Influence of Lens Fluorescence on Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) Fundus Imaging and Strategies for Its Compensation.

Purpose: To explore the contribution of crystalline lens fluorescence to fluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) and to propose a computational model to reduce the lens influence. Methods: FLIO, which detects autofluorescence decay over time in a short-wavelength spectral channel (SSC, 498-560 nm) and a long-wavelength spectral channel (LSC, 560-720 nm), was performed on 32 patients before and after cataract extraction. The mean autofluorescence lifetime (tau(m)) of the fundus was determined from a three-exponential fit of the postoperative fluorescence decays. The preoperative measurements were fit with series of exponential functions in which one fluorescence component was time-shifted in order to represent lens fluorescence. Results: Postoperatively, tau(m) was 185 +/- 22 ps in the SSC and 209 +/- 34 ps in the LSC at the posterior pole. These values were best reproduced by fitting the postoperative measurements with a three-exponential model with a time-shifted third fluorescence component (SSC, 203 +/- 45 ps; LSC, 215 +/- 29 ps), whereas disregarding time-shifted lens fluorescence resulted in significantly (P < 0.001) longer tau(m) values (SSC, 474 +/- 206 ps; LSC, 215 +/- 29 ps). The fluorescence of the cataract lens contributed to the total fluorescence by 54.2 +/- 10.6% (SSC) and 29.5 +/- 9.9% (LSC). Conclusions: Cataract lens fluorescence greatly alters fluorescence lifetimes measured at the fundus by FLIO, resulting in an overestimation of the lifetimes; however, this may be compensated for considerably by taking lens influence into account in the fitting model. Translational Relevance: This study investigates cataract fluorescence in FLIO and a mathematical model for compensation of this influence.