Duplication of the optic disc is rare in humans and is classified as either true duplication or pseudoduplication. True duplication of the optic disc occurs with separation of the optic nerve into two or more strands.1 The presence of two optic foramina (confirmed on orbital x-ray) or two optic nerves (confirmed on B-scan ultrasonography, computed tomography, or magnetic resonance imaging) on one side and dual blind spots in the same visual field all indicate true duplication of the optic disc.1 Pseudoduplication of the optic disc is also a rare, congenital anomaly characterized by the presence of an additional optic disc–like lesion mostly within a peripapillary area.2–13 The presence of a single optic nerve is the key feature distinguishing pseudoduplication from true duplication of the optic disc.1,8,12 Owing to apparent cupping, associated vasculature, and surrounding chorioretinal atrophy, pseudoduplication of the optic disc is distinguishable from other retinal lesions such as staphyloma and inflammatory foci.1 Pseudoduplication of the optic disc is considered to be caused when the fetal fissure fails to close and is typically located inferiorly and slightly nasally to the optic disc.1,8,12
Patients with pathologic myopia can show a fundus lesion resembling pseudoduplication of the optic disc. This presentation has not been reported in the literature and could not be found in a literature search with the keywords “pathologic myopia,” “optic disc,” and “duplication or pseudoduplication.” Thus, its prevalence among patients with pathologic myopia and its pathogenesis have never been investigated. The aims of this study were (1) to explore the pathogenesis of this lesion using enhanced depth imaging optical coherence tomography (EDI-OCT), (2) to determine its prevalence among patients with pathologic myopia, and (3) to evaluate distinguishing features between true duplication and pseudoduplication of the optic disc and those between our cases and other cases with pseudoduplication of the optic disc. To further clarify pseudoduplication and true duplication of the optic disc, a literature review was conducted and the clinical and morphologic characteristics of these conditions were summarized.
To estimate the prevalence of acquired pseudoduplication of the optic disc, a retrospective chart review was performed for 128 consecutive patients diagnosed as having pathologic myopia between January 2010 and December 2012. This study was conducted in accordance with the tenets of the Declaration of Helsinki and approved by the institutional review board of Seoul National University Bundang Hospital. Pathologic myopia was defined as myopia accompanied by degenerative changes in the posterior segment of eyes with refractive errors greater than −8.00 diopters (D) or axial lengths greater than 26.5 mm.14 All cases with pathologic myopia were reviewed for the presence of acquired pseudoduplication of the optic disc.
All patients underwent a complete ophthalmic examination, including measurement of best-corrected visual acuity (BCVA) and refraction, slit-lamp biomicroscopy, binocular indirect ophthalmoscopy, and fundus photography. Axial length was measured with IOL Master 500 (Carl Zeiss Meditec Inc, Jena, Germany). The area of pseudoduplication of the optic disc (pseudodisc) was examined with EDI-OCT (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany), which visualizes ocular tissues at a deeper level than conventional time-domain or spectral-domain OCT. Fluorescein angiography (FA) or indocyanine green angiography was performed using the Heidelberg Retina Angiograph 2 (HRA2; Heidelberg Engineering).
A MEDLINE search of literature written in the English language between 1960 and 2013 was conducted using the keyword combination “doubling OR duplication AND optic disc.” All reported cases of true duplication or pseudoduplication of the optic disc were collected. A table listing the condition description, demographic and clinical features, fundoscopic pseudodisc features, imaging results, number of optic nerves, histopathology, and systemic associations was created.
Among 128 patients with pathologic myopia, 3 patients (2.3%), including 2 women and 1 man, showed acquired pseudoduplication of the optic disc. Table 1 shows the clinical characteristics of the patients. The ages of patient 1, 2, and 3 were 54, 69, and 81 years, respectively. Fundus examination showed focal (patient 1) or diffuse (patients 2 and 3) chorioretinal atrophy throughout the posterior pole and a round, pinkish lesion with vasculature within the area of atrophy (Figs. 1A, 2A, and 3A). Fluorescein angiography and indocyanine green showed that the vessels were ciliary arteries. The round pinkish area penetrated by a ciliary artery through its center can confuse an observer to judge it as another optic disc. Enhanced depth imaging optical coherence tomography of the patients revealed choroidal atrophy and focal scleral excavation without overlying retinal tissues in the pseudodisc (Figs. 1D, 2C, and 3B).
