June 2023
Volume 64, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2023
Exploring multispectral photorefraction to measure fundal blood pulsation and oxygenation
Author Affiliations & Notes
  • Frank Schaeffel
    Institute of Molecular and Clinical Ophthalmology Basel, Basel, Basel-Stadt, Switzerland
    Section of Neurobiology of the Eye, Ophthalmic Research Institute, Tuebingen, Germany
  • Barbara Swiatczak
    Institute of Molecular and Clinical Ophthalmology Basel, Basel, Basel-Stadt, Switzerland
  • Footnotes
    Commercial Relationships   Frank Schaeffel Zeiss Vision Lab Tuebingen, Code C (Consultant/Contractor); Barbara Swiatczak None
  • Footnotes
    Support  Institute of molecular and clinical ophthalmology Basel (IOB)
Investigative Ophthalmology & Visual Science June 2023, Vol.64, 4161. doi:
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      Frank Schaeffel, Barbara Swiatczak; Exploring multispectral photorefraction to measure fundal blood pulsation and oxygenation. Invest. Ophthalmol. Vis. Sci. 2023;64(8):4161.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Choroidal thickness and choroidal blood flow increase in emmetropic, but not myopic subjects when they are myopically defocused, suggesting that the emmetropic retina can generate eye growth inhibiting signals. To provide a rapid and non-invasive assessment of changes in fundal blood oxygenation, the potential of measuring multispectral fundal reflectance by photorefraction was explored.

Methods : Brightness of the pupil during photorefraction depends on the wavelength of light, reflectivity of the fundus, and pupil size. Fundal reflectivity may vary with changes in blood oxygenation. We used a multispectral camera (MSC2-BIO-1-A, Spectral Devices Inc., Ontario, Canada), a f/1.4, 85mm lens (Carl Zeiss, Jena) and a custom-built retinoscope with broadband IR-LEDs (830+50nm), at 48 cm distance from the eye to illuminate the pupil from behind. Since light absorption of oxyhemoglobin increases at 865 nm but remains stable at 800 nm, the difference in pupil brightness between both wavelengths was recorded over time by custom developed software under Visual C++.

Results : Despite single pixel noise of about 1 percent, the pulsation signal (amplitude 0.2-0.5 pixels) was nicely recordable on skin at a distance of 48 cm, when 400 pixels in a rectangular area of 20x20 pixels (equivalent to 3.28x3.28 mm, smaller than the pupil) were averaged. Measurements through the pupil were more challenging because pupil brightness (in pixel values) was strongly correlated with pupil area (brightness = 0.0374*area (number of pixels) + 41.612, R=0.96) and small fluctuations in pupil area had a large effects on the strength of the signal at 800 and 865 nm: a change in pupil area by about 10 pixels caused a change in pupil brightness of a similar magnitude as the blood pulsation signal. Therefore, pupil size needed to be tracked with a resolution of 0.32 percent (about 0.02 mm at 6 mm), to correct the pulsation signal for pupil size fluctuations. Nevertheless, a pulsation signal of similar amplitude as on skin could be recorded in two young subjects in the optic disc, at pupil sizes of 6.1-6.5 mm. No pulsation signal was measured in the fovea.

Conclusions : Preliminary data suggest that multispectral photorefraction may provide a fast and non-invasive way to measure blood oxygenation in the optic disc from a distance.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

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