The following was written by Bill Evans and published in the Coolum and North Shore News, Ask the Professionals page on Friday, 29th November 2013.
Q: What is the eye’s blind spot?
A: Everyone’s eyes have a normal or physiological blind spot. This spot represents part of the retina where the optic nerve passes through, and is devoid of photoreceptors. In the eyes of humans and all vertebrates, our photoreceptors actually sit behind the optic nerve fibre layer; light must pass through this nerve fibre layer before it reaches the photoreceptors of the retina. This is because our eyes developed as specialised areas of the brain. All of these nerve fibres leave the eye through an area of retina called the optic disc. Normally we don’t notice our blind spot; it is in a different location in the right eye compared to the left, and even if we close one eye our brain tries its best to fill in the missing information using the surrounding photoreceptors. Octopii, squids, cuttlefish and other cephalopods have eyes that don’t have a blind spot, as their optic nerve layer lies behind the photoreceptors.