Wide field of view handheld smart fundus camera for telemedicine applications

Abstract

Purpose: We report that a large field-of-view (FOV) retinal image can be acquired by a smart fundus camera. Approach: This handheld system consists of a Raspberry Pi board, a touch screen display, a customized optical lens group, a ring light-emitting diode, and a Li-battery. Results: Wide FOV of $\sim 57\mathrm{deg}$ is observed with proper lens configuration and can be expanded using image stitching algorithms. Conclusions: This customized handheld fundus camera provides better image quality than cellphone-based fundus imaging solutions and offers more operational features than traditional portable fundus cameras. It may benefit field-portable ophthalmic diagnostic applications.

Keywords: Raspberry Pi; fundus camera; image stitching; retinal imaging; telemedicine.

Fig. 1

3D schematic of the fundus camera system.

Fig. 2

(a) Image of LED ring light at 7 mm from the 90D lens and (b) 3D intensity distribution captured by using a 15-bit laser beam profiler with pixel number on the $x$ and $y$ coordinates. (c) The $x$ and $y$ intensity distributions across the center of image in (a) shows clearly the inner and outer diameters of the dotted ring pattern with a 1.65 imaging factor.

Fig. 3

Intensity distribution along the central (a) $x$ axis and (b) $y$ axis on a hollow 25.4-mm diameter semi-sphere target by the ring LED light.

Fig. 4

Optical spectrums of our fundus camera with red, blue, and green curves at three power setting of $305\mu \mathrm{W}$ (LED high), $208\mu \mathrm{W}$ (LED medium), and $135\mu \mathrm{W}$ (LED low), respectively. The spectrum of the Canon CF-60UVi at maximum power of 7 mW is shown in black curve for comparison.

Fig. 5

Power distribution and general communication lines for RPi-based handheld fundus camera.

Fig. 6

(a) Image acquisition interface for intuitive retinal image capturing. (b) Data information GUI to access different layers of information ranging from user information to patient information and connectivity status.

Fig. 7

Data transmission pipeline. Each stage requires proper security and authentication techniques to ensure user and patient information is not compromised.

Fig. 8

One of patient information page that shows optical eye images uploaded from our fundus camera system.

Fig. 9

Fully assembled and packaged RPi fundus camera displaying previously taken retinal image.

Fig. 10

(a) Three images of a model eye retina (Ocular Instruments OEMI-7) each with a different viewing angle and (b) the stitched image with a wider FOV of $\sim 75\mathrm{deg}$.