Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) of Macular Pigment

Abstract

Purpose: To describe different patterns of macular pigment (MP) seen in fluorescence lifetime imaging ophthalmoscopy (FLIO) and to analyze ex vivo fluorescence characteristics of carotenoids.

Methods: A total of 31 eyes of young healthy subjects, 4 eyes from patients with albinism, 36 eyes with macular telangiectasia type 2 (MacTel), 24 eyes with retinitis pigmentosa, and 1 eye with a macular hole were included in this clinic-based, cross-sectional study. All subjects underwent Heidelberg Engineering FLIO and MP measurements (dual-wavelength autofluorescence). Fundus autofluorescence (FAF) lifetimes of a 30° retinal field were detected in two spectral channels (SSC: 498-560 nm; LSC: 560-720 nm), and amplitude-weighted mean fluorescence lifetimes (τm) were calculated. Additionally, autofluorescence lifetimes of known dilutions of lutein and zeaxanthin were measured in a cuvette in free- and protein-associated states.

Results: MP shows a significant inverse correlation to foveal FAF lifetimes measured with FLIO (SSC: r = -0.608; P < 0.001). Different distribution patterns can be assigned to specific disease-related changes. Two patients with albinism, who did not have MP, were found to be missing short FAF lifetimes. In solvent, lutein and zeaxanthin show very short autofluorescence lifetimes (∼50-60 ps; SSC), as do their respective binding proteins (∼40-50 ps; SSC). When combining carotenoids with their specific binding proteins, the decay times shift to longer means (∼70-90 ps; SSC).

Conclusions: This study expands upon previous findings of an impact of MP on short FAF lifetimes by describing ex vivo autofluorescence lifetimes of carotenoids and different in vivo autofluorescence patterns that can be associated with certain diseases.

Figure 1

Mean FAF lifetimes of the short spectral channel (SSC: 498–560 nm; top row) and dual wavelength AFI-MP images in a healthy eye and different retinal diseases (bottom three rows). Row 2: En face image of macular pigment distributions obtained by dual wavelength AFI. Row 3: Decremental slope of MP decline as a function of distance from foveal center. Row 4: Three-dimensional projection of MP. Only the MacTel patient shown in this figure was on supplementation (10 mg zeaxanthin daily).

Figure 2

Pearson correlation of mean FAF lifetimes within the short spectral channel (498–560 nm; SSC) with MPV: r.0608, P < 0.001 (A) as well as three different MP distribution patterns in three healthy subjects: B, broad; C, cone; and D, ring-like. En face FAF lifetime images as well as three-dimensional projection of MPV are shown.

Figure 3

Mean FAF lifetime and intensity images of two spectral channels (SSC: 498–560 nm; LSC: 560–720 nm) as well as OCT and macular pigment optical density of two patients with albinism. Both eyes are shown. patient 1: male, 47 years old; patient 2: female, 42 years old.

Figure 4

Mean FAF lifetime and intensity images of the short spectral channel (498–560 nm) as well as MP optical density of two patients with retinitis pigmentosa. Both eyes are shown. Both patients are female. The unsupplemented patient is 26 years old, and the carotenoid supplemented patient (on 10 mg lutein for 2 years) is 14 years old.

Figure 5

FAF lifetime decay curves of ex vivo carotenoids. Possible fit-mechanisms with different components (Comp) are presented.