Fred Crittenden says it took him about a year to come to terms with his blindness. Today, more than 35 years later, he doesn’t see light at all. But there’s plenty he doesn’t need help with — including syncing up with the 24-hour day/night cycle.
, a neurobiologist at Boston Children’s Hospital and the Harvard Medical School. “The melanopsin cells — their arms reach out and overlap with the arms of other melanopsin cells to form a mesh over the retina.”Dim light reflects off a mug and a clock on the wall in Crittenden’s home.
So that’s the mystery we started with, solved: Fred Crittenden has no functioning rods or cones, but, he does have melanopsin cells.Crittenden’s experience offers insight into an important system in the brain and retina that is maintained in certain people who are blind. This system of special melanopsin cells is likely what allows Crittenden’s brain to use light to help synchronize his internal clock.
This story is part of our periodic science series “Finding Time — a journey through the fourth dimension to learn what makes us tick.” DANIEL: Every baseball season, 73-year-old Fred Crittenden plants himself in front of his television, where he listens to the games. He doesn’t watch them because he can’t see.DANIEL: Crittenden has retinitis pigmentosa, an inherited condition that led to the deterioration of his retinas. He lost all his rods, the cells that help us see in dim light, and all his cones, the cells that let us see color in brighter light.
MARLA FELLER: If you never saw any light, you would slowly shift your sleep cycle so that you’d start falling asleep later and later.FELLER: But what happens is every day you go out and look at the sun, and it entrains this circadian clock to be on the 24-hour cycle.DANIEL: And yet his internal clock marches to the 24-hour beat of a sunlit world, give or take a few minutes.
DANIEL: The entire mesh is sensitive to light. The tentacles of those melanopsin cells – they radiate all over our brains.
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