Anisometropia is the leading cause of amblyopia and one of the most common causes for vision loss in children and adolescents in the United States.1 In individuals with anisometropic amblyopia, the differences in refraction have been strongly associated with the depth of amblyopia.2 In general, a difference in myopia of more than 2.00 diopters (D), hyperopia of more than 1.00 D, and astigmatism of more than 1.50 D may result in amblyopia. Furthermore, a difference in myopia of more than 6.00 D or hyperopia of more than 4.00 D has been found to cause amblyopia in all cases.3 The first line of treatment for anisometropic amblyopia includes spectacles, contact lenses, patching, and pharmacologic penalization of the dominant eye. These therapies can fail for several reasons, including patient noncompliance, comorbid neurobehavioral issues, or severity of the degree of anisometropia. In these patients, refractive surgery including laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), excimer laser, and refractive phakic intraocular lens implantation have been used.1,4–11
Refractive surgery for the treatment of anisometropic amblyopia has been found to be effective and safe. Most studies evaluating such procedures have reported follow-up periods of 3 to 36 months.7,12–20 Autrata et al.21 published 5-year follow-up data of PRK in children, Astle et al.22 reported follow-up of up to 8 years after PRK and LASEK in the pediatric population, and Brugnoli de Pagano and Pagano23 followed up patients ages 11 to 52 years for up to 8 years after LASIK for accommodative esotropia. However, there are few publications with further long-term results in these refractive surgeries in children.
Our institution participated in a single-center study investigating unilateral LASIK correction of anisomyopia in five pediatric patients in 1999. In the initial 1999 study, five patients received unilateral LASIK for significant myopic anisometropia in the more myopic eye. They were identified by the pediatric ophthalmologists as being at high risk for permanent vision loss due to failure of traditional methods of amblyopia treatment. These children were ages 5 to 8 years with anisometropic myopia of at least 6.00 D spherical difference between eyes who had failed repeated attempts at correction with spectacles and demonstrated amblyopia. Sixteen years later, we were able to follow up on two of the five patients to assess their visual function, corneal topography, and quality of life. This case series and the original prospective single-institution pilot study received approval from the institutional review board of the University of Pittsburgh.
This case series and the original prospective, single-site pilot study received approval from the institutional review board of the University of Pittsburgh. During the initial 1999 pediatric LASIK procedures, a laryngeal mask airway was found to be superior to a face mask when delivering general anesthesia because gas leakage is minimized and unimpeded access to the globe is possible. Anesthesia and primary ocular immobilization were achieved using sevoflurane and/or halothane and/or nitrous oxide. This was supplemented with fentanyl for anesthesia induction and additional ocular anesthesia was achieved with topical anesthetic drops.
Patient fixation was not possible in sedated children. In the early era of LASIK, without eye tracking or iris registration, this posed additional difficulty in performing pediatric LASIK. The authors found the Carriazo-Barraquer microkeratome suction ring (Moria, Antony, France) to be helpful in aiding fixation and centration because it had a “low vacuum” setting. The high vacuum setting was used during creation of the corneal flap and switched to low vacuum until the excimer ablation was complete and the flap was repositioned. Intraocular pressure was raised to only approximately 40 mm Hg so retinal vasculature was not compromised during low vacuum application to the globe. This allowed the surgeon full control of the globe during these critical steps of LASIK without compromising retinal blood flow for a prolonged period of time. Preoperative pilocarpine was used to avoid excessive pupil dilation, which would make surgeon fixation difficult. Assessment of angle kappa was made after pilocarpine drops were instilled and determined by subjective assessment of two observers.
LASIK was performed on the more myopic, amblyopic eye with the VISX Star S2 excimer laser (Johnson & Johnson Vision, Santa Ana, CA). Unlike adult LASIK, where emmetropia is generally the goal, the refractive endpoint for pediatric LASIK for anisomyopic amblyopia was balance with the fellow eye. Ketorolac was used for control of inflammation and immediate postoperative pain. A clear eye shield was fitted after the procedure and removed only for instillation of tobramycin and dexamethasone drops four times daily for at least 1 week. Patients were seen for follow-up at 1 day, 1 week, and then 1, 3, 6, and 12 months.
