In this particular episode of Ask an Eye Doc, you will learn:
- How nearsighted people experience vision
- About axial length
- How eye length makes you nearsighted
For you readers out there, here’s the answer in written form:
A lot of people confuse the terms “nearsighted”, “farsighted” and “presbyopia“. This episode will explain nearsightedness, also known as myopia.
Nearsightedness describes your natural vision without any glasses. If you’re NEARsighted, it means you see better up close (near) than far away. If you can hold something close to your face and see it clearly and things far away are blurry, you’re most likely nearsighted.
If you’re slightly nearsighted, your far point might be 40 inches away from your face. Anything past that point is blurry. If you’re very nearsighted, your far point might be 2 inches away from your face. People who are this nearsighted tend to refer to themselves as “blind without glasses”.
Some people are nearsighted with a lot of astigmatism, so even their near vision is blurry. This is called compound myopic astigmatism. Check out episode 1 to learn more about what astigmatism is.
What causes myopia is the length of your eye from front to back. This distance is called axial length. Nearsighted people have a longer axial length than people who are not nearsighted.
Axial length matters because the cornea and crystalline lens, two focusing lenses in the front part of the eye, have a specific focal length. If the retina is too far away, the image projected onto it will be out of focus.
If this doesn’t make sense, check out epsiode 7 to learn about what the retina is and how the eye is like a movie theater. Also check out episode 4 to learn more about one of these focusing lenses and how it can affect your near vision when you get older.
In essence what makes you nearsighted is the fact that your eye just grew too long from front to back to match the internal focal length of your eye. The movie screen is too far away from the projector.
And that’s what nearsightedness is. Long eyeballs!