Ophthalmic Surgery, Lasers and Imaging Retina

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Brief Report 

Melanocytoma of the Optic Disc Associated With Visual Field Defects: Clinical Features and Imaging Characteristics

Omar S. Punjabi, MD; Christine F. Lin, BS; Hak-Sung Chung, MD; Manjot K. Gill, MD

Abstract

The authors studied the clinical features, visual field, and spectral-domain optical coherence tomography (SD-OCT) characteristics of peripapillary melanocytoma associated with visual field defects in two eyes of two patients. Both eyes had hyperreflective anterior surface and posterior optical shadowing in the region of peripapillary melanocytoma on SD-OCT imaging. The retinal nerve fiber layer was thin adjacent to these lesions, and this corresponded to the opposite hemifield defect on Humphrey Visual Field testing. Three-dimensional imaging of the melanocytoma revealed an irregular elevation in the peripapillary region. SD-OCT, when used in conjunction with clinical examination and Humphrey Visual Field testing, provided useful information that may assist clinicians in treating patients with peripapillary melanocytoma, particularly when observing them over time.

Abstract

The authors studied the clinical features, visual field, and spectral-domain optical coherence tomography (SD-OCT) characteristics of peripapillary melanocytoma associated with visual field defects in two eyes of two patients. Both eyes had hyperreflective anterior surface and posterior optical shadowing in the region of peripapillary melanocytoma on SD-OCT imaging. The retinal nerve fiber layer was thin adjacent to these lesions, and this corresponded to the opposite hemifield defect on Humphrey Visual Field testing. Three-dimensional imaging of the melanocytoma revealed an irregular elevation in the peripapillary region. SD-OCT, when used in conjunction with clinical examination and Humphrey Visual Field testing, provided useful information that may assist clinicians in treating patients with peripapillary melanocytoma, particularly when observing them over time.

From the Department of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

Presented at the Association for Research in Vision and Ophthalmology (ARVO) annual meeting; May 3–7, 2009; Fort Lauderdale, Florida.

Supported by an unrestricted grant from Research to Prevent Blindness, New York, New York.

The authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Omar S. Punjabi, MD, 645 N. Michigan Ave., Suite 440, Chicago, IL 60611. E-mail: omar_punjabi@yahoo.com

Received: December 12, 2010
Accepted: June 20, 2011
Posted Online: August 11, 2011

Introduction

Melanocytoma is a darkly pigmented, benign lesion with feathery edges that classically occurs at the optic disc.1 It may involve the adjacent peripapillary choroid, but can arise anywhere in the uveal tract.2 Generally, these tumors remain stable over time and have few local complications. However, subtle enlargement over the span of several years has been found in 10% to 15% of cases, and malignant change is estimated to occur in 1% to 2% of cases.1 Occasionally visual loss can occur secondary to optic disc atrophy from chronic neural compression, central retinal vein obstruction, tumor necrosis, choroidal neovascularization, or malignant transformation.3,4

The diagnosis of a melanocytoma can usually be made through recognizing its typical funduscopic appearance: a homogenous dark brown to black color and location in or close to the optic disc. In most instances, fluorescein angiography demonstrates marked hypofluorescence due to blocking of the dye in the region of the tumor.5 Their small size (average dimension 2.0 mm, average thickness 1.0 mm) makes it difficult to define them through ocular ultrasonography or computed tomography.2 Magnetic resonance imaging has been found to have some diagnostic value by helping to define the posterior extent of the melanocytoma.6

Optical coherence tomography (OCT) has been used to provide high-resolution imaging of the vitreoretinal interface and to further characterize features of optic disc melanocytoma.4 More recently, the introduction of spectral-domain optical coherence tomography (SD-OCT) has allowed improvements in image acquisition speed and image quality compared with time-domain OCT systems.7 The segmentation of SD-OCT images can display retinal surfaces in three-dimensional space and improve visualization. We studied the clinical features and high-definition OCT characteristics of two cases of optic disc melanocytoma with consistent visual field defects using SD-OCT.

