Light‐field imaging for glaucoma diagnosis—reproducibility on one patient

Abstract

PurposeA suspicious optic nerve head appearance with abnormal cupping or increased cup‐to‐disc ratio is considered as a strong risk factor for glaucoma. Typical systems to measure this deformation are optical coherence tomography or scanning laser ophthalmoscopy. We show that the needed depth information for glaucoma diagnosis can be obtained reliably with a commercial fundus camera using an adapted light‐field camera providing a one‐shot 3d retinal image.MethodsWe examined the left eye of a glaucoma suspect (male, 39 years) 11 times in compliance with the Declaration of Helsinki. For each examination, the glaucoma suspect repositioned himself and the device was readjusted. The images were taken with a fundus camera (FF450, Carl Zeiss Meditec AG) combined with a modified light‐field camera (Raytrix R12, Raytrix GmbH). The eye was illuminated with a wavelength of 520 nm (±20 nm). The absolute virtual depth (VD) values were exported from the Raytrix software (RxLive 5.0, Raytrix GmbH) and further processed in Matlab R2018. All data were aligned to each other to measure at similar locations. The maximum VD on a vessel segment above the rim and the minimum above the root of the vessel inside the optic nerve head was determined to calculate the depth difference.ResultsAll images showed a clearly identifiable optic nerve head structure and allowed a successful and reliable determination of the depth information. The average relative depth difference over all examinations was 6.1 ± 0.34VD. The 95% confidence interval was between 5.86 and 6.34VD. Besides the depth values also the lateral values are virtual because of an aperture mismatch between fundus camera and light‐field camera. A successful depth estimations of the Raytrix software require high contrast images with textures. Caused by the objective of the fundus camera image distortions existed.ConclusionsThe presented results from our preliminary system show the potential of the light‐field technique to be used for glaucoma diagnostics and progression analysis based on the optic nerve head in 3D. Reliable and reproducible measurements of this technique can enhance the informative value of the classical fundus photography.