Fully refractive accommodative esotropia is present in patients with uncorrected hyperopia and a poor fusional divergence. The ratio between accommodative convergence and convergence is normal. Optical correction of refractive error1 (hyperopia, myopia, or astigmatism) eliminates the angle of deviation. Eyeglasses or contact lenses are generally employed to correct the refractive error and to reduce fully refractive accommodative strabismus. In 1983, Trokel and coauthors2 was the first to suggest the use of excimer lasers in refractive surgery. Since the mid-1990s, it has become an increasingly popular tool for correction of refractive errors and is supported in terms of safety and stability by positive results.
This study was conducted to evaluate whether the correction of the refractive error by excimer laser refractive surgery (photorefractive keratectomy [PRK] and laser in situ keratomileusis [LASIK]) in patients with fully refractive accommodative esotropia could reduce the angle of deviation.3–7
PATIENTS AND METHODS
Between March 1999 and March 2001, a prospective study was conducted with 18 consecutive patients (6 men and 12 women; mean age 32.4 years ± 9.4 [SD], range 21 to 52 years) with fully refractive accommodative esotropia (normal ratio accommodative convergence and convergence). There was not a statistically significant difference between the 2 groups regarding preoperative angle of deviation with and without optical correction (P>.05). Before refractive surgery, all patients wore glasses. They were divided into 2 groups: 8 patients had primary PRK (group A), and 10 patients had primary LASIK (group B). The target of refractive surgery was emmetropia.
A detailed sensorimotor eye evaluation was performed before and after refractive surgery by 1 surgeon (L. Sabetti). Ocular alignment was assessed using prisms and cover testing in all gaze positions. Primary position alignment was recorded both with and without glasses. Stereopsis was evaluated with the TNO stereopsis test (TNO), and the fusional amplitude was quantified.
Ophthalmologic examination included measurement of visual acuity (uncorrected [UCVA] and best corrected), manifest refraction, and cycloplegic refraction (1 instillation of cyclopentolate and of tropicamide 1%). Videokeratographic examination (EyeSys Lab) and pachymetry (Sonogage, Corneo-Gage Plus) were obtained in all patients. Before performing refractive surgery, all patients wore contact lenses (cycloplegic refraction) for 30 days to simulate their postoperative refractive condition. Then they had an orthoptic evaluation to estimate the angle of deviation and the binocular cooperation. Only patients who manifested orthophoria or a reduction of the angle of deviation had refractive surgery.
Inclusion criteria were age over 21 years, fully refractive accommodative esotropia, no suppression, stability of the refractive error for a minimum of 1 year, contact lens intolerance, and lack of optical correction with glasses. Exclusion criteria were nonaccommodative strabismus, paralytic strabismus, presence of systemic or local pathologies interfering with the corneal repairing process, presence of active posterior segment pathologies and neuromuscular affections, and an estimated postoperative corneal curvature higher than 48 diopters (D). All patients signed informed consent before participation in the study.
An excimer laser Mel 70 (Carl Zeiss-Meditec) set at 193 nm, 35 Hz frequency, and 180 mJ/cm2 fluency with a 0.25 μm ablation rate, was used. The laser uses a 1.8 mm diameter flying spot with a Gaussian profile. Follow-up for PRK was performed 1 week, 2 weeks, 2 months, 6 months, 1 year, and 2 years after surgery. Follow-up for LASIK was performed 1 day, 1 week, 2 weeks, 2 months, 6 months, 1 year, and 2 years after surgery. Data from the most recent evaluation are shown in this study. Orthoptic evaluation was carried out 6 months, 1 year, and 2 years after surgery. The software program Primit (1994, version 3.03) was used for statistical analysis (Student t test).
All patients were in compliance with the treatment. After follow-ups of 1 and 2 years, results were evaluated.
