Green light for red channel?

Using the red colour channel when screening for diabetic retinopathy could aid the detection of eye disease

09 Feb 2017 by Selina Powell

A tweak in diabetic screening techniques may aid detection of eye disease in minority ethnic groups.

Researchers from the Indiana University School of Optometry studied standard colour fundus photographs from 2047 adult diabetes patients. Of this patient group, 90% of patients were from a non-white minority ethnic group.

The retinal photographs showed clinically significant macular oedema in 148 patients, including 13 patients who had a cystoid pattern of macular oedema.

The researchers compared the findings on standard colour fundus photographs with those of images divided into the red (long wavelength) and green (shorter wavelength) colour channels.

They found that macular cysts were easier to detect using the red channel images, while five of the 13 cystoid macular oedema cases were not visible by examining the green channel images.

All five patients with “missed” cystoid macular oedema using the green colour channel had a dark-coloured fundus.

Professor Ann Elsner, of the Indiana University School of Optometry, told OT that grading of diabetic retinopathy is often done with red-free images, or images from the green channel of the colour image. 

This method often increased the contrast of blood vessel abnormalities, but was more likely to produce dim images of dark eyes, she explained.

“We may be missing important pathology in the eyes of diabetic patients, particularly those with dark eyes,” she emphasised.

Using a red channel image might provide a better view of the macular in dark-eyed patients than a monochromatic image from the green channel or red-free image.

“This is readily obtained with software,” Professor Elsner added.

Diabetic retinopathy and diabetic macular oedema are the main cause of vision loss in working-age adults.

Screening had the potential to identify patients who were at risk of visual impairment, Professor Elsner emphasised.

“More sensitive detection of vision-threatening pathology can help prevent vision loss,” she added. 

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