Abstract
Purpose: :
To investigate the feasibility of quantitative and qualitative fundus autofluorescence (AF) assessment for monitoring lipofuscin accumulation in the Abca4-/- mouse, and to correlate findings with retinal function, histology and measurements of A2E.
Methods: :
Confocal scanning laser ophthalmoscopy (cSLO) was used for in vivo fundus AF excited at 488 nm in pigmented Abca4-/- mice and wild type controls. For quantitative AF analysis, the mean grey level on fundus AF images acquired with standardized detector sensitivity was measured within a ring shaped midperipheral area. Additional analysis included electroretinography (ERG), post-mortem histological assessment of the outer nuclear layer thickness, and measurements of A2E using HPLC.
Results: :
Fundus AF intensity was similar in four weeks old animals. With age, a steady increase of AF occurred, which was more pronounced in Abca4-/- mice compared to wild type controls. Fundus AF was significantly higher (p<0.01) in Abca4-/- mice at 9 weeks and older. The grey level ratio between Abca4-/- and age-matched wild type mice, which accounts for confounding factors such as pupil size or other age-related changes, was 1.2 at 4 weeks, 2.0 at 3 months, and 2.25 at 6 months. A fleck pattern of high fundus AF was clearly visible in 6 month old Abca4-/- mice, but not in wild type controls. In Abca4-/- mice 12 months and older, there were spots of decreased AF suggesting atrophic changes of the retinal pigment epithelium.ERG a-wave and b-wave amplitudes and the outer nuclear layer thickness were not significantly different between Abca4-/- mice and wild type controls up to an age of 9 months. Total A2E measurements increased similar to fundus AF measures. However, the ratio was 4-5 times higher than on fundus AF measures, possibly due to other fluorophores contributing to the overall difference.
Conclusions: :
cSLO imaging in mice allows detecting significant differences in fundus AF intensity and pattern between Abca4-/- mice and wild type controls in age groups that show no significant difference in photoreceptor function (ERG) and number (outer nuclear layer thickness). Thus, fundus AF imaging is a useful technique to assess potential treatments aiming at reducing lipofuscin accumulation in the retinal pigment epithelium.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal pigment epithelium