Abstract
Purpose :
Retinal perfusion near the foveal avascular zone (FAZ) depends upon sparse capillaries, mapped with either OCT angiography (OCTA) or adaptive optics scanning laser ophthalmoscopy (AOSLO). We hypothesized that diabetic retinas with vessel remodeling on AOSLO have a microenvironment that is detrimental to cones, particularly if the FAZ enlarges. We compared the numbers of foveal cones within a 600 micron radius of the foveal center to FAZ area.
Methods :
OCTA measures of FAZ were compared to AOSLO measures of cones for 10 diabetic patients (29-79 yr, 54.5 +/- 12.7 yr). Each patient had retinal microvascular remodeling on AOSLO, despite total retinal thicknesses on OCT within normal limits. All subjects were consented and tested in a manner approved by the Indiana University Institutional Review Board, which adhered to the Declaration of Helsinki. SLO, SD-OCT, and OCT-A data (Heidelberg Spectralis II) provided FAZ area. Confocal images, 1.9 x 1.6 deg, 780 x 520 pixels at 769 nm, visualized both dark and bright cones. Foveal cones within a central 600 micron radius were computed from our 2 parameter exponential model. Cones and FAZ were scaled by axial length (IOLMaster). Age-similar control groups provided 95% confidence limits for foveal cones and FAZ area.
Results :
The OCTA intermediate capillary plexus slab gave the clearest and smallest FAZ vessel in all 10 patients. FAZ area was 0.04 to 0.47 mm2 (0.29 +/- 0.11 mm2), similar to controls (0.32 +/- 0.077), and when corrected for axial length (FAZc) was 0.24 +/- 0.094 mm2. The FAZ shape was fairly symmetric in our roughly emmetropic sample: axial lengths 21.99 to 23.84. Two diabetic subjects had foveal cones similar to control subjects, 38,400 and 39,200. The other 8 diabetic subjects had fewer foveal cones than the average for older subjects: 35,600, but no qualitative or quantitative differences in the choriocapillaris on OCTA. Foveal cones (24,100 to 32,100) were negatively correlated with FAZc in this group. A linear regression of foveal cones on FAZc area was statistically significant: foveal cones =31,700 – 21,400* FAZc, p = .0201, but young controls foveal cones =43,000 – 51,000* FAZc, p = .20.
Conclusions :
In 8 of 10 diabetic patients with vascular remodeling, the number of foveal cones is less than expected from control data and decreases systematically with an increase in FAZ area. This is consistent with foveal cones decreasing with a lack of metabolic support.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.