The mean preoperative angle of deviation without correction was 14.4Δ esotropia (ET) (range 19 to 10Δ ET) at near and 11.6Δ ET (range 14 to 8Δ ET) at distance; with correction, it was 5Δ ET (range 6 to 4Δ ET) at near and 2.4Δ ET (range 4 to 2Δ ET) at distance. The TNO showed a mean stereopsis of 71.2 ± 42.2 sec/arc; the mean fusional amplitude is reported in Table 1. Thirty days after continuous use of contact lenses to correct the cycloplegic refraction, the mean angle of deviation at near was 2Δ esophoria (range 2Δ esophoria) and at distance it was 1.2Δ esophoria (range 2Δ esophoria to orthophoria). The mean attempted correction (cycloplegic refraction) was +4.6 ± 0.8 D (range +3.50 to +6 D) with a mean UCVA of 20/30 and a mean best spectacle-corrected visual acuity (BSCVA) of 20/20.
At 1-year follow-up, the mean angle of deviation at near (without correction) was 1.2Δ esophoria (range 2Δ esophoria to orthophoria), and at distance without correction, all patients manifested orthophoria. Two years after treatment, a worsening of the angle of deviation was evident at near without correction 2Δ esophoria (range 4Δ esophoria to orthophoria; percentage of reduction 86.1%) and at distance without correction 0.4Δ esophoria (range 2Δ esophoria to orthophoria; percentage of reduction 96.5%) (Table 2). The mean spherical equivalent (SE) at 1-year follow-up was +0.02 D; at 2-year follow-up, it was +0.17 D. Mean UCVA was 20/25, and the mean BSCVA was 20/20 (Tables 3 and 4).
The mean preoperative angle of deviation without correction was 13.4Δ ET (range 21 to 8Δ ET) at near and 11.5Δ ET (range 19 to 6Δ ET) at distance; with correction it was 5.4Δ ET (range 8 to ET/2Δ ET) at near and 2.8Δ ET (range 6Δ ET to orthophoria) at distance. The TNO showed a mean stereopsis of 81 ± 42 sec/arc; the mean fusional amplitude is reported in Table 5. Thirty days after continuous use of contact lenses to correct the cycloplegic refraction, the mean angle of deviation was 2.5Δ esophoria (range 4 esophoria to +2Δ esophoria) at near and 1.1Δ esophoria (range 2Δ esophoria to orthophoria) at distance. The mean attempted correction (cycloplegic refraction) was +6.46 ± 1.1 D (range +5 to +8.50 D) with a mean UCVA of 20/30 and a mean BSCVA of 20/20. At 1-year follow-up, the mean angle of deviation without correction was 1.7Δ esophoria (range 2Δ esophoria to orthophoria; percentage of reduction 87.3%) at near and without correction 0.2Δ esophoria (range 2Δ esophoria to orthophoria; percentage of reduction 98.2%) at distance. Results were unchanged at 2-year follow-up (Table 6). The mean spherical equivalent correction was plano at 1- and 2-year follow-ups, and the mean UCVA was 20/20 (Tables 7 and 8).
No significant complications (decentrations, infections, epithelial irregularity, halos, glare, or haze) were observed during follow-up. No patient lost any lines of BSCVA. For both groups at 2-year follow-up, the Student t test showed a statistically significant difference between preoperative and postoperative angle of deviation (P<.06), but no statistically significant difference between the 2 groups regarding the angle of deviation at near (P = .56) or at distance (P = .74) or regarding the SE (P = .16).
In the previous 10 years, refractive surgery has become an efficient solution to the correction of refractive errors (myopia, hyperopia, and astigmatism) in terms of safety and stability. Alio et al.8 and Singh9 maintain that the excimer laser can be considered a valid tool for the correction of anisometropia in pediatric patients because it improves the functional prognosis of amblyopia.
