TNOA Journal of Ophthalmic Science and Research

CASE REPORT
Year
: 2022  |  Volume : 60  |  Issue : 1  |  Page : 55--56

Hypermetropia, myelinated retinal nerve fiber and amblyopia: Reverse straatsma syndrome


Saranya Settu, Muthumeena Muthumalai 
 Department of Paediatric Ophthalmology, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. Muthumeena Muthumalai
Department of Paediatric Ophthalmology, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu
India

Abstract

Myelinated retinal nerve fibers (MRNF) are a common developmental anomaly. MRNF is commonly associated with myopia. The association of MRNF with myopia, amblyopia, and strabismus is well documented. The amblyopia may be refractory to treatment. We report a case of a child with MRNF and amblyopia in the more hyperopic eye, a case of reverse Straatsma syndrome.



How to cite this article:
Settu S, Muthumalai M. Hypermetropia, myelinated retinal nerve fiber and amblyopia: Reverse straatsma syndrome.TNOA J Ophthalmic Sci Res 2022;60:55-56


How to cite this URL:
Settu S, Muthumalai M. Hypermetropia, myelinated retinal nerve fiber and amblyopia: Reverse straatsma syndrome. TNOA J Ophthalmic Sci Res [serial online] 2022 [cited 2022 Dec 1 ];60:55-56
Available from: https://www.tnoajosr.com/text.asp?2022/60/1/55/340365


Full Text



 Introduction



Myelinated retinal nerve fibers (MRNF) are usually asymptomatic.[1] Uncommonly, they may be associated with significant visual loss.[1] Amblyopia associated with MRNF, myopia, and strabismus is referred to as Straatsma syndrome.[2] The amblyopia does not usually respond well to treatment.[2] We report a case of a child with MRNF, hyperopia, strabismus, and amblyopia.

 Case Report



A 3-year-old male child was referred for refraction. His birth history and development were normal. There was no family history of any ocular disorders. On examination, the child was found to have refractive error. Cycloplegic refraction was done. His vision in right eye was 6/9 with +1.00 D. Vision in left eye was 6/60 with +3.00 D. On cover test, there was a small left convergent squint. Ocular motility was full and free in all directions of gaze in both eyes. On slit-lamp examination, the anterior segment of both eyes was within normal limits. On fundus examination, the right eye fundus was normal. The left eye showed MRNF continuous with the optic nerve head extending inferior to the disc [Figure 1]. The rest of the posterior pole and periphery were normal. The axial length of the right eye was 21.58 mm and left eye was 19.88 mm. The systemic examination was unremarkable. The child was advised glasses and part-time occlusion of the right eye.{Figure 1}

 Discussion



MRNF are present in about 1% of patients. In an autopsy series, MRNF were found in 0.98% of the cases and were bilateral in 7.7%.[3] They were first described by Virchow in 1856.[1] Histology shows that MRNF possess sheaths composed of concentrically laminated lipoproteins (myelin), produced by oligodendrocytes, a cell type usually not present in the retina.[3]

MRNF appear as white, grey-white striated patches with feathery edges often distributed around or contiguous with the optic disc and surrounding the vascular arcades.[1] MRNF were continuous with the optic nerve head in 14 (33%) and discontinuous with the optic nerve head in 28 (66%) affected eyes in the autopsy series done by Straatsma.[3]

Myelination of the optic nerve begins in the lateral geniculate body and ends posterior to the lamina cribrosa due to the dense aggregation of astrocytes that prevent oligodendrocytes from migrating to the retina.[4] MRNF may result from an imbalance between myelination and formation of the lamina cribrosa which proceeds posteriorly from the corneoscleral limbus.[4] Myopic eyes may be predisposed to develop MRNF, because myelination may reach the intraocular optic nerve fibers before the lamina cribrosa closes.[4] However, it should be noted that MRNF were not contiguous with the optic disc in 66% of eyes in a large autopsy series.[3] It does not explain myelination of eyes without increased axial lengths. Our patient had myelinated nerve fibers in the shorter, more hyperopic eye. Anomalous presence of oligodendrocytes in retina is also postulated as a cause of retinal nerve fiber myelination.[1],[3]

