Macular coloboma is believed to result from either a developmental abnormality or intrauterine inflammation.1 Bilateral macular coloboma has been described earlier.12345 It has been seen in association with ocular or systemic abnormailities.1 Optical coherence tomography (OCT) can enhance visualization of abnormal retinal structure. Here, we report a case of unilateral macular coloboma with macular dystrophy and its OCT characteristics.
A 30-year-old healthy young gentleman presented with complaints of blurred vision in the left eye which was noticed three months back when he had visited an ophthalmologist with the complaint of itching. There was no significant history suggestive of systemic illness. On examination, his best-corrected visual acuity was 20/25, N6 in the right eye and 20/160, N18 in the left eye. Color vision test on Ishihara's color test was normal. Amsler grid test was normal in the right eye and showed a central scotoma in the left eye. Intraocular pressure on applanation tonometry was 16 and 18 mmHg in the right and left eye respectively. Anterior segment examination was unremarkable in both eyes. Fundus examination showed focal areas of altered retinal pigment epithelium (RPE) and subretinal yellowish lesion in the foveal area [Fig. 1] in the right eye. Left eye showed a punched out circumscribed lesion in the center of the macula with thin foveal roof suggestive probably of the internal limiting membrane [Fig. 2]. A surrounding area of altered RPE was seen around the macular lesion.
Pattern electroretinogram (ERG) showed normal finding in the right eye and subnormal amplitude with mildly delayed implicit time in the left eye. Multifocal ERG showed normal appearance in right eye and depressed waveforms within 15° in the left eye which was more marked within 10°. Full field ERG for photopic and scotopic responses was normal. The OCT of the right eye showed normal study [Fig. 1]. Left eye showed bowl-shaped punched out morphology with shelving edge [Fig. 2]. A thin highly reflective membrane was seen central to the sharp edge. This characteristic contour was within the fovea. The findings were highly suggestive of coloboma. Fundus fluorescein angiography showed multiple stippled hyperfluorescence with late staining and minimal leakage in the macula in the right eye [Fig. 1]. Left eye showed a well-circumscribed darkly hypofluorescent area with relative hypofluorescence in the late phase [Fig. 2]. A surrounding area of RPE window defect was seen. Based on the clinical and investigative findings, a diagnosis of macular coloboma in the left eye and possible macular dystrophy in the right eye was made.
Macular coloboma has been classified into three groups based on the ophthalmoscopic appearance.4 Often, it is associated with previous intrauterine infection and/or systemic abnormalities, and usually they are bilateral. This unique pattern of bowl-shaped defect in the fovea with shelving edge and without scleral ectasia was the characteristic finding on OCT, which was never described before. The present case also describes a unilateral macular coloboma with macular dystrophy. The clinical picture of the right eye could mimic Best's dystrophy but OCT features were not characteristic. An electro-oculography could have ruled out Best's disease. However, macular coloboma or dysplasia can occur in patients with congenital retinal dystrophy.4
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