Abstract
Purpose :
Functional assessment of photoreceptors can facilitate the diagnosis and monitoring of degenerative retinal diseases. This pilot study investigates novel methods that use optical coherence tomography (OCT) to objectively measure photoreceptor response to light stimulus. Our approach does not require resolving single cells, therefore enabling reliable and fast surveying of the macula.
Methods :
We built a prototype ultrahigh-resolution spectral-domain OCT with 2.4 µm axial and 12 µm lateral resolution (full-width-half-maximum), respectively. The A-line rate was 250 kHz. Volumetric scans were acquired over a 3mm×1mm area (600×200 A-lines) centered on the fovea every 0.5 seconds. After a pair of baseline scans, a white-light striped visual stimulus of 0.3-s duration was applied to bleach an estimated 4.2% of cone opsins. Three additional volumes were acquired 0.0, 0.5, and 1.0 seconds post-stimulus. Involuntary eye movements between scans were compensated for using sub-pixel image registration. Subsequently, OCT signal changes within the photoreceptor outer segment band were detected and quantified using the split-spectrum amplitude decorrelation algorithm.
Results :
7 eyes from 7 healthy volunteers were imaged to date. Optoretinogram (ORG) signal was detected in all eyes. Maximum ORG contrast was observed ~0.3-0.5 seconds post-stimulus. The en face response map matches the pattern of the light stimulus. The peak signal-to-noise ratio between the stimulated and unstimulated retinal area was 2.8±1.2, limited by flow-projection and motion noise.
Conclusions :
2D ORG map can be achieved without the use of adaptive optics to resolve single photoreceptors. Only 3 scans are needed to cover the center 3mm×3mm macula (<10s total scan time); and a 6mm×6mm area can be covered using automated mosaicking protocol within minutes. Volumetric OCT ORG may provide an objective and quantifiable functional biomarker for photoreceptor damage in age-related macular degeneration and inherited retinal diseases.
This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.