Look into my eyes – The Physics Congress 2003

Eye diseases and circulation problems can now be observed in full colour thanks to the development of a scanning laser ophthalmoscope (SLO) that operates simultaneously with low-power red, green and blue lasers. Dr Ayyakkannu Manivannan will report the latest test results on the SLO at the Institute of Physics Congress at Heriot-Watt University on Tuesday 25 March. He will demonstrate how the SLO system can reveal early retinal damage in diabetic patients and inflammatory macular disease in the elderly.

A clear view of the blood system behind the retina, at the back of the eye, the fundus, can be used to reveal the early onset of degeneration that can lead to blindness and to the early stages of circulatory diseases, such as hardening of the arteries, atherosclerosis. According to Dr Manivannan conventional cameras for looking deep into a patient’s eye do not provide depth information. Previously available SLOs provide only monochrome images, says Dr Manivannan. A full-colour view would provide much more information and allow diagnosis of problems to take place with more accuracy than previously possible.

Manivannan and his colleagues at Aberdeen University have developed a system that uses a sequence of short low-power laser pulses from three lasers combined with fibre optics. A brief red, green, and blue flash one after the other lights up a point at the back of the eye. The laser pulses under computer control scan the whole of the back of the eye and a frame grabber built into the system then merges the three different coloured scans to produce a full-colour image. Images are captured every 40 ms (25 images/second).

At the meeting, Dr Manivannan will explain how the SLO results compare favourably with conventional fundus cameras. He points out that the sequence of coloured pulses means that the total exposure time for imaging the fundus remains the same as with a conventional SLO and 100 times lower than a conventional fundus camera. However, the colour SLO has the great advantage of true colour representation of the back of the eye. The system also has all the advantages of digital photography in that there is no development stage and the images can be stored and compared directly on computer as soon as they are taken.