Multiscale Imaging for Low-Cost Ultrawide-field Opthalmoscopes

Abstract

Purpose : Ocular and optical aberrations limit high-fidelity ophthalmic imaging to an instantaneos field of view of about 60°. Wider field of views are possible with reduced resolution and require higher optical complexity and cost. We report a multi-scale optical design that corrects the off-axis ocular aberrations of the eye to enable the recording of 40MP, 150° images - constituting a 10x increase on current widefield retinal imaging systems. The technique can be implemented at low cost ($5k) in a hand-held device suitable for use in low and middle-income countries.

Methods : Multi-scale optical design employs a spherical array of lenses to segment the full field of the retina into many sub fields of views, which are then imaged onto an array of cameras. Each lens is optimised specifically for a specific sub-field, which allows correction of field-variant ocular aberrations. Computational fusion of sub images enables aberrations-corrected imaging across a wider field of the retina than is possible without the use of, for example, adaptive optics.
Transscleral illumination enables eradication of ocular reflections over an extreme field of view without the use of scanning. This also enables a compact handheld design that produces natural colour images.

Results : We have demonstrated the feasibility of the design with a rigorous Zemax optical model of a 19-camera, 40 Mpixel, 150° retinal camera supported by experimental demonstrations of sub components. This includes high-quality, glare-free retinal imaging of subjects with a range of retina/skin pigmentations.

Conclusions :
There is an unmet need for a ultra-widefield, low cost, handheld retinal imaging system. We have demonstrated the feasibility of multi-scale ophthalmic imaging, with transslceral illumination for handheld imaging with a field of view and resolution of 40MP, for <$5k. This corresponds to a 10x increase in performance using a low-cost technology suitable for a global market.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.

 

a) Side profile of a 19 camera system which achieves a 150° horizonal field of view. The performance of each camera is shown in b). Due to the local correction of ocular aberrations achieved by a phase plate, there is a significant increase in performance over a conventional single aperture system.