Diagnosing MacTel

• Blunting or lack of the foveolar reflex. This observation is restricted to early-stage disease.
• Crystalline deposits, located in the inner retina at the level of the inner limiting membrane. They may appear as hyperreflective dots at the anterior surface of the nerve fiber layer in OCT scans. The deposits are present at all stages of disease. In participants of the MacTel Natural History Study, 46% of patients had crystalline deposits. For those with deposits, 60% showed deposits bilaterally.
• Reduced retinal transparency in the parafoveolar area may be one of the first visible changes in the retina. This symptom is also referred to as retinal graying.

• Mildly ectatic capillaries affect primarily the deeper capillary network, though telangiectatic vessels have been observed in inner and outer retinal circulation.
• Blunted, slightly dilated venules are often associated with ectatic capillaries and, in later disease stages, with retinal pigment plaques. These vessels don’t appear to narrow as they approach the foveola, rather, they suddenly seem to dive at right angles into the deeper retinal layers.
• Foveal atrophy. This may appear as small foveal non-prominent cysts, or a pseudo-lamellar macular hole, or as slightly altered foveal reflectivity. Atrophy can be missed on fundus images. Atrophy of the outer retinal photoreceptor layer is the endpoint of MacTel, and results in localized loss of visual function.
• Abnormal distribution of macular pigment. Macular pigment deposition is normally concentrated in the fovea. In MacTel eyes, there is a loss of macular pigment from the central retina. Instead, MacTel eyes show a ring of pigments about 12 degrees in diameter, much larger than the normal 1-2 degrees in diameter. This can be visualized with autofluorescence imaging. Studies found that dietary supplementation with lutein and zeaxanthin enhanced the existing ring of macular pigments, but does not restore normal macular pigment distribution.
• Retinal pigment plaques (pigment-hyperplasia) seem to originate from small foci of RPE hyperplasia that migrate into the neurosensory retina. Photoreceptor atrophy precedes, and may cause, the presence of retinal pigment plaques. Retinal pigment plaques may be surrounded by RPE atrophy.

• A small round yellow spot may be found centered on the fovea, roughly ½-disc diameter size.
• Small retinal hemorrhages in the absence of a neovascular complex. These are transient, usually resolving in a few weeks.
• True lamellar, or full thickness macular holes, may occur. This is a complication of the disease, possibly resulting from the progressive degeneration and atrophy of the retina. Cellular death may destabilize the fovea, leading to a macular hole which may be more difficult to surgically treat than other types of macular holes.
• Neovascular complexes may develop at any time point, and complicate the natural course of the disease. These are most commonly located temporal to the foveola. They seem to originate from the retinal vasculature, not the choroid as is seen in age-related macular degeneration. In MacTel, these neovascular complexes may, however, still gain access to the subretinal space and develop chorio-retinal shunts.

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.

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.

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.