Patients and Methods

An observational study was performed in two patients diagnosed as having melanocytoma of the optic disc. Both patients had associated visual field defects. We used a commercially available Cirrus SD-OCT system (Carl Zeiss Meditec, Inc., Dublin, CA) that has an axial resolution of approximately 5 μm and is capable of acquiring approximately 26,000 A-scans per second. Compared with StratusOCT (Carl Zeiss Meditec, Inc.), where six B-scans are acquired in a radial line pattern centered on the patient’s fixation point, SD-OCT can acquire approximately 200 B scans, with each B scan having 100 to 200 A-scans in a 6 × 6 mm cube pattern centered on the patient’s fixation point or an operator-selected point in one scan set.

For the current study, SD-OCT scans were obtained using two protocols. First, we used A-scan pattern composed of 4,096 A-scans in each of the five B-scans obtained in 0.5 seconds. The second protocol obtained 128 B-scans (with each B-scan having 512 A-scans) in 2.6 seconds, covering a 6 × 6 × 2 mm volume of the retina.

Report

Case 1

A 67-year-old woman sought follow-up for known cataracts and glaucoma. Best-corrected visual acuity (BCVA) in the left eye was 20/30 and the patient reported no new visual complaints. Anterior segment examination was unremarkable except for trace nuclear sclerotic cataract. Funduscopic examination of the left eye revealed peripapillary atrophy, inferior cupping of the optic disc, and an irregular dark brown pigmented lesion superotemporally with involvement of the adjacent peripapillary choroid (Fig. 1). The appearance was suggestive of a melanocytoma. There was no associated macular or subretinal fluid, secondary retinal detachment, or any vascular abnormality. Funduscopic examination of the right eye was unremarkable. Humphrey 24-2 visual field examination of the left eye showed an inferior altitudinal defect that corresponded with the superiorly located melanocytoma (Fig. 2). On SD-OCT imaging (Fig. 3), retinal nerve fiber layer (RNFL) thickness maps of the left eye showed superotemporal thinning around the optic nerve corresponding to the opposite hemispheric visual field defect (Fig. 3A). SD-OCT B-scans in the region of the melanocytoma revealed a hyperreflective inner retinal surface with posterior shadowing that obscured the underlying tissue detail (Fig. 3B). SD-OCT reconstructed fundus images obtained from B-scans allowed accurate image registration. Regions of the melanocytoma that had deeper pigmentation had a thinner band of inner retinal reflectance and more posterior shadowing (Fig. 3B). In some regions, the highly reflective pigment band appeared to extend beyond the lamina cribrosa.

Case 1. Optic nerve photograph showing a medium-sized, densely pigmented superotemporal optic disc melanocytoma.

Figure 1. Case 1. Optic nerve photograph showing a medium-sized, densely pigmented superotemporal optic disc melanocytoma.

Case 1. Humphrey Visual Field 24-2 showing an inferior altitudinal deficit that corresponds with the superiorly located melanocytoma and the superior retinal nerve fiber layer thinning seen on spectral-domain optical coherence tomography.

Figure 2. Case 1. Humphrey Visual Field 24-2 showing an inferior altitudinal deficit that corresponds with the superiorly located melanocytoma and the superior retinal nerve fiber layer thinning seen on spectral-domain optical coherence tomography.

Case 1. (A) Optic nerve retinal nerve fiber layer thickness map of the left optic nerve showing superior thinning in the left eye, significantly more than the inferior retinal nerve fiber layer of the same eye and more than the right eye. (B) Optical coherence tomography scans of the melanocytoma showing a hyperreflective inner retinal surface with posterior shadowing. (C) Internal limiting membrane contour map of the left eye showing a “bump”located superotemporally in the region of the melanocytoma (arrow).

Figure 3. Case 1. (A) Optic nerve retinal nerve fiber layer thickness map of the left optic nerve showing superior thinning in the left eye, significantly more than the inferior retinal nerve fiber layer of the same eye and more than the right eye. (B) Optical coherence tomography scans of the melanocytoma showing a hyperreflective inner retinal surface with posterior shadowing. (C) Internal limiting membrane contour map of the left eye showing a “bump”located superotemporally in the region of the melanocytoma (arrow).

Three-dimensional visualization of melanocytoma was possible following segmentation of the internal limiting membrane and retinal pigment epithelium. Internal limiting membrane contour mapping of the left eye also illustrated the “bump” superotemporally in the region of melanocytoma (Fig. 3C).

