A new study¹ by the Centre for Public Health at the Queen’s University in Belfast, Northern Ireland, has shown that multicolour imaging has a higher sensitivity for detecting early age-related macular degeneration (AMD) compared to colour fundus photography (CFP).

The study which used a sample of 105 eyes and the Spectralis Diagnostic Imaging Platform muliticolour option, was led by Professor Usha Chakravarthy.

“This systematic analysis of colour fundus photography versus multicolour demonstrated the robustness of multicolour imaging in the detection of early AMD features,” she said. “The ability to delineate atrophy and fibrosis in late stage AMD gives added value in the clinical setting, as these components of the wet AMD lesion have an important impact on visual function.”

In cases with discrepancies, an analysis of OCT also showed better agreement with multicolour for all AMD lesions, with the exception of haemorrhage and non-geographic atrophy hypopigmentation. For pigment clumping, CFP and multicolour were in equal agreement to OCT, the study found. Multicolour imaging was able to identify soft drusen in 85% of the eyes studied, reticular drusen in 83% and atrophy and fibrosis in 100% of cases where these abnormalities were seen on CFP. When using multicolour as the basis for analysis, however, CFP was less sensitive. In this study, soft drusen were identified in only 58%, reticular drusen in 28%, atrophy in 83%, and fibrosis in 68% of the cases where such changes were seen on multicolour images.

Dr Jim Borthwick of Southern Eye said he’s been using the Spectralis multicolour module for nearly three years and is impressed with its capabilities for macular degeneration. “It is great. I’ve found it very useful for macular degeneration because it shows up the deeper layers.”

Compared with CFP, the multicolour platform is proving to be particularly useful for spotting reticular pseudodrusen, which have been recognised as important for both identifying MD and assessing its severity, he said, and for better visualisation of epiretinal membranes for preoperative evaluation.

But you do have to get used to using it, said Dr Borthwick, and it too has its limitations. “For example, it’s not as good at showing up naevi as a colour photograph. So, they both have a role. But it’s certainly a very useful extra tool for macular degeneration.”

The Spectralis MultiColor Module, is a newer imaging modality which uses confocal scanning laser technology with light of discrete wavelengths instead of standard optics and white light to visualize the retina. It uses three laser wavelengths - blue, green and infrared - simultaneously to provide diagnostic images that show distinct structures at different depths within the retina. Each offers unique details, said the company, due to the penetration depth and reflectance properties of each individual wavelength used: the infrared reflectance image shows deeper structures in the choroid and the retinal pigment epithelium; the green reflectance image is useful for examining blood, blood vessels, and exudates; while the blue reflectance image is best for identifying changes in superficial retinal structures, like epiretinal membranes or retinal nerve fibre layer defects.

“It is encouraging to see the clinical significance of the multicolour module proven in a large study related to a prevalent pathology such as AMD. Beyond the clinical value, clinicians also appreciate the fact that multicolour images can be acquired through undilated pupils and in patients with media opacity or even nystagmus. While we don’t see multicolour as a substitute for colour fundus photography... it is a particularly useful diagnostic tool that can be combined with other imaging modalities,” said Dr Kester Nahen, managing director of Heidelberg Engineering, maker of the Spectralis.

References

1. Identifying features of early and late AMD: A comparison of multicolour versus traditional colour fundus photography by Katie W. Graham, Usha Chakravarthy, Ruth E. Hogg, K. Alyson Muldrew, Ian S. Young and Frank Kee, was published digitally in August and will appear in the November issue of Retina