Detection And Intervention Of Impaired Oxygen Consumption In Patients With Primary Open-angle Glaucoma

Part 1Retinal and Choroidal Oxygen Saturation of Optic Nerve Head in Open-angle Glaucoma Subjects by Multispectral ImagingObjective:To determine whether there are differences in supply of oxygen to the optic nerve head(ONH)from retinal and choroidal vascular layers in patients with primary open-angle glaucoma(POAG)using the method of multispectral imaging(MSI).Design:Observational,cross-sectional study.Methods:Multispectral images of the fundus were acquired on 38 eyes of 19 patients with POAG,and 42 healthy eyes of 21 matched volunteers with Annidis’ RHA multispectral digital ophthalmoscopy.The superficial and deeper oxygen saturation levels of optic disc were represented by the average gray value of ONH of retinal and choroidal oxy-deoxy maps respectively.Statistical analysis was performed to detect the differences of ONH oxygen saturation between the two groups.With glaucoma patients,the ONH oxygen saturation levels with severe glaucoma were compared to those of fellow eyes.The same test was used to compare oxygen saturation of right eyes with left eyes of normal subjects.Linear correlation analysis was performed to assess the possible association of ONH oxygen saturation with ocular parameters in glaucoma individuals and control subjects respectively.Results:(1)No statistical difference was found in retinal and choroidal oxygen saturation of ONH when all glaucoma patients were compared with healthy individuals(all p>0.05).(2)In glaucoma patients,the mean ONH oxygen saturation in retinal oxy-deoxy map was lower in eyes with worse visual fields than in those with good visual fields(t = 4.009,p =0.001),while there was no significant difference in choroidal oxy-deoxy map(t =-1.029,p = 0.317).In healthy control subjects,there was no significant difference between both eyes.(3)In patients with POAG,retinal oxygen saturantion of ONH showed significant dependence on the MD and RNFLT(r = 0.511,0.504,p = 0.001,0.001,respectively),whereas the choroid vasculature oxygen saturation was only inversely related to RNFLT(r=-0.391,p=0.015).(4)An age dependence of retinal oxygen saturation of ONH was found in both POAG and healthy group(r = 0.473,0.410,p = 0.003,0.007,respectively).Conclusion:MSI revealed a significant correlation between functional as well as structural damages in glaucoma and ONH oxygen saturation on retinal oxy-deoxy map.Using MSI might allow early objective assessments of perfusion impairments of glaucomatous ONH.Part 2Investigation of Oxygen Saturation of Retinal Vessels in Primary Open-angle GlaucomaObjective:To determine whether retinal vessel oxygen saturation is affected in patients with primary open-angle glaucoma(POAG)and to evaluate the relationship between oxygen saturation and retinal nerve fibre layer thickness(RNFLT)and mean deviation of visual field defect(MD)in patients with POAG.Design:Observational,cross-sectional study.Methods:Thirty-one patients with POAG and 32 matched healthy subjects were included.The oxygen saturation and diameters of retinal arteries and veins were measured using a spectrophotometric retinal oximeter(Oxymap T1).Retinal arterial(SaO2)and venous(SvO2)oxygen saturation were evaluated according to the difference of the extinction spectra of haemoglobin and oxyhaemoglobin(577 nm and 600 nm).The arterio-venous difference(AVD)was calculated by(SaO2-SvO2).Statistical analysis was performed to detect the differences of SaO2,SvO2,and AVD between the two groups.Linear correlation analysis was performed to assess the possible association of retinal oxygen saturation with RNFLT and MD in subjects with POAG.Results:Compared with healthy volunteers,the arterio-venous difference in oxygen saturation was significantly lower in patients(t = 2.128,p = 0.039).But there was no significant difference in arterial and venous oxygen saturation between the two groups(t = 0.296,-1.904,p = 0.768,0.063).In patients with POAG,the retinal venous oxygen saturation was inversely related to MD and RNFLT(r =-0.646,-0.772,p = 0.000,0.000),whereas the arterio-venous difference in oxygen saturation showed significant dependence on MD and RNFLT(r = 0.572,0.749,p = 0.001,0.000).No correlation was found between retinal arterial oxygen saturation and MD,RNFLT,or either of parameters(all p>0.05).Conclusion:Glaucomatous damage is associated with increased retinal venous oxygen saturation and decreased arterio-venous difference in oxygen saturation.These data suggest that in eyes with POAG,reduced retinal oxygen consumption is consistent with tissue loss.Part 3Effect of Electrical Fastigial Nucleus Stimulation on Retinal Vessel Oxygen Saturation and Diameter in Primary Open-angle GlaucomaPurpose:To determine how electrical fastigial nucleus stimulation(FNS)affects the supply of oxygen to the retina in primary open-angle glaucoma(POAG).Methods:Twenty-four patients with POAG and 26 matched healthy volunteers were included.Both patients and volunteers received 30 minutes of FNS.Oxygen saturation and the diameters of one major temporal artery and vein were measured using a spectrophotometric retinal oximeter(Oxymap T1).Oximetry was performed at baseline and after stimulation.Retinal arterial(SaO2)and venous(SvO2)oxygen saturation were evaluated according to the difference of the extinction spectra of haemoglobin and oxyhaemoglobin.The arterio-venous difference(AVD)was calculated by(SaO2-SvO2).Statistical analysis was performed to investigate the difference in reaction to FNS between the two groups.Results:A significant increase in oxygen saturation caused by FNS was only found in the retinal artery of patients with POAG(t =-2.484,p = 0.021).Further,stimulation induced both arterial and venous vasodilation in patients with POAG(t ＝-2.330,-2,113,p =0.029,0.046,respectively).In healthy controls,there was no FNS-induced change in oxygen saturation(all p>0.05)and significant vasodilation induced by FNS only occurred in the retina veins(t ＝-2.629,p = 0.014).Conclusion:FNS induces an increase in retinal blood flow and retinal oxygen saturation in patients with POAG.It may offer a new approach to providing neuroprotection in patients with POAG or other ischemic optic neuropathy.