Case 2

A 78-year-old man with glaucoma and prior cataract extraction presented for routine follow-up. BCVA was 20/40 in the left eye. Anterior chamber examination was unremarkable. Posterior segment examination revealed a dark brown pigmented lesion with feathery edges located over the inferior aspect of the left optic disc, consistent with melanocytoma (Fig. 4). Funduscopic examination of the right eye was unremarkable. Humphrey 24-2 visual field examination showed a superior hemifield defect in the left eye corresponding to the inferiorly located melanocytoma that was stable compared with prior yearly field examinations (Fig. 5). Fluorescein angiography of the patient’s left eye demonstrated typical blocked fluorescence by the melanocytoma (Fig. 6). SD-OCT imaging of the optic disc (Fig. 7) revealed inferior RNFL thinning (Fig. 7A). SD-OCT thickness mapping also showed temporal and inferior RNFL thinning. B-scans demonstrated a domed tumor contour in the region of the melanocytoma with inner hyperreflective tissue and dense posterior shadowing. There was associated traction on the optic nerve from the hyaloid face (Fig. 7B). Internal limiting membrane contour mapping of the left eye also illustrated the “bump” inferonasally in the region of melanocytoma (Fig. 7C).

Case 2. Optic nerve photograph showing a dark brown pigmented inferior optic disc melanocytoma.

Figure 4. Case 2. Optic nerve photograph showing a dark brown pigmented inferior optic disc melanocytoma.

Case 2. Humphrey Visual Field 24-2 showing a superior altitudinal deficit that corresponds with the inferiorly located melanocytoma and the inferior retinal nerve fiber layer thinning seen on spectral-domain optical coherence tomography.

Figure 5. Case 2. Humphrey Visual Field 24-2 showing a superior altitudinal deficit that corresponds with the inferiorly located melanocytoma and the inferior retinal nerve fiber layer thinning seen on spectral-domain optical coherence tomography.

Case 2. Fluorescein angiography of the left optic nerve demonstrating marked hypofluorescence in the region of the melanocytoma.

Figure 6. Case 2. Fluorescein angiography of the left optic nerve demonstrating marked hypofluorescence in the region of the melanocytoma.

Case 2. (A) Optic nerve retinal nerve fiber layer thickness map of the left optic nerve showing inferior and temporal thinning in the region of the melanocytoma, significantly more than that of the right eye. (B) Optical coherence tomography showing the melanocytoma with a hyperreflective anterior tumor surface and posterior shadowing. Traction on the optic nerve from the hyaloid face is also present. (C) Internal limiting membrane contour map of the left eye showing an inferiorly located “bump” in the region of the melanocytoma (arrow).

Figure 7. Case 2. (A) Optic nerve retinal nerve fiber layer thickness map of the left optic nerve showing inferior and temporal thinning in the region of the melanocytoma, significantly more than that of the right eye. (B) Optical coherence tomography showing the melanocytoma with a hyperreflective anterior tumor surface and posterior shadowing. Traction on the optic nerve from the hyaloid face is also present. (C) Internal limiting membrane contour map of the left eye showing an inferiorly located “bump” in the region of the melanocytoma (arrow).

Discussion

Historically, optic disc melanocytomas were often misdiagnosed as malignant melanomas. Since being described by Zimmerman and Garron,8 it is now known to be a benign tumor both clinically and histopathologically that carries an excellent prognosis. It is important to differentiate the benign melanocytoma from other optic disc tumors, including combined hamartoma of the retina and retinal pigment epithelium, choroidal nevus, optic disc glioma, adenoma of the retinal pigment epithelium, and primary or metastatic melanoma.1,9 The diagnosis of optic disc melanocytoma can usually be made using ophthalmoscopy alone, based on characteristic clinical features including its homogeneous dark brown to black color, fibrillated margin, and location predominantly within the optic disc.

Melanocytomas have been found to cause a variety of visual field defects.10,11 Osher et al. evaluated 20 patients with Goldmann perimetry and found visual field defects in 90%.11 In a study of 11 patients, Usui et al.13 found visual field defects in 7 patients (70%). A total of 86% of those visual field defects corresponded with the location of the tumor and retinal nerve fiber bundle defect.13 The most frequent visual field defect reported with melanocytomas is a greatly enlarged blind spot (75%). Osher found that the enlargement of the blind spot approximated the extension of pigmented tumor beyond the boundary of the disc, and had less of an association with the absolute size of the tumor. In patients in whom the tumor was confined entirely within the disc boundaries, no blind spot enlargement was noted. Other visual field defects described included a minimal blind spot (15%), nasal step (10%), absolute arcuate defect (20%), and relative nerve fiber bundle defects (20%). There is still speculation regarding the pathogenesis of these visual field defects, but it is thought to be due to compression of the nerve fibers by melanocytoma cells producing pressure atrophy, or by compression of disc or retinal microcirculatory systems producing ischemic axonal loss. An afferent pupillary defect was found in 30% of patients, usually in those with more substantial visual field defects.12

