Fluorescence Lifetime Changes Induced by Laser Irradiation: A Preclinical Study towards the Evaluation of Retinal Metabolic States

Abstract

Fluorescence Lifetime (FLT) of intrinsic fluorophores may alter under the change in metabolic state. In this study, the FLT of rabbit retina was investigated in vivo after laser irradiation using fluorescence lifetime imaging ophthalmoscopy (FLIO). The retina of the Chinchilla bastard rabbits was irradiated with a 514 nm diode laser. FLIO, fundus photography, and optical coherence tomography (OCT) were conducted 30 min and 1 to 3 weeks after treatment. After strong coagulation, the FLT at laser spots was significantly elongated immediately after irradiation, conversely shortened after more than a week. Histological examination showed eosinophilic substance and melanin clumping in subretinal space at the coagulation spots older than one week. The FLT was also elongated right around the coagulation spots, which corresponded to the discontinuous ellipsoid zone (EZ) on OCT. This EZ change was recovered after one week, and the FLT became the same level as the surroundings. In addition, there was a region around the laser spot where the FLT was temporarily shorter than the surrounding area. When weak pulse energy was applied to selectively destroy only the RPE, a shortening of the FLT was observed immediately around the laser spot within one week after irradiation. FLIO could serve as a tool to evaluate the structural and metabolic response of the retina to laser treatments.

Artificial Intelligence in Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) Data Analysis—Toward Retinal Metabolic Diagnostics

“…Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a new diagnostic tool that measures the fluorescence lifetime (FLT) of retinal intrinsic fluorophores [1][2][3]. FLIO has been shown to indicate not only structural but also metabolic changes in the retina [4][5][6][7]. It utilizes a blue laser diode (473 nm) for the excitation of fluorophores, and the emitted photons are detected by two different detectors: the short spectral channel (SSC: for 498-560 nm) and long spectral channel (LSC: for 560-720 nm).…”

Impact of cigarette smoking on fluorescence lifetime of ocular fundus

“…Our previous ex vivo study showed the change in FLT of RPE under sublethal oxidative stress or after laser irradiation 16 , 18 . An in vivo study rather showed transient changes in FLT around selectively treated laser spots 19 . As for clinical study, patients with type 2 diabetes without diabetic retinopathy 20 as well as patients with Alzheimer’s disease 21 revealed changes in FLT without structural changes, which underlines the potential of FLIO in the observation of metabolic disease mechanisms.…”