Vitreous opacities are not a precursor to glaucoma. Vitreous opacities can be divided into physiological and pathological types. Physiological vitreous opacities generally do not affect vision, and one may see variously shaped black shadows in front of the eyes. Pathological vitreous opacities can impact vision and should be further examined by an ophthalmologist. The precursors of glaucoma include eye pressure, eye pain, photophobia, tearing, relief after rest, and a decrease in vision, along with halos seen around lights. If these symptoms occur, active treatment should be sought. Glaucoma can be classified into primary, secondary, congenital, and mixed types.