In-vivo evidence of lamina cribrosa deformations induced by chronically elevated IOP in non-human primates

Abstract

Purpose : To measure in vivo lamina cribrosa (LC) deformations induced by chronically elevated intraocular pressure (IOP). Specifically, we measure session-to-session (S2S) LC stretch, compression, shear and effective strains.

Methods : The optic nerve heads (ONHs) of both eyes of three monkeys were imaged using optical coherence tomography (OCT, Spectralis) at baseline and longitudinally (S2S interval 7 to 22 days, 7 to 17 sessions) after unilateral laser-induced chronic elevated IOP (experimental glaucoma EG). To remove acute IOP effects and isolate chronic deformations all scans were acquired after IOP was set to 10 mmHg for 30 minutes. Digital volume correlation (DVC) was then employed to determine the local S2S LC deformations. LC deformations were compared longitudinally and between the EG and control eyes of each monkey.

Results : S2S LC changes were much larger in the EG eyes after lasering compared to the baseline sessions and control eyes. As expected, laser-induced IOP increases were highly variable, prompting further treatments. However, the LC changes induced by the transient increases in IOP were not resolved after IOP returned to normal. S2S LC deformations reached low two digits, locally as large as 10% compression and 16% stretch, suggestive of tissue loss. Interestingly, further analysis indicated that in the sessions immediately after lasering, a small anterior-posterior LC stretch was detected, suggesting that the lamina undergoes thickening, not thinning. Later on, the LC exhibited the expected compression consistent with thinning. S2S LC changes were significantly larger in the EG after lasering compared with the baseline sessions and the control eyes (p<0.001) .

Conclusions : The monkey LC suffers clearly detectable deformations as a result of chronically elevated IOP. Changes can be detected even after only a few days of elevated IOP, and are not immediately resolved even if IOP comes back to the normal range.

This is a 2021 ARVO Annual Meeting abstract.

 

Data from Monkey 1 illustrating the effects on IOP of lasering. LC deformations were measured between consecutive sessions. For interpretation we split the steps into four groups.