Correlation of Retinal Oxygen Saturation With Retrobulbar Blood Flow With in Patients Primary Open Angle Glaucoma

Abstract

Purpose: : To investigate the correlation of retinal oximetry images with retrobulbar blood flow in patients with primary open–angle glaucoma (POAG).

Methods: : The MultiSpec Patho–Imager^TM is a new non–invasive analysis technique that calculates an index proportional to hemoglobin (Hb) O₂ saturation (SO₂) in retinal structures. Retinal oximetry images were obtained in a randomly chosen study eye in patients (n=14) with POAG. Images contained 605 nm and 586 nm (isosbestic) (±2.5nm) light acquired instantaneously and quantified with a 16–bit scientific digital camera (SBIG ST7E, Santa Barbara Imaging Group, Santa Barbara CA). Camera noise was quantified with a black image, and subtracted from the retinal image. Optical density ratios (ODRs) were calculated by manually placing two perpendicular lines each on a retinal artery and vein pair. Customized automated software (LabView 7.1, National Instruments Corp., Austin, TX) fit 20 evenly spaced cross–sectional lines between the two user–defined lines, and located the minimum (darkest) pixel value within the vessel, and maximum (lightest) pixel value within the adjacent tissue. Optical densities (OD) were calculated as: OD=ln(average light/average dark). OD’s were calculated for arteries and veins at 5nm bandwidth wavelengths centered at 586nm (isosbestic) and 605nm, with the optical density ratio (ODR) defined as OD605/OD586. Immediately following retinal oximetry, color Doppler Imaging (CDI) (Siemens Quantum 2000) was used to evaluate the Peak Systolic Velocity, End Diastolic Velocity, and Resistive Index of the Ophthalmic Artery and Central Retinal Artery.

Results: : CDI ophthalmic artery systolic velocity was significantly correlated with superior venular optical density ratio (p = 0.038, r² = 0.482). Diastolic velocity was weakly correlated with superior arteriolar optical density ratio (p = 0.06, r² = 0.339).

Conclusions: : Higher ophthalmic artery blood flow is associated with higher levels of oxygen saturation in superior retinal arteries and veins. Retinal oximetry images may reveal oxygen delivery to retinal tissues in proportion to the corresponding blood flow.

Keywords: blood supply • imaging/image analysis: clinical • retina