Macular Telangiectasia - MacTel Features

MacTel Features

Although MacTel is uncommon, its prevalence is probably higher than most physicians believe. The early findings are subtle, so the diagnosis is likely often missed by optometrists and general ophthalmologists. MacTel was detected in 0.1% of subjects in the Beaver Dam study population over age 45 years (Ronald Klein, MD, personal communication), but this is probably an underestimate because identification was made based only on color photographs.

No major new biomicroscopic features of MacTel have been identified since the early work of Gass and colleagues.1,3 The advent of optical coherence tomography (OCT) has allowed better characterization of the nature of the inner and outer lamellar cavities. Loss of central masking seen on autofluorescence studies, apparently due to loss of luteal pigment, is now recognized as probably the earliest and most sensitive and specific MacTel abnormality. Using adaptive optics, it is possible to image areas of photoreceptor damage in vivo.

The condition may remain stable for extended periods, sometimes interspersed with sudden decreases in vision. Patients’ loss of visual function is disproportionately worse than the impairment of their visual acuity, which is only mildly affected in many cases (Table 1).4

In patients with MacTel, as compared with a reference population, there is a significantly higher prevalence of systemic conditions associated with vascular disease, including history of hypertension, history of diabetes, and history of coronary disease (Table 2).

Familial transmission is now recognized in a small proportion of people with MacTel (Figure 1); however, the nature of any related genetic defect or defects remains elusive. The MacTel genetic study team hopes that exome analysis in the affected population and relatives may be more successful in identifying related variants.

Histopathology studies of a single post-mortem specimen have shown a loss of Mueller cell markers from central retina, suggesting that Mueller cell death may be involved in the pathogenesis. One animal model in which the receptor for very low density lipoproteins is “knocked out” mimics many of the clinical characteristics of the disease and other models are being developed in the laboratories. Animal studies using the established model have shown an anti-oxidant diet and a special form of gene therapy to be effective in preserving visual function in these mice.

Treatment options are limited. No treatment has to date been shown to prevent progression. The variable course of progression of the disease makes it difficult to assess the efficacy of treatments. Retinal laser photocoagulation is not helpful. It is hoped that a better understanding of the pathogenesis of the disease may lead to better treatments.

The use of vascular endothelial growth factor (VEGF) inhibitors, which have proven so successful in treating age-related macular degeneration in the past 5 years, has been investigated in pilot studies for treatment of subretinal neovascularization in MacTel. Ranibizumab given before the development of subretinal neovascularization dramatically reduces the vascular leak seen on angiography, although microperimetry suggests that neural atrophy may still proceed in treated eyes.