In the current series, the original five study patients were contacted based on information located in their medical records, most of which had not been updated since their initial treatment. Attempts were made via telephone and mailed information packets. Two patients were reached and agreed to participate in the follow-up visit. The authors could not find up-to-date contact information for the remaining three original study patients.
The two patients were evaluated in a single clinic visit with standard visual acuity, non-cycloplegic refraction, corneal topography with Oculus Pentacam (Oculus Optikgeräte, Wetzlar, Germany), axial length measurement with the Haag-Streit LenStar (Haag-Streit USA, Mason, OH), stereopsis testing with the Stereo Fly OS-001 (Stereo Optical Company, Inc., Chicago, IL), slit-lamp examination, undilated fundus examination, and visual function assessment with the National Eye Institute Visual Function Question-25, Version 2000 (NEI-VFQ-25).
Case 1 was a 23-year-old man who was 7 years and 2 months old at the time of his LASIK procedure in the right eye. He lived and worked locally in Pittsburgh, Pennsylvania. At follow-up, he did not wear glasses or contact lenses. He reported that he was able to function well overall with his current level of visual acuity. The only visual difficulties he noted were aligning the benching bar at the gym and shaving on the right posterior side of his neck. A summary of his CDVA and refraction is found in Table 1. Anterior segment examination revealed a clear cornea, well-healed LASIK flap, and no fluorescein staining in the right eye and a clear cornea in the left eye. Undilated fundus examination revealed symmetric and normal cup-to-disc ratios. Stereopsis testing 16 years after surgery revealed 200 seconds of arc with left eye dominance. This had improved compared to pre-LASIK (300 seconds of arc) and early post-LASIK (nil) stereo-acuity. Axial length measurements were 27.21 mm in the right eye and 24.5 mm in the left eye. Corneal topography revealed central corneal thickness of 532 µm in the right eye with a mildly decentered LASIK ablation bed without evidence of ectasia (Figure 1A) and 570 µm in the left eye with no ectasia (Figure 1B). NEI-VFQ-25 testing revealed overall high quality of life scores, with the lowest categories of general vision and general health.
Patient Refraction and Visual Acuity
Pentacam (Oculus Optikgeräte, Wetzlar, Germany) results for case 1 at 16-year follow-up. There is slight temporal decentration of the ablation bed, symmetric between the left and right eye, and no evidence of ectasia.
Case 2 was a 24-year-old woman who was 7 years and 4 months old at the time of her LASIK procedure of the left eye. As an adult, she lived out of town but visited her family, who remained in Pittsburgh, Pennsylvania. Prior to her 16-year follow-up visit, she had presented for an earlier visit approximately 14 years after LASIK. At that time, her CDVA was 20/20 in the right eye with a refraction of −4.40 +0.25 × 056 and 20/50 in the left eye with a refraction of −3.75 +0.25 × 169. At the 16-year follow-up visit, she reported that her vision was good with correction. She felt that her visual acuity declined in the right (non-LASIK) eye during her pregnancy and had not returned to baseline. A summary of her CDVA and refraction is found in Table 1. Anterior segment examination revealed a clear cornea in the right eye and a clear cornea, well-healed LASIK flap, and no fluorescein staining in the left eye. Undilated fundus examination revealed symmetric and normal cup-to-disc ratios. Stereopsis testing 16 years after surgery revealed 100 seconds of arc with right eye dominance. This was an improvement compared to pre-LASIK (400 seconds of arc) and early post-LASIK (400 seconds of arc) stereo-acuity. Axial length measurements were 25.88 mm in the right eye and 26.59 mm in the left eye. Corneal topography revealed a central corneal thickness of 596 µm in the right eye with no ectasia (Figure 2A) and 577 µm in the left eye and a slightly decentered LASIK ablation without evidence of ectasia (Figure 2B). NEI-VFQ-25 testing revealed overall high quality of life scores, with the lowest categories of general vision and ocular pain.
