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Difference between revisions of Frequently Asked Questions/Myopia
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==Does 20/20 mean perfect eyesight?== | ==Does 20/20 mean perfect eyesight?== | ||
In most cases, an [[optometrist]] will prescribe glasses for 20/20 vision. Optometrists are not perfectly accurate in many aspects ({{awesome}}), and so you might actually have a small amount of [[myopia]] or [[hyperopia]] in reality. | In most cases, an [[optometrist]] will prescribe glasses for 20/20 vision. Optometrists are not perfectly accurate in many aspects ({{awesome}}), and so you might actually have a small amount of [[myopia]] or [[hyperopia]] in reality. In a lot of cases, 20/20 does mean perfect eyesight. It means you can read the 20/20 line on a [[Snellen chart]] without using [[Active Focus]]. | ||
{{jake says|No, 20/20 is definitely not equal to perfect eyesight. | |||
The entire premise, the eye chart, the way your visual acuity is measured, is actually a very, very rough approximation of your eyesight. It’s “good enough” for the mainstream to “prescribe” you lenses, but you should be aware that it’s about as scientifically representative of your vision as a stick figure is of your real person. | |||
Toshiki recently offered a very apt summary of eye chart testing, in the forum: | |||
{{quote|20/20 is just an 1861 approximation of the average visual acuity of a human. Today we know that for adolescents and young adults (up to say 35) it’s nothing unusual to have 20/10 and better vision. It’s just unusual for optometrists/ophthalmologists to actually find 20/10 or better, because… | |||
…the optometrist’s setup with rather poor lighting tends to cut off anything better than 20/15, | |||
…the small distances between symbols that you have for high acuity lines lead to an effect called crowding, which makes anything smaller than 20/15 hard to recognize even for those with 20/8 vision, and finally | |||
…most eye charts stop at 20/13, which is probably a good thing, because otherwise a lot more young folks would be (jay-)walking on the streets staring at their smartphones 15cm in front of their eyes while wearing glasses that give them ants-from-outer-space vision. | |||
Given these facs, I don’t see why getting better than 20/20 vision should require any lenses at all. On good days and with decent lighting, I am now at 20/16 without correction (only left eye, right is still 20/32…20/50).}} | |||
Consider too that many jurisdictions require 20/40 vision for driver’s license exams to be passed without corrective lenses. And if you’re curious, print an eye chart online and compare your vision in shaded outdoor light to results you get with indoor lighting. You might notice dramatic differences! | |||
So what’s 20/20? | |||
20/20 is a barn door. It’ll do, as far as determining a ballpark for your eyesight, and a means to figure out how much lens correction will give you the clearest possible vision. Consider this, the tool used by optometry, and it’s vaguest accuracy, before ‘blindly’ trusting the mainstream lens sales with your eyesight.}} | |||
==What is axial elongation?== | ==What is axial elongation?== | ||
[[Axial elongation]] is the increase in length of the eyeball. It happens when you wear glasses and look at screens for extended periods of time. Specifically, it happens due to [[hyperopic defocus]] as a result of [[close work]] combined with [[glasses]] that are [[overprescribed]] for the [[focal distance]] in question. | [[Axial elongation]] is the increase in length of the eyeball. It happens when you wear glasses and look at screens for extended periods of time. Specifically, it happens due to [[hyperopic defocus]] as a result of [[close work]] combined with [[glasses]] that are [[overprescribed]] for the [[focal distance]] in question. | ||