緑内障：概要

Glaucoma develops when aqueous humor drainage becomes impaired, causing fluid to accumulate in the eye. In open-angle glaucoma, the trabecular meshwork stiffens, slowing drainage. In angle-closure glaucoma, the iris bulges and blocks the iridocorneal angle, preventing outflow entirely. Both mechanisms disrupt the balance between aqueous humor secretion and drainage, progressively raising intraocular pressure.

The ciliary body epithelium continuously secretes aqueous humor into the posterior chamber. This fluid flows through the trabecular meshwork and drains via the canal of Schlemm at the iridocorneal angle. In a healthy eye, the secretion rate equals the drainage rate, maintaining normal intraocular pressure and preventing optic nerve damage.

Open-angle glaucoma occurs when the iridocorneal angle remains open but the trabecular meshwork stiffens, causing slow, progressive fluid accumulation and gradual pressure increase. Angle-closure glaucoma develops when the iris bulges and blocks the iridocorneal angle, preventing aqueous humor outflow and causing rapid, severe pressure elevation. Angle-closure glaucoma is a medical emergency.

Elevated intraocular pressure damages the retina and optic nerve, causing irreversible vision loss and blindness. This damage accumulates over time as pressure remains elevated. Early detection and treatment are critical because the structural damage cannot be reversed once it occurs, making prevention of pressure elevation essential.

Aqueous humor drains through the trabecular meshwork, a specialized tissue that filters fluid, and then exits via the canal of Schlemm. Both structures are located at the iridocorneal angle, where the iris and cornea meet. In glaucoma, blockage or stiffening of these drainage pathways prevents normal fluid outflow, leading to pressure accumulation.

Glaucoma is managed using either pharmacological or surgical interventions. Medications aim to reduce aqueous humor production or increase drainage to lower intraocular pressure. Surgery may be performed when drugs are insufficient or when rapid pressure reduction is needed, particularly in angle-closure glaucoma emergencies.

The ciliary body epithelium, located in the posterior chamber, continuously produces aqueous humor. This fluid is essential for maintaining eye shape and providing nutrients to avascular structures like the lens and cornea. The secretion rate of aqueous humor must be balanced by its drainage rate to maintain normal intraocular pressure.