Extraneous factors affecting retinal oximetry

Purpose To identify extraneous factors that can impact the outcome of retinal oximetry calculations and to discuss how these factors might be negated. Methods 1. Empiric observation of extraneous factors suspected to impact the outcome of retinal oximetry. 2. Controlled studies of established and suspected extraneous factors. Results 1. The repeatability of a manual oximetry technique was found to be good. The standard deviations of Optical Density (OD) values ranged from 0.01 to 0.06 OD units and from 0.01 to 0.07 OD units for first degree arterioles and venules, respectively. The Co‐efficient of Repeatability (CoR) ranged from 0.02 to 0.11 OD units (relative to a mean OD of 0.15 [0.06‐0.23] OD units) for arterioles and 0.03 to 0.14 OD units (relative to a mean OD of 0.25 [0.17‐0.31] OD units) for venules. Good reliability (p<0.001) was found for arterioles and venules. 2. Dual ratiometric calculations of retinal oxygen saturation (SO2) demonstrated a significant decrease of arterial SO2 during hypoxia. 3. The order of acquisition of spectral images did not influence the outcome of retinal oximetry results. 4. The manual calculation of SO2 values from reflectance data was significantly influenced by the selected retinal locations within and either side of a given retinal vessel. Other extraneous factors included: 5. Variation in retinal pigmentation; 6. Density of retinal pigmentation); 7. Instrument flash intensity; 8. Lenticular irregularities; 9. Tear film irregularities. Conclusion Although the assessment of retinal SO2 in ocular diseases would seem to be of clinical value, a number of extraneous factors must first be taken into account to avoid erroneous conclusions.Commercial interest