Abstract
Purpose:
To introduce and evaluate a novel illuminating unit for fundus cameras to apply different light configurations by programming. In fundus imaging retinal vessel contrast is often reduced due to stray light caused by illumination of anterior segments of the eye, e.g. lash, lid, or pupil margin. Here, we present a novel programmable LED-based illuminating unit reducing stray light effects and first in-vivo results.
Methods:
We designed a segmented LED illuminating unit for a standard fundus camera. It is comprised of 12 optical fibers, coupled each to a green LED (peak wave length 518nm), an annular-shaped socket to reproduce the generic radiant ring structure (standard configuration), and a Field Programmable Gate Array to operate and to spatially control the LEDs. Fiber coupling efficiency and light distribution was simulated and optimized using the optical software Zemax. The LED illuminating unit was connected to the fundus camera utilizing the default port. In-vivo measurements were performed in one mydriatic Asian eye applying two different illumination configurations: standard ring (c1), customized pattern (c2). For each configuration 10 images were captured at the same radiant flux level (0.5mW) measured in the pupil plane in air. To quantify the effect of blurring, vessel contrast (Michelson) and histogram-based energy-distribution were used in constant ROIs. For vessel contrast analysis a vein central above the optic disc and the macula was selected. For energy analysis a rectangular area between the optic disc and the macula was chosen.
Results:
The novel illuminating unit was successfully adapted to a standard fundus camera. The mean contrast for the vein in c1 was 0.303 (±0.013). In c2 the contrast was 0.359 (±0.013), which means an improvement of 18.5% compared to standard illumination (c1). The histogram for c1 reveals a broader distribution in comparison to c2. The mean FWHM for c1 was 75 gray values and 44 gray values for c2.
Conclusions:
We present a spatially programmable LED-based illuminating unit connectable to a standard fundus camera. The novel system can be used to adapt to patient-specific obstructive anterior eye segments causing stray light if illuminated. The system presented enables high flexibility in anatomical, age-related, and pathological conditions for constant contrast fundus imaging, e.g. in retinal vessel analysis.
Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) •
688 retina •
551 imaging/image analysis: non-clinical