Macular Telangiectasia type 2: multimodal assessment of retinal function and microstructure

Purpose: To assess the impact of neurodegenerative morphologic alterations due to macular telangiectasia type 2 (MacTel) on microperimetry (MP) and multifocal electroretinography (mfERG).

Methods: Thirty-five eyes of 18 patients with MacTel were examined using spectral domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF), mfERG and MP. Software was used to match SD-OCT B-scans with the corresponding retinal sensitivity map and multifocal electroretinograms (mfERGs), thus enabling direct structure/function correlation.

Results: Loss of the ellipsoid zone (EZ) had the strongest negative association with retinal sensitivity (16.77 dB versus 4.58 dB, adj. p < 0.001) of all parameters examined, and a limited negative effect on mfERGs (0.32 SD versus -1.97 SD adj. p = 0.121). Ellipsoid zone (EZ) irregularity was associated with reduced MP values but preserved mfERGs. There was a significant association between areas of inner retinal hyporeflectivity and loss of MP sensitivity (adj. p < 0.001) but the reduction in sensitivity was less than in locations with EZ loss. Areas of mfERG abnormality showed similar sensitivity loss with either inner retinal hyporeflectivity or EZ loss (adj. p = 0.063). In areas with EZ loss alone, preservation of the external limiting membrane (ELM) was associated with higher MP values than in areas with additional ELM loss; the integrity of the ELM alone was not associated with changes either in MP or mfERG. Increased FAF was observed in 51% of eyes, mixed/reduced FAF in 40%, and no abnormality was detected in 9% of eyes.

Conclusion: The data suggest both MP and mfERG to be useful non-invasive modalities for detecting localised macular dysfunction in MacTel. The findings suggest a different sensitivity of the two modalities to inner and outer retinal changes in macular function and are therefore complementary.