Association of Functional Loss With the Biomechanical Response of the Optic Nerve Head to Acute Transient Intraocular Pressure Elevations

Abstract

Importance: The acute biomechanical response of the optic nerve head (ONH) to intraocular pressure (IOP) elevations may serve as a biomarker for the development and progression of glaucoma.

Objective: To evaluate the association between visual field loss and the biomechanical response of the ONH to acute transient IOP elevations.

Design, setting, and participants: In this observational study, 91 Chinese patients (23 with primary open-angle glaucoma [POAG], 45 with primary angle-closure glaucoma, and 23 without glaucoma) were recruited from September 3, 2014, through February 2, 2017. Optical coherence tomography scans of the ONH were acquired at baseline and at 2 sequential IOP elevations (0.64 N and then 0.90 N, by applying forces to the anterior sclera using an ophthalmodynamometer). In each optical coherence tomography volume, lamina cribrosa depth (LCD) and minimum rim width (MRW) were calculated. The mean deviation (MD) and the visual field index (VFI), as assessed by automated perimetry, were correlated with IOP-induced changes of LCD and MRW globally and sectorially.

Main outcomes and measures: The LCD, MRW, MD, and VFI.

Results: Among the 91 patients, 39 (42.9%) were women; the mean (SD) age was 65.48 (7.23) years. In POAG eyes, a greater change in LCD (anterior displacement) was associated with worse MD and VFI (R = -0.64; 95% CI, -0.97 to -0.31; P = .001; and R = -0.57; 95% CI, -0.94 to -0.19; P = .005, respectively) at the first IOP elevation, and a greater reduction in MRW was also associated with worse MD and VFI (first IOP elevation: R = -0.48; 95% CI, -0.86 to -0.09; P = .02; and R = -0.57; 95% CI, -0.94 to -0.20; P = .004, respectively; second IOP elevation: R = -0.56; 95% CI, -0.98 to -0.13; P = .01; and R = -0.60; 95% CI, -1.03 to -0.17; P = .008, respectively), after adjusting for age, sex, and baseline IOP. A correlation was found between the reduction in MRW in the inferior-temporal sector and the corresponding visual field cluster in POAG eyes at the second elevation (ρ = -0.55; 95% CI, -0.78 to -0.18; P = .006).

Conclusions and relevance: The biomechanical response of the ONH to acute IOP elevations was associated with established visual field loss in POAG eyes, but not in primary angle-closure glaucoma eyes. This suggests that ONH biomechanics may be related to glaucoma severity in POAG and that the 2 glaucoma subgroups exhibit inherently different biomechanical properties.

Figure 1.. Measurement of Lamina Cribrosa Depth and Minimum Rim Width From Bruch Membrane Opening Reference Plane

Red arrow indicates the reference plane at the Bruch membrane opening (white dots); cyan arrows, minimum rim width from the Bruch membrane opening; dark blue arrows, lamina cribrosa depth; and white line, surface of the anterior lamina cribrosa.

Figure 2.. Relationships Between Glaucomatous Visual Field Loss and Lamina Cribrosa Displacement at the First Intraocular Pressure Elevation With Force of 0.64 N

The positive data points at the right side of each graph indicate that the lamina cribrosa displaced anteriorly following acute intraocular pressure elevation, whereas the negative values at the left side of each graph indicate that it displaced posteriorly. PACG indicates primary angle-closure glaucoma; POAG, primary open-angle glaucoma; SAP, standard automated perimetry; and VFI, visual field index.