Cataracts and glaucoma are distinct eye diseases affecting different parts of the visual system. A cataract involves the clouding of the eye’s natural lens, which gradually impairs vision. Glaucoma is a group of conditions characterized by damage to the optic nerve, which transmits visual information from the eye to the brain. Although separate, an advanced, untreated cataract can directly cause a form of secondary glaucoma by physically or chemically interfering with the eye’s internal fluid dynamics. This causal relationship is a serious complication requiring immediate attention to prevent permanent vision loss.
Defining the Conditions and Their Independent Effects
A cataract forms when proteins within the lens begin to clump together, turning the lens opaque. The lens is a clear, disc-shaped structure situated directly behind the iris. This clouding obstructs the passage of light to the retina, resulting in blurred vision, glare, and difficulty seeing at night. The vision loss caused by cataracts is generally reversible through surgical intervention.
Glaucoma is primarily a disease of the optic nerve, often associated with elevated intraocular pressure (IOP). The front part of the eye is filled with aqueous humor, a constantly circulating fluid that nourishes the eye’s structures. This fluid is produced and drains out through the trabecular meshwork, which maintains pressure inside the eye. If the drainage system malfunctions, pressure builds up, eventually damaging the sensitive optic nerve fibers. Unlike cataract-related vision loss, the damage to the optic nerve from glaucoma is permanent and irreversible.
The Mechanism of Causation
A cataract must be significantly advanced or “hypermature” to trigger secondary glaucoma. This causation occurs through two primary mechanical or chemical mechanisms, both involving the cataract interfering with the eye’s delicate fluid drainage system.
Phacomorphic Glaucoma
Phacomorphic glaucoma is a form of angle-closure glaucoma that arises when the cataractous lens swells, a condition known as intumescence. As the lens increases in volume, it pushes the iris forward, physically narrowing the drainage angle for the aqueous humor. This narrowing can lead to a sudden, complete blockage of the trabecular meshwork, causing a rapid spike in intraocular pressure. This sudden obstruction is considered an ophthalmic emergency due to the high risk of rapid optic nerve damage.
Phacolytic Glaucoma
The second mechanism is phacolytic glaucoma, a type of open-angle glaucoma. In this scenario, proteins within a hypermature cataract break down and leak out of the lens capsule. These lens proteins circulate in the aqueous humor, clogging the drainage channels of the trabecular meshwork. The obstruction is compounded by immune cells called macrophages that attempt to engulf the proteins but block the outflow pathways further. This process results in a gradual but persistent elevation of intraocular pressure, often accompanied by inflammation.
Treatment Strategies for Secondary Glaucoma
When secondary glaucoma is caused by an advanced cataract, the definitive treatment is surgical removal of the obstruction. Cataract extraction involves removing the cloudy lens and replacing it with an artificial intraocular lens. This procedure is effective because it immediately eliminates the source of the problem.
In phacomorphic glaucoma, removing the bulky lens quickly deepens the anterior chamber and opens the blocked drainage angle, resolving the pressure crisis. For phacolytic glaucoma, removing the hypermature lens eliminates the source of protein leakage, allowing the drainage system to clear over time.
Before surgery, clinicians often use medications to urgently lower the intraocular pressure and manage the severe inflammation present in both types of secondary glaucoma. The timing of the cataract surgery is often urgent to prevent irreversible damage to the optic nerve.
If the glaucoma has already resulted in significant, irreversible damage to the optic nerve, lens removal alone may not be sufficient to achieve healthy long-term pressure. In these cases, the cataract surgery is often combined with a traditional glaucoma procedure, such as a trabeculectomy, or a minimally invasive glaucoma surgery (MIGS). These combined surgeries aim to restore vision and provide a long-term mechanism for fluid drainage to protect the remaining optic nerve function.