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Dr. Chan
Dr. Chan, Ophthalmologist
Category: Eye
Satisfied Customers: 356
Experience:  Board Certified in ophthalmology
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My husband had an eye exam today because he wanted to be sure

Resolved Question:

My husband had an eye exam today because he wanted to be sure he had better than 20/40 vision for renewal of his Commercial Driver License. His vision has always been great, but he had shingles in the left eye a couple of years ago and has some degradation in that eye. I think his vision is still very good, he just notices it because he is used to perfect vision. Also, he had some elevated pressure in the left eye after the shingles, but that seems to have resolved. The examiner gave him a prescription, but did not really answer his primary concerns.

1. His prescription reads OD Plano = -25 x 32 and OS +75 = -50 x 80. How does this convert to the layman's scale of 20/20, 20/30 or the like?
Submitted: 8 years ago.
Category: Eye
Expert:  Dr. Chan replied 8 years ago.



You cannot convert a prescription to what the acuity is. The prescription is merely a measurement of how his eye focuses images onto the retina. This is the focusing power needed in a lens to aid his eye to focus an image perfectly onto the retina.


How this image, once focused, is received in the retina and sent to the brain and processed as vision is measured by the acuity (this is the 20/20, etc.).


So, a prescription can focus the image; but if you have a bad retina or optic nerve or brain, it will not translate into good vision.


So a glass prescription cannot be translated into acuity. You will just have to call the office and ask what his best corrected acuity is.


Hope this helps.

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