Variations in optic nerve head morphology by intraocular pressure in open-angle glaucoma

Area of Science:

• Ophthalmology
• Glaucoma Research
• Optic Nerve Head Imaging

Background:

• Glaucoma diagnosis and management rely on assessing optic nerve head (ONH) structure and visual function.
• Intraocular pressure (IOP) is a key risk factor, but glaucoma can occur at various IOP levels, including normal-tension glaucoma (NTG) and high-tension glaucoma (HTG).
• Differentiating glaucoma subtypes based on ONH morphology is crucial for understanding disease progression and treatment strategies.

Purpose of the Study:

• To compare optic disc topography between different intraocular pressure (IOP) groups using advanced imaging techniques.
• To investigate if spectral domain optical coherence tomography (SD-OCT) and confocal scanning laser ophthalmoscopy can differentiate glaucoma based on IOP levels.
• To adjust for the degree of glaucomatous damage, measured by retinal nerve fiber layer (RNFL) thickness and visual field loss, in the comparison.

Main Methods:

• Recruited 184 eyes from 112 patients with primary open-angle glaucoma into three baseline untreated IOP groups: <15 mmHg (very low), 15-20 mmHg (medium), and ≥21 mmHg (high-tension glaucoma [HTG]).
• Utilized scanning laser ophthalmoscopy (SLO), SD-OCT, and Humphrey visual field testing for comprehensive eye assessments.
• Employed univariate and multivariate models, incorporating RNFL thickness and visual field mean deviation (MD) to account for retinal ganglion cell (RGC) loss.

Main Results:

• No statistically significant morphological differences in HRT or OCT parameters were found among the IOP groups when adjusted for RNFL thickness or MD (p < 0.0063).
• A trend of shallower mean cup depth was observed in the IOP <15 mmHg group compared to the IOP ≥21 mmHg group (p < 0.05).
• This trend was consistent across both MD (p < 0.011) and OCT RNFL (p < 0.014) damage criteria.

Conclusions:

• Optic nerve head topography, assessed by HRT and OCT, does not reliably distinguish between normal-tension glaucoma and high-tension glaucoma.
• The degree of glaucomatous damage, as determined by visual field testing, is a critical factor in evaluating ONH morphology.
• These findings suggest that IOP level alone, without considering functional damage, is insufficient to differentiate glaucoma subtypes based on structural imaging.