Abstract
Purpose :
Retinal densitometry is a technique developed to measure visual pigment density; however, densitometers were not previously capable of measuring both topographically and changes over time, simultaneously. The novel high fidelity imaging retinal densitometry (IRD) can measure visual pigment optical density (OD) and regeneration rates (RR) across the central retina. The purpose of this observational clinical study was to establish the effect of age on rod and cone visual pigment OD and RR, which has not been assessed objectively in vivo in the same cohort of participants.
Methods :
Fifty-two healthy participants aged 25 to 85 years old were recruited. IRD involved obtaining multispectral reflectance data from the central retina (21°) to determine OD and RR for each participant, after 30 minutes of dark adaptation. Data was collected for 1 minute before exposure to a ‘white’ light that bleached >95% of rod and cone pigments, and then for a further 10 minutes post-bleach. The procedure was undertaken on two different days and an average was produced for each participant. The topographical IRD images were summarized for cones by extracting data from a single pixel at the fovea (0.4°) and for rods by averaging data from within an annulus of 6°-8° radius. Linear regression was then used to establish the effect of age. Heat map images were produced to describe the effect of age on rod and cone OD and RR across the central retina.
Results :
Over the age range of 25 to 85 years old, the summary measures show that rod OD increased by 63.77% (from 0.10 to 0.17 OD, p=<0.001), while the absolute rate at which rhodopsin regenerated did not alter (mean rate 0.17±0.05 OD/s, p=0.259). In contrast, cone OD did not change across the age range (mean 0.33±0.08 OD, p=0.128), but the recovery rate at the fovea declined by 42.19% (from 1.56 to 0.90 OD/s, p=<0.001).
Conclusions :
For cones, the efficiency of the ‘visual cycle’, assessed using visual pigment regeneration rates, reduces with age, a finding in agreement with psychophysical measures of cone dark adaptation. However, the efficiency of the rod ‘visual cycle’ is unchanged as age increases. Consequently, this suggests that the widely reported age-related slowing of the rod dark adaptation may not be due to a compromised ‘visual cycle’, but rather an increase in the total amount of visual pigment that needs to be synthesized.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.