Abstract
Purpose: To assess ocular rigidity using dynamic optical coherence tomography (OCT) videos in glaucomatous and healthy subjects, and to evaluate how ocular rigidity correlates with biomechanical and morphological characteristics of the human eye.Methods: Ocular rigidity was calculated using Friedenwald's empirical equation which estimates the change in intraocular pressure (IOP) produced by volumetric changes of the eye due to choroidal pulsations with each heartbeat. High-speed OCT video was utilized to non-invasively measure changes in choroidal volume through time-series analysis. A control-case study design was based on 23 healthy controls and 6 glaucoma cases. Multiple diagnostic modalities were performed during the same visit including Spectralis OCT for nerve head video, Pascal Dynamic Contour Tonometry for IOP and ocular pulse amplitude (OPA) measurement, Corvis ST for measuring dynamic biomechanical response, and Pentacam for morphological characterization.Results: Combining glaucoma and healthy cohorts (n = 29), there were negative correlations between ocular rigidity and axial length (Pearson R = −0.53, p = 0.003), and between ocular rigidity and anterior chamber volume (R = −0.64, p = 0.0002). There was a stronger positive correlation of ocular rigidity and scleral stiffness (i.e., stiffness parameter at the highest concavity [SP-HC]) (R = 0.62, p = 0.0005) compared to ocular rigidity and corneal stiffness (i.e., stiffness parameter at the first applanation [SP-A1]) (R = 0.41, p = 0.033). In addition, there was a positive correlation between ocular rigidity and the static pressure-volume ratio (P/V ratio) (R = 0.72, p < 0.0001).Conclusions: Ocular rigidity was non-invasively assessed using OCT video and OPA in a clinic setting. The significant correlation of ocular rigidity with biomechanical parameters, SP-HC and P/V ratio, demonstrated the validity of the ocular rigidity measurement. Ocular rigidity is driven to a greater extent by scleral stiffness than corneal stiffness. These in vivo methods offer an important approach to investigate the role of ocular biomechanics in glaucoma.
Highlights
Accumulating clinical and scientific evidence has confirmed the critical roles of biomechanics in ocular health and disease, in glaucoma [1,2,3,4]
Twenty-nine subjects with processable Optical coherence tomography (OCT) videos and valid intraocular pressure (IOP) measurements were included in this study (23 healthy controls and 6 glaucoma cases)
The calculated AL was strongly correlated with the measured AL (p < 0.00001, Figure 2A), and the paired t-test suggested that there was no statistically significant difference (p > 0.1), validating our approach for axial length assessment using the OCT device
Summary
Accumulating clinical and scientific evidence has confirmed the critical roles of biomechanics in ocular health and disease, in glaucoma [1,2,3,4]. Glaucomatous axonal damage initiates at the optic nerve head (ONH) where the retinal nerve fibers (axons of ganglion cell) exit the eye [6, 7]. Mathematical modeling and animal studies have suggested that scleral stiffness is a major determinant of the ONH susceptibility to the damage [8,9,10,11]. In vivo evaluation of scleral stiffness remains limited. Assessing the ocular biomechanics in glaucoma, especially in a clinic setting, is imperative to gain a deeper understanding of tissue behavior using newer technologies
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