Myopia in patients with MRNF is often axial and not refractive.[1],[2] The presence of MRNF in hypermetropies is rare.[5] In patients with bilateral hypermetropia, MRNF is usually found in the less hypermetropic eye.[5] It is not clear whether MRNF predisposes to myopia or myopia facilitates the development of MRNF.[6] It has been postulated that eyes with extensive myelinated nerve fibers develop myopia secondary to visual deprivation induced by blurring of images due to the presence of MRNF leading to elongation of the eye as found in eyes with unilateral congenital cataract or severe ptosis.[7] Eyes with high myopia tend to have larger areas of myelinated nerve fibers and macular involvement.[5],[7] However, scotomas in myelinated retinas are generally smaller than predicted by the extent of myelination, suggesting that light penetrates to the photoreceptor layer despite the myelin interference.[3]

Straatsma described a specific syndrome comprising amblyopia, high myopia, and myelinated retinal fibers.[2] Strabismus is a frequent association. Amblyopia associated with MRNF can be refractory to intensive therapy consisting of full refractive correction and amblyopia treatment.[2] Kee and Hwang found that in only one-third of eyes with MRNF visual acuity improved to 20/30 or better.[8] The reason for amblyopia is not clear. It may be due to anisometropia. However, anisometropic amblyopia generally shows good response to occlusion therapy. It may also be due to associated strabismus, deprivation amblyopia due to blurring of images by MRNF, or any other organic cause.[1],[9] Abnormal maculae were found in eyes that responded poorly to amblyopia treatment.[1]

Amblyopia with MRNF and hypermetropia is termed “reverse” Straatsma's syndrome.[6],[8] This may refute the existing relationship between MRNF and myopia. The amblyopia may be purely due to anisometropia without any association with MRNF. A refractive difference of 1.25 D or greater in hyperopes usually causes amblyopia. The anisometropia was +2.00D in our patient. Lempert proposed smaller optic disc size as an organic reason for decreased vision in hyperopic anisometropia.[10] Anisometropia may have a greater influence on the relative visual acuity than the presence of MRNF.[10] Amblyopia associated with MRNF and hypermetropia has shown good response to occlusion therapy similar to anisometropic amblyopia.[5]

 Conclusion



MRNF is more commonly associated with myopia than hypermetropia. The association of MRNF and amblyopia with hypermetropia is termed reverse straatsma syndrome. This may repudiate the relationship between myopia and MRNF. Anisometropia may have a greater impact on vision than MRNF.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Tarabishy AB, Alexandrou TJ, Traboulsi EI. Syndrome of myelinated retinal nerve fibers, myopia, and amblyopia: A review. Surv Ophthalmol 2007;52:588-96.
2Straatsma BR, Heckenlively JR, Foos RY, Shahinian JK. Myelinated retinal nerve fibers associated with ipsilateral myopia, amblyopia, and strabismus. Am J Ophthalmol 1979;88:506-10.
3Straatsma BR, Foos RY, Heckenlively JR, Taylor GN. Myelinated retinal nerve fibers. Am J Ophthalmol 1981;91:25-38.
4Lee MS, Gonzalez C. Unilateral peripapillary myelinated retinal nerve fibers associated with strabismus, amblyopia, and myopia. Am J Ophthalmol 1998;125:554-6.
5Lee JC, Salchow DJ. Myelinated retinal nerve fibers associated with hyperopia and amblyopia. J AAPOS 2008;12:418-9.
6Wang Y, Gonzalez C. Unilateral myelinated nerve fibers associated with hypertropia, strabismus and amblyopia? Reverse straatsma syndrome? Binocul Vis Strabismus Q 2008;23:235-7.
7Schmidt D, Meyer JH, Brandi-Dohrn J. Wide-spread myelinated nerve fibers of the optic disc: Do they influence the development of myopia? Int Ophthalmol 1996;20:263-8.
8Kee C, Hwang JM. Visual prognosis of amblyopia associated with myelinated retinal nerve fibers. Am J Ophthalmol 2005;139:259-65.
9Shenoy R, Bialasiewicz AA, Al Barwani B. Bilateral hypermetropia, myelinated retinal nerve fibers, and amblyopia. Middle East Afr J Ophthalmol 2011;18:65-6.
10Ruttum MS, Poll J. Unilateral retinal nerve fiber myelination with contralateral amblyopia. Arch Ophthalmol 2006;124:128-30.