Investigation of blood flow regulation and oxygen saturation of the retinal vessels in primary open-angle glaucoma

Purpose

To examine the supply of oxygen to the retina in primary open-angle glaucoma (POAG).

Methods

Forty-one patients with primary open-angle glaucoma (mean age 64.1?±?12.9 years) and 40 healthy subjects (63.6?±?14.1 years) were included. Fundus images, centered at the optic disc, were taken using the Retinal Vessel Analyzer (RVA). The vessel diameters were calculated as central retinal artery (CRAE) and vein equivalent (CRVE) from diameter measurements in the peripapillary vessels. The oxygen saturation of the arteries and veins was investigated employing a two-wavelengths technique. After the measurement at baseline, the vascular response to flicker light exposure was measured.

Results

In glaucoma patients the mean oxygen saturation of the retinal veins at baseline was higher than in the healthy controls (64.36?±?7.11 vs. 59.78?±?8.47, p?=?0.01), whereas the mean arteriovenous oxygen saturation difference was lower (33.07?±?5.24 vs. 37.53?±?6.95, p?=?0.002). The arterial oxygen saturation as well as the arterial and venous diameters showed no difference between the groups. The increase of the CRVE during flicker light stimulation (3.72?±?3.29 % vs. 5.43?±?4.04, p?=?0.039), as well as the change of the venous oxygen saturation (2.08?±?3.74 % vs. 4.18?±?3.88 %, p?=?0.016) and the arteriovenous saturation difference (?2.1?±?3.31 % vs. ?4.43?±?3.6 %, p?=?0.003) were smaller in POAG patients than in the healthy group.

Conclusions

The reduction in the arteriovenous difference in oxygen saturation in POAG patients might show a decreased oxygen demand of the retina caused by the glaucomatous loss of neuroretinal tissue. The lower extent of the flicker light-induced change of the diameter of retinal veins and the venous oxygen saturation could indicate an impairment of blood flow regulation.     

Comparative study of brain magnetic resonance imagings in normal tension glaucoma,primary open-angle glaucoma,and normal subjects

Purpose : To evaluate and compare the presence and extent of ischemic findings in brain magnetic resonance images (MRI) of patients with normal tension glaucoma (NTG), primary open-angle glaucoma (POAG), and control subjects. Method : Seventeen patients with NTG underwent MRI. Cortical atrophy and cerebral infarcts were graded in a masked fashion by a neuroradiologist and findings were compared with age- and sex-matched POAG patients and controls. Results : In terms of CNS ischemia, patients with NTG showed more pathological findings compared to POAG and controls. The latter two were found to be statistically similar. Also, these findings were not related to age.     

Reproducibility of retinal vessel oxygen saturation measurements in healthy young subjects

Purpose: An adequate oxygenation and perfusion is essential for the function of the inner retina. Recently, several techniques for the measurement of retinal oxygen saturation became available. We set out to evaluate reproducibility of the measurements using a modified Retinal Vessel Analyzer. Methods: A total of 20 healthy female and male subjects aged between 18 and 35 years (22.9 ± 3.9; mean ± SD) were included. The measurement of retinal oxygen saturation with the retinal oximeter employed in this study is based on optical reflectometry using the different absorption characteristics of oxygenated and deoxygenated haemoglobin. The intraclass correlation coefficients and the coefficients of variation (CV) for test–retest, short‐term as well as day‐to‐day measurements were calculated. Results: The intraclass correlation coefficients were between 0.91 and 0.94 for retinal branch arteries and between 0.84 and 0.88 for retinal branch veins. In retinal arteries, we calculated a test–retest CV of 3.24 ± 3.18% for oxygen saturation measurements. In retinal veins, data were slightly less reproducible with a CV of 4.92 ± 3.57%. Short‐term reproducibility of both measurement cycles on each study day was in the same range (CV in retinal arteries: 2.91 ± 2.42% and CV in retinal veins: 4.76 ± 3.14%). The day‐to‐day coefficient of variation was slightly higher (CV in retinal arteries: 3.97 ± 2.87% and CV in retinal veins: 6.18 ± 3.36%). Conclusion: The reproducibility of haemoglobin oxygen saturation measurements using the retinal oximeter is acceptable. Further studies on the validity of the obtained results are, however, required.     

