A 9-Year-Old Boy With Strabismus, Anisometropic Amblyopia, and Myopia in the Left Eye, Associated With Myelinated Retinal Nerve Fibers Syndrome, Managed With Multimodal Therapy

Introduction

Myelinated retinal nerve fibers (MRNF) syndrome is a rare, benign congenital condition in which white nerve fibers can be seen extending from the optic nerve to involve the retina [1]. MRNF is a developmental anomaly that is present in approximately 0.4% of all eyes [2]. The condition is usually asymptomatic, but some cases of MRNF syndrome are associated with axial myopia, amblyopia (lazy eye), and strabismus (squint) [3–5]. As the condition is non-progressive and the myelination cannot be eliminated, the treatment of MRNF primarily focuses on its complications, especially the correction of refractive error and amblyopia therapy [6]. Younger patients without strabismus and with parafoveal fixation have been reported to respond more favorably to amblyopia treatment [7]. It is essential to acknowledge the significance of timely diagnosis and customized intervention for enhancing outcomes.

Multimodal therapy for amblyopia includes optical correction, occlusion or penalization, vision therapy, and photobiomodulation. Pattern visual evoked potential (PVEP) is a non-invasive electrophysiological detection method that assesses the functional integrity of the entire visual pathway from the retina to the striate cortex by recording the electrical activation of cortical neurons in response to specific visual stimulation [8]. Amblyopia is associated with significant PVEP changes, notably reduced amplitudes and delayed peak times. PVEP provides an objective measure of visual pathway function during treatment [9]. This report describes the case of a 9-year-old boy with strabismus, anisometropic amblyopia, and myopia in the left eye associated with MRNF syndrome, managed with multimodal therapy and evaluated with PVEP testing.

Case Report

A 9-year-old boy reported decreased vision in the left eye for 3.5 years. During this initial period at another institution, the patient was treated symptomatically, with optical correction treatment by a rigid gas-permeable contact lens for the left eye and part-time occlusion therapy of the right eye (4 hours/day). Over this period, his best-corrected visual acuity (BCVA) in the left eye improved from 20/125 to 20/80. Upon presentation to our hospital, the patient’s BCVA was 20/20 in the right eye and 20/80 in the left eye. Cycloplegic refraction results demonstrated emmetropia in the right eye and high myopia with astigmatism in the left eye (−10.00 DS/−1.00 DC*120°). Ocular alignment revealed a left exotropia of 12° with full ocular motility and normal anterior segment. There was no stereopsis, and sensory testing revealed suppression of the left eye. Intraocular pressure was normal. Fundoscopy of the left eye demonstrated diffuse myelinated retinal nerve fibers along superotemporal and inferotemporal arcades occupying the posterior pole by foveal reflex (Figures 1A, 2B), contrasting with normal right fundus (Figures 1C, 2A). The axial length was 23.08 mm in the right eye and 27.22 mm in the left eye. Central choroidal thickness was 333 μm in the right eye compared with 133 μm in the left (Figure 1B 1C). Similarly, retinal thickness was asymmetric: 205 μm in the right eye vs 167 μm in the left. PVEP amplitude was decreased and latency was significantly prolonged in the amblyopic eye (Figure 3A).

The patient underwent a 2-month intensive treatment at our center, including full-time occlusion of the right eye with weekly monitoring, repeated low-level red light therapy (650 nm, 3 minutes, twice daily) for myopia control, red flicker therapy (630 nm, 15 minutes, 3 times daily) for amblyopia stimulation, accommodative training, eye-tracking training and afterimage therapy for vision therapy. Following this 2-month intervention, the patient’s left eye BCVA improved from 20/80 to 20/30. Axial length shortened by 0.03 mm, choroidal thickness increased by 41 μm (from 133 μm to 174 μm) (Figure 1A, 1B), and both PVEP and contrast sensitivity also improved (Figure 3B). Over the 2-month period, the right eye was continuously occluded and checked weekly to prevent occlusion amblyopia. At the 6-month follow-up after initiating our therapy, outcomes remained stable, BCVA was maintained, left exotropia had improved to 5°, and axial length was 23.11 mm in the right eye and 27.19 mm in the left eye. All other examinations were stable.

Discussion

This case illustrates that aggressive multimodal therapy can improve visual function and control myopia progression in MRNF-associated amblyopia, even in older children. MRNF is typically a benign condition, but when associated with high anisometropia, strabismus, and amblyopia, it presents significant challenges. The degree of anisometropia and proximity of myelination to the macula influence visual outcomes [10]. These factors may explain the poor treatment response observed in many patients despite aggressive treatments [4].

In this patient, limited benefit was achieved after 3.5 years of treatment with rigid gas-permeable contact lens correction combined with part-time occlusion, indicating a refractory condition. Amblyopia patients older than 7 years of age require over 400 hours of patching and penalization [11]. In this case, the patient was young and at high risk of myopia progression. The comprehensive approach we undertook aimed to balance visual rehabilitation with myopia control.

A recent shift to intensive treatment with full-time occlusion, accommodative training, and adjunctive red-light therapies led to remarkable short-term improvement in visual acuity. These findings align with previous reports suggesting that extended occlusion and active vision therapy may be more effective for high anisometropia [12]. Furthermore, while occlusion therapy produces slow visual acuity gains, perceptual learning can accelerate improvement, serving as a valuable supplement to conventional treatment [11]. To mitigate myopia progression, near-intensive exercises were avoided, and outdoor activity was encouraged. Low-intensity red light therapy was applied for myopia control and had no impact on the amblyopia treatment [13].

The treatment outcome was notable. BCVA showed remarkable short-term improvement, corroborating reports such as that by Vide-Escade and Prior Filipe, which reported that intensive occlusion led to 20/30 vision within 4 months [12]. Following treatment, the improvement in BCVA in our patient was objectively confirmed by PVEP responses. PVEP served as an objective tool to confirm true visual improvement, which is particularly valuable in amblyopia management and may have forensic applications [14]. The gain in visual function suggests possible sparing of the foveal microstructure, consistent with optical coherence tomography findings. Axial length was shortened by 0.03 mm and choroidal thickness increased by 41 μm. The intensive multimodal therapy enhanced accommodative training and occlusion duration, thereby balancing visual rehabilitation with myopia control.

For MRNF-associated amblyopia that responds poorly to conventional therapy, a multimodal approach centered on full-time occlusion and supplemented with systematic active vision training may yield significant functional gains. The 6-month follow-up of our patient supported the short-term efficacy and safety of this combined protocol, though longer-term studies are needed to evaluate sustained benefits.

Conclusions

This case highlights that it is mandatory to improve vision in children despite the presence of multiple indicators of MRNF syndrome, associated with a complex of strabismus, anisometropic amblyopia, and high myopia. Although there is no treatment for MRNF, a program of intensive multimodal treatment centering on full-time occlusion and training with myopia control can improve visual function and ocular structure in refractory MRNF-associated amblyopia, even in older children. Therefore, amblyopia treatment should be prioritized, as improved visual acuity may itself lead to a reduction in strabismus.