Reproducibility of Lamina Cribrosa Microstructure Measurements in Varying Intraocular and Intracranial Pressure Settings

Abstract

Purpose : To examine the effect of varying levels of intraocular (IOP) and intracranial pressure (ICP) on the reproducibility of lamina cribrosa (LC) microstructure measurements.

Methods : Spectral-domain OCT scans of the optic nerve head (ONH) were obtained from adult healthy rhesus macaque monkeys while IOP and ICP were changed in a controlled environment. Gravity-based perfusion through a needle inserted into the anterior chamber controlled IOP (low, medium, high settings). Perfusion through the lateral ventricle controlled ICP (low, high settings). Scans were registered in 3D and LC microstructure measurements (beam thickness, pore diameter) were calculated from shared regions among scans acquired at each setting using a previously described segmentation algorithm. Microstructure measurement results were used to calculate the beam/pore ratio of each scan, and a 2-way ANOVA test compared the effect of different IOP and ICP settings on measurement reproducibility.

Results : The results of 2 eyes were analyzed. For average beam thickness IOP had a significant effect on measurement reproducibility but ICP did not (p=0.005, p=0.66, respectively). For average pore diameter IOP also had a significant effect on measurement reproducibility but ICP did not (p=0.009, p=0.97, respectively). The effect of IOP and ICP on beam/pore ratio reproducibility was not significant (p=0.23, p=0.80, respectively). Results are summarized in Figure 1.

Conclusions : Our study provides evidence that beam/pore ratio measurements are reproducible regardless of acquisition at different IOP and ICP settings. This parameter is less influenced by scanning angle and image quality than other measurements. This information supports direct comparison of beam/pore ratio measurements obtained in varying pressure settings.

This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.

 

Figure 1. Effect of Intraocular Pressure (IOP) and Intracranial Pressure (ICP) on Lamina Cribrosa Measurements. 2-way ANOVA test was used for comparison; data from 2 eyes was aggregated. Varying IOP significantly affected beam thickness and pore diameter but did not affect beam/pore ratio. ICP did not have a significant effect on any of the measurements.