青光眼视网膜血氧饱和度与结构功能损害程度的相关分析

目的比较青光眼与正常人视网膜血氧饱和度的差异,分析青光眼患者中视网膜血氧饱和度与结构功能损害程度的相关性。方法病例对照研究。选取原发性开角型青光眼患者28例（35眼）为青光眼组,记录患者年龄、性别、眼压、血压、杯盘比,并进行中心30°阈值视野检测和光学相干断层扫描（OCT）检测视乳头旁视网膜神经纤维层（RNFL）厚度,并纳入27例（41眼）正常人作为对照组,采用视网膜血氧饱和度分析仪测量青光眼患者和正常人视网膜血管血氧饱和度。2组动静脉血氧饱和度差异比较采用独立样本t检验。采用Pearson或Spearman秩相关分析对青光眼组视网膜血氧饱和度与年龄、眼压、血压、杯盘比、视野平均缺损（MD）、视野指数（VFI）、视乳头旁RNFL厚度进行相关分析。结果青光眼组与正常对照组的视网膜动脉血氧饱和度差异无统计学意义,青光眼组静脉血氧饱和度较对照组高（t=4.017,P＜0.001）,动静脉血氧饱和度差值较小（t=-4.431,P＜0.001）。青光眼组视网膜动脉血氧饱和度、静脉血氧饱和度、动静脉血氧饱和度差值与年龄、眼压、血压均无线性相关性。视网膜动脉血氧饱和度与杯盘比、视野MD、VFI、视乳头旁RNFL厚度等均无线性相关。视网膜静脉血氧饱和度与杯盘比、视野MD值呈正相关（杯盘比：r=0.418,P=0.012;视野MD：r=0.504,P=0.002）,与RNFL厚度、VFI呈负相关（RNFL：r=-0.514,P=0.002;VFI：r=-0.470,P=0.004）。视网膜动静脉血氧饱和度差值与杯盘比、视野MD均呈负相关（杯盘比：r=-0.390,P=0.021;视野MD：r=-0.478,P=0.004）,与VFI、视乳头旁RNFL厚度呈正相关（VFI：r=0.449,P=0.007;RNFL：r=0.385,P=0.022）。结论随着青光眼加重,静脉血氧饱和度增加,动静脉血氧饱和度差值降低。青光眼患者视网膜耗氧量降低可能与视网膜神经组织萎缩有关。     

可疑青光眼患者视野指数与眼底血管变化的关系

目的探讨可疑青光眼者眼底血氧饱和度的基本特征及其与视野指数的关系。方法采用横断面研究设计,对可疑青光眼者及正常对照者应用视网膜血氧饱和度测量仪测量眼底血氧饱和度,同时进行中心30°阈值视野检测;统计分析平均视网膜光敏感度（ MS）、平均视野缺损度（MD）及丢失方差（LV）三个视野指数,以及视网膜血氧饱和度,并进行相关分析。结果可疑青光眼者与正常者MD存在统计学差异（P ＜0．05）;可疑青光眼者平均视网膜动脉血氧饱和度及视网膜鼻下支动脉血氧饱和度与正常者比较存在统计学差异（P ＜0．05）;可疑青光眼者视野检测的MD与NIA存在相关性,（r ＝0．368,P ＝0．045）。结论可疑青光眼者眼底血管可能发生了相应的变化,视网膜血氧饱和度状况与视野指数间存在一定联系。     

Oxygen saturation measurements of the retinal vasculature in treated asymmetrical primary open-angle glaucoma using hyperspectral imaging

Purpose

To determine whether there are differences in retinal vascular oxygen saturation measurements, estimated using a hyperspectral fundus camera, between normal eyes and treated eyes of subjects with asymmetrical primary open-angle glaucoma (POAG).

Methods

A noninvasive hyperspectral fundus camera was used to acquire spectral images of the retina at wavelengths between 556 and 650 nm in 2-nm increments. In total, 14 normal eyes and both eyes of 11 treated POAG subjects were imaged and analyzed using algorithms that use the spectral variation of the optical densities of blood vessels to estimate the oxygen saturation of blood within the retinal vasculature. In the treated POAG group, each of the eyes were categorized, based on the mean deviation of the Humphrey visual-field analyzer result, as either more-advanced or less-advanced, glaucomatous eyes. Unpaired t-tests (two-tailed) with Welch''s correction were used to compare the mean oxygen saturation between the normal subjects and the treated POAG subgroups.

Results

In less-advanced and more-advanced-treated POAG eyes, mean retinal venular oxygen saturations (48.2±21.6% and 42.6±18.8%, respectively) were significantly higher than in normal eyes (27.9±9.9% P=0.03 and 0.01, respectively). Arteriolar oxygen saturation was not significantly different between normal eyes and treated POAG eyes.

Conclusions

The increased oxygen saturation of the retinal venules in advanced-treated POAG eyes may indicate reduced metabolic consumption of oxygen in the inner retinal tissues.     

Study of retinal nerve fiber layer thickness within normal hemivisual field in primary open-angle glaucoma and normal-tension glaucoma

PURPOSE: To determine if nerve fiber layer thickness (NFLT) in glaucoma patients decreases before the development of visual field loss, and if there is a difference in the thinning of NFLT between primary open-angle glaucoma (POAG) and normal-tension glaucoma (NTG) eyes. METHODS: Thirty patients (33 eyes) with POAG and 31 patients (31eyes) with NTG, who had visual field defects localized in either the upper or the lower hemifield verified by Humphrey Field Analyzer (HFA), were measured for NFLT by scanning laser polarimetry (Nerve Fiber Analyzer). Twenty-three normal subjects (23 eyes) matched in refraction and age with the glaucoma patients were recruited as the control group. The total deviation (TD) in each hemifield obtained by HFA and the 180 degrees NFLT of each corresponding hemifield was calculated. Relationships between the TD of the normal or abnormal visual hemifield and the NFLT of the corresponding hemifield were compared among the POAG, NTG, and control groups. RESULTS: The NFLT of the corresponding normal hemifield was decreased both in the POAG group and in the NTG group when compared with the corresponding measurements in control subjects. In POAG eyes, thinning of the NFLT in the corresponding normal hemifield was more remarkable if the TD of the abnormal hemifield was greater, but this tendency was not observed in NTG eyes. CONCLUSION: NFLT is already decreased when the visual field is still normal both in POAG eyes and in NTG eyes. However, the pattern of retinal nerve fiber layer damage in POAG may differ from that in NTG.     

