How is Visual Acuity like for short sightedness?!
Question:
How is Visual Acuity like for short sightedness?
Is it something like 20/20 etc? Can elaborate more?
Additional Details5 days ago
thanks Doodlestuff ! :=) i almost forget that as part of a question i could ask. yes, seeing the letter on eye chart perhaps doesn't mean to see it in clarity. i appreciate your input. keep them coming :=)
5 days ago
Mach. thats very good info more than i can perhaps get from the net. Your info helps not me but anyone who cares to stop and read.
Answers:
Short sightedness is also called near-sightedness and the medical term is myopia. Myopia, translated from Greek means to squint. Young people that have no problem seeing close or near, but have difficultly seeing distant objects, will sometimes squint in an effort to see better. The usual cause of myopia is that the eyeball is too long or the cornea is too steep and results in the image being focused before the retina at the back of the eye. Using a concave lens can extend the point of focus onto the retina and the image becomes clear. The cornea is the transparent dome-shaped window covering the front of the eye, and provides about two-thirds of the eye's focusing power.
Let's say that Dave can see the 20/20 line on the chart from 20 feet. If he now stands 50 feet from the chart he won't be able to see the 20/20 line, but he will be able to see somewhat larger letters (the 20/50 line). He is considered to have normal vision and can drive safely and adequately see road signs without the use of corrective lenses.
Sarah, on the otherhand, cannot see the 20/20 line from 20 feet. She has to read the larger letters of the 20/50 line in order to identify those letters. Her eyes have trouble seeing distant objects and so she will be required to use corrective lenses, contacts or surgery to make up for her vision problem. In diopters, her correction would probably be from minus 1.00 to minus 1.25 (-1.00 to -1.25).
Of course making the eyeball longer would not be easy, so flattening the cornea can correct myopia. In LASIK surgery, the cornea is sliced open to make a flap and then a laser is used to vaporize the material underneath (the stroma) and the flap is laid back down. the result is that the cornea is flatter.
By the way, about one-third of the population has myopia.