Although you can’t really “tear” your eyeball, you can injure it in such a way that the cells of the cornea essentially get ripped apart a little bit. Corneal abrasions, which can include a scratch, a burn, or other injury, generally heal up in just a few days. While more serious injuries can have more serious repercussions, a torn cornea causes blindness only in rare circumstances.
Blindness, the Eye, and the Cornea
The eyeball is made up of several key parts. They all work together, ultimately sending information to the visual cortex, which allows you to “see.” Because of this, blindness can be the result not only of an abnormality of a part of the eye’s anatomy, but there can be something amiss in the brain as well. The cornea (the clear lens across the iris and pupil) is designed to send light into the eyeball at a certain angle. Light signals go into the pupil, through the vitreous body, and onto the retina. The retina changes the light signals into electric impulses, which are then sent up the optic nerve and into the visual center of the brain, where sense is made of the impulses.
The cornea itself is made of five layers. The epithelium helps deflect dangerous particles (from sawdust to bacteria), as well as absorb nutrients. Bowman’s membrane is made up of collagen and protein fibers; unfortunately, it is easy to scar during injuries, which can interfere with vision. The third layer, the stroma, is very thick and is the key in light passage. It is made up of mostly water and collagen. Descemet’s membrane is a second protective barrier, made of a different sort of collagen and fueled by the fifth layer. The endothelium pumps extra water out of the stroma. When the endothelium is damaged, whether from injuries or a corneal disease, it does not heal.
Consequences of a Corneal Abrasion
The symptoms of a torn cornea depend largely on just how thoroughly you hurt your eye. Generally, your eye may be a little sore, possibly feeling as if there is something lodged in it. This might mean there are still particles in the eye or be caused by the scratched cells themselves. There are thousands of nerve endings in the epithelial layer, so you definitely know when you hurt your eye. Additionally, your eye may be red, sensitive to light, or watery. The surrounding eyelids may swell, and you may experience blurry vision. Your eye becomes more subject to infection because the protective barrier that keeps out microscopic pathogens is no longer completely protective.
Can a Torn Cornea Cause Blindness?
Ultimately, yes. In actuality, it’s probably not going to happen. Since the clarity of the cornea is so necessary to good vision, excessive scratching is going to make it difficult to retain transparency. Additionally, as new cells form, they are not as closely interlinked with the pre-existing cells, making it easier for the area of healing to get ripped back off (a corneal erosion). Furthermore, the depth of the abrasion is going to have an impact on how well your eye heals. If something rips all the way through to the endothelium, not only will the innermost layer not heal -- the rest of the cornea likely won’t heal very well either. Some bacteria that invade the eye can cause serious infections, potentially interfering with your vision. Fortunately, what happens to one cornea doesn’t necessarily happen to other -- which means a torn cornea isn’t going to cause blindness in both eyes, at least.
