Portable ultra-widefield fundus camera for multispectral imaging of the retina and choroid

Abstract

Multispectral imaging (MSI) of the retina and choroid has increasing interest for better diagnosis and treatment evaluation of eye diseases. However, currently available MSI systems have a limited field of view (FOV) to evaluate the peripheral retina. This study is to validate trans-pars-planar illumination for a contact-mode ultra-widefield MSI system. By freeing the available pupil for collecting imaging light only, the trans-pars-planar illumination enables a portable, non-mydriatic fundus camera, with 200° FOV in a single fundus image. The trans-pars-planar illumination, delivering illumination light from one side of the eye, naturally enables oblique illumination ophthalmoscopy to enhance the contrast of fundus imaging. A broadband (104 nm) 565 nm light-emitting diode (LED) is used for validating color fundus imaging first. Four narrowband (17-60 nm) 530 nm, 625 nm, 780 nm, and 970 nm LEDs are tested for MSI. With 530 nm illumination, the fundus image reveals retinal vasculature predominantly. 625 nm and 780 nm illuminations enhance the visibility of choroidal vasculature. With further increased wavelength of 970 nm, the fundus image is predominated by large veins in the choroid, with multiple vortex ampullas observed simultaneously in a single fundus image.

Quantitative evaluations of vortex vein ampullae by adjusted 3D reverse projection model of ultra-widefield fundus images

“…This is mainly due to the inability to obtain images of the entire extent of the choroid with no distortion for quantification. There was a recent report of a technique that uses local anesthesia and contact lenses to observe the entire choroid 12 , but the images obtained are in 2D making it difficult to quantify the distance and angle within the eye. A 3D projection method was developed in which the fundus photographs are reverse stereo projected onto a 3D eyeball model 13 .…”

Impact of illumination spectrum and eye pigmentation on image quality from a fundus camera using transscleral illumination

“…Additionally, Toslak et al. 16 investigated the differences in observable features in retina images illuminated with LEDs of different central wavelength.…”

“…It is worth noting that most features require illumination at wavelengths between 500 and 600 nm for optimum contrast. Additionally, Toslak et al 16 investigated the differences in observable features in retina images illuminated with LEDs of different central wavelength.…”

“…This parameter differs widely across the population 15 and affects the transmission of light through the sclera, thereby significantly influencing the optical signal levels and the resulting quality of the images. Toslak et al 16 obtained retinal images using trans-pars-planar illumination from a subject with high pigmentation, but they do not provide further details on pigmentation level or quantitative influence of pigmentation on signal levels. The choice of the illumination source (especially its wavelength) also has an effect on image quality and contrast, which is important for detection of specific diseases (e.g., diabetic retinopathy 17 ).…”

“…Toslak et al. 16 obtained retinal images using trans-pars-planar illumination from a subject with high pigmentation, but they do not provide further details on pigmentation level or quantitative influence of pigmentation on signal levels. The choice of the illumination source (especially its wavelength) also has an effect on image quality and contrast, which is important for detection of specific diseases (e.g., diabetic retinopathy 17 ).…”