Myelinated retinal nerve fibers may be discovered on consultation for reduced visual acuity, strabismus, or leukocoria, and in the vast majority of cases, the condition is discovered on routine ophthalmic examination.1 The prevalence of myelinated retinal nerve fibers in the general population approaches 1%, and there may be multiple patches with a single eye.1–3 Funduscopically, myelinated retinal nerve fibers are feathery white densities that follow the pattern and arcuate the architecture of the retinal nerve fiber layer.
It has been long believed that myelinated nerve fibers represented a congenital anomaly that would be identifiable at birth or soon after. However, it has been documented that myelination of retinal nerve fibers can be acquired later in life and actually may advance over time, although this seems to be uncommon.4–7
Atrophy and regression of myelinated retinal nerve fibers has also been documented to occur as a result of several neurodegenerative conditions.8–12 However, atrophy and regression of myelinated retinal nerve fibers has only been rarely photodocumented, and there appears only to be one published case of this occurring in a patient with uncontrolled glaucoma.11
In January 2003, a 48-year-old black female presented for ophthalmic examination. The patient’s medical history was significant for diabetes mellitus type 2 for which she was treated with metformin. She had a history of vision reduction OD since childhood. Best-corrected visual acuity was 20/600 OD (measured with a Feinbloom chart and converted to Snellen acuity) with a refractive error of −14.00 to 0.75 × 060 and 20/20 OS with a refractive error of +0.50 to 0.50 × 0.90. Pupils were equal, round, and reactive to light, with a relative afferent papillary defect OD. Intraocular pressure (IOP) by Goldmann applanation was 38 mm Hg OD and 37 mm Hg OS. Gonioscopy revealed anterior chamber angles open to the ciliary body band with mild trabecular meshwork pigmentation in each eye. The right eye manifested a myopic disc and fundus with an extensive myelination of the retinal nerve fiber layer. There was also a congenital vascular loop on the right optic disc. Because of the extensive myelination and myopic appearance, it was difficult to discern glaucomatous rim defects in that eye. The fellow eye manifested mild equivocal inferior neuroretinal rim damage. The patient repeatedly performed poorly on threshold perimetry with a high degree of false-positive responses.
The patient was diagnosed with primary open angle glaucoma OU and refractive amblyopia OD and placed on travoprost (Travatan; Alcon, Ft. Worth, TX), which brought the patient’s IOP down to the high teens throughout follow-up that year. Scanning laser polarimetry with variable corneal compensation (GDxVCC; Laser Diagnostic Technologies, San Diego, CA) demonstrated profound artifact and an uninterpretable image in the right eye caused by the extensive myelination. The left eye image was interpreted as a normal nerve fiber layer based on normal thickness and deviation maps and all TSNIT parameters falling within a 95% confidence interval.
The patient was lost to follow-up from June 2004 until January 2006. Upon returning, it was revealed that she had not used travoprost for approximately 1 year, and her IOP at this time was 28 mm Hg OD and 30 mm Hg OS. The patient was counseled regarding potential vision loss caused by nonadherence to medical therapy and was offered more definitive surgical options, which she refused. Travoprost was represcribed, and the patient was scheduled for a progress evaluation in 1 month.
The patient was again lost to follow-up until March 2008. She returned again not using any topical medications, and IOP at this time was 46 mm Hg OU. Gonioscopy was unchanged. The patient was represcribed travoprost and timolol 0.5% (Falcon, Ft. Worth, TX) was added two times per day OU, bringing IOP down to the mid-teens through subsequent follow-up examinations. Scanning laser polarimetry was performed again in 2009, this time with enhanced corneal compensation (GDxPro; Carl Zeiss Meditec, Dublin, CA) due to our facility upgrading the technology. At this time, the right eye continued to manifest artifact from the myelination, and the image could not be interpreted. The left nerve fiber layer, however, was interpreted as significantly damaged based on abnormalities in the thickness and deviation maps and highly significant departures from the normative database on all RNFL parameters. Visual inspection revealed a significant change from the previous image, indicating a progression in the nerve fiber layer damage. However, this subjective determination of change must be tempered because of inherent differences in the devices used at baseline and follow-up.
