Nearsightedness and Lens Power Question...?

Question

This question assumes no astigmatism, just myopia. What power lens "generally" corresponds what fractional value given to eyesight? i.e. would a prescription of -0.5 be equal to 20/30 vision? Would a script of -1.0 be equal to 20/40 vision? Is there a doctor here who can tell me this or post a link to this information? It's for a school project and I would like to know from -0.5 to -5.0 - Thanks in advance. I'm only looking for myopia (negative) numbers but hyperopia (positive) numbers would also be interesting. Is there a common mathematical formula to determin this information?

Answer 1

This is a rough rule of thumb.... for myopia, the amount of the prescription is roughly 0 to -0.25 for each line on the chart.  For example, if you see 20/30  you might be -0.50 or -0.75, if you see 20/50, you might be -1.00 to -1.25.  Of course this does not have a linear progression.  The theory tends to fall apart at higher prescriptions.

This link may help:  http://forums.studentdoctor.net/showthre...

Answer 2

Well in the UK we certainly do not issue a predetermined prescription dependent on the visual acuity. 6/6 or what you would call 20/20 vision is optimal for people to see. You will gradually insert lens power until they reach this visual acuity. Someone with -2.00 shortsightedness could possibly see (uncorrected) 20/40 and so could someone who is -1.00. I'm not an optometrist myself but i have worked in optical practice for over 3 years and i have never heard of a mathematical formula. Hope this is of some help to you.