DEC 11, 2012
By Daniel Miller MD PhD
Retina/Vitreous
The authors describe novel electron microscopy findings in a postmortem specimen of a patient with documented macular telangiectasia (MacTel) type 2. These findings include vascular degeneration in all layers of the retina, as well the accumulation of subretinal debris with minimal change to the retinal pigment epithelium (RPE). Higher magnification suggested that the subretinal deposits consist of degenerated photoreceptors.
A separate review by the same authors of ophthalmoscopy, autofluoresence imaging, and OCT findings in a cadre of patients with MacTel 2 identified subtle subretinal deposits in the perifoveal region. Of the 65 MacTel subjects, three (5 percent) had prominent yellow hyperautofluorescent material at the fovea.
The authors speculate that this material represents degenerate photoreceptor outer segments and note that it is similar to that found in foveomacular vitelliform dystrophy. This suggests a common origin from the outer segments of photoreceptors, which contain lipofuscin-associated pigments.
They write that while obvious subretinal debris was only seen in 5 percent of the cases, it is possible that subclinical debris may be present in many MacTel type 2 eyes where it may reflect an underlying process of impaired phagocytosis by the RPE.
The fact that the vascular changes were symmetrical in the six cases in which the material was detected in only one eye suggests that the excessive accumulation of subretinal debris is independent of, rather than caused by, the vasculopathy. This would be consistent with an upstream Muller cell defect, which might be expected to affect blood vessels and photoreceptors independently.
They conclude that both clinical and ultrastructural observations demonstrate that accumulation of subretinal debris is a feature in a subset of patients with MacTel type 2, which may further implicate Muller cells in the pathogenesis of the disease.