Glaucoma is caused primarily by damage to the optic nerve, often related to increased pressure inside the eye. This pressure builds up due to a blockage or malfunction in the eye's drainage system, which normally allows fluid called aqueous humor to flow out of the eye. When this fluid does not drain properly, it accumulates, raising the internal eye pressure (intraocular pressure), which can damage the optic nerve. Key causes and contributing factors include:

• Increased intraocular pressure from fluid buildup due to inadequate drainage through the trabecular meshwork (the tissue at the angle where the iris and cornea meet).
• Types of glaucoma differ in how the drainage angle is affected: In open-angle glaucoma, the angle remains open but drainage is slow and ineffective; in angle-closure glaucoma, the iris bulges and blocks the drainage angle, causing sudden pressure rise.
• Normal-tension glaucoma occurs even with normal eye pressure, likely due to optic nerve sensitivity or reduced blood flow.
• Secondary causes such as eye injury, inflammation, certain medications (like corticosteroids), other eye diseases, or systemic diseases like diabetes.
• Congenital glaucoma in children, due to abnormal eye development or blockages.
• Pigmentary glaucoma caused by pigment granules clogging drainage channels.

Additional risk factors include age (especially over 55), family history, certain ethnicities (African, Hispanic, and Asian descent), thin corneas, extreme nearsightedness or farsightedness, and taking corticosteroids. In summary, glaucoma is mainly caused by increased pressure inside the eye due to impaired fluid drainage or less commonly by optic nerve vulnerability even at normal pressures. This pressure damages the optic nerve, leading to vision loss over time. Vigilance through regular eye exams is important because damage can occur before symptoms are noticed. This understanding is based on current medical knowledge from authoritative sources including the Mayo Clinic, Penn Medicine, and glaucoma specialized organizations.