Although melanocytomas can cause a variety of visual field defects, most do not cause significant visual impairment.7 In 75% of involved eyes, the visual acuity ranges from 20/15 to 20/30.14 Mild or severe visual impairments are thought to be caused by local complications such as disc edema, adjacent retinal edema, subretinal fluid, yellow retinal exudation, and adjacent retinal hemorrhage. Shields et al.’s retrospective review of 115 cases found that although these local complications were generally mild, they occurred in up to 25% of patients.6 In their study, the most common visual field defects included arcuate scotoma, enlargement of the blind spot, paracentral scotoma, and altitudinal field defect, which is consistent with the study by Osher et al.11

With the advent of new imaging modalities, our understanding of optic disc melanocytomas has continued to evolve. OCT evaluation of optic disc melanocytoma has depicted a dome-shaped tumor configuration with a hyperreflective anterior surface and posterior optical shadowing.3,4,12,15 It is thought that the dark pigmentation of the lesion blocks light transmission through the tumor and prevents visualization of internal tumor detail. Even so, OCT has been found useful for evaluating adjacent retinal tissue, differentiating melanocytomas from other optic disc tumors, obtaining exact measurements of the lesion, and monitoring its growth pattern in patients over time.4,9,10 A recent study demonstrated histopathologic and combined OCT and scanning laser ophthalmoscopy features of melanocytoma,16 which included disruption of the internal limiting membrane, disorganization of the retina overlying the tumor, and visualization of the tumor’s subretinal surface. Compressive and infiltrative changes in the optic nerve, peripapillary choroid, and retina were correlated directly to combined OCT and scanning laser ophthalmoscopy images.

The introduction of SD-OCT has allowed improvements in image acquisition speed and image quality compared with time-domain OCT systems. Higher acquisition speeds allow for the transition from two- to three-dimensional imaging, scans of larger regions of retina, improved signal to noise ratios corresponding to better image quality, exact image registration and localization, and objective, quantitative, reproducible images.15 In our two patients, SD-OCT revealed an elevated lesion in the region of the optic disc having a highly reflective inner layer with dense posterior shadowing. Reconstructed fundus images obtained from these B-scans allowed accurate image registration. Three-dimensional visualization of the lesions showed a “bump” corresponding to the location of the melanocytoma. The lesions appeared elevated in the peripapillary region. We also report visual field defects in both patients that corresponded to the region of RNFL thinning.

Thus, in addition to providing information about the morphology of the melanocytoma and extent of retinal involvement, SD-OCT can help to further characterize the lesion by depicting the location of RNFL thinning in relation to the melanocytoma. In our two patients, RNFL thickness maps showed considerable thinning of the retina in the regions surrounding the tumor that corresponded to the altitudinal visual field defects in the hemisphere opposite the tumor. SD-OCT may be useful for following the natural course of RNFL thinning in these patients over time. It is currently unknown whether the RNFL thinning is of a progressive nature, or whether it remains stable with stable tumor size. SD-OCT has been used successfully in detecting progression of RNFL thinning and optic disc cupping in conditions such as glaucoma.17 The new advances in SD-OCT may help us better characterize the clinical course of melanocytoma and its associated RNFL thinning and visual field defects. A combination of clinical examination, visual field evaluation, and OCT may be useful for monitoring patients with melanocytoma and consistent visual field defects.

References

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Authors

From the Department of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

Presented at the Association for Research in Vision and Ophthalmology (ARVO) annual meeting; May 3–7, 2009; Fort Lauderdale, Florida.

Supported by an unrestricted grant from Research to Prevent Blindness, New York, New York.

The authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Omar S. Punjabi, MD, 645 N. Michigan Ave., Suite 440, Chicago, IL 60611. E-mail: omar_punjabi@yahoo.com

10.3928/15428877-20110804-06

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