A 48-year-old white woman was referred after an evaluation for photorefractive keratectomy. She had been told 5 years previously that her right optic disc was abnormal in appearance because it was darker than the left one. She denied any change in vision over the past 5 years, and she had no prior medical problems.
Best-corrected visual acuity was 20/15 in both eyes. Color vision with Ishihara plates, Amsler grid testing, and automated perimetry were all normal. External examination was unremarkable without any nevi or other pigmented lesions near her eyelids or elsewhere on her face. Pupils were briskly reactive without an afferent pupillary defect, and extraocular motility was full. Anterior segment examination was normal, and no pigmented lesions were seen on the iris or conjunctiva. Intraocular pressure was 15 mg Hg bilaterally. There were no vitreous cells, and funduscopy revealed that the right optic disc was entirely pigmented and flat, measuring 1.8 mm vertically (Fig. 1). While the contour of the right optic disc was difficult to assess due to the dark pigmentation, the cup-to-disc ratio was estimated at 0.1. There were retinal pigment epithelial (RPE) changes temporal to the disc, and small spots of intraretinal pigment were noted around the optic disc. The left optic disc measured 2 mm vertically, was pink in color without any appreciable pigmentation, and had a cup-to-disc ratio of 0.3. Subtle RPE changes were noted temporal to the left disc but were less prominent than on the right disc (Fig. 1). Optical coherence tomography (OCT) of the retinal nerve fiber layer showed relative thinning superiorly on the right (Fig. 2). The appearance of each optic disc was unchanged from photographs obtained 5 years previously.
Pigmentation of the optic disc is an uncommon finding. It can be categorized as primary and secondary. Most patients in the primary group have other associated ocular abnormalities, including distended retinal vessels, iris transillumination defects, ptosis, and nystagmus (1,2). In reviewing reported cases, we were unable to find photographic documentation of benign pigmentation of the entire optic disc without other ocular abnormalities.
Secondary optic disc pigmentation may be due to pigmentation from melanocytoma, hemorrhage, and that associated with congenital anomalies of the optic disc, such as optic nerve hypoplasia. Our patient's pigmented optic disc was slightly smaller than that of the fellow eye, with thinning of the retinal nerve fiber layer on OCT (Fig. 2). Her findings may represent a case of mild optic disc hypoplasia with pigmentation.
The etiology of primary optic disc pigmentation is unknown. Reese (3) noted that although the lamina cribrosa usually does not contain pigment cells, eyes with considerable pigmentation in the uveal tract may have chromatophores in the lamina cribrosa. He postulated that individuals with darker complexion would be more subject to such pigmentation. Our patient, however, had a light complexion. Another potential explanation for disc pigmentation is migration or extension of the RPE into the optic nerve head. Peripapillary disturbances, such as inflammation, may result in RPE proliferation causing hyperpigmentation (2). There was no evidence of this in our patient.
Secondary optic disc pigmentation may be due to pigment granules found between the nerve fiber bundles, resulting from hemolysis due to hemorrhage within the optic nerve, globe, or orbit. Iron salts within the optic disc, secondary to extensive siderosis of the globe, have also been described as a cause of optic disc pigmentation (3).
Sectoral pigmentation of the optic disc has been described in 3 of 16 Japanese women with nevus of Ota (4). These patients had good vision and no visual symptoms. Our patient did not have any other areas of pigmentation on her skin or conjunctiva, suggestive of nevus of Ota.
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