Spectroscopic oximetry in the eye: a review

Abstract

Introduction: Non-invasive measurement of blood oxygen saturation via spectroscopic imaging has facilitated insights into the development and progression of a variety of ocular conditions, including retinal vascular occlusion, diabetic retinopathy and glaucoma. Major developments since the late 90s have been enabled by advancements in imaging technology, computational image analysis, and experimental methods. Areas covered: We review the theory of spectroscopic oximetry, the ocular blood vessels targeted for oximetry, imaging systems used for oximetry, and oximetry validation methods. Important physiological and clinical insights provided by oximetry in the eye are detailed. Expert commentary: Oximetry has revealed physiological norms and auto-regulatory effects in the retina, choroid, episcleral, and bulbar conjunctival blood vessels. Retinal oximetry has provided crucial insight into the development of diabetic retinopathy and glaucoma, and has enhanced the evaluation and treatment of retinal vessel occlusion. Commercially available retinal oximetry systems have enabled oximetry in the clinic. The development more sophisticated phantoms that resemble in vivo environments has oximetry validation in diverse oximetry applications. New insights into ocular physiology and disease are likely to be gleaned from future studies.

Oximetry using multispectral imaging: theory and application

“…MSI oximetry can be applied with various imaging techniques to image blood vessels in different bodily tissues. For example, MSI retinal fundus cameras are utilized for measuring blood oxygen in the eye [6], and MSI microscopes can be used to measure oxygen within individual red blood cells (RBCs) [5]. Emerging imaging modalities such as photoacoustic tomography (PAT) and spectroscopic optical coherence tomography (S-OCT) have also been utilized to provide enhanced oximetry imaging capabilities: PAT enables oximetry in deep tissue, and S-OCT provides simultaneous 3D mapping of both tissue and OS (see section 6).…”

“…MSI oximetry has been applied to diverse applications in vivo, including measurement of blood OS in the spinal cord [7], the brain [8], muscle tendons [9,10], the bowel [11], the oral microvasculature [12], and the skin [13]. In the eye, MSI oximetry has established the oxygen dynamics and physiological norms of the retina [6], the choroid [14], the bulbar conjunctiva [15], and the episcleral blood vessels [15].…”

“…Various diseases have been studied with MSI oximetry, including diabetic retinopathy [16,17], glaucoma [18][19][20], retinal vessel occlusion [2,6], stroke [8], rheumatoid arthritis [10], diabetic foot ulcers [13,21], and cancerous tumour development [3,22]. For the full applications of oximetry to the monitoring of retinal disease, readers are referred to recent reviews [6,23,24].…”

“…Photoacoustic techniques have enabled deep-tissue oximetry of the brain, cancer tumours, and entire small animals [41], and S-OCT has enabled complimentary 3D mapping of OS and tissue structure [42]. Across all MSI modalities, advancement and application of MSI oximetry technology has yielded considerable insights into physiological norms and disease development [6]. Section 6 provides further details on the applications and optical principles underpinning these emerging MSI modalities.…”

Automation improves repeatability of retinal oximetry measurements

“…Changes in retinal vessel oxygen saturation have been found in diabetic retinopathy, glaucoma, age-related macular degeneration, and other common diseases affecting the retina [5][6][7][8] as well as systemic and brain disease [9]. Measurements of retinal vessel oxygen saturation were first attempted in 1959 [10], and several groups have experimented with different approaches since then (for review, see [11][12][13][14]).…”