Lamina Cribrosa Deformation Response to Lowering Intracranial Pressure (ICP)

Abstract

Purpose : To measure the deformation of the lamina cribrosa (LC) from ICP lowering by cerebrospinal fluid (CSF) drainage in normal pressure hydrocephalus (NPH) patients.

Methods : Nine eyes (6 patients, 67.17±9.85 years of age) were imaged by optical coherence tomography (OCT) prior to and after CSF drainage, where a catheter is inserted into the lumbar spine to drain 300-400 ml of CSF over 2 days to determine shunt candidacy. On the day of the procedure before lumbar puncture, the intraocular pressure (IOP) was measured by iCare tonometer, and 3 sets of radial OCT scans were imaged by Spectralis (Heidelberg Engineering). IOP was remeasured, and another set of scans was acquired 20 minutes after the procedure. Digital volume correlation (DVC) was used to correlate 2 consecutive pre-treatment images to calculate the baseline error and the pre- and post-treatment images to estimate the LC strains and LC border displacement (ALD, Czerpak 2022).

Results : ICP decreased from 11.1±2.0 mmHg to 0.25±0.0 mmHg (n=6 patients) while IOP increased by 1.2 ± 3.7 mmHg (n=9 eyes). The baseline error for the anterior-posterior strain E_zz in the LC was 0.081%±.0.098% (n=9) and accurate DVC correlation was obtained for 42.0%±17.6% of the LC area, in line with those in a prior study for IOP change from suturelysis (Czerpak 2022). ICP lowering caused a borderline significant 3.0±4.2 μm posterior ALD displacement (p=0.063, n=9), a significant E_zz = -0.57%± 0.44% (p=0.004, n=9) that was greater in magnitude than baseline error (p=0.009), and significant maximum tensile strain E_max = 0.53% ± 0.25% and maximum shear strain γ_max = 0.74% ± 0.28% (both p<0.001, n=9). The E_zz was also smaller and opposite in direction from those measured after IOP lowering in the prior study (Czerpak 2022).

Conclusions : DVC analysis of OCT images accurately measured strains caused by ICP lowering by CSF drainage in NPH patients. The mean compressive E_zz was larger than the baseline error and in the opposite direction as that measured for IOP lowering. We will continue to image patients to increase the sample size. Mixed linear models will correlate the average LC strains to ICP change, IOP change, axial length, baseline IOP and ICP, and age.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

A radial SDOCT scan in the nasal-temporal direction, showing (a) the original OCT image acquired pre (b) the image after contrast enhancement, and c) the contour of the anterior-posterior strain E_zz superimposed.