In 1995, Singh9 reported an improvement of visual acuity in a hyperopic and amblyopic patient, associating the pleottica to the photorefractive treatment. A recent study demonstrated that refractive accommodative esotropia (RAE) can be treated with refractive surgery as an alternative to the optical correction. The authors performed hyperopic LASIK in 18 eyes affected by RAE, and the 1-year follow-up showed a remarkable reduction of esodeviation (Hoyos JE, presented at the Keratomileusis Study Group, Pisa, Italy, 2000). Nemet and coauthors6 demonstrated that LASIK can reduce the strabismic deviation for accommodative and partially accommodative esotropia related to hyperopia in 6 patients and for exotropia related to myopic anisometropia in 2 patients. In our study, 18 patients with fully refractive accommodative esotropia were treated with an excimer laser to reduce their refractive error and correct their strabismus. At 2-year follow-up, all patients presented with a reduction of refractive error and there was no statistically significant differences between the 2 groups (P = .16). Only 1 patient presented with a regression of the refractive error and manifested a worsening of the UCVA (BSCVA was unchanged) and of the binocular cooperation. Yildirim and coauthors10 reported a similar case of a 44-year-old woman who had LASIK for correction of an intermittent left exotropia of 35 prism diopters. After a myopic regression, the divergent deviation reappeared.
We obtained better results than Stidham and coauthors5 because we took into consideration the results obtained with the continuous use of contact lenses for 30 days to simulate the postoperative situation and treated only patients who manifested a significant reduction of the angle of deviation. We excluded patients with partial or no refractive accommodative strabismus, whereas Stidham included such patients. Moreover, all but 1 patient presented emmetropia at the 2-year follow-up in contrast to Stidham's subjects in whom the average residual SE was +2.1 D. None of our patients lost a line of BSCVA in contrast to Stidham's patients (23% lost 1 or more lines of BSCVA). Finally, in our study, no significant complications were observed after refractive surgery, whereas substantial complications were reported in eyes treated with LASIK in Stidham's study.
These promising results suggest a new possibility for the treatment of various forms of strabismus in conjunction with optical correction. It is important to perform an accurate evaluation of patients' sensorial and fusional status. In fact, the best results are obtained when the patient presents a valid fusion and binocular cooperation. Moreover, poor binocular cooperation could worsen in the period between the treatment of the first and second eyes; the aniseikonia present in this period causes a breakdown of the stereoscopic function. After treating the first eye, the different brightness between the 2 eyes is determined by the presence of an uncorrected visus compared with the corrected visus of nontreated eye characterized by spherochromatic aberrations and halos.11 A decompensate heterophoria could be prevented, reducing the period between the treatment of the 2 eyes to a minimum.
A complete study of ocular motility and binocular cooperation should be performed after a long period of total optical correction with contact lenses. It would thus be possible to unmask any latent ocular motility disturbance. This examination is important for bilateral refractive errors and fundamental for unilateral errors. It is therefore important to decide whether the dominant or nondominant eye should be treated first. Hashim12 demonstrated that there is no statistically significant difference in treating with PRK the dominant or nondominant eye first. However, treating the nondominant eye first may determine a selective stimulation of this eye, causing a penalization of the dominant eye in the period between the 2 treatments. Consequently, this may cause a better functional recovery. The preoperative examination with contact lenses cannot avoid the surgery risk for undercorrection or overcorrection of the refractive error; for this reason, a possible retreatment of the residual refractive error could be useful. Note the case of patient PE (Tables 1 and 2) who manifested a regression of the refractive error and a worsening of the esophoria at the 2-year follow-up.
Surgical correction of accommodative strabismus with an excimer laser should be performed in adult patients because it is necessary to have a stable accommodative and refractive status. We do not recommend use of this procedure in children because their development is not complete and it is therefore possible to have a modification of the refractive status that would notably alter the procedure's effects. Moreover, a possible necessary monocular occlusion after the treatment of the first eye could generates ambliopia. According to Campos,13 the angle without correction becomes less evident in adults. The future of these treatments depends on customization of the procedures and reduction of the optical aberrations.
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