Use of FLIO in retinal disease

The older your grow, the more you glow – tracking retinal disease with FLIO imaging

Dermot McGrath

Posted: Sunday, September 1, 2019

Fluorescence life-time imaging ophthalmoscopy (FLIO) is a new, non-invasive imaging technique capable of capturing highly reproducible measurements in the retina and revealing valuable information on a wide range of retinal diseases, according to Martin Zinkernagel MD, PhD.
“I think this has a lot of potential going forward as the measurements obtained by the device are very reproducible. It can provide information about outcomes measures for macular pigment even in the presence of macular atrophy in diseases such as age-related macular degeneration (AMD) or geographic atrophy (GA). We can also identify disease-specific patterns and it may provide additional parameters for outcomes in diseases such as Stargardt or choroideremia,” he told delegates attending the European Society of Ophthalmology (SOE) meeting in Nice, France.
Unlike conventional fundus autofluorescence imaging, which measures the intensity of endogenous fluorophores, and primarily lipofuscin, in retinal tissue, FLIO measures the average amount of time a fluorophore remains in the excited state before emitting a photon to return to the ground state.
“We use a laser to excite the fluorophore, which then releases photons to get back to the ground state. This time can be calculated and assessed, as fluorescence lifetimes are specific for individual fluorophores and depend on the metabolic environment,” he said.
FLIO is based on a Spectralis HRA system (Heidelberg Engineering), which uses a picosecond-pulsed diode laser at 473nm wavelength and 80MHz repetition rate to excite the retinal fluorophores. Fluorescence decay times are then measured in both a short (498-560nm) and long (560-720nm) spectral channel by time-correlated single photon counting. The detection of emitted single fluorophores over time results in a fluorescence decay curve for every pixel within the field of registration, explained Dr Zinkernagel.
“The lifetimes are represented in topographic colour-coded imaged scales, with short lifetimes in red and long lifetimes in blue,” he said.
Studying the FLIO maps in healthy individuals established the high reproducibility and repeatability of the lifetime values, and also showed a correlation of fluorescence lifetimes with age, said Dr Zinkernagel.
“Basically, the older you grow, the longer you glow. Older individuals exhibit longer fluorescence lifetimes, possibly due to progressive accumulation of visual cycle end products within the retina,” he added.
Potential applications of FLIO include tracking and monitoring a broad range of retinal diseases such as AMD, GA, central serous chorioretinopathy and inherited retinal diseases such as Stargardt’s disease. It may also help to identify potential biomarkers in certain diseases and to monitor patients’ responses to therapies, including novel and innovative therapeutic strategies, he concluded.

Martin Zinkernagel: