In vivo Optic Nerve Head Change Due to Artificially Increased Intraocular Pressure

Abstract

Purpose: : Transient increases in intraocular pressure (IOP) have been shown ex-vivo to increase cupping of the optic nerve head (ONH) and peripapillary displacement. The purpose of this study was to use confocal scanning laser ophthalmoscopy (CSLO) and spectral domain optical coherence tomography (SDOCT) to observe in-vivo changes in the ONH under transient IOP increase.

Methods: : In 6 healthy subjects, IOP was raised with a ring over the eyelids connected to a pulley system where weight was added to increase the pressure by the ring. Weight ranged from 0 to 500g in 100g intervals. At each of the weights, Goldmann applanation tonometry, corneal topography (Pentacam; Oculus, Lynnwood, WA), CSLO (HRT3; Heidelberg Engineering, Heidelberg, Germany) and SDOCT raster scan (Bioptigen, Durham, NC) were acquired. Topographic Change Analysis (TCA) was used to identify areas of change, and mixed effects models were fit to standard HRT3 parameters with IOP and reference plane as explanatory factors. SDOCT images were observed for disc shape changes and to measure maximum cup depth.

Results: : Pentacam found no significant change in astigmatism power and axis or central corneal thickness. IOP across subjects ranged from 13±2.7mmHg baseline to 43±6.9mmHg with 500g. TCA showed change clusters on various vessels in all eyes in consistent locations for each subject, with cluster size and amount of change increasing with increasing IOP. Clusters of depression near the disc margin extending into the disc, and areas of topographic increase in the peripapillary region occurred in 5 of 6 subjects. IOP was negatively and statistically significantly associated with HRT rim volume globally and in more sectors than any other parameter. SDOCT presented widening and deepening of the cup with IOP increase, as well as posterior bending of Bruch’s membrane ends. SDOCT cup depth had to be modeled quadratically; as IOP increased, cup depth initially increased, then decreased.

Conclusions: : TCA results indicate vascular changes at higher IOP. SDOCT qualitative results and HRT parameter model quantitative results suggest posterior bowing of the disc and peripapillary region are occurring.

Clinical Trial: : www.clinicaltrials.gov NCT00343746

Keywords: intraocular pressure • optic nerve • imaging/image analysis: clinical