Light‐field fundus imaging under astigmatism – An eye model study

Abstract Purpose One strong risk factor for glaucoma is a suspicious optic nerve head appearance and an increase in depth. With the upcoming light‐field (LF) technology one‐shot 3D retinal imaging and measuring is possible. Due to optical aberrations such as astigmatism, the imaged depth can be distorted. The study presented here investigated the influence of astigmatism on LF image quality and depth estimation using an eye model. Methods We developed a new eye model that added astigmatism by integrating an additional cylindrical lens between the cornea and lens. We used cylindrical lenses from −4 to 0 dpt in 1 dpt steps in vertical and horizontal orientations. The fundus was modelled as a half hollow sphere with a radius of 10 mm and a central papilla with 0.8 mm depth. The fundus was coated with red acrylic lacquer, and vessels were drawn with a thin brush with black acrylic lacquer. LF fundus images (15 for each cylindrical lens and orientation) were taken with a fundus camera (FF450, Carl Zeiss Meditec AG, Germany) equipped with an industrial LF camera (RX12, Raytrix GmbH, Germany). Depth measurements were performed with the Raytrix LF software (RxLive 5.0.046.0) as difference from a vertical vessel to a horizontal orientated vessel. The same measuring point was used for all images. Results The LF images taken with a cylindrical lens show a visually poorer image quality. Depth estimates were only possible in the central image area. The fundus images show increasing depth differences between vertical and horizontal vessels with increasing astigmatism up to 0.37 mm at −4 dpt in contrast to the flat imaged fundus without cylindrical lens. The sign of the depth differences changes when the orientation of the inserted cylindrical lens is changed. Conclusions The imaged LF of a fundus of an astigmatic eye model is measurably distorted and affects vertical and horizontal structures differently. This must be taken into account when evaluating and interpreting LF depth measurements.