OCTA provides high-speed, three-dimensional images of both small and large vessels within the retina in real time using motion contrast.
The technique uses comparisons of repeat scans acquired at the same position in the retina to detect changes in blood flow.
This microvascular mapping provides details of perfusion in the retina and optical nerve head without the use of contrast media and using equipment that is currently available in most ophthalmologic practices.
“OCTA may require a software upgrade, but it is available on almost all platforms used in ophthalmology practices today,” Dr. Chopra said. “The capability has been there and we are finally working out the practicalities of using OCTA to assess glaucoma as routinely as the retina specialists use the technology in retinal diseases.”
The UCLA team used OCTA to compare optic nerve head and peripapillary retinal vessel densities in age-matched groups of normal eyes versus pre-perimetric glaucoma versus early POAG. Retinal blood vessel density measurements using OCTA showed a consistent stepwise decrease from normal eyes to pre-perimetric glaucoma eyes to mild POAG eyes. There was a statistically significant difference in peripapillary vessel density, optic nerve head vessel density, and papillary vessel density among all three groups (p < 0.001).
Dr. Chopra’s results mirror a growing list of similar studies that have found clear association between reduced blood flow at the retina and optic nerve head and glaucoma. Reduction in retinal vascular density alone is sufficient to distinguish among the three groups of normal, pre-perimetric glaucoma, and early POAG.
What is most illuminating and interesting is that the data suggest the vascular changes in the retina may develop early in the glaucoma process, well before the recognition of any deterioration of the visual field.
Retinal vascular changes may not develop solely as a result of glaucomatous atrophy, but likely begin before the moderate-to-advanced stages of disease. That suggests that reduced retinal density and reduced retinal blood flow measurements could provide additional parameters that might be used in the clinical setting for earlier glaucoma diagnosis and management.
“These parameters have the potential to be used in a complementary fashion to currently utilized OCT-derived retinal nerve fiber layer measurements in earlier stages of glaucoma, and even be correlated to visual field defects in moderate and advanced stages of glaucoma,” Dr. Chopra said. “The problem is that, at this point, OCTA gives qualitative measures of retinal blood flow, but not yet the kind of quantitative measure or score needed for routine clinical use. Deriving a clinically useful score is just a matter of tweaking the algorithms that are already in place and collecting additional data.”