Low-cost, portable fundus camera for 3D-like images of the back of the eye
Glaucoma is one of the most common causes of blindness in the world, and experts estimate that there will be over 110 million cases worldwide by 2040. Timely screening and early diagnosis are essential for preventing irreversible visual damage caused by this disease. Unfortunately, ophthalmologists are currently in high demand and must tend to an ever-increasing number of patients, which makes routine screening more challenging.
One way to detect glaucoma and monitor its progression is by observing the shape and features of the optic disc, a structure found at the back of the eye where the optic nerve bundle exits the eye. To visualize the optic disc, ophthalmologists typically use fundus cameras, devices that illuminate the inside of the eye by shining a ring-shaped light through the edges of a dilated pupil. While much progress has been made in recent years to make these cameras more accessible, operating them still requires the expertise of an experienced technician.
But what if there were a fundus camera that could be used by patients themselves to capture detailed images of their optic discs while they stayed at home? In a recent study published in the Journal of Optical Microsystems, a research team from Tohoku University, Japan, reported an innovative design for a portable, inexpensive, and wide-field fundus camera that could revolutionize the screening of eye diseases.
The key feature of the proposed device is “oblique illumination.” Put simply, instead of illuminating the back of the eye homogeneously, this approach uses asymmetric illumination by shining light at an angle. This casts shadows from different structures of the fundus as well as at the interfaces of different types of tissues. As a result, one obtains a 3D-like image of the fundus with enhanced contrast, highlighting details relevant for diagnosis, such as the shape and depth of the optic disc and its vasculature.
To realize oblique illumination, the proposed design uses two infrared LEDs that shine light through the white regions of the eye (sclera) rather than directly through the pupil. Illuminating the eye through the sclera forgoes the need to chemically dilate the pupil of the patient, which simplifies the diagnostic procedure and makes it less traumatizing. Using both LEDs at the same time provides homogeneous illumination, while employing only one creates oblique illumination.
The researchers designed the proposed fundus camera using off-the-shelf optical components, simple 3D-printed pieces, and a commercial full HD webcam with minor modifications. Using this camera to take wide-field images of the fundus is quite straightforward. The ergonomic handheld device can stream images to a laptop in real time so that the patient can position the camera over one of their eyes while looking at the laptop screen with the other to ensure proper alignment.
To make the diagnosis of glaucoma and other diseases of the eye even easier, the team implemented an algorithm to automatically calculate the depth of the optic disc. Notably, the math behind this algorithm was originally conceived to calculate the depth of craters in celestial bodies by observing the shadow cast when illuminated by the sun at an angle. By adapting the calculations for this new purpose, the researchers demonstrated that this strategy could also be used to accurately estimate the depth of the optic disc, as confirmed using optical coherence tomography measurements on swine eyes.
Overall, the proposed fundus camera is a testament to human ingenuity and resourcefulness. With any luck, this low-cost device will make screening for eye diseases like glaucoma more accessible, helping prevent visual deterioration and blindness.
Read the Gold Open Access paper by Kaushik et al., “Imaging and qualitative depth analysis with a portable nonmydriatic fundus camera using oblique illumination,” J. Opt. Microsys. 3(2) 024502 (2023) doi: 10.1117/1.JOM.3.2.024502.
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