Fluorescence Lifetime Imaging Ophthalmoscopy May Detect AMD Changes Early

Fluorescence lifetime imaging ophthalmoscopy (FLIO) may provide information clinicians can use to detect the progression of age-related macular degeneration (AMD), according to a report published in Acta Ophthalmologica. Researchers suggest that FLIO, typically used to evaluate drusen itself, can detail alterations to the retinal pigment epithelium (RPE) on top of drusen, a potential indicator of AMD progression.

FLIO illustrates fluorescence lifetime and decay rate (τm) of fundus autofluorescence (FAF), as well as peak emission wavelength (PEW) — autofluorescence intensity. The researchers reviewed data from 40 eyes of 38 consecutive patients with intermediate, nonexudative AMD (mean age, 75.1±7.1 years) treated at a university hospital clinic. Tests for progression included optical coherence tomography (OCT) and color fundus photography (CFP).

Although the results revealed FAF lifetimes and PEW of hyperautofluorescent drusen varied from surrounding RPE and exhibited evolution during AMD’s course, variations may have represented changes in RPE fluorescence and advancing RPE dysmorphia, such as relocation or disappearance of lipofuscin pigment. “However, molecular changes affecting tissue fluorescence properties might precede morphologic alterations seen with CFP and OCT,” the study authors explain. “The prolongation of FAF lifetimes along with the shortening of PEW may provide additional diagnostic information enabling the detection of patients at risk.”

Specifically, in 210 baseline drusen, 149 without hyperpigmentation displayed shorter FAF lifetimes and shorter PEW — in short- and long-wavelength spectral channels, compared with surrounding RPE (all P <.001). 

Follow-up included 26 participants in a period 1 to 3 years after first assessment, 10 individuals during the 3 to 6 year interval, and 7 in both phases. During follow-up, FAF lifetime generally became longer and PEW even shorter for drusen without initial hyperpigmentation. 

For those whose disease eventually progressed, baseline FAF lifetimes for drusen without hyperpigmentation were significantly longer and PEW shorter in the short-wavelength FLIO channel at 282±102 picoseconds (ps), compared with nonprogressing eyes, 245±98 ps (P <.001). Similarly, progressing eyes’ baseline lifetimes were also longer in the long-wavelength channel, 365±44 ps, compared with nonprogressing eyes, 336±48 ps (P =.025).

Previous research indicated drusen hyperfluorescence and size may be related. However, this investigation found no correlation between FAF lifetime or PEW and drusen size in those that became hyperfluorescent.

Because FAF lifetimes in progressing eyes are typically longer near the posterior pole, it is unclear whether longer lifetimes are due to drusen characteristics or RPE injury. 

However, since longer FAF lifetimes and shorter PEWs are connected with AMD progression, this may indicate that fluorophores in RPE — as well as characteristics inside RPE cells, such as viscosity and pH — could be driving forces of change in fluorescence.

FLIO prioritizes time resolution, so it produces less depth detail among layers. Other limitations of this study include examination of large, soft drusen only — which are associated with high progression risk. The overall population sample was small. Conversely, strengths comprise imaging with multiple technologies, and long follow-up of close to 6 years.