Adaptive Optics Scanning Laser Ophthalmoscopy Demonstrates Reduced Foveal Cone Density in Early Idiopathic Macular Telangiectasia

Abstract

 

Purpose:

 

Macular telangiectasia (MacTel) has been considered primarily a vascular disease affecting juxtafoveal retinal capillaries, but recent evidence suggests that neuronal changes may occur early in disease development. In order to study early pathologic changes in MacTel, we studied patients affected with classic MacTel in one eye who had subtle or no clinical findings the other eye, using adaptive optics scanning laser ophthalmoscopy (AOSLO) to evaluate the foveal cone photoreceptors in the less affected eyes.

 

Methods:

 

Three patients were identified with asymmetric MacTel and complete eye examinations including fluorescein angiography were performed. The less affected eyes were evaluated with AOSLO reflectance imaging. AOSLO near-infrared reflectance images were obtained in square fields centered on the fovea and a 3.5x3.5 degree montage of the photoreceptors was generated. Cone counting was performed in a 2x2 degree retinal area centered on the fovea using custom cone marking software followed by manual editing. A cone density map within this area was calculated using a 36x36 µm sliding window with 10 µm overlap of each window.

 

Results:

 

In each case, one eye was affected with MacTel, and the other eye was clinically normal or near-normal, with visual acuity 20/25 or better and subtle angiographic leakage. We successfully imaged the complete foveal cone mosaic in all three patients. The cone mosaics were continuous with normal distribution of reflectance but larger than expected spacing. Peak cone packing densities were 85.7x10³, 84.7x10³, and 71.8x10³cones/mm², in all three cases below the previously reported minimum density in normal subjects (normal peak cone density 199.2±87.2 x10³ cones/mm²).

 

Conclusions:

 

Foveal cone packing density was decreased in the clinically less affected eyes in patients with asymmetric MacTel. This study suggests that the cone photoreceptor loss may precede vascular changes in MacTel.

 

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • photoreceptors • retina: distal (photoreceptors, horizontal cells, bipolar cells)