title: Inter-eye comparison of retinal oximetry and vessel caliber between eyes with asymmetrical glaucoma severity in different glaucoma subtypes.
abstract: BACKGROUND
  To compare retinal vessel oxygenation and vessel caliber in primary angle-closure glaucoma (PACG), primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), and normal controls, as well as between eyes of asymmetrical glaucoma severity.
  
  
  METHODS
  This was a prospective, cross-sectional study. The 159 subjects (PACG, n=39; POAG, n=41; NTG, n=41; normal controls, n=38) underwent retinal oxygen saturation measurements using the Oxymap T1 Retinal Oximeter, optical coherence tomography, and Humphrey visual field testing. Retinal oxygen saturation and vessel diameter were compared between the glaucoma groups and normal controls, as well as between eyes of asymmetrical glaucoma severity. Kruskal-Wallis test was performed for comparison among different subtypes of glaucoma. Wilcoxon signed-rank test was used to compare the inter-eye differences.
  
  
  RESULTS
  Compared to normal controls, arteriolar oxygen saturation was increased in PACG eyes (P=0.048) but not in POAG or NTG eyes. There were no significant differences in oxygen saturation in venules or arteriovenous (AV) difference in all three glaucoma groups. Venular diameter was significantly reduced in all glaucoma groups compared to normal controls (P<0.001), but no such change was observed in arteriolar diameter (P=0.10). When comparing between eyes of asymmetrical glaucoma severity, arteriolar oxygen saturation (P=0.03) and AV difference (P=0.04) were significantly higher, while arteriolar diameter was significantly lower (P=0.001) in the worse eye in PACG group. There were no significant differences in oximetric parameters or vessel calibers between the worse and the better eyes in POAG and NTG groups.
  
  
  CONCLUSIONS
  Eyes with PACG showed increased arteriolar oxygen saturation and increased AV difference. This was not observed in POAG and NTG eyes. Arteriolar diameter in PACG and venular diameter in all three glaucoma groups were reduced. The difference observed in PACG eyes may be due to an increased metabolic demand in the disease process compared to open-angle glaucoma.
authors.affiliation: Department of Ophthalmology, Tan Tock Seng Hospital; Department of Ophthalmology, Singapore National Eye Centre.
authors.forename: Clarissa Shu Ming
authors.initials: CS
authors.lastname: Cheng
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre.
authors.forename: Yi Fang
authors.initials: YF
authors.lastname: Lee
authors.affiliation: Yong Loo Lin School of Medicine, National University of Singapore.
authors.forename: Charles
authors.initials: C
authors.lastname: Ong
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre.
authors.forename: Zhu Li
authors.initials: ZL
authors.lastname: Yap
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre.
authors.forename: Andrew
authors.initials: A
authors.lastname: Tsai
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre.
authors.forename: Aditi
authors.initials: A
authors.lastname: Mohla
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Monisha E
authors.initials: ME
authors.lastname: Nongpiur
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre; Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.affiliation: Department of Ophthalmology, Singapore National Eye Centre; Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Shamira A
authors.initials: SA
authors.lastname: Perera
keywords: glaucoma; imaging; oximetry; retinal vessels