Cellular and subcellular factors influencing autofluorescence signal strength of human RPE
. Light enters from above (
arrow) to excite fluorophores within cells. Emissions exit above to be detected by a device (e.g., fundus camera or scanning laser ophthalmoscope). Factors causing hyperautofluorescence (greater signal strength) are shown in (
A–
G) and hypoautofluorescence (lesser signal strength) in (
H–
M). The combined L/ML population is shown. (
A) Normal cell contains multiple fluorophores in L/ML, screened anteriorly by M in apical processes and apical cell body (
B) Higher concentration of L/ML granules. (
C) Altered mix of emitted spectra, either due to a different fluorophore mix or changes in the fluorophore environment (e.g., altered lysosomal pH) that move more spectra into device detection. (
D) Basolateral positioning of M to reduce screening (as in aging).
22 (
E) Taller individual cells (e.g., due to rounding)
23,29 that increase the path length of exciting light through fluorophores. (
F) Stacking of cells lengthens the light path through fluorophores.
23,29 (
G) Anterior migration of cells lengthens the light path through fluorophores.
23,25,29 (
H) Normal cell. (
I) Redistribution of L/ML leaving cytosol devoid of granules, due to degranulation (empty cytoplasm on the left) or aggregation (clustered organelles on the right).
25,26 (
J) Altered mix of emitted spectra, either due to different fluorophores or changes in the fluorophore environment that move spectra out of device detection range. (
K) Apical positioning of M to increase screening (as under the fovea).
94 (
L) Flattened RPE, shortening the light path through fluorophores.
23 (
M) Absent RPE.