It’s happened to all of us: we’re at a pool and walk inside to grab some watermelon — when, suddenly, it seems that everything has gone black. You can’t coordinate your next step, let alone get to the watermelon a few feet in front of you! It takes a few seconds for your eyes to adjust before you can take a moment to sink your teeth into the cool, sweet fruit. But why?
Name: Suresh Viswanathan, BOpt, MS, PhD, FAAO
Capacity: Associate Professor and Chair of the Department of Biological and Vision Sciences
Campus: SUNY College of Optometry
Research: Focuses on developing tests for the early detection of neuronal dysfunction in glaucoma and understanding some of the early mechanisms that contribute to neuronal cell death. These investigations use electrophysiological, psychophysical and in vivo imaging techniques.
Q: Why is it hard to see when I walk indoors on a sunny day?
A: It’s the rods and cones.
Dr. Viswanathan explains:
We have two types of cells in our retina that absorb light, the rods and the cones. The rods help us to see in the dark or under dimly lit conditions and the cones help us to see under bright light conditions.
When you are walking outside on a sunny day the bright sunlight bleaches all the light absorbing pigments in your rods and these cells cannot function normally again until the bleached pigments are restored back to their unbleached state and this takes time. This is mainly why it seems like you can’t see anything for a short time after you walk indoors into a dimly lit room on a bright sunny day.
So, this explains why using sunglasses helps avoid this effect; your rods are less susceptible to the sun’s “bleaching”.