Purpose. To evaluate visual function and disease progression in the retinal structural abnormalities of three patients from two unrelated families with macular telangiectasia (MacTel) type 2.
Methods. Adaptive optics scanning laser ophthalmoscopy (AOSLO) and AOSLO microperimetry (AOMP) were used to evaluate the structure and function of macular cones in three eyes with MacTel type 2. Cone spacing was estimated using histogram analysis of intercone distances, and registered spectral-domain optical coherence tomography (SD-OCT) scans were used to evaluate retinal anatomy. AOMP was used to assess visual sensitivity in and around areas of apparent cone loss.
Results. Although overall lesion surface area increased, some initially affected regions subsequently showed clear, contiguous, and normally spaced cone mosaics with recovered photoreceptor inner/outer segment (IS/OS) reflectivity (two of two eyes). The AOMP test sites fell within three categories: normal-appearing cones (N), dimly reflecting cones (D), and RPE cell mosaics (R). At N sites, AOMP threshold values (arbitrary units [au]) increased with increasing eccentricity (slope = 0.054 au/degree, r2 = 0.77). The N thresholds ranged from 0.04 to 0.27 au, D thresholds from 0.04 to 0.33 au, and R thresholds from 0.14 to 1.00 au. There was measurable visual sensitivity everywhere except areas without intact external limiting membrane (ELM) and with diffuse scattering in the IS/OS and posterior tips of the outer segments (PTOS) regions on OCT.
Conclusions. Visual sensitivity and recovery of cone visibility in areas of apparent focal cone loss suggests that MacTel type 2 lesions with a preserved ELM may contain functioning cones with abnormal scattering and/or waveguiding characteristics. (ClinicalTrials.gov number, NCT00254605.)