Glaucoma and cataracts are often confused because both are age-related eye diseases that impair vision. However, they are distinct disorders affecting different parts of the eye. Cataracts involve a physical change to the eye’s focusing mechanism (the lens), while glaucoma causes progressive damage to the optic nerve, which connects the eye to the brain.
Glaucoma: Damage to the Optic Nerve
Glaucoma is a group of disorders characterized by progressive damage to the optic nerve, which transmits visual information to the brain. This damage is usually associated with abnormally high intraocular pressure (IOP). As the nerve fibers die due to pressure, blind spots develop in the visual field.
The pressure buildup results from an imbalance in the eye’s fluid dynamics. The eye constantly produces aqueous humor, a clear fluid that nourishes the front of the eye. This fluid must drain through the trabecular meshwork at the same rate it is produced to maintain a healthy IOP.
In primary open-angle glaucoma, the most common form, the drainage angle is open, but the trabecular meshwork is inefficient. This causes the fluid to drain slowly, leading to a gradual increase in IOP. The pressure compresses the nerve fibers, restricting nutrient flow and causing irreversible vision loss.
Cataracts: Clouding of the Lens
Cataracts are the clouding of the eye’s natural lens, located behind the iris and pupil. The lens is normally clear and focuses light onto the retina. When cataracts form, the lens becomes opaque, causing light to scatter and resulting in blurred or hazy vision.
This cloudiness results from the aggregation of proteins within the lens. The lens contains structural proteins called crystallins, which must remain transparent for clear vision. Over time, due to factors like oxidative stress or UV exposure, these proteins break down and clump together.
These protein clumps prevent light from passing cleanly through the lens, causing visual impairment. Since this is a physical change to the lens structure, it is considered an opacity or physical barrier. The severity of impairment depends on the density and location of the protein aggregation.
Key Differences in Symptoms and Progression
The patient experience differs significantly between the two conditions. Glaucoma is often called the “silent thief of sight” because open-angle glaucoma is usually painless and progresses slowly without early symptoms. Vision loss begins in the periphery, and patients often do not recognize the problem until significant, irreversible “tunnel vision” has occurred.
Cataract symptoms are experienced as a general reduction in visual clarity across the entire field of vision. Patients report cloudy or blurry vision, fading or yellowing colors, and difficulty seeing at night. Intense glare or halos around lights is a defining symptom, occurring because the cloudy lens scatters incoming light.
The outcome of vision loss also separates the conditions. Glaucoma-related vision loss is permanent because optic nerve damage cannot be reversed. Management focuses on preventing further progression and preserving remaining vision. In contrast, cataract vision loss is potentially reversible because the physical clouding of the lens can be corrected.
Distinct Treatment Approaches
Glaucoma treatment focuses on lowering intraocular pressure (IOP) to prevent further optic nerve damage. Management often begins with prescription eye drops that decrease the production of aqueous humor or improve its outflow.
If medication is insufficient, laser procedures or conventional surgery, such as trabeculectomy, may be used to create a new drainage path for the fluid. The goal of all glaucoma interventions is to control eye pressure and slow the progression of vision loss, as sustained damage cannot be cured. Micro-invasive glaucoma surgery (MIGS) is sometimes performed alongside cataract surgery to lower IOP.
Cataract treatment is a surgical correction procedure that is generally curative. The procedure, known as phacoemulsification, involves making a small incision to remove the cloudy natural lens. The opaque lens is then replaced with a clear, artificial intraocular lens (IOL). This process restores the eye’s light-focusing function and typically results in significant vision improvement.