) inverse relationship was found between the preoperative logMAR BSCVA and the improvement in logMAR BSCVA 3 months after surgery. Figure 2 compares the change in lines of VA between patients with a preoperative BSCVA of 0.8 (decimal Snellen fraction notation, or 20/25) or worse (n = 102) and those with a preoperative BSCVA of 0.6 (20/33) or worse (n = 35). The percentage of patients with improved lines of VA was higher within the group with worse preoperative BSCVA. In fact, 31.43% (11 eyes) in the group of 35 eyes with a preoperative BSCVA of 0.6 or worse versus 15.88% (27 eyes) in the group of 170 eyes with a preoperative BSCVA higher than 0.6 had an increase of more than one line in BSCVA. No significant correlation was found between the improvement in logMAR BSCVA and either the preoperative cylinder or sphere ( P = .3 and P = .2, respectively).
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