Preliminary investigation of multispectral retinal tissue oximetry mapping using a hyperspectral retinal camera.

Oximetry measurement of principal retinal vessels represents a first step towards understanding retinal metabolism, but the technique could be significantly enhanced by spectral imaging of the fundus outside of main vessels. In this study, a recently developed Hyperspectral Retinal Camera was used to measure relative oximetric (SatO2) and total hemoglobin (HbT) maps of the retina, outside of large vessels, in healthy volunteers at baseline (N = 7) and during systemic hypoxia (N = 11), as well as in patients with glaucoma (N = 2). Images of the retina, on a field of view of ∼30°, were acquired between 500 and 600 nm with 2 and 5 nm steps, in under 3 s. The reflectance spectrum from each pixel was fitted to a model having oxy- and deoxyhemoglobin as the main absorbers and scattering modeled by a power law, yielding estimates of relative SatO2 and HbT over the fundus. Average optic nerve head (ONH) saturation over 8 eyes was 68 ± 5%. During systemic hypoxia, mean ONH saturation decreased by 12.5% on average. Upon further development and validation, the relative SatO2 and HbT maps of microvasculature obtained with this imaging system could ultimately contribute to the diagnostic and management of diseases affecting the ONH and retina.

Change in vision after retinal pigment epithelium tear following the use of anti-VEGF therapy for age-related macular degeneration.

PURPOSE: We investigated visual acuity outcomes and their associations in the setting of retinal pigment epithelium tear (RPET) following the use of anti-vascular endothelial growth factor (anti-VEGF) agents. METHODS: This retrospective review included all patients treated for neovascular age-related macular degeneration (AMD) with an anti-VEGF agent who subsequently developed an RPET. All patients who developed an RPET were identified and outcome measures data were recorded and analysed. The main outcome measures were best corrected visual acuity (BCVA) and spectral domain optical coherence tomography characteristics. RESULTS: Among the 14 participants identified, a subfoveal RPET was associated with the loss of one or more lines of vision from baseline (p = 0.03). There was no association between the size of the RPET and BCVA at the time of the RPET or final BCVA. The development of a disciform scar was associated both with a BCVA at the time of the RPET of < 6/24 (p = 0.02) and a final BCVA of < 6/24 (p = 0.02). Ongoing treatment with an anti-VEGF agent following an RPET saw five patients (35.7 %) have an improvement in their BCVA and all patients maintained their BCVA following the RPET with ongoing anti-VEGF treatment. CONCLUSIONS: Visual decline following an RPET is associated with subfoveal location of the RPET (p = 0.03) and later development of a disciform scar. These data also suggest that the ongoing use of an anti-VEGF agent may stabilise vision in some patients following an RPET and for some patients there may be an improvement in visual acuity despite the RPET, depending on its location.

Retinal perfusion changes in radiation retinopathy.

PURPOSE: To investigate retinal blood flow and oxygen saturation changes in patients diagnosed with retinopathy following plaque radiation treatment to treat choroidal melanoma. METHODS: Eight patients (mean age 55.75 years, SD 12.58 years) who have developed unilateral ischaemic radiation-related retinopathy as confirmed by wide-field fluorescein angiography were recruited for the study. The fellow eye with no other ocular or retinal pathology was used as control. Both eyes underwent measurement of total retinal blood flow (TRBF) and retinal blood oxygen saturation using prototype methodologies of Doppler Spectral Domain Optical Coherence Tomography (OCT) and Hyperspectral Retinal Camera, respectively. RESULTS: The average TRBF in the retinopathy eye was significantly lower compared to the fellow eye (33.48 ± 12.73 µl/min versus 50.37 ± 15.26 µl/min; p = 0.013). The arteriolar oxygen saturation (SaO2 ) and venular oxygen saturation (SvO2 ) were higher in the retinopathy eye compared to the fellow eye (101.11 ± 4.26%, versus 94.45 ± 5.79%; p = 0.008) and (62.96 ± 11.05% versus 51.24 ± 6.88%, p = 0.051), respectively. CONCLUSION: The ionizing radiation seems to have an impact on the TRBF, SaO2 and SvO2 , clinically presenting similar to a rapidly developing diabetic retinopathy. The results show an altered retinal vascular physiology in patients with radiation-related retinopathy.

