Optic Nerve Head Strain Inversely Associated With Retinal Sensitivity in Glaucoma

A study published in Ophthalmology found an inverse association between intraocular pressure (IOP)-induced optic nerve head (ONH) strains and retinal sensitivity among patients with glaucoma.

Researchers recruited 229 participants with primary open angle glaucoma (POAG) who had either high-tension glaucoma (HTG; n=91; 32 women; mean [SD] age, 69 [5] years) or normal-tension glaucoma (NTG; n=91; 41 women; mean [SD] age, 67 [6] years) and included 182 in the final analysis. Participants underwent refraction, axial length, central corneal thickness, anterior chamber depth, and visual field measurements. Spectral domain optical coherence tomography (SD-OCT) was used to image the ONH at primary gaze with and without acute IOP elevation caused by ophthalmodynamometry. The primary objective was to map ONH strains in an elevated IOP state in order to correlate retinal sensitivity with strains.

Baseline analysis revealed no significant differences between participants with HTG and those with NTG for systolic blood pressure (141 vs 140 mm Hg), diastolic blood pressure (75 vs 74 mm Hg), axial length (24.2 vs 24.4 mm), visual field mean deviation (-7.54 vs -6.56 dB), and IOP (17.3 vs 16.0 mm Hg).

In patients with HTG, a 1% increase in effective strain correlated with a 1.1 dB decrease in retinal sensitivity (β, -1.1; P <.001). Stratified by tissues, all were significantly associated with retinal sensitivity (all P <.001), and the pre-lamina tissue (β, -1.1), sclera (β, -1.0), lamina cribrosa (β, -0.9), and choroid (β, -0.9) had the strongest associations.

No associations were observed between average retinal sensitivity and average effective strain among individuals with NTG (P >.4).

Significant associations were observed between high strain regions and low retinal sensitivities among both the HTG (P <.001) and NTG (P =.004) cohorts. For the HTG group, the highest strain (11.3%) and lowest mean retinal sensitivity (13 dB) were observed in the superior-nasal region. In patients with NTG, the highest strain (4.1%) and lowest sensitivity (22 dB) occurred in the inferior-temporal region.

Researchers highlight the significance of this finding, suggesting that an independent IOP etiology may exist for NTG.

“[W]e observed no global associations between ONH strains and retinal sensitivity in NTG subjects on average for all ONH tissues nor for each specific ONH tissue,” according to the researchers. “This is an interesting finding since all HTG and NTG subjects were matched demographically and both groups had similar visual field indices. On the surface, this could imply that IOP elevation (or its fluctuation) may not influence ONH biomechanics in NTG subjects in a way that directly translates to visual field loss.”

Study limitations include failure to stratify participants according to glaucoma stage, the use of non contact tonometry to measure baseline and elevated IOP, and failure to include participants who were not of Chinese ethnicity.

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or clinical research organizations. Please see the original reference for a full list of authors’ disclosures.