The eyes have it!

Siblings have moments of jealousy, most of the time for minor things. Growing up I was I often jealous of my sister, McKenzie, who I thought was lucky enough to be nearsighted and had to get glasses in the fourth grade.

I am older now but still do not need glasses. Since both my mom and dad wear glasses, however, it seems inevitable that one day I will too.

Why do glasses help people see and when people have Lasik eye surgery, what exactly happens to their vision? In order to know this, we must first know more about how the eye works.

The iris, pupil and sclera are parts of the eye we all see when we look in the mirror. The iris (colored part) and pupil (black dot) work together to control how much light enters the eye. The sclera (white part), because it is made of the fibrous tissue, helps protect the eye.

Light travels to the back of the eye through the lens to the retina. The retina contains around 120 million rods and roughly 7 million cones. These specialized cells help to process the light and send it to the brain via the optic nerve. Once there the brain helps make sense of it all by interpreting the nerve signals and by flipping the upside down image the lens sees right side up.

Many of my students have dissected bovine eyeballs and they discover that the lens seems to be kind of like a buried treasure. A cow’s eyeball is about the size of a small marble and difficult to cut through because it is hard and slippery and has several layers like an onion. The lens is a part of the third layer.

The need for glasses is often directly related to the shape of one’s eye. McKenzie is nearsighted (myopia), which means she can see things that are close very clearly, but objects far away are blurry and out of focus. She either has too long an eyeball or her cornea has too much curvature that prevents the light entering her eye from focusing correctly. Her glasses are what are called a minus lens, which means it moves the focus of an object farther back.

Farsightedness, or hyperopia, is almost the opposite of myopia. People can see things far away clearly but not close up. These people either have too short of an eyeball or too little curvature in the cornea and use a plus lens in their glasses.

Some people after years of wearing glasses opt for Lasik surgery to help with their eyesight. For the surgery, doctors use a tool that actually burns the cornea into the correct shape.  

I am sorry, Mac, for my crazy jealousy with you and your glasses. It is only a matter of time until I too will need to get glasses. When I do, it will more than likely be for presbyopia, the “old eye,” and I will need to get bifocals.