Fundus autofluorescence

Imaging helps to evaluate AMD, macular dystrophies, retinitis pigmentosa and other retinal disorders

Dermot McGrath

Posted: Wednesday, May 1, 2019

Quantitative autofluorescence measurements allow comparison of AF values among subjects. AF increases with age. Warmer colours indicate higher AF. Courtesy of Thomas Ach MD, FEBO

Fundus autofluorescence (FAF) imaging continues to offer a safe, non-invasive, easy-to-perform and reproducible diagnostic method that delivers useful information about retinal health and metabolism, according to Thomas Ach MD, FEBO.

“FAF images are technically easy to acquire, take just a few seconds and are repeatable. They enable us to track patients over a long period and monitor disease progression and are still used as an endpoint in clinical trials,” he told delegates attending the 9th Euretina Winter Meeting in Prague.

Dr Ach explained that FAF uses the autofluorescent properties of tissues, in particular the retinal pigment epithelium (RPE) and its fluorophores. It can be used to evaluate diseases such as age-related macular degeneration (AMD), macular dystrophies, retinitis pigmentosa and various other retinal disorders.

“It gives us a good indication of outer retinal health, with the loss of autofluorescence usually signalling a point of no return for retinal pigment epithelial (RPE) cells,” said Dr Ach, University Hospital of Würzburg, Germany.

Lipofuscin, the term given to fine granules composed of lipid-containing residues of lysosomal digestion (though exact composition is still unknown), is one of the main sources of RPE autofluorescence, said Dr Ach.

“Each RPE cell has hundreds of autofluorescent granules and they show a very characteristic retinal distribution in normal ageing. The exact mechanisms behind the accumulation of lipofuscin are still unclear and there is a lot of debate as to whether it is just a natural marker of age or an actual disease trigger in pathologies such as AMD,” he said.

FAF allows visualisation of different stages of RPE transition in various diseases, from healthy to atrophic in histological slides, said Dr Ach.

Thomas Ach MD, FEBO

“We can clearly identify this transition zone, which can be referred to as ‘between heaven and hell’. Once an RPE cell is in this transition zone and starts losing autofluorescent granules, as in AMD, it seems to go into atrophy and the RPE changes subsequently its phenotype,” he said.

Another recent evolution of these imaging techniques, known as quantitative AF, has opened the door to measuring these degenerative changes in the retinal cells over time, said Dr Ach.

“It allows us to compare autofluorescence intensities among subjects and at different time points in specific areas of the retina. We can use images from age-matched healthy controls that show that the qAF value increases with age based on the accumulation of lipofuscin. In diseases such as AMD the qAF values decrease due to intracellular granule re-organisation and loss of lipofuscin,” he explained.
Another exciting area of research lies in analysis of AF emission tissue spectra of RPE, drusen and sub-RPE deposits, said Dr Ach.

“On histology we see specific emission signals for sub-RPE deposits including drusen, which might be used as a possible marker for early AMD. Our current goal is to adapt this ex vivo technique into in vivo clinical imaging,” he reported.

Thomas Ach:

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