The patient has been followed through 2013 but has had a difficulty maintaining medical adherence, with IOP varying from the mid-teens on therapy to the mid-20s and low 30s when not using medications. Comparison of retinal photographs demonstrated a profound atrophy of the myelinated retinal nerve fibers in the right eye through the 8-year period from 2003 to 2011 (see Fig. 1). We presumed that the myelination atrophy is most likely caused by poorly controlled and progressive glaucoma through this period. Although original photographs of the left eye from 2003 could not be located in the patient’s hard chart to compare against current digital images, it appears as though the glaucoma did progress structurally in the left eye based on nerve fiber layer analysis.
During normal development, retinal ganglion cell myelination begins in the lateral geniculate nucleus and proceeds anteriorly to the optic nerve, stopping at the lamina cribrosa in most cases. This process is completed shortly after birth.1,13 Normally, the retina is not myelinated because oligodendroglia, the cells responsible for myelination in the central nervous system, are absent anterior to the lamina cribrosa in the retina. An anomalous distribution of oligodendroglia is thought to be the etiology of myelinated nerve fibers.
There have been reports of atrophy and regression of myelinated retinal nerve fibers, mostly in the face of neurodegenerative conditions. Chavis and Tabarra12 reported on a 39-year-old Behcet’s patient that demonstrated demyelination of retinal myelinated nerve fibers after recurrent papillitis and vitritis during a 5-year period. Sharpe and Sanders10 noted a similar atrophy and regression of myelinated retinal nerve fibers in demyelinating optic neuritis and felt that the phenomenon signified retrograde degeneration of retinal nerve fibers from multiple sclerosis. Williams and Fekrat9 described a case of extramacular myelinated retinal nerve fibers disappearing after pars plana vitrectomy for an epiretinal membrane and macular edema, postulating that postoperative nerve fiber layer atrophy or ischemia may have been the cause.
Only rarely is this atrophy photodocumented as with Katz and Weber,11 who noted the regression to occur in a patient with uncontrolled primary open angle glaucoma. They speculated that the loss of myelinated nerve fibers in the retina occurs as a nonspecific anterograde axonal degeneration seen with any form of optic atrophy.
It appears that several neurodegenerative conditions could cause atrophy and regression of myelinated retinal nerve fibers. This phenomenon has only been rarely reported to occur in eyes with glaucoma, and the patient presented here may be only the second with photodocumented evidence of such atrophy. Katz and Weber11 suggested that the apparent paucity of glaucoma patients with retinal myelin was more likely caused by late referral rather than any inherent protective effect of retinal myelin against elevated IOP or the glaucomatous process in general. In fact, it may well be that atrophy and regression of myelinated retinal nerve fibers may occur more commonly than thought. There is an inherent difficulty in the subjective determination of changes in myelinated retinal nerve fibers simply through observation during ophthalmic examination. Typically, eyes with myelinated retinal nerve fibers and no other comorbidities often do not undergo baseline photography as a matter of routine course. Thus, documenting true change in nerve fiber layer myelination through photography comparison is often not possible.
Myelinated retinal nerve fibers are found on routine ophthalmic examination with a low prevalence in the general population. The finding is typically considered to be congenital and unchanging. This belief may not actually be correct, however, because atrophy and regression of myelinated retinal nerve fibers has been documented to occur in eyes with neurodegenerative conditions. The case presented here may represent only the second photodocumented atrophy of myelinated retinal nerve fibers occurring in a glaucomatous eye with poorly controlled IOP. Glaucomatous nerve fiber layer loss may also include atrophy of myelination when present.
Joseph W. Sowka
College of Optometry
Nova Southeastern University
3200 South University Drive
Ft. Lauderdale, FL 33322
Joseph W. Sowka is a consultant for Alcon Labs.
Received January 9, 2013; accepted April 6, 2013.
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