Retinal vessel oxygen saturation in healthy subjects and early branch retinal vein occlusion

AIM: To measure the retinal oxygen saturation in healthy subjects and early branch retinal vein occlusion (BRVO) in Chinese population. METHODS: The retinal vessel oxygen saturation of the healthy subjects and BRVO patients were measured by a noninvasive retinal oximeter (Oxymap ehf., Reykjavik, Iceland). RESULTS: The study included 22 patients with unilateral BRVO (mean age: 55.1±8.8y) in the study group and 91 healthy participants (mean age: 37.5±14.0y) in the control group. In the healthy individuals, mean arterial and venous oxygen saturation were significantly (P<0.001) higher in the superior nasal quadrant (98.5%±10.1% and 57.3%±8.7%, respectively) than in the inferior nasal quadrant (94.2%±9.0% and 54.1%±9.6%, respectively), followed by the superior temporal quadrant (89.1%±10.1% and 51.9%±8.9%, respectively) and the inferior temporal quadrant (86.4%±9.4% and 46.6%±9.6%, respectively). In patients with ischemic BRVO, arterial oxymetric values were significantly higher and venous measurements significantly lower for the affected vessel (107.5%±9.7% and 46.4%±14.2%, respectively) than the unaffected vessel in the same eye (99.2%±12.2% and 55.5%±7.9%, respectively) and as compared to the vessel in the unaffected fellow eye (93.1%±6.9% and 55.7%±6.8%) (P=0.005 and P=0.02, respectively). In the patients with non-ischemic BRVO, mean venous oxygen saturation was lower in the affected vein (39.8%±12.2%) than in the unaffected vessels of the same eye (50.8%±10.5%) and in the fellow eye (58.21%±5.7%) (P=0.03). Mean arterial oxygen saturation did not differ significantly (P=0.42) between all three groups. CONCLUSION: In patients with BRVO, the venous oxygen saturation in the affected vessels is decreased potentially due to decreased blood velocity and flow. Interestingly, the arterial oxygen saturation in eyes with ischemic BRVO is increased in the affected arteries.     

Investigations on the measurement of oxygen saturation in retinal vessels using polarized light

The accuracy of the spectrometric measurement of the oxygen saturation in retinal vessels is limited by its signal-to-noise ratio. The aim of this study was to investigate the possibility of enhancement of the reflection signal by the use of polarized light. MATERIALS AND METHODS: The Jena ophthalmospectrometer was equipped with two polarizing filters: one in the illumination and the other in front of the detector. Reflection spectra of erythrocytes streaming through a cuvette in the focus of an artificial eye were recorded. The influence of the polarization on the reflection spectra was investigated by rotating the polarizer in front of the detector. Furthermore, the degree of polarization of the light reflected from retinal vessels in vivo was determined. RESULTS: The degree of polarization of the light reflected from the erythrocytes was 0.6-0.8, whereas the polarization of light reflected by a standard white reflectance target was virtually zero. CONCLUSION: Polarized light can be used for the reduction of error in retinal vessel oximetry.     

原发性开角型青光眼患者及正常人的眼压日内波动趋势

目的研究原发性开角型青光眼（POAG）、正常眼压性青光眼（NTG）患者及正常人双眼眼压昼夜波动趋势及其眼压峰值出现的规律，比较双眼眼压波动趋势是否一致。设计前瞻性病例系列。研究对象POAG、NTG患者及正常对照各30例。方法用Goldmann压平眼压计测量眼压日曲线，比较双眼的日眼压波动模式及眼压峰值分布。主要指标眼压测量值。结果眼压峰值出现于非办公时段的正常人为右眼6．7％、左眼10．0％；NTG患者为右眼20．0％、左眼23．3％；POAG患者为右眼23．3％、左眼20.0％。结论POAG、NTG患者和正常人有着不同的眼压昼夜波动模式，且双眼的波动趋势不尽相同，不能完全将双眼等同看待；部分观察对象的峰值眼压分布于非办公时段，办公时段多次眼压测量不能完全代替一日眼压监测。（眼科，2007,16：33．36）     

Gonioscopic differences between primary open-angle glaucoma and normal subjects over 40 years of age.

Gonioscopy was performed on 110 patients with primary open-angle glaucoma over 40 years of age and an equal number of normal sugjects, matched by race and age. The frequency distribution of various angle features differed in the two groups: in the glaucoma group, there were more iris processes at all levels of insertion, a higher insertion of the iris root and more trabecular pigmentation. A congenital angle anomaly is one important factor in the pathogenesis of the elevated pressure.