While patching her left eye, the child was noticed to adopt a head tilt to use her temporal field of vision in the right eye. Amblyopia treatment was continued with patching of the left eye four hours daily to force the brain to develop vision in the affected right eye. The refractive error was corrected with eyeglasses. This refractive error caused blurry vision and contributed to her initial visual acuity of 20/200 and the subsequent onset of amblyopia and strabismus. The patient was also found to have high myopia in the affected eye. One year after the initial presentation, she required eye muscle surgery to realign the right eye. In the patient, the exotropia was a large-sized deviation that was poorly controlled at distance fixation. The patient was therefore diagnosed with strabismus (intermittent exotropia), high myopia, and amblyopia, as well as MRNF layer of the right eye. The left eye, on the other hand, had a normal dilated fundus examination (Figure (Figure2 2). The dilated fundus examination of the right eye revealed flat, white patches in the retina (superotemporal and inferotemporal regions) in a distribution consistent with a MRNF layer (Figure (Figure1). The slit lamp examination was normal bilaterally. She was also found to have a high refractive error in her right eye (-6.50 diopters). She was found to have intermittent monocular exotropia of the right eye. On examination, the patient’s visual acuity was 20/200 in her right eye and 20/40 in her left eye. There was a family history of strabismus in the patient’s maternal uncle. Other significant ocular history included a high refractive error and eyeglasses wear. This occurred especially at distance fixation and was first noticed when the patient was 10 months old. This case report presents a five-year-old, otherwise healthy female who was seen in the pediatric ophthalmology clinic for the chief complaint of right eye drifting outward. MRNF can also present with leukocoria, in which case the differential diagnoses must include the sight-threatening conditions of retinoblastoma, chorioretinitis, coloboma, or cataract. Because myelin blocks light transmission to the underlying retinal cells, there is a high possibility of some vision loss or enlarged blind spot in affected patients. Although most children are asymptomatic, few can present with associated ocular findings of high refractive error, strabismus, and amblyopia or failed vision screening. Most cases are diagnosed incidentally in healthy individuals by ophthalmoscopy. Clinically, the fibers appear as gray-to-white patches with well-defined borders on the anterior surface of the retina. MRNF was first described in 1856 by a German pathologist, Rudolf Virchow, who described the retina as “white, very thick and wrinkled”. Rarely, it has been reported to be acquired or progressive. MRNF typically occurs at birth and involves static lesions. This anomaly can be present in up to 1% of the population, and approximately 7% of the affected patients will have bilateral involvement. Although the direct cause is unknown, MRNF occurs when the myelination extends past this point and is detectable on the fundus examination, obscuring the underlying retinal vessels. Normally, the optic nerve myelination does not extend past the lamina cribrosa and into the retina. Myelinated retinal nerve fiber (MRNF) layer is a rare and mostly benign congenital anomaly in which the retinal nerve fibers anterior to the lamina cribrosa have a myelin sheath.
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