Abstract
Purpose :
Major clinical signs of glaucoma still require a large amount of retinal ganglion cell death to occur before they can be detected. To this end, novel outcome measures are needed. We have developed an advanced imaging instrument based on adaptive optics optical coherence tomography (AO-OCT) that can measure and track intrinsic optical properties of retinal cells and tissues in the living eye. Here we test the feasibility of measuring reflectance and retardance at the cellular scale using the new instrument.
Methods :
We used a polarization diversity detection channel with two high-speed spectrometers (Cobra-S, Wasatch), simultaneously acquiring orthogonal components of the AO-OCT spectral interferogram at a speed of 250 kHz, to measure both reflectance and retardance in the living retina. The axial resolution was 4.7 µm in tissue with a superluminescent laser diode (λ = 790 +/-45 nm; Superlum). In the sample arm, we used a large-stroke deformable mirror (DM97-15; ALPAO) and a custom-made CMOS wavefront sensor (Emergent Vision) to correct monochromatic aberrations across a 7 mm pupil and achieve 2.3 µm lateral resolution. We deployed off-axis reflective relay telescopes where we minimized both the off-axis aberrations (astigmatism and coma) and the coating-induced polarization aberrations without tilting any active optical components under the constraint that the angle of incidence is less than 6°. The optical power delivered to the eye was 420 µW. The incident beam was circularly polarized at an axis ratio of 0.99. The measured diattenuation was less than 0.01, negligible in our retardance measurement. To test, we captured a series of 4-second retinal videos of a normal and healthy subject.
Results :
More than 100 reconstructed AO-OCT volume images were acquired, successfully registered to a global coordinate system, and averaged to improve the quality by correcting significant eye motion artifacts many times larger than the microstructure that determines intrinsic optical properties. Rich structural information provided by the AO-OCT machine, combined with the eye motion correction algorithm, enables us to track changes in intrinsic optical properties at the cellular scale.
Conclusions :
We demonstrated in vivo measurements of reflectance and retardance at the cellular scale using a multifunctional AO-OCT device.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.