Purpose:
The eye is subject to many acute intraocular pressure (IOP) spikes during day-to-day life (e.g. eye rubbing). This study investigated the biomechanical response of the choroid and optic nerve (ON) to an acute IOP change in vivo in normal human volunteers.
Methods:
Spectral domain optical coherence tomography (SD-OCT; Spectralis HRA-OCT, Heidelberg Engineering, Heidelberg, Germany) was used to scan the eyes of normal subjects (n = 10). The scan parameters were modified to scan a single section through the center of the optic disc over a period of 5 s at approximately 120 frames per second, allowing direct, real-time visualization of the deformation of the tissues of the posterior eye. Eyes were imaged undergoing acute IOP elevation as described previously (Flanagan, J.G., et al. IOVS 2009;50:ARVO E-Abstract 4894). The resulting image sets were segmented and analyzed using custom software developed in MATLAB (The Mathworks Inc., Natick, MA). Peripapillary choroidal thickness and the morphometry of the ON were measured.
Results:
The choroid was observed to thin by up to 20% during a step 20 mmHg IOP increase (see example in Fig.), and returned to its original thickness within approximately 150 ms when pressure was removed. The ON flattened and rebounded during the same pressure pulse, and a change in reflectance was seen to project outwards from the ON in some eyes. Choroidal thickness tended to thin and thicken uniformly across the region measured.
Conclusions:
Real-time visualization of the ON can provide insight into the biomechanical response of the eye to changes in IOP. The biomechanical environment of the ON is dynamic, with dramatic changes evident in less than a second. Pressure-induced thinning of the choroid may act as a second-to-second modulator of acute changes in IOP.
Keywords: intraocular pressure • choroid • imaging/image analysis: non-clinical