Abstract
Purpose: :
Despite modern technologies for examination of the optic nerve and visual field, there remains controversy about the functional and morphological differences between normal (NTG) and open angle high tension glaucoma (HTG). Aim of the study was to compare the visual field (VF) loss in normal tension (NTG) and high tension (HTG) glaucoma with the same glaucomatous structural damage of optic nerve.
Methods: :
The retrospective study included 126 eyes with NTG which were matched on a case-by-case basis to 126 eyes with HTG with same optic disc area and cup/disc-ratio. The glaucomatous damage of the optic nerve was verified by analysis of neuroretinal rim volume and rim area. The nerve fiber layer was measured by HRT (RNFL) and GDxVCC. Visual field (VF) was examined by Humphrey full threshold 30-2 program, calculating values for the mean deviation (MD), pattern standard deviation (PSD) and the probability scores.
Results: :
Eyes with NTG have significantly less visual field loss than those with HTG (mean ± SD: MD -3.69 ± 5.03 dB vs. -9.77 ± 7.99dB, P=0.0001; PSD 4.80 ± 4.47dB vs. 7.17 ± 4.41, P=0.0001). There were no differences in the HRT parameter disc area (NTG 2.32 ± 0.25mm² vs. HTG 2.32 ± 0.23mm², P=0.342), rim area (NTG 1.03 ± 0.26mm² vs. HTG 1.00 ± 0.30mm², P=0,279) or rim volume (NTG 0.2 ± 0.08mm³ vs. HTG 0.19 ± 0.11mm³; P=0,274). The NTG eyes have a better preserved retinal nerve fiber layer (RNFL: NTG 0.17 ± 0.05mm vs. HTG 0.16 ± 0.07mm², P=0.099; GDx sup: NTG 57.2 ± 10.4µm vs. HTG 49.9 ± 13.12mm², P=0,0001). Total and focal visual field loss is significantly correlated with the structural damage of the optic nerve in both glaucoma groups
Conclusions: :
The cupping in eyes with NTG seems related to a primary loss of glial tissue compared to HTG, which results in a less affected retinal nerve fiber structure. This might be the reason for less visual field defects in this subgroup. The findings might support the classification of glaucoma as a primary neurodegenerative disease.
Keywords: optic disc • perimetry • intraocular pressure