Viper GTS:
Ophthalmologists routinely dilate the eyes of most patients; optometrists may or may not; opticians almost never dilate (and in some states may not legally do so.) If you dislike having your eyes dilated, and have no family history of vascular illnesses, diabetes, or glaucoma, you might want to choose an optometrist or optician affiliated with one of the discount-eyeware chains. I don't recommend this, but for a young person like yourself, it's probably okay.
Why is dilation of the eyes done? The back portion of your eye, which includes the peripheral retina, the macula lutea, and the optic nerve (all of which are essential to maintain normal vision,) cannot be examined without dilating the pupils, since pupils reflexively constrict when the bright examining light is shone into the eyes. The chemicals which are used as "dilating drops" serve two purposes: to enlarge the pupil's diameter and to make it nonreactive when light is shone into the eye.
This procedure assists the physician in early detection of conditions such as cataracts, glaucoma, macular degeneration, and diabetic retinopathy, all of which can lead to blindness if not treated in early stages.