Plastic crystals are typically a quick fix with a good plastic polishing compound and a low speed setting on the dremel. The trick is to use a slow speed as to not heat up the crystal and essentially melt it. I have never been able to sucessfully polish out scratches from mineral or sapphire crystals . . . I just replace them.
In ophthalmology, convergence is the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object. This action is mediated by the medial rectus muscle, which is innervated by Cranial nerve III. It is a type of vergence eye movement. Near point of Convergence (NPC) is measured by bringing an object to the nose and observing when the patient sees double, or one eye deviates out. Normal NPC values are up to 10 cm. Any NPC value greater than 10 cm is remote, and usually due to high exophoria at near.
Convergence is when two or more things come together to form a new whole, like the convergence of plum and apricot genes in the plucot. Convergence comes from the prefix con-, meaning together, and the verb verge, which means to turn toward.