Under Pressure: Lamina Cribrosa Pore Path Tortuosity in Response to Acute Pressure Modulation.

Abstract

Lamina cribrosa (LC) deformation is hypothesized to play a major role in glaucoma pathogenesis. The purpose of this study was to determine in vivo how varying intraocular pressure (IOP) under fixed intracranial pressure (ICP), and vice versa, deforms the pore paths throughout the LC volume. Spectral-domain optical coherence tomography scans of the optic nerve head were acquired from healthy adult rhesus monkeys under different pressures. IOP and ICP were controlled with gravity-based perfusion systems into the anterior chamber and lateral ventricle, respectively. IOP and ICP were modulated from baseline to high (19-30 mmHg) and highest (35-50 mmHg) levels while maintaining a fixed ICP of 8 to 12 mmHg and IOP of 15 mmHg, respectively. After three-dimensional registration and segmentation, the paths of pores visible in all settings were tracked based on their geometric centroids. Pore path tortuosity was defined as the measured distance divided by the minimal distance between the most anterior and posterior centroids. The median pore tortuosity at baseline varied among the eyes (range, 1.16-1.68). For the IOP effect under fixed ICP (six eyes, five animals), two eyes showed statistically significant increased tortuosity and one showed a decrease (P < 0.05, mixed-effects model). No significant change was detected in three eyes. When modulating ICP under fixed IOP (five eyes, four animals), a similar response pattern was detected. Baseline pore tortuosity and the response to acute pressure increase vary substantially across eyes. LC pore path tortuosity could be associated with glaucoma susceptibility.