What must I do after stealing a sum of money from my father to buy glasses that are necessary due to my weak eyesight, and must I return the amount, the exact value of which I do not know?

It is permissible to take from the father's money without his permission when there is a need for expenses such as medical treatment, if the father is stingy or withholds it. This is based on the hadith (definition) of Hind bint Utbah. However, this is conditional on not having your own money or your husband's money; otherwise, the money must be returned and repentance made.