This case illustrates the value of spectral-domain optical coherence tomography (SD-OCT) for both understanding the structural changes underlying visual loss in type 2 idiopathic macular telangiectasia (IMT).

A 63-year-old woman presented with decreased vision and upon examination, she had perifoveal changes in the retinal pigment epithelial (RPE). Fluorescein angiography (FA) showed bilateral leakage from the retinal vessels. These diagnostic findings resulted in a diagnosis of type 2 IMT.

TD-OCT VS SD-OCT
Time-domain OCT (TD-OCT; Figure 1) of her right eye shows hyporeflective spaces underneath the fovea. SPECTRALIS SD-OCT (Heidelberg Engineering, Heidelberg, Germany) at a similar plane shows these hyporereflective spaces (Figure 2) but also reveal other abnormalities in the area of telangiectasia that are not evident with TD-OCT. Figures 2 and 3 are additional SDOCT scans from different planes that demonstrate clear differences between the TD- and SD-OCT technologies. In the SPECTRALIS image (Figure 3), the bottom hyper-reflective line is the RPE and the line just above it is the intersection between the outer and inner segments of the photoreceptor layer. The inner segments and outer segments of the photoreceptors, the space between the two red arrows (Figure 3), are disrupted in the area of telangiectasia and that most likely accounts for the decrease in visual acuity in the right eye. We also see areas of moderate reflectivity, which could either represent areas of pigment migration or areas of old, inactive, subretinal neovascularization. These layers are not well distinguished in the TD-OCT (Figure 4).

In another SPECTRALIS image in a more superior location (Figure 5), we continue to see hyporeflective spaces within the retina as well as disruption of the photoreceptor layer. Figure 6 is a magnified view of the central area, providing a closer look at the separated vitreous, the hyporeflective structure under the fovea, and the disrupted photoreceptor layer.

DISCUSSION
This case clearly illustrates the utility of SD-OCT, particularly in macular diseases where there is disruption of the photoreceptors. Although SD-OCT is not critical in the diagnosis of type 2 IMT, it is necessary in order to understand why the vision loss has occurred and can be helpful in educating patients about the vision loss.

Diana V. Do, MD, is an Assistant Professor of Ophthalmology at the Wilmer Eye Institute Johns Hopkins School of Medicine in Baltimore. Dr. Do's spouse, Quan Dong Nguyen, MD, has served on the Scientific Advisory Board for Heidelberg Engineering. Dr. Do can be reached via e-mail at ddo@jhmi.edu.