Anisometropia is a condition in which there is a considerable difference in the refractive power between the two eyes. The prevalence of anisometropia increases between the age of 5 and 15 years, when one eye grows shorter or longer than the other, resulting in hyperopic or myopic anisometropia respectively. Myopic anisometropia of ≥ 4 diopters (D) is a frequent cause of amblyopia due to inequality of the retinal images of both eyes which is known as aniseikonia. When foveal fusion fails to correct aniseikonia, patients suffer from altered binocular vision and decreased stereoacuity. The defocused image from the amblyopic eye is usually suppressed and the severity of amblyopia directly correlates with the magnitude of anisometropia. Anisometropic amblyopia is frequently associated with sensory strabismus and diplopia that increase the depth of amblyopia and further interfere with education, sports, self-esteem, and future career choice.
The basic treatment of pediatric anisometropic amblyopia relies on correcting the refractive error along with modulated occlusion or penalization of the dominant eye. Children may tolerate full binocular glasses correction up to 6 D difference, however, they may not sustain binocular vision due to the associated aniseikonia. If they cannot tolerate full binocular glasses correction, contact lenses can be tried with the advantage of larger visual field and better quality of vision. In the case of contact lenses intolerance and poor compliance, refractive surgery should be considered to preserve the visual functions, eliminating aniseikonia, restoring stereopsis and binocular fusion. Previous studies have demonstrated the short-term and intermediate-term safety and efficacy of refractive surgery in treating pediatric myopic anisometropic amblyopia. This includes photorefractive keratectomy (PRK), laser assisted in situ keratomileusis (LASIK), laser-assisted subepithelial keratectomy (LASEK), implantation of phakic intraocular lenses and refractive lens exchange. The purpose of this study by Hashem and Sheha was to evaluate the long-term safety, effectiveness, and stability of unilateral LASIK in pediatric refractory myopic anisometropic amblyopia.
This retrospective study included children who received unilateral LASIK for myopic anisometropia of >6 D, after mandatory 6-month occlusion/penalization therapy. They were evaluated at 6 months, 1 year, 2 years and biannually until 10 years. Outcome measures included visual acuity, refraction, ocular alignment, stereopsis, corneal clarity, and corneal topography.
32 patients (16 girls) with mean age of 8.6 ± 2.3 years completed 10 years of follow up after unilateral LASIK. Mean preoperative spherical equivalent refraction (SER) was −10.3D ±2.0D in the affected eye, with anisometropic difference of −9.5D ±1.7D. Mean post-LASIK SER was −1.3D±0.8D (p< 15°) regained orthophoria in all gazes, while 5 of 10 who had constant exotropia with large angle (>30°) required strabismus surgery for ocular alignment. BCVA improved from 0.04±0.6 Decimal at baseline to 0.6 ±0.2 after LASIK and occlusion therapy (p< 0.001). Despite insignificant refractive regression in both eyes, patients have maintained orthophoria, improved stereopsis, clear cornea, and the topography showed no evidence of post-LASIK ectasia.
This is the largest series (n=32) with the longest follow-up period (10 years) that demonstrated long-term safety, effectiveness, and stability of unilateral LASIK in children with high myopic anisometropia (SER −9.5D ±1.7D) associated with deep amblyopia. Anisometropia was significantly reduced, and amblyopia markedly improved after strict pre- and post-LASIK occlusion/penalization therapy. The CCT of 564±31µm enabled full myopic refractive correction in some patients with emmetropic fellow eyes. The remaining patients had post LASIK refraction within the targeted ±2.0D of the fellow eyes and tolerated small prescription glasses. Along with good compliance to amblyopia therapy, children maintained a mean BCVA of 0.6±0.1 Decimal throughout the follow- up.
In conclusion, LASIK procedure appears safe, effective, and stable for correcting refractory pediatric myopic anisometropia. It resulted in improvement of refractive error, visual acuity and consequently binocular vision and stereopsis. However, there are many special considerations in performing pediatric LASIK regarding preoperative assessment, amblyopia therapy, anesthesia, fixation, microkeratome selection, size of the globe, and refractive endpoint that make the surgery different from adult LASIK. Therefore, pediatric candidates for LASIK refractive surgery should be carefully selected and LASIK procedure should be considered only when conventional measures have been exhausted, or chronic non-compliance or intolerance of conventional treatments endanger normal visual development.
Source: Hashem and Sheha; Clinical Ophthalmology 2022:16
https://doi.org/10.2147/OPTH.S387302