I wear glasses, and have since I was… eight, I think. For a while, to say the least. And when I was small, I was fascinated by my parent’s glasses. I’d put them on, once in a while, and marvel at how – even though I wore glasses and my mom and my dad also wore glasses – the world looked so different and so strange through their glasses.
I think this must be a universal thing, because my son is fascinated by the glasses my wife and I wear. He doesn’t need them right now, and I hope he never will, but he’s fascinated by them. And every once in a while, I’ll let him try mine on. He peers through the lenses, his eyes magnified and looking huge, and then he’ll take them off and hand them back. One time when he did, he looked at me and asked “why do you guys wear glasses?”
Well, I wear them specifically because I’m nearsighted and have astigmatism. My wife wears them because she’s nearsighted as well. So was my mom, terribly so, but my father was farsighted. So I explained to him that my eyes don’t work right, and the lenses let me see better. His response? “Why?”
Nearsightedness is medically termed “myopia”. It comes from the Greek myōpía meaning near-sighted (literally “to shut eye”). According to the American Optometric Association, it “is a vision condition in which close objects are seen clearly, but objects farther away appear blurred. Nearsightedness occurs if the eyeball is too long or the cornea, the clear front cover of the eye, has too much curvature. As a result, the light entering the eye isn’t focused correctly and distant objects look blurred.”
Approximately 30% of the US population suffers from myopia. The tendancy to develop myopia is inherited, but the development is also affected by doing intense close visual work such as reading or working at a computer. The AOA notes, however, that you generally cannot become nearsighted just because you read – the actual onset of the condition is a combination of both genes and environment.
Farsightedness, by contrast, is medically termed “hyperopia”. It derives from the Greek hyper (over, above) and the Greek -ōpia (view, look). According to the American Optometric Association, it “is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly.”
Unlike myopia, the AOA does not give any figures about how many people in the US suffer from hyperopia. The do note, however, that “common vision screenings, often done in schools, are generally ineffective in detecting farsightedness. A comprehensive optometric examination will include testing for farsightedness.”
Astigmatism or astigmia is the medical term for a “vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.” It derives from the prefix “a-” (not or without) and the Greek stigma (tattoo mark), so I’ll be honest and say I don’t understand the derivation of the word at all.
The AOA notes that astifmatism is an extremely common vision condition. Most people have it to one degree or another, but most don’t have it to a degree that it impacts vision.
How Glasses Work
All of these vision problems keep your cornea – the lens at the front of your eye – from focusing light properly on your retina. A healthy eye has the focus on the retina. With myopia the focal point falls in front of the retina, and with hyperopia your focal point falls behind the retina. And astigmatism just makes the focal issues worse. So the lens of the glasses simply changes how the light enters your eyes, adjusting your focal point to fall on the retina once more.
“Simply”. Yeah, you have to love how our understanding of optics has advanced to the point that we can regard this as a “simple” process.