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Dr. Andrew Rynne
Dr. Andrew Rynne

Family Physician

Exp 50 years

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What is the purpose of prism in eyeglasses?

Answered by
Dr. N. K. Misra


Practicing since :1977

Answered : 1253 Questions

Posted on Mon, 29 Aug 2016 in Vision and Eye Disorders
Question: want to discuss prescription glasses, specifically a BU prism. Doc added a 1.00 BU Vertical prism in my glasses (right eye). What does this do? I have strabismus; my left eye is too high sometimes and turns out sometimes. How does putting a prism in my other eye help? Can this be correct?
Answered by Dr. N. K. Misra 7 hours later
Brief Answer:
Vertical squint

Detailed Answer:
My dear,
Thanksa for sending your query to us.
Prism shifts the image towards the base.Since your left eye image is high up,shifting the right eye image up by BUPrism up the two images coincide and you see and ideally you should have lot of relief in eye strain,if you had any.Otherwise it technically makes the image as one.So this is good for you and carry on with this.
Any further query in this regard, please do get back to me.
Above answer was peer-reviewed by : Dr. Yogesh D
Follow up: Dr. N. K. Misra 24 minutes later
Thank you for your reply. Does a prism distort the images at all? It would seem to be that the prism should be in the lens of my weaker eye, since I have low vision, amblyopia, in that eye.

Are there advantages of putting the prism over my "good eye" instead of my weaker one? Does it matter which eye, generally, the prism is added?

I had three surgeries about 6 years ago, so prisms are a new thing to me. Before, my eye was so bad that prisms would not help. The look cosmetically acceptable now, or at least a lot better.

So, to be clear on my question, a BU would make my good eye appear higher up and in-line with my weaker eye?

Answered by Dr. N. K. Misra 1 hour later
Brief Answer:
Vertical squint.

Detailed Answer:
My dear
Good of you to get back to me.
Lets get this clear,prisms are used to shift the image and not to shift the eye cosmstically.This makes the images of two eyes coincide and there is no double vision and image is sharpe.
So you appear to be in good hands and they are managing you well.
Above answer was peer-reviewed by : Dr. Priyanka G Raj

The User accepted the expert's answer

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