Abstract
Purpose :
We assessed the intervisit and intravisit repeatability of FLIO lifetimes and capillary erythrocyte velocities in a non-human primate (NHP) model of acute intraocular pressure (IOP) elevation.
Methods :
We assessed FLIO (Heidelberg Engineering, Heidelberg, Germany) lifetimes and erythrocyte velocities in eleven experiments of four eyes of two rhesus macaques at baseline and elevated intraocular pressure. The NHPs were anesthetized and paralyzed to control eye motion. Erythrocyte velocities were measured using erythrocyte mediated angiography (EMA). In two eyes of one NHP, FLIO lifetimes were measured at baseline, IOP of 25, 35, and 45 mm Hg multiple times at each IOP. Pressure was maintained at these levels during imaging with cannulation of the eye and controlled with a syringe pump. FLIO Fluorescence data were analyzed using imaging software (SPCImage; Becker & Hickl GmbH, Berlin, Germany). The fluorescence decay was approximated by calculating the least-square fit of a series of two exponential functions. The NHP's exhibited no discernable lens fluorescence on the rising side of the decays and no correction was applied to the fits for this.The amplitude-weighted mean fluorescence decay time (τm) was used for further analysis in two spectral channels (498–560 nm; 560–720 nm). Intersession and intrasession variability was determined by calculation of the coefficient of variation at baseline and at each IOP level.
Results :
:The average fluorescence lifetime at baseline ranged from 302.1 – 343.3 ps in the long channel and 381.6 – 408.6 ps in the short channel. Intrasession variability of FLIO lifetimes ranged from 0-6.3% in the long channel and 0-3.3% in the long channel at baseline. At elevated pressures, CoV ranged from 0 – 7.5%. Intersession variability of FLIO lifetimes ranged from 4.1-7.5% in the long channel and 3.0-4.8% in the short channel. Intrasession variability for capillary erythrocyte velocities was 7.0% at baseline.
Conclusions :
In an acute IOP elevation NHP model, Fluorescence lifetimes were highly reproducible at baseline as well as at elevated IOP, suggesting that rather subtle changes can be reliably measured in this model. Further work is needed to determine changes in fluorescence lifetime with IOP elevation, which may provide important information about glaucoma and other ocular diseases.
This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.