If a patient needs a 3 prism base in for convergence, could the prism have been specified using any other system acceptable to British Standards other than giving 1.5 base in on right eye and left eye?
I am not entirely sure what you mean, but if someone needs a total amount of 3 prism dioptres base in, this can be put in one eye only, or split between the two eyes, not necessary equal in both. For example, there could be 2 prism dioptres in one eye and 1 in the other. How this is prescribed however, depends on clinical tests, and it is up to the optometrist to specify the prism required in either eye.
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