Bilateral optic disc drusen: An accidental finding in identical twins

Twin brothers, 48-year-olds, presented for regular eye checkup, both of them being known cases of seizure disorder, under medication for 30 years. Twins 1 and 2 have a best corrected visual acuity of 20/30 and a normal intraocular pressure in both eyes. The anterior segment of both patients is normal. On dilated fundoscopy, whitish, pearl-like lesions present at the disc in both eyes of both patients, with optic disc giving a ‘lumpy bumpy’ appearance with difficulty in assessing the cup-disc ratio [Fig. 1]. In optical coherence tomography of the retinal nerve fiber layer, focal RNFL thinning was noted. In B-scan ultrasonography, highly reflective foci are seen at the optic nerve head in both eyes of both patients [Fig. 2]. On visual field examination in Humphrey Visual Field testing in 30-2 test, slight visual field defects were noted inferiorly in both eyes of twin 1 [Fig. 3] and central and paracentral scotoma were seen in twin 2 [Fig. 4]. After 6 months of follow-up, no significant change in visual field defect was noticed. Their elder brother was also thoroughly examined, and optic disc drusen was not present in his eyes.Figure 1: Fundus photograph of the right eye and left eye of Twin 1 (a and b) and Twin 2 (c and d) showing lumpy bumpy appearance of optic disc depicting optic disc drusenFigure 2: B-Scan ultrasonography images of twin 1 (a) and twin 2 (b) showing hyperechoic foci at optic nerve headFigure 3: (a, b) Perimetry findings of twin 1 showing field defects in the inferior quadrant in both eyesFigure 4: (a, b) Perimetry findings of Twin 2 showing field defects like central and paracentral scotoma in both eyesDiscussion Pathophysiology may be due to enlarging calcific bodies in a crowded space, exerting mechanical stress on structures within the prelaminar scleral canal, leading to significant visual field loss. With compression, drusen may promote nonarteritic anterior ischemic optic neuropathy.[1] The slowly progressive decrease in vision may be due to the direct effect of the mechanical forces as described earlier, which cause axonal dysfunction followed by gradual axonal degeneration. The inheritance pattern of optic disc drusen is suggested to follow an autosomal dominant pattern with reduced penetrance.[2] This was an accidental finding showing characteristic changes of optic disc drusen in identical twins. Though asymptomatic, careful clinical examination and patient’s history are required, confirmed by autofluorescence or ultrasonography. Optic nerve drusen on their own does not require any treatment and has good visual prognosis, and is re-evaluated periodically.[3] Authors contributions Dr. Pramod Sharma conceptualized the article. It was designed by Dr. Pooja Pattnaik with the help of Dr Prativa Behera who also helped in literature research. All the authors contributed in intellectual content definition, data acquisition and analysis. Manuscript preparation was done by Dr. Pooja Pattnaik which was further reviewed and edited by all the authors. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and all clinical information to be reported in the journal. The patients understand that their names and initials will not be published and their identities will be concealed but anonymity cannot be guaranteed. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.