Disc Drusen

Abstract

We read Lee, Woo and Hwang's article entitled “Differentiation of Optic Nerve Head Drusen and Optic Disc Edema with Spectral-Domain Optical Coherence Tomography,”1Lee K.M. Woo S.J. Hwang J.M. Differentiation of optic nerve head drusen and optic disc edema with spectral-domain optical coherence tomography.Ophthalmology. 2011; 118: 971-977Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar with great interest, as we have also been following buried disc drusen and identified quite a different appearance. We would like to share with the authors an image showing a cross-section of an optic nerve druse on spectral-domain optical coherence tomography (SD-OCT) with a corresponding retinal photo (Fig 1; available at http://aaojournal.org). Please note that the retinal photo clearly shows a druse, very close to the surface, which is ophthalmoscopically identifiable. The corresponding region on SD-OCT shows a round, hyporeflective space just below the surface. Other, similar hyporeflective zones can be visualized deeper within the same slice of the optic nerve head. Accordingly, the photo shows multiple bulges and irregularities over the area of the optic nerve, typical of the appearance of buried disc drusen (Fig 2; available at http://aaojournal.org). B-Scan ultrasound was performed, confirming the diagnosis of buried drusen. Having identified the hyporeflective nature of the above druse, critical evaluation of several patients suspected of buried disc drusen has consistently revealed multiple, small, round hyporeflective spaces at various depths. Literature review has revealed a scant number of references to the appearance of optic nerve drusen on OCT, reporting both hyporeflective and hyperreflective appearance. Patel et al2Patel N.N. Shulman J.P. Chin K.J. Finger P.T. Optical coherence tomography/scanning laser ophthalmoscopy imaging of optic nerve head drusen.Ophthalmic Surg Lasers Imaging. 2010; 41: 614-621Crossref PubMed Scopus (18) Google Scholar report “lucencies”; Wester et al3Wester S.T. Fantes F.E. Lam B.L. Characteristics of optic nerve head drusen on optical coherence tomography images.Ophthalmic Surg Lasers Imaging. 2010; 41: 83-90Crossref PubMed Scopus (26) Google Scholar report an “optically empty cavity, sometimes with a perceptible reflection from the posterior surface”3Wester S.T. Fantes F.E. Lam B.L. Characteristics of optic nerve head drusen on optical coherence tomography images.Ophthalmic Surg Lasers Imaging. 2010; 41: 83-90Crossref PubMed Scopus (26) Google Scholar; Yi et al4Yi K. Mujat M. Sun W. Imaging of optic nerve head drusen: improvements with spectral domain optical coherence tomography.J Glaucoma. 2009; 18: 373-378Crossref PubMed Scopus (41) Google Scholar describe them as “signal-poor regions with high-signaled borders.” In contrast, Murthy et al5Murthy R.K. Storm L. Grover S. et al.In-vivo high resolution imaging of optic nerve head drusen using spectral-domain optical coherence tomography.BMC Med Imaging. 2010; 7: 10-11Google Scholar report “scattered spots with high reflectivity,” which is consistent with this article's description. The hyporeflective appearance we have identified would suggest that the composition of drusen is highly uniform. The uniformity simply indicates that the index of refraction does not change throughout the region. Therefore, in the same way that leaking fluid or a cyst appears hyporeflective on SD-OCT, dense, homogenous material may appear hyporeflective as well. The composition of buried disc drusen remains unresolved. It is possible that multiple types of disc drusen exist, with variable composition between types. Until we gain a better understanding of the nature of the coalescing material(s), it would be important that clinicians keep an open mind as to the nature of the appearance of buried disc drusen on SD-OCT. Figure 2Spectral domain-optical coherence tomography (SD-OCT) image obtained on Topcon 3D-OCT (shown in 1:1 ratio). Retinal photo shows surfacing druse at superior aspect of optic nerve (left eye, left marker). OCT slice through surfacing druse (left marker) depicts round hyporeflective region between 2 vascular structures, below the surface. A buried druse is also observed in this slice, temporal to the surfacing druse (right marker, not visible ophthalmoscopically).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Differentiation of Optic Nerve Head Drusen and Optic Disc Edema with Spectral-Domain Optical Coherence TomographyOphthalmologyVol. 118Issue 5PreviewTo evaluate the efficacy of spectral-domain optical coherence tomography (SD-OCT) in differentiating optic disc edema (ODE) and optic nerve head drusen (ONHD) and to reveal the differential points. Full-Text PDF Author replyOphthalmologyVol. 119Issue 3PreviewWe thank Dr. Slotnick and Dr. Sherman for their interest in our article. Our article1 mainly focused on determining the differences between optic disc edema and optic nerve head drusen (ONHD) by using spectral-domain optical coherence tomography (SD-OCT); therefore, detailed descriptions regarding the nature of the drusen were not provided. We appreciate this precious opportunity to share our experiences with ONHD in more details. Full-Text PDF