Intervisit Repeatability of Retinal Blood Oximetry and Total Retinal Blood Flow Under Varying Systemic Blood Gas Oxygen Saturations.

PURPOSE: The aim of the study is to validate and calibrate the Doppler spectral-domain optical coherence tomography (SD-OCT) derived total retinal blood flow (TRBF) and metabolic hyperspectral retinal camera (MHRC) derived oxygen saturation (SO2) of major retinal vessels in human volunteers using a novel and exact provocation technique (RespirAct) that allows the precise control of the end-tidal partial pressure of oxygen (PETO2). Between visit repeatability of the TRBF and retinal blood SO2 also were studied. METHODS: One eye of 11 young healthy subjects was chosen randomly for the study. Total retinal blood flow and retinal SO2 measurements were obtained under conditions of normoxia, hyperoxia, and hypoxia. The order of hyperoxia and hypoxia was randomized between subjects. The measurements were repeated after a week interval. RESULTS: When the arterial PETO2 was increased from baseline (PETO2 = 100 mm Hg) to 200 and 300 mm Hg, the TRBF significantly reduced (P = 0.02) from 44.60 (±8.9) to 40.28 (±8.9) and 36.23 (±4.6) µL/min. Lowering the arterial PETO2, from baseline to 80, 60, and 50 mm Hg, TRBF significantly increased (P = 0.04) from 43.17 (±12.7) to 45.19 (±5.5), 49.71 (±13.4), and 52.89 (±10.9) µL/min with simultaneous reduction in the arterial blood SO2 content from 99.3% (±5.8) to 95.6% (±5.1), 89.6% (±2.8), and 83.3% (±3.9), respectively (P = 0.00). The coefficient of repeatability (COR) of TRBF, retinal arterial, and venous blood SO2 values are 21.8 µL/min, 18.4%, and 15.2%, respectively. CONCLUSIONS: Total retinal blood flow and retinal blood SO2 measurements performed under safe levels of hypoxia and hyperoxia were repeatable in healthy adults over the range of SO2 investigated.

Cerebral oxygen saturation: graded response to carbon dioxide with isoxia and graded response to oxygen with isocapnia.

BACKGROUND: Monitoring cerebral saturation is increasingly seen as an aid to management of patients in the operating room and in neurocritical care. How best to manipulate cerebral saturation is not fully known. We examined cerebral saturation with graded changes in carbon dioxide tension while isoxic and with graded changes in oxygen tension while isocapnic. METHODOLOGY/PRINCIPAL FINDINGS: The study was approved by the Research Ethics Board of the University Health Network at the University of Toronto. Thirteen studies were undertaken in healthy adults with cerebral oximetry by near infrared spectroscopy. End-tidal gas concentrations were manipulated using a model-based prospective end-tidal targeting device. End-tidal carbon dioxide was altered ±15 mmHg from baseline in 5 mmHg increments with isoxia (clamped at 110±4 mmHg). End-tidal oxygen was changed to 300, 400, 500, 80, 60 and 50 mmHg under isocapnia (37±2 mmHg). Twelve studies were completed. The end-tidal carbon dioxide versus cerebral saturation fit a linear relationship (R(2) = 0.92±0.06). The end-tidal oxygen versus cerebral saturation followed log-linear behaviour and best fit a hyperbolic relationship (R(2) = 0.85±0.10). Cerebral saturation was maximized in isoxia at end-tidal carbon dioxide of baseline +15 mmHg (77±3 percent). Cerebral saturation was minimal in isocapnia at an end-tidal oxygen tension of 50 mmHg (61±3 percent). The cerebral saturation during normoxic hypocapnia was equivalent to normocapnic hypoxia of 60 mmHg. CONCLUSIONS/SIGNIFICANCE: Hypocapnia reduces cerebral saturation to an extent equivalent to moderate hypoxia.