Reply—Optic Disc Doubling or Pseudo-Optic Disc in Colobomatous Retinal Abnormality?
We thank Gerth-Kahlert and Wildberger for their comments on our article dealing with optic disc doubling (1). In their case, the blood vessels that appear to arise from the coloboma inferior to the disc are actually a continuation of the blood vessels emerging from the optic disc. This is an example of a lesion simulating the optic disc or pseudo-disc doubling.
In contrast, in our patient, there is no connection on the surface of retina between the 2 groups of vessels. The emerging retinal vasculature from the optic disc has a normal configuration except for an absent inferotemporal venous trunk. The superonasal part of the inferior disc is occupied by the cup, and the inferonasal portion shows the origin of another independent but incomplete retinal vascular system. It consists of superotemporal and inferotemporal venous and superotemporal and inferonasal arterial arcades, converging at one point. There is a single foveal avascular zone corresponding to the true optic disc at a level slightly lower than its normal position. The inferotemporal portion of the perifoveal capillary net is formed by the tributaries from the superotemporal vascular arcade from the second disc. Fundus fluorescein angiography shows simultaneous and similar filling patterns of both vascular systems.
The arcuate visual field defect in our patient demonstrates that the inferior optic disc is nonfunctioning. The hypopigmented bridging track possibly indicates an embryological relationship between the 2 discs. The 2 separate vascular systems, the presence of 2 blind spots on visual field testing, and the crater-like depression over the inferior disc in optical coherence tomography (OCT) suggest that our patient has true doubling of the optic disc.
With regard to our OCT findings, unfortunately we do not have a horizontal line scan passing across the inferior disc to show nasotemporal asymmetry of the nerve fiber layer. We agree with Gerth-Kahlert and Wildberger that discontinuation of the junction of the inner and outer photoreceptor segment is difficult to assess because of the quality and angulation in the scan. Ultrahigh resolution OCT passing across both optic discs would give better delineation of the adjacent retinal architecture.
© 2013 by North American Neuro-Ophthalmology Society
1. Padhi TR, Samal B, Kesarwani S, Basu S, Das T. Optic disc doubling. J Neurophthalmol. 2012;32:238–239.