Abstract
Purpose :
Elevated intraocular pressure (IOP) in the non-human primate (NHP) results in progressive loss of retinal ganglion cells (RGCs). As with most glaucoma models, animals with similar IOP profiles have variability in the rate of loss. We hypothesize that the extent of glaucomatous loss may reflect differences in scleral remodeling. In this study, we determine the relationship between changes in axial length and neural tissue at an early stage of experimental glaucoma.
Methods :
Data were collected from 21 healthy adult NHPs. Following baseline testing, unilateral experimental glaucoma was induced by lasering the trabecular meshwork, and animals were monitored at two-week intervals. Intraocular pressure was measured using a Tono-Pen XL (Reichert, Inc), and the difference between the two eyes was used to calculate a cumulative IOP (mmHg.days). Anterior chamber depth, lens thickness, and axial length were obtained using optical biometry (Lenstar LS900, Haag-Streit). OCT scans acquired, included a 20° radial and 20x20° raster scan (Spectralis OCT, Heidelberg Engineering). Minimum rim width (MRW) and circumpapillary retinal nerve fiber layer (RNFL) thickness were used to monitor RGC loss. At 1000mmHg.days, a time point at which biometry changes had stabilized, the percent loss of MRW and of RNFL were compared to changes in biometry.
Results :
On average, three (2.9±1.4) laser sessions were needed to achieve sustained elevated IOP. Animals reached 1000mmHg.days in 82±42 days following the final laser session. At this point, the axial length had increased by 0.84±0.4mm, and the anterior chamber depth by 0.1±0.2mm (p<0.01). The mean and highest IOPs were 29.1±6.5mmHg and 41.5±7.8mmHg, respectively. The percent loss of MRW and RNFL were not related to either the mean or highest IOP (p>0.09). However, the percent loss of MRW and of RNFL were related to the change in axial length (R2=0.79 and R2=0.67, respectively, p<0.01).
Conclusions :
In NHP experimental glaucoma, losses of RGCs are correlated with axial elongation. The lengthening of the eye likely reflects scleral remodeling, but its role in RGC loss is unknown. It is possible that axial elongation stretches axons, making them more susceptible to damage.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.