Choroidal Thickness Changes in Response to Acute Increase in Intraocular Pressure

Abstract

Purpose: : To investigate the biomechanical response of the optic nerve (ON) and parapapillary retina to acute increase in intraocular pressure (IOP), invivo in normal, human volunteers, using spectral domain, optical coherence tomography (SD-OCT).

Methods: : The sample consisted of 10 normal subjects, age range 20 to 50 year, 5 female. Eyes were imaged using a SD-OCT (Spectralis HRA-OCT, Heidelberg Engineering, Heidelberg, Germany). Volume scan reference images (scan area - 15^o x 10^o; 49 sections; 10 scans per scan line) were acquired at baseline along with IOP by Goldmann applanation tonometry (GAT). Follow up scans were acquired, relative to the baseline reference image, while IOP was raised by ophthalmodynamometry (OD) (Bailliart) with a force of 20 grams applied to the temporal sclera. IOP was then measured by GAT during OD. Images were segmented and analyzed with respect to average retinal thickness, average choroidal thickness, cup depth and ON diameter as defined by the termination of Bruch’s membrane.

Results: : IOP at baseline ranged from 10 to 18mmHg (mean 14.8mmHg). Following OD, IOP ranged from 41 to 60mmHg (mean 54mmHg). There was no difference in cup depth (mean difference -12.5µ; p=0.155), horizontal ON diameter (mean difference -1.9µ; p=607) or retinal thickness (p=0.825). With high IOP there was collapse of the central retina vessels and a significant reduction of the thickness of the choroid (Baseline-mean 130.2µ SD 28.5; High IOP-mean 108.9µ SD 22.1; p<0.001), with a mean change of 16.4% (SD 6.75; range 6 to 28%). There was no correlation between change in IOP and change in choroidal thickness.

Conclusions: : There was a rapid and significant thinning of the choroid in posterior poll of the normal human eyes in response to an acute increase in IOP.

Keywords: optic nerve • intraocular pressure • choroid