Multicolor Imaging of Myelinated Nerve Fibers Contiguous to the Optic Disc

Myelinated nerve fibers (MNF) are characterized as whitish, relatively sharply demarcated, feather-like structures located in the retinal nerve fiber layer. MNF are located quite frequently in contiguity with the optic nerve head. This may lead to a diagnostic dilemma by preventing clear visualization of the optic disc margins. We herein describe the utility of multicolor imaging (MCI) in identifying optic disc anatomy in a case of MNF contiguous to the disc. MCI and infrared reflectance were superior to color fundus photography in delineating disc margins. Our pilot study describes the efficacy of MCI in delineating optic disc anatomy in a case of MNF.

Photo Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Multicolor Imaging of Myelinated Nerve Fibers Contiguous to the Optic Disc Subhajit Bhattacharya, DO, DNB, Sugandha Goel, DNB, Kumar Saurabh, MS, Rupak Roy, MS FIG. 1. A. Color fundus photography of the left eye shows myelinated nerve fibers (MNF) in contiguity with the optic disc. The optic disc margins are difficult to delineate. B. Optic disc margins (red arrows) are well delineated from surrounding MNF (greenish hue) using multicolor imaging (MCI). Disc margin hemorrhages (blue arrows) can only be visualized using MCI (B) and are not well seen in the color fundus photographs (A). C. Optic disc margins (arrows) are better visualized in using infrared reflectance as compared to green reflectance (D). D. Green reflectance image showing optic disc margins (arrows). Abstract: Myelinated nerve fibers (MNF) are characterized as whitish, relatively sharply demarcated, feather-like structures located in the retinal nerve fiber layer. MNF are located quite frequently in contiguity with the optic nerve head. This may lead to a diagnostic dilemma by preventing clear visualization of the optic disc margins. We herein describe the utility of multicolor imaging (MCI) in identifying optic disc anatomy in a case of MNF contiguous to the disc. Journal of Neuro-Ophthalmology 2020;40:104–105 doi: 10.1097/WNO.0000000000000810 © 2019 by North American Neuro-Ophthalmology Society Department of Vitreo Retina, Aditya Birla Sankara Nethralaya, Kolkata, India. The authors report no conflicts of interest. A Address correspondence to Rupak Roy, MS, Aditya Birla Sankara Nethralaya, 147, Mukundapur, E.M. Bypass, Kolkata 700 099, India; E-mail: [e-mail] 104 MCI and infrared reflectance were superior to color fundus photography in delineating disc margins. Our pilot study describes the efficacy of MCI in delineating optic disc anatomy in a case of MNF. 49-year-old man presented with blurred vision in both eyes. Best-corrected visual acuities were 20/200 in the right eye and 20/40 in the left eye. Fundus examination showed nonproliferative diabetic retinopathy in both eyes and myelinated nerve fibers (MNF) in contiguity with the Bhattacharya et al: J Neuro-Ophthalmol 2020; 40: 104-105 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo Essay optic discs; there were hard exudates in the macular area of the left eye (Fig. 1A). Optic disc margins could not be delineated apart from temporal edges. However, optic disc margins (arrow heads) could be well delineated from surrounding the MNF using multicolor imaging (MCI) (greenish hue, Fig. 1B). Disc margins were better visualized using infrared reflectance (IR) (Fig. 1C) as compared to green reflectance (Fig. 1D). Interestingly, disc margin hemorrhages could only be visualized using MCI (Fig. 1B) and were not well-visualized in color fundus photographs (Fig. 1A). MNF are a relatively rare finding in general ophthalmology clinics, but patients with MNF may be referred to neuro-ophthalmologists (1). MNF are characterized as whitish, relatively sharply demarcated, feather-like structures located in the retinal nerve fiber layer (RNFL). Patches of MNF occur more often at the superior sectors of the nerve head and in the inferotemporal retina than in other areas (2). MNF may be located quite frequently in contiguity with optic nerve head; this leads to diagnostic dilemmas by preventing clear visualisation of the optic disc margins. MCI is a new noninvasive retinal imaging modality available in Spectralis optical coherence tomography (OCT) platform (Heidelberg Engineering, Heidelberg, Germany). This technology simultaneously acquires 3 reflectance images of the retina using 3 individual lasers. A composite image is produced, thereby allowing for analysis of changes at various levels within the retina (3,4). Shelton et al described multimodal imaging of the MNF (5). On infrared and red-free imaging, the MNF appear white. MNF create a dark appearance on autofluorescence as it blocks detection of underlying autofluorescent material. MCI characteristics of MNF are not yet described in the literature. Our report highlights that MCI may be better than color fundus photographs in detecting optic disc margins and in identifying additional lesions such as disc mar- Bhattacharya et al: J Neuro-Ophthalmol 2020; 40: 104-105 gin hemorrhages. MNF lead to RNFL thickening that is detected by confocal imaging of MCI. MNF appear greenish or greenish orange on MCI; this variation in appearance is due to the amount of retinal thickening. Among the component channels, the IR channel was better for identifying retinal thickening. This may be due to the high melanin content of MNF. In our image, we have also seen a feathered appearance of the MNF that are not as well assessed by color fundus photography. The frayed or feathered borders correspond in shape and distribution to ganglion cell layer axons. Our study illustrates the capacity for MCI to delineate optic disc anatomy in patients with MNF contiguous to the optic nerve head. MCI may emerge as a useful imaging modality in the assessment of disc swelling, particularly for distinguishing MNF. ACKNOWLEDGMENTS The authors thank Marina Parvin and Moupiya Das. REFERENCES 1. Duke-Elder S. Medullated nerve fibers. In: Duke-Elder S, ed. System of Ophthalmology. Vol 3. London, United Kingdom: Kimpton, 1964:646–651. 2. Kodama T, Hayasaka S, Setogawa T. Myelinated retinal nerve fibers: prevalence, location and effect on visual acuity. Ophthalmologica. 1990;200:77–83. 3. Tan AC, Fleckenstein M, Schmitz-Valckenberg S, Holz FG. Clinical application of multicolor imaging technology. Ophthalmologica. 2016;236:8–18. 4. Thomas NR, Ghosh PS, Chowdhury M, Saurabh K, Roy R. Multicolor imaging in optic disc swelling. Indian J Ophthalmol. 2017;65:1251–1255. 5. Shelton JB, Digre KB, Gilman J, Warner JE, Katz BJ. Characteristics of myelinated retinal nerve fiber layer in ophthalmic imaging: findings on autofluorescence, fluorescein angiographic, infrared, optical coherence tomographic, and redfree images. JAMA Ophthalmol. 2013;131:107–109. 105 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.