Do Fish Blink?
Wow. I was very surprised by how many patients asked me if fish can blink. Fish don’t “blink” their eyes quite like humans do. But when asked this question, I wasn’t immediately ready with a complete explanation as to why. I had to look into this one, to provide an accurate answer.
Let’s look first at why we blink. The outer most part of our eyeball, the cornea, is a perfectly clear optical layer exposed to the air that must stay lubricated to function well. Our eyelids, both upper and lower, are equipped with glands that secrete the proper components onto our eye surface to keep things moist. The action of our lids closing and touching each other, on average every four or five seconds, keeps everything constantly well distributed and working properly. Anything that interferes with this mechanism causes damage to our cornea and conjunctiva. People who don’t close their eyes completely when they sleep, for instance, can have serious keratinitis issues in that area left exposed to the air night after night.
So, what about fish? Obviously fish live underwater so the risk of their corneas being exposed to the air is not an issue to them. So they do not have eyelids. If you don’t have eyelids, you can’t blink. But the closing of eyelids is not solely to distribute a tear film. It’s also for protection. We certainly know about our amazingly fast ability to blink and/or keep our eyes closed in the face of danger. It’s a normal survival skill. The average speed of a human blink is 1/10th of a second! But what about fish? They run into danger all the time. What do they do? Nothing. They are stupid and they die and we eat them. End of story.
No, seriously, fish are way faster than us in their protective reflexes. They have to be because they don’t have our brain power to make higher decisions like we do. They also have evolved in ways that provide camouflage by having “eyeball-like” spots on the other side of their bodies to throw off predators. I have read about a few species of shark that actually do have a type of eyelids that move laterally, like the opening and closing of elevator doors, but you’d need to do your own Googling to look into that further.
Isn’t our planet amazing?