In-vivo Modulation of Intraocular and Intracranial Pressures Causes Nonlinear and Non-monotonic Deformations of The Lamina Cribrosa

Abstract

Purpose : Our goal was to measure the in-vivo effects on the optic nerve head (ONH) of acute modulation of intraocular and intracranial pressures (IOP and ICP).

Methods : In 4 eyes of 3 monkeys, IOP and ICP were modulated through cannulas inserted into the eye and ventricle. Each pressure was set at 4 levels (low, baseline, high, very high), and the ONHs imaged with a SD-OCT. The anterior lamina cribrosa (ALC) and scleral canal opening at Bruch membrane (BMO) were manually marked in 18 radial sections per scan (Fig 1A). Custom code was used to reconstruct 3D ALC surfaces and register BMOs. ALC depths were computed relative to the BMO best-fit plane within regions visible in all scans of an eye (Fig 1B) and normalized to baseline in each monkey. Hence, ALC depth less than 100% meant more anterior ALC and vice versa.

Results : IOP and ICP had nonlinear and effects on the median ALC depth (Fig 2). The ranges for normalized median ALC depth were 78-116%, 36-122%, 65-105%, and 66-104% in eyes 1R, 2R, 3R and 3L. There were strong interaction between the pressures effects, meaning that effects of one pressure depended strongly on the other pressure. Pressure effects were non-monotonic. For example, in eye 3R at 20 mmHg ICP, the LC displaced anteriorly when IOP increased from 8 to 15mmHg, and posteriorly for IOP from 15 to 30mmHg (Fig 2C). In all 4 eyes, the most anterior LCs occurred with IOPs below baseline (15mmHg) and very high ICP (20-45mmHg).

Conclusions : Acute modulation of either IOP or ICP above or below baseline can cause substantial deformations of the ALC, sometimes anteriorly and other times posteriorly. These deformations were non-linear and non-monotonic, with strong interactions between IOP and ICP.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Figure 1. Manual delineation and reconstruction of ONH structures. (A) Example markings on a radial slice (B) Example heat map of ALC depth, calculated as distance from ALC surface (reconstructed red radial markings) to best-fit BMO plane (outline shown in blue).

 

Figure 2: Nonlinear and non-monotonic effects of IOP and ICP on in-vivo LC deformations. All ALC depths were normalized to baseline values (IOP=15 mmHg, ICP=8-10 mmHg) and median values (%) were plotted (blue=more anterior, red=more posterior). Green asterisks (*) corresponded to pressure conditions. Dotted green line showed an example of non-monotonic effect of increasing IOP at ICP=20 mmHg in monkey 3-right.