I believe you are referring to the additional standard deduction amount. If you are claiming the standard deduction, it will be increased by $1250.00 to $1550 depending on your filing status.
As far as whether or not you can file as legally blind it depends on what your corrected vision was in your best eye.
Please look at the information you can find at the link below:
https://turbotax.intuit.com/tax-tools/tax-tips/General-Tax-Tips/Tax-Tips-for-the-Blind/INF23092.html
