Fluorescence lifetime imaging ophthalmoscopy

Abstract

Imaging techniques based on retinal autofluorescence have found broad applications in ophthalmology because they are extremely sensitive and noninvasive. Conventional fundus autofluorescence imaging measures fluorescence intensity of endogenous retinal fluorophores. It mainly derives its signal from lipofuscin at the level of the retinal pigment epithelium. Fundus autofluorescence, however, can not only be characterized by the spatial distribution of the fluorescence intensity or emission spectrum, but also by a characteristic fluorescence lifetime function. The fluorescence lifetime is the average amount of time a fluorophore remains in the excited state following excitation. Fluorescence lifetime imaging ophthalmoscopy (FLIO) is an emerging imaging modality for in vivo measurement of lifetimes of endogenous retinal fluorophores. Recent reports in this field have contributed to our understanding of the pathophysiology of various macular and retinal diseases. Within this review, the basic concept of fluorescence lifetime imaging is provided. It includes technical background information and correlation with in vitro measurements of individual retinal metabolites. In a second part, clinical applications of fluorescence lifetime imaging and fluorescence lifetime features of selected retinal diseases such as Stargardt disease, age-related macular degeneration, choroideremia, central serous chorioretinopathy, macular holes, diabetic retinopathy, and retinal artery occlusion are discussed. Potential areas of use for fluorescence lifetime imaging ophthalmoscopy will be outlined at the end of this review.

Two-photon imaging of the mammalian retina with ultrafast pulsing laser

“…Two-photon FLIM has been used to visualize exogenous fluorophores in living mice (68). An additional advantage of using wide-bandwidth pulses is the ability to visualize the subcellular distribution of endogenous fluorophores, markers of the health of retinal biochemical processes, based on FLIM (Figure 8) (69). Retinyl esters are not excited efficiently with 790-nm or longer wavelengths, whereas retinal condensation products are optimally excited with 780-to 850-nm light ( Figure 2B).…”

Fluorescence Lifetimes in Patients With Hydroxychloroquine Retinopathy

“…The theories and technical details behind FLIO have been described in more detail in previous publications. [9][10][11][12][13] Analysis of Fluorescence Lifetime Data…”

“…8 Fluorescence lifetime imaging ophthalmoscopy (FLIO), an in vivo FLIM method, is a novel noninvasive imaging modality currently in clinical use to identify and quantify metabolic abnormalities in retinal diseases by imaging lifetimes of endogenous retinal fluorophores. [9][10][11][12][13] The fluorescence lifetime represents the time span an intrinsic fluorophore spends in a higher energy level following an excitation with a blue laser before returning to its ground level by releasing a photon with a longer emission wavelength.…”

“…For each participant a standardized sequence of investigations was performed including a general ophthalmologic examination with measurement of the best-corrected visual acuity (Snellen chart). 10 Pupils were dilated with tropicamide 0.5% and phenylephrine HCl 2.5%. In both eyes, fundus color images (Zeiss FF 450plus; Zeiss, Oberkochen, Germany), optical coherence tomography (OCT) scans of the macula (Heidelberg Spectralis HRAþOCT; Heidelberg Engineering, Heidelberg, Germany), Octopus 10-2 visual fields, FAF images, and fluorescence lifetime images were obtained.…”

Simultaneous in vivo confocal reflectance and two-photon retinal ganglion cell imaging based on a hollow core fiber platform

“…FLIM measurements as presented in [Figs. 3(c) and 3(f)] have the potential to provide critical and complementary information about cell status 20,21 and differentiate among RGC subtypes with different levels of vulnerability to damage. This work is currently in progress.…”