Publisher Summary Glaucoma is not a disease in itself but a symptom-complex occurring in a variety of pathological conditions with the characteristic sign of raised intra-ocular pressure common to them all. This increased tension is caused in one of three ways: (1) an increased pressure in the intra-ocular capillaries causing congestion and increased secretion of fluid; (2) a normal secretion of intra-ocular fluid with diminished drainage at angle of anterior chamber or obstructed circulation at the pupil; and (3) biochemical changes in the intra-ocular fluid resulting in increased protein or cell content. Since the uveal tract is spongy in structure, when congested it can easily become sufficiently engorged to impede or even obstruct the canal of Schlemm, the normal drainage channel of the eye. This chapter discusses that glaucoma is classified under two headings: (1) primary, where the cause of the condition is still uncertain, and (2) secondary, where the cause is known. It also describes infantile glaucoma—buphthalmos—that is totally different clinically from the adult form of glaucoma. The earliest symptoms are photophobia, lacrimation, and general ocular discomfort.