A white "pimple" on the white of the eye is most likely a pinguecula, according to MedlinePlus. A pinguecula is a common non-cancerous growth found on the surface of the white of the eye.
MedlinePlus reports that a pinguecula grows most commonly on either side of the cornea. The causes are unknown, though long-term sun exposure or eye irritation may be a factor. Pinguecula are rarely harmful and treatment is usually unnecessary. In some cases, the growth may need to be removed if it grows large enough to cause discomfort. The formation of a pinguecula may be prevented by using eye lubricants or wearing good-quality sunglasses.