Venous oxygen saturation is reduced and variable in central retinal vein occlusion

Abstract

Dear Editor;We thank Gokce et al. for their comments on our article about reduced and variable venous oxygen saturation in central retinal vein occlusion (CRVO) [1]. They suggest that environmental chronic cold exposure of our subjects, which is not mentioned in the study, might have affected the results by modifying hematologic and cardiovascular risk factors for CRVO.We would be careful of making any assumptions about the impact of climate on hematological and cardiovascular risk factors in our study population. In Iceland, the average winter temperature is about 0°C (32°F), and during the months when the study was performed, the average temperature was 5°C (ranging from 0 to 12.7°C). Plenteous geothermal natural resources provide relatively inexpensive space heating, which is abundantly used by the nation, and indoor temperatures are 20-25°C. The oximetry measurements were made in this temperature range.To the best of our knowledge, there is no evidence that links cold exposure to the pathogenesis and prevalence of CRVO, and we do not consider our study subjects susceptible to cold temperature eye injury. Intraocular temperature has been related to the core temperature of the body [2]. Both in vitro and in vivo experiments at an ambient air temperature of −40°C indicate the role of corneal tissue in limiting heat conductivity between the corneal surface and intraocular environment, thus providing a stable temperature of about +37°C in the anterior chamber compared with +24.3°C on the corneal surface [2].In our study, we used comparable images of the fellow unaffected eye of the same patient, which is exposed to the same temperature and risk factors, to measure oxygen saturation in retinal arterioles and venules for comparative statistical analysis. We think the most likely reason for the marked reduction in venular oxygen saturation in CRVO eyes (p<0.0001, paired t-test) is stagnation of blood due to the venous occlusion. We also suggest that the apparent variability in retinal venous oxygen saturation in CRVO eyes (both within each eye and between eyes) reflects individual differences in the severity of the venous obstruction [3], which may partly be explained by the various compensatory mechanisms against the venous occlusion. Conflict of interest

Retinal Oxygen Saturation Correlates With Visual Acuity but Does Not Predict Outcome After Anti-VEGF Treatment in Central Retinal Vein Occlusion

“…7,8 However, the study also extends these studies by verifying a higher oxygen saturation in retinal arterioles, which was suggested in a previous study but could not be confirmed due to lack of statistical power. 9 The results are also in agreement with findings of increased arterial oxygen saturation in patients with peripheral retinal ischemia secondary to proliferative diabetic retinopathy 14 that correlates with the severity of peripheral retinal ischemia.…”

“…5 Retinal ischemia leads to hypoxia in the larger retinal vessels, which can be measured quantitatively by oximetry based on fundus photographs obtained at two different wavelengths. 6 Previous studies have confirmed that the oxygen saturation is reduced in the larger retinal venules in patients with CRVO, 7,8 and that the oxygen saturation improves after treatment of the disease with anti-VEGF medication. 9 However, the relation between visual acuity and retinal oxygen saturation and the predictive value of retinal oxygen saturation for visual outcome in patients with CRVO have not been studied in detail.…”

“…In the eyes affected by CRVO the variation in the oxygen saturation was much higher in retinal venules than in arterioles which confirms the results of a previous study. 8 This may indicate that the venous oxygen saturation is related to the individual factors, such as the severity of ischemia and hypoxia in the retinal area affected by the occlusion, 17 whereas the arterial oxygen saturation is a more unspecific response to the presence of a venous occlusion as such. An investigation of this issue should be the subject of a future study.…”

Radial Peripapillary Capillary Network Visualized Using Wide-Field Montage Optical Coherence Tomography Angiography

“…19,20 Therefore, the CFZs beside the first branches may be narrower in order to oxygenate the adjacent retinal tissues. Because changes in the retinal oxygen saturation in retinal vascular disorders have been reported, [21][22][23][24] the CFZs may change. Further studies are needed to elucidate the features of the CFZs.…”

Comment on Eliasdottir et al., Venous oxygen saturation is reduced and variable in central retinal vein occlusion

“…We read with great interest the study by Eliasdottir et al describing reduced venous oxygen saturation in central retinal vein occlusion (CRVO) [1]. The authors proved that oxygen saturation in the retinal venules of eyes with CRVO is significantly reduced.…”