A team of researchers has developed a cheap, portable camera that can photograph the retina without the need for pupil-dilating eye drops.

Made out of simple parts mostly available online, the camera's total cost is about $185. "As residents seeing patients in the hospital, there are often times when we are not allowed to dilate patients -- neurosurgery patients for example," said Dr Bailey Shen, an ophthalmology resident at University of Illinois' Chicago College of Medicine.

"There are times when we find something abnormal in the back of the eye but it is not practical to wheel the patient all the way over to the outpatient eye clinic just for a photograph," Shen added.

The prototype camera can be carried in your pocket and can take pictures of the back of the eye without eye drops. The pictures can be shared with other doctors, or attached to the patient's medical record. The camera is based on the Raspberry Pi 2 computer, a low-cost, single-board computer designed to teach children how to build and programme computers. 

A handful of other components -- a lens, a small display screen and several cables -- make up the rest of the camera.

Shen and his co-author Dr Shizuo Mukai, associate professor of ophthalmology at Harvard Medical School and a retina surgeon at Massachusetts Eye and Ear, describe their camera and provide a shopping list of parts, instructions for assembly and the code needed to programme the camera in the Journal of Ophthalmology.

"This is an open-source device that is cheap and easy to build," said Mukai. "We expect that others who build our camera will add their own improvements and innovations."

"The device is currently just a prototype, but it shows that it is possible to build a cheap camera capable of taking quality pictures of the retina without dilating eye drops, " Shen said.