Pentacam (Oculus Optikgeräte, Wetzlar, Germany) results for case 2 at 16-year follow-up. There is slight temporal decentration of the ablation bed, symmetric between the left and right eye, and no evidence of ectasia.
Quality of life data at follow-up are presented in Figure 3. Figure 4 shows the change in Snellen lines of CDVA and Figure 5 shows the difference in spherical equivalent refraction for both patients.
National Eye Institution Visual Function Questionnaire-25 (VFQ-25), Version 2000, at follow-up. Scores are based on a scale from 0 to 100, with higher numbers representing higher quality of life. Data included for cases 1 and 2 only.
Change in Snellen lines of corrected distance visual acuity (CDVA) over time between preoperative and immediate postoperative visit. Data included for all cases.
Stability in the difference in spherical equivalent refraction between both eyes over time. Data included for cases 1 and 2 only.
In our series, CDVA remained stable in the immediate postoperative period, whereas refractive error and stereoacuity were largely unchanged. However, there was improvement in stereopsis in both patients 16 years after surgery. Looking at data of all five of the original patients in the 1999 study, there was overall no change to improvement in Snellen lines of CDVA and no patients lost CDVA (Figure 4). There was significant improvement in the difference in spherical equivalent refraction between the two eyes after LASIK and the improvement was stable over time (Figure 5).
There have been concerns of decentered ablations, flap dislocation, and corneal haze as immediate and long-term complications of refractive surgery, especially in the pediatric population. In our 1999 study, only one patient was found to have mild diffuse lamellar keratitis, which cleared rapidly with steroids. Furthermore, one child was caught rubbing her eye within the first 24 hours after LASIK, but there was no evidence of flap striae or dislocation.
Both patients were found to have slightly temporally decentered ablations (Figures 1–2). This may be partially attributed to use of a mechanical microkeratome to create the LASIK flap with a nasal hinge. These pediatric LASIK procedures were also performed in an era prior to eye tracker and iris registration technology; therefore, centration for these pediatric LASIK cases was determined by subjective assessment of angle kappa and ablation was controlled manually by the surgeon. Given the challenges of fixation, the authors are pleased by the level of centration of the ablation beds. Importantly, the two patients in the series had no evidence of ectasia 16 years postoperatively. Additionally, in long-term follow-up, both patients reported a positive memory surrounding the experience with eye surgery. They reported good quality of life and were relieved of the burden of having a significantly imbalanced spectacles prescription, which could lead to visual distortion, aniseikonia, and aesthetic concerns.
There are limitations to our case series, particularly the small sample size of patients included in follow-up. Three of five of the patients in the original study were lost to follow-up, with outdated contact information in the medical record system. Long-term follow-up is particularly difficult in the pediatric and adolescent population because they move away from home for schooling or work and often change addresses. Furthermore, the original pediatric patients were referred to our institution for the purpose of LASIK, then returned to their pediatric ophthalmologists after the immediate postoperative period. This further limited the authors' ability to follow the patients over time. Testing in the pediatric population is also limited, due to variability in cooperation. Additionally, not all of the parameters evaluated in the long-term follow-up study were included in the initial 1999 study. Despite these limitations, our series provides valuable information regarding the long-term safety and efficacy of LASIK in the pediatric population.
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Patient Refraction and Visual Acuity
|Parameter||Case 1||Case 2|
| OD||−9.00 −3.50 × 180||plano sphere|
| OS||+2.00 −2.75 × 180||−5.75 −1.25 × 020|
|Immediately after LASIK|
| OD||−1.75 sphere||plano −0.25 × 170|
| OS||+1.25 −1.00 × 100||−0.75 −0.25 × 070|
| F/U||4 mo||4.5 mo|
| OD||plano +1.00 × 005||−5.75 sphere|
| OS||plano sphere||−4.75 +0.50 × 156|
| F/U||16 y||16 y|