Abstract
Purpose :
To increase light capture efficiency of photons returning from the eye in high-speed confocal line-scanning laser ophthalmoscopes (LSLO). LSLOs are often used to achieve high-speed imaging for ophthalmic applications where capturing high speed events is desirable such as retinal blood flow, or to avoid motion artifacts such as ocular pulse related movements within the iridocorneal angle (ICA). For high speed imaging the light-capture efficiency is crucial to maintain the signal-to-noise ratio while minimizing tissue light exposure. These systems generally used beam splitters or split-pupil approaches, and either requires an optical power tradeoff between the illumination and detection beams, wasting a large percentage of light, or sacrificing resolution.
Methods :
This system was designed using Zemax™ Optic Studio to image both the ICA of the eye using a specialized gonioscopic lens, and the retina. Light for the LSLO (λ=800nm) is coupled into the system by focusing light on a 20µm elliptical reflector custom deposited on an optically flat glass plate located at a conjugate pupil plane. A cylindrical lens focuses the beam into a line, relayed to a galvanometer mirror, and sequentially, to the eye creating a 900×2µm (2.5°) line at the image plane. Light returning from the eye is first de-scanned and then focused to a 5.25mm line on the glass plate. A CMOS linear detector array (Teledyne™ Octoplus, 2048px of 200×10µm) operating at 200kHz is used to obtain full frame images at up to a 400Hz frame rate and a pixel size (at the image plane) of ~0.8µm.
Results :
Taking advantage of the asymmetry involved in scanning a line through a slit pupil and collecting light scattered from a diffuse target using the full pupil, we designed an asymmetric scanning system which delivers diffraction-limited performance while using almost all the light from the source projected onto the target and collects 98% of the light returning from the target onto the detector. A traditional system only uses 10%-50% of the illumination source, and 50-90% of the light returning from the eye.
Conclusions :
This LSO is the highest light-efficient ophthalmoscope available to our knowledge. Avoiding the use of an intensity beam splitter minimizes the need for high-power light sources for ophthalmic imaging, and can increase signal-to-noise ratio for high-speed imaging while using the entire pupil to deliver diffraction-limited performance at the ICA.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.