A 54-year-old man was referred for duplication of the optic disc in the right eye, discovered in a preoperative examination for cataract surgery. His BCVA was 20/50 OD and 20/20 OS. Axial length was 33.77 mm OD and 27.79 mm OS. Fundus examination of the right eye revealed patchy chorioretinal atrophy and a pinkish round lesion within the area of atrophy (Fig. 1A, arrow). Additionally, vessels were seen originating from the center of this lesion. Indocyanine green angiography revealed the central vessels to be lateral short posterior ciliary arteries, distinct from retinal arteries or veins (Fig. 1B, arrowhead). Humphrey visual field test showed an enlarged blind spot and a temporally located arcuate scotoma (Fig. 1C) that was worse in the inferior field. Enhanced depth imaging optical coherence tomography showed patchy chorioretinal atrophy (Fig. 1D, between arrowheads) and focal excavation causing a scleral defect within the atrophy corresponding to the pseudodisc area (between arrows). A short posterior ciliary artery (yellow arrowhead), running toward the inner retinal layers, was noted in the image. In the true optic disc, the sclera showed posterior displacement but the change in scleral contour was not as abrupt as that seen in the pseudodisc (Fig. 1E).
A 69-year-old woman was referred to our clinic for an evaluation of her myopic macular degeneration. Her BCVA was 20/30 in the right eye and hand motion in the left eye. Refractive error was −0.125 D in the right eye and −14.50 D in the left eye. Axial length was 23.81 mm in the right eye and 30.66 mm in the left eye. Fundus examination showed diffuse chorioretinal atrophy over the retinal posterior pole in the left eye (Fig. 2A). A round pinkish lesion (Fig. 2A, arrow) with penetrating ciliary arteries (Fig. 2A, arrowheads) was also found in the left eye. Images from FA (Fig. 2B) more clearly demonstrated short posterior ciliary arteries that were distinct from retinal arteries and veins. Additionally, EDI-OCT images of the pseudodisc area revealed choroidal atrophy and focal scleral excavation with no overlying retinal tissue (Fig. 2C, between arrows).
An 81-year-old woman visited our clinic for progressive vision loss in her left eye. She was previously diagnosed as having pathologic myopia in both eyes and had undergone cataract surgery 7 years earlier. Her BCVA was 20/200 in the right eye and hand motion in the left eye. Slit-lamp examination revealed an intraocular lens within the capsular bag in both eyes. Fundus examination of the right eye showed diffuse chorioretinal atrophy and a pinkish round lesion nasal to the fovea. Within the lesion, ciliary arteries (Fig. 3A, arrowheads) were seen. Images obtained with OCT showed focal scleral excavation (Fig. 3B, between arrows), which had more abrupt scleral contour changes than the true optic disc (between arrowheads).
True or Pseudoduplication of the Optic Disc in the Literature
The results of the literature review are summarized in Table 2. A total of 16 English-language reports of true duplication or pseudoduplication of the optic disc were identified.1–6,8–10,12,13,15–19 Common morphologic features of pseudodisc included a well-circumscribed disclike lesion, vessels passing over the lesion, and surrounding chorioretinal atrophy. However, the size of the pseudodisc varied from less than 0.5 to 3 disc diameters (DD) in these reports. Pseudodisc color ranged from pale to pink or orange. Our cases of acquired pseudoduplication of the optic disc had relatively small pseudodiscs (<0.5 DD), but the common morphologic features were present.
A common OCT finding among reported cases of pseudoduplication of the optic disc was a crater-like depression, similar to that seen in a true optic disc. In agreement with observations made by Padhi et al.,19 our patients had two crater-like depressions of similar shape in an OCT cross-sectional image covering both the true optic disc and pseudodisc. Padhi et al.19 observed an excavation with no epithelium reflex on OCT images in their case of true duplication of the optic disc, very similar to our findings observed in the pseudodisc of case 2. In summary, morphologic similarities of OCT findings between our cases and reported cases of true or pseudoduplication of the optic disc included absence of a retinal pigment epithelium reflex, absence of the choroid, and presence of a posterior scleral depression.
This study demonstrates that a lesion mimicking pseudoduplication of the optic disc may occur in eyes with pathologic myopia. The presence of a ciliary artery in the pseudodisc suggests that the pathogenesis of a myopic pseudodisc may result from myopic chorioretinal atrophy and scleral excavation or defects caused by the penetration of a ciliary artery through the staphyloma. Round scleral thinning or defects made the underlying peribulbar tissue appear pinkish similar to the optic disc.
