Glaucoma encompasses a group of eye conditions that progressively damage the optic nerve, which transmits visual information from the eye to the brain. This damage can lead to irreversible vision loss and is a leading cause of permanent blindness. Early detection of glaucoma is important because any vision loss that occurs from the condition is permanent.
The Eye’s Fluid Dynamics
The eye contains a clear fluid called aqueous humor, which helps maintain its shape and nourishment. This fluid is continuously produced by the ciliary body, behind the iris. The aqueous humor flows from the posterior chamber, through the pupil, and into the anterior chamber of the eye.
For healthy eye function, this fluid’s production and drainage must remain balanced. The primary drainage system for aqueous humor is the trabecular meshwork, a spongy tissue at the angle where the iris and cornea meet. From the trabecular meshwork, the fluid moves into Schlemm’s canal, where it re-enters the bloodstream. When there is an imbalance between aqueous humor production and drainage, fluid can accumulate, leading to increased intraocular pressure (IOP). This elevated pressure is a key factor in glaucoma development.
The Optic Nerve and Vision Loss
The optic nerve transmits visual signals from the eye’s retina to the brain, where they are interpreted as images. This nerve is composed of delicate nerve fibers susceptible to damage. Sustained or elevated intraocular pressure can compress these nerve fibers, leading to their deterioration.
Damage to the optic nerve results in a progressive loss of peripheral vision. This early vision loss often goes unnoticed because central vision remains unaffected. As damage advances, blind spots can expand, impacting central vision and potentially leading to blindness if untreated. In some instances, such as in Normal-Tension Glaucoma, optic nerve damage can occur even when eye pressure is within the typical range, suggesting that other factors like blood flow irregularities to the optic nerve may contribute to the damage.
Specific Forms and Their Development
Glaucoma manifests in several distinct forms:
- Primary Open-Angle Glaucoma (POAG): This is the most common type. It has an open drainage angle, but the trabecular meshwork does not function efficiently, causing aqueous humor to drain too slowly. This leads to a gradual buildup of intraocular pressure.
- Angle-Closure Glaucoma (ACG): This occurs when the iris blocks the drainage angle, preventing aqueous humor from reaching the trabecular meshwork. This blockage can cause a sudden, severe increase in eye pressure, known as an acute attack, with rapid onset of symptoms like pain, blurred vision, and halos around lights. Angle closure can also develop gradually.
- Normal-Tension Glaucoma (NTG): This involves optic nerve damage and vision loss despite intraocular pressure remaining within the normal range. This suggests that factors beyond elevated pressure, such as reduced blood supply to the optic nerve or a particularly sensitive optic nerve, may contribute to the disease progression.
- Secondary Glaucoma: This develops as a complication of other underlying conditions or external factors. These can include eye injuries, inflammation within the eye (uveitis), or certain medications like long-term corticosteroids that increase eye pressure. Other conditions like advanced cataracts or diabetes can contribute to its development.
- Congenital Glaucoma: This is a rare form present at birth or developing shortly thereafter, stemming from abnormal development of the eye’s drainage system during fetal growth.
Contributing Risk Factors
Several factors can increase the likelihood of developing glaucoma. Age is a significant factor, with risk increasing for individuals over 60, and for African Americans after age 40. Family history also plays a role; individuals with a direct relative who has glaucoma are at higher risk.
Ethnicity influences risk; for example, people of African descent have a higher risk of Primary Open-Angle Glaucoma, while those of Asian and Inuit descent have a higher risk of Angle-Closure Glaucoma. Certain medical conditions, including diabetes, high blood pressure, and heart disease, have been linked to an increased risk of glaucoma. Eye trauma can damage the drainage system, increasing susceptibility. Refractive errors like nearsightedness (myopia) can increase the risk of open-angle glaucoma, while farsightedness (hyperopia) is associated with a higher risk of angle-closure glaucoma.