Group 1: 25 participants from each decade from 20-90. Those from 50+ will be recruited from the NICOLA study and retinal/lens images assessed to confirm normality (drusen <63µm or clear retina, LOCS III <1). Those younger will be recruited via advertisements in the University and targeting friends and relatives or NICOLA participants. This will enable the rate of decline with age to be calculated. Linear, bilinear, and simple nonlinear candidate functions of parameter vs. age will be applied to determine which best characterises the change.