Abstract
Purpose :
It is known that both optic nerve head (ONH) and trabecular meshwork tissues are stiffer in glaucomatous eyes, and this has been suggested as a causative mechanism of damage. We sought to determine whether blood vessels within the ONH also stiffen, by using Laser Speckle Flowgraphy (LSFG) to characterize the pulsatile cycle.
Methods :
176 eyes of 94 participants with glaucoma or glaucoma suspects were tested using LSFG and standard automated perimetry, every six months, for six visits. This included 91 “glaucoma suspect” eyes (Glaucoma Hemifield Test [GHT] within normal limits on the first test) and 85 “glaucoma” eyes (initial GHT outside normal limits / borderline). Native LSFG software was used to parameterize the pulsatile cycle at pixels corresponding to major vessels inside the ONH, as detailed in Fig 1. The Rising Rate and Falling Rate parameters were age-corrected to the equivalent value for a 60-year-old, based on linear regression among a separate group of 90 healthy eyes of 59 subjects. The rate of change of perimetric Mean Deviation (MD) over the six visits was compared against the mean of the six values of each LSFG parameter, using generalized estimating equations to account for inter-eye correlations.
Results :
Among “glaucoma suspect” eyes, higher mean Rising Rate was associated with more rapid functional loss (Fig 2A, correlation r=-0.313, p=0.015). However, mean Falling Rate was not significantly associated with rate of loss (Fig 2A, r=-0.058, p=0.564). Among “glaucoma” eyes, rate of functional loss was not associated with either Rising Rate (Fig 2B, r=-0.124, p=0.285) or Falling Rate (Fig 2B, r=0.047, p=0.734). Neither Rising Rate nor Falling Rate were correlated with level of functional loss (average MD) in either subset (all p>0.5).
Conclusions :
Among glaucoma suspect eyes, higher Rising Rate, which may indicate higher vessel stiffness, was associated with more rapid functional loss. This is particularly interesting because these eyes did not initially have significant functional loss, nor was Rising Rate associated with current severity of functional loss; and it has also been shown to be independent of IOP. Vessel stiffening within the ONH may be part of the pathophysiology of early glaucoma, providing a link between the mechanical and vascular hypotheses of glaucoma development.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.