Abstract:

Objective

The aim of this study is to explore the relationship between damages in optic nerve morphology and changes in blood flow density and blood oxygen metabolism in glaucoma.

Methods

From February 2016 to October 2019，108 patients（210 eyes） with primary open-angle glaucoma and 110 healthy control subjects（220 eyes）were recruited from Beijing Tongren Hospital affiliated with Capital Medical University.Among them，there were 128 males（252 eyes）and 90 females（178 eyes），with an average age of（55.1±7.5）years old（ranging from 45 to 66 years old）.Optical coherence tomography angiography（OCTA）was used to measure vascular parameters around the optic disc and inner the optic disc.The average thickness of the retinal nerve fiber layer（rNFL）around the optic disc was used to measure by optical coherence tomography（OCT）.the retinal arterial and venous oxygen saturation was used to measure by retinal oximeter.The mean defect（MD）of visual field was to detect using Humphrey visual field analyzer.The Kolmogorov Smirnov statistical method was used to test intraocular pressure，RNFL thickness，visual field MD，parameters of retinal blood vessels and retinal oxygen saturation as normal distribution，and expressed as ±s，and compared by independent sample t test for intergroups，and one-way analysis of variance for multiple groups.The relationship between retinal vascular parameters，retinal oxygen saturation，and the severity of glaucoma were analyzed using Pearson correlation analysis.

Results

Comparing between the glaucoma and the control group，the whole optic disc vascular density，as well as the vascular density inside the optic disc and radial peripapillary capillary（rPC），were（40.5±8.5）%，（42.8±9.5）%，（41.9±9.9）%，（49.6±3.8）%，（50.6±5.6）%，and（51.5±4.4）%，respectively，with statistically significant differences（t＝-2.382，-2.543，-2.074；P＜0.05）.The whole optic disc vascular density of patients with mild，moderate，and severe glaucoma was（47.4±3.8）%，（41.8±5.5）%，and（32.8±6.3）%，respectively，with statistically significant differences between the groups（F＝143.52，P＜0.05）.The whole vascular density of optic disc and the radial peripapillary capillary were positively correlated with the visual field MD of glaucoma，and the correlation was statistically significant（r＝0.784，P＜0.05）.There was positive correlation between the radial peripapillary capillary and visual field MD，and the correlation was statistically significant（r＝0.742，P＜0.05）.RNFL thickness and the optic rim area were positively correlated with the visual field MD of glaucoma，and the correlation was statistically significant（r＝0.625，P＜0.05）.The optic rim area was positively correlated with visual field MD，and the correlation was statistically significant（r＝0.544，P＜0.05）.The mean values of total retinal venous oxygen saturation，the upper retinal venous oxygen saturation，and the lower retinal venous oxygen saturation in the glaucoma group and control group were（62.9±10.4）%，（63.8±11.0）%，（59.7±11.9）%，（57.3±6.5）%，（59.2±7.1）%，and（54.0±8.6）%，respectively，showing statistical significance（t＝3.214，2.942，2.348；P＜0.05）.The mean differences of retinal arterial and venous oxygen saturation in the total，the upper and the lower retina in the glaucoma group and the control group were（30.2±13.1）%，（28.3±12.6）%，（32.4±11.2）%，（34.2±5.4）%，（32.6±7.9）%，and（38.2±8.9）%，respectively.The difference was statistically significant（t＝-2.535，-1.983，-2.164；P＜0.05）.The difference of retinal arterial and venous oxygen saturation in glaucoma was reduced.The retinal artery oxygen saturation in the mild glaucoma group and the severe glaucoma group were（92.0±7.1）% and（91.7±10.2）%，respectively，showing no statistically significant difference（t＝-1.457，P＞0.05）.The average retinal venous oxygen saturation in the mild glaucoma group and the severe glaucoma group were（64.6±10.1）%and（67.9±8.5）%，respectively，with statistically significant difference（t＝2.093，P＜0.05）.The difference of retinal arterial and venous oxygen saturation in the mild glaucoma group and the severe glaucoma group were（27.2±8.1）% and（23.6±6.7）%，respectively，showing statistically significant difference（t＝-2.454，P＜0.05）.Retinal venous oxygen saturation was correlated with cup volume，cup to disc ratio，visual field MD，RNFL thickness，and optic rim area，and the correlation showing statistically significant（r＝0.333，0.317，-0.459，-0.337，-0.319，P＜0.05）.The peripapillary RNFL thickness in the lower retina corresponding to the upper visual field of patients with abnormal lower visual field and normal upper visual field in the glaucoma group and control group were（73.0±8.3）μm and（111.0±6.9）μm，respectively，the difference showing statistically significant（t＝-2.458，P＜0.05）.The inferior macula ganglion cell complex（GCC）values in the glaucoma and control group were（74.0±6.4）μm and（99.0±5.8）μm，respectively，and the difference was statistically significant（t＝-2.094，P＜0.05）.The inferior peripapillary vascular density in the glaucoma group and control group were（41.0±6.2）% and（51.0±4.5）%，respectively，with statistically significant differences（t＝-2.213，P＜0.05）.The inferior retinal venous oxygen saturation in the glaucoma group and control group were（59.0±6.7）% and（54.0±8.6）%，respectively，with statistically significant differences（t＝2.274，P＜0.05）.

Conclusions

Changes in optic disc vascular density detected with OCTA and retinal venous oxygen saturation in glaucoma are correlated with changes of visual field and RNFL thickness measured with OCT.Before glaucomatous optic nerve damage and visual field loss，decreasing in optic disc vascular density and increasing in retinal venous oxygen saturation have been found，indicating decreased metabolism of retinal nerve tissue.Vascular factor is one of the reasons of the progression of glaucomatous opitc nerve damage.

Key words: Optical coherence tomography angiography, Retinal vascular oxygen saturation, Glaucoma, Visual field, Retinal nerve fiber layer