Diagnosing MacTel

Fluorescein angiography is commonly used to detect vascular alterations that occur due to MacTel. Fluorescein angiography typically shows telangiectatic capillaries temporal to the foveola in early-stage MacTel. In late-stage disease, fluorescein angiography shows a diffuse hyperfluorescence. It should be noted that MacTel causes retinal changes that cannot be seen by fluorescein angiography. This tool is not be effective, alone, to detect early cases of MacTel.

Optical coherence tomography (OCT) is a non-invasive imaging technique that uses long-wavelength light to generate high-resolution images of the retina in cross-section. OCT can be used to detect changes related to MacTel at very early stages. OCT shows asymmetry in the foveal dip very early. It also shows hyporeflective cavities of the inner and outer neurosensory retina, and increased reflectivity of inner neurosensory layers. Importantly, OCT is used to measure the IS/OS break, which is the disruption of the border between inner and outer photoreceptor segments, and has been one of the inclusion criteria for participation in clinical trials.

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Confocal Reflectance Imaging with a blue laser at 488 nm shows an increased reflectance in the parafoveolar region of MacTel eyes, surrounded by decreased reflectivity. This has also been referred to as “blue light reflectance imaging.” The images can be captured with a fundus camera and confocal scanning laser ophthalmoscope. The area of increased reflectance is coincident with the loss of macular pigment. Imaging macular pigment loss is a more reliable marker of early disease.

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Macular Pigment Density can be imaged in MacTel by a variety of techniques: two-wavelength fundus autofluorescence, two-wavelength reflectance maps, and spectral fundus reflectometry.

Confocal Adaptive Optics Scanning Laser Ophthalmoscopy is a non-invasive imaging technique that can be used to see individual photoreceptors in the back of the eye, along with other features, like cysts, blood vessels, and the RPE cell layer. Using adaptive optics, it is possible to begin to understand how MacTel affects photoreceptor health and function. Adaptive optics is time-consuming and requires very specialized instrumentation. Adaptive optics imaging is not widely available, and is not appropriate for diagnostic purposes, but it is being used in the ongoing clinical trials.

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