Abstract
Purpose :
Objective, non-invasive measurement of the optical density (OD) of human macular pigment (MP) can be performed in vivo using fundus autofluorescence (FAF) imaging. Depending on the protocol used, the exam duration may be lengthened by the need for pupil dilation, repeat image acquisitions, and/or separate calibration for crystalline lens fluorescence. In this study, we investigate the feasibility of quantifying macular pigment optical density (MPOD) using a slit-scanning ophthalmoscope with a single-flash measurement protocol.
Methods :
A slit-scanning ophthalmoscope (CLARUSTM 500, ZEISS, Dublin, CA) with prototype software was used to perform non-mydriatic measurements of MPOD, derived from pairs of FAF images obtained with blue (λpeak = 459nm, well-absorbed by MP) and green (λpeak = 520nm, much less absorbed) excitation sources. The illumination rapidly alternates between the sources during a single scan, completing in under 0.2 seconds. The image sensor records separately the partial images of stripes of illuminated retina. Retinal autofluorescence appears only within the illuminated stripe, but unwanted crystalline lens fluorescence appears nearly uniformly across the partial image (allowing it to be removed). A fluorescent phantom, incorporating a yellow-colored filter of known OD, was used to test the implementation. MPOD measurements were performed on 5 human subjects.
Results :
The manufacturer specified OD for the test phantom is shown in Figure 1A. From the FAF images (Figure 1B-C), the 2-D spatial MPOD profile for the test phantom is derived (Figure 1D). The mean MPOD was within 2.5% of the specified value. For human subjects, we present FAF images and the derived MPOD profiles (an example is shown in Figure 2) for the central 5° around the fovea.
Conclusions :
A slit-scanning ophthalmoscope can perform objective FAF measurements of MPOD in a single perceived flash, through non-dilated pupils. This gives encouragement that such a method can be practical for screening, for example for risk of age-related macular degeneration. Validation of such an approach for in vivo use will require careful consideration of confounding effects, such as secondary fluorophores and photobleaching.
This is a 2021 ARVO Annual Meeting abstract.