An Illumination System based on Indirect Ophthalmoscopy for Retinal Imaging Photoplethysmography Assessment

This paper presents an illumination system based on indirect ophthalmoscopy for smartphone ophthalmoscope to support retinal imaging photoplethysmography (iPPG) assessment. An experimental demonstration is carried out to measure the light source profile of smartphones and portable fundus camera. An illumination system: i) external illumination system of a smartphone with two lens arrangement and ii) internal illumination system of the eye. The illumination systems are demonstrated using Pre-designer and Winlens 3D open-source software. The outcome of experimental work shows that the smartphone exhibited a similar light source spectrum as a fundus camera with slightly high-power intensity. The illumination systems showed a good convergence of spot diagram at the centre of a FOV with a fair resolution of the Gaussian beam. The quality of the produced image depends on the choice of lens, lens arrangement, desired stopper distance, and focal length setting. The outcomes are essential to implement a high coverage fundus image of a smartphone ophthalmoscope prototype that increases its screening reliability.