The EDI-OCT images revealed chorioretinal atrophy, commonly seen in eyes with pathologic myopia, and scleral excavation, which is characteristic of acquired pseudoduplication of the optic disc in pathologic myopia. Compared to the true optic disc, the shape of crater-like depressions was similar, but relatively abrupt changes in scleral contour (scleral excavations) were noted in the pseudodisc. Our pseudodisc OCT findings are similar to those previously reported for crater-like lesions8 and colobomatous defects.2
True duplication of the optic disc can be diagnosed when imaging techniques reveal two optic nerves leaving the eye. The optic discs have separate retinal vascular supplies as demonstrated by FA, and the extra optic disc is supplied with nerve fibers.4 Pseudoduplication of the optic disc shows a well-circumscribed disclike coloboma with vasculature and surrounding chorioretinal atrophy, which is usually inferior to the normal optic disc. However, our cases showed characteristic ophthalmic features such as scleral excavation and a ciliary artery within the pseudodisc, distinct from the reported cases of true double disc or congenital pseudoduplication. Furthermore, our patients did not show any systemic findings suggesting congenital malformations associated with pseudoduplication of the optic disc.
As determined by histopathologic analyses, most cases of pseudoduplication of the optic disc result from a focal, juxtapapillary retinochoroidal coloboma that has an abnormal vascular anastomosis with the optic disc.2–13 In contrast to these cases, our cases of acquired pseudoduplication had a focal retinochoroidal coloboma with abrupt scleral contour changes and no anastomosis with the optic disc. This absence of an anastomosis with retinal vessels may be explained by the origin of the vessels that passed over the pseudodisc, short posterior ciliary arteries.
The morphologic abnormalities of the sclera in our cases were compatible with the scleral contour changes occurring in eyes with pathologic myopia.20 Posterior displacement of the entire scleral layer with changes in the curvature of the neighboring sclera and large intrascleral vessels, as identified by swept-source OCT, have similar morphologic features with our cases.20 Regarding the pathogenesis of the scleral excavation in our cases with pathologic myopia, we hypothesized that a short posterior ciliary artery in the sclera, running toward the inner retinal layers, may be associated with a morphologic change, as the vessels were colocalized with the change. Ohno-Matsui et al.21 described structures in the peripapillary area (which they named “peripapillary pits”) that were similar to the pseudodisc observed in our cases. They suggested that these peripapillary pits develop in eyes with pathologic myopia from a stretch-associated scleral schisis in areas of openings of posterior emissary for the short posterior ciliary arteries. On the basis of our findings, we believe that acquired pseudoduplication of the optic disc forms in a similar manner, which needs validation in a longitudinal study with a larger number of patients.
We found that 2.3% of patients with pathologic myopia had acquired pseudoduplication of the optic disc. Eyes with pathologic myopia may demonstrate many pathologic conditions, including myopic choroidal neovascularization, myopic macular retinoschisis, and myopic chorioretinal atrophy. Ohno-Matsui et al.20 suggested that highly myopic eyes could develop lesions that mimic a congenital anomaly owing to extensive eye elongation. Our cases with acquired pseudoduplication of the optic disc may be one of the examples, which add pseudoduplication of the optic disc as another presentation of pathologic myopia. However, as we estimated the prevalence of acquired pseudoduplication of the optic disc in a clinic-based sample of patients with pathologic myopia, the prevalence should be confirmed in a population-based study using a larger sample size of patients with pathologic myopia.
One may argue that the lesions in our patients with pathologic myopia do not mimic the optic disc as the lesions are too small. However, patient 1 was referred by a general ophthalmologist as having a “disclike lesion.” Any ophthalmologists who are not familiar with pathologic myopia might consider the finding presented in our report as pseudoduplication of the optic disc. As shown in Table 2, sizes of the pseudodisc in previous reports vary widely. Additionally, previous reports by Ren et al.17, Andonegui et al.2, and Vedantham et al.12 described their disclike lesions, which were similar to ours in size, as “pseudodisc” or similar terms. We believe that scleral excavation can be wider than our cases in some eyes with pathologic myopia, and in this case, the lesion might more resemble the true optic disc. Although the finding of pseudoduplication of the optic disc can be subjective, depending on the clinician’s expertise, the discovery that scleral excavation and penetrating ciliary arteries can occur in pathologic myopia, which may mimic the optic disc, is noteworthy in this report.
In conclusion, acquired pseudoduplication of the optic disc may develop in eyes with pathologic myopia, although it was found only in 2.3% of the patients. Enhanced depth imaging optical coherence tomography showed chorioretinal atrophy and focal scleral excavation in the area showing the pseudodisc. The pathogenic association between pathologic myopia and acquired pseudoduplication of the optic disc should be further validated in future studies.
Department of Ophthalmology
Seoul National University College of Medicine
Seoul National University Bundang Hospital
166, Gumiro, Bundang-gu
Seongnam, Gyeonggi-do 463-707
Seong Joon Ahn and Se Joon Woo contributed equally to this work and are considered co-first authors.
Received October 29, 2013; accepted April 3, 2014.
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