Glaucoma is a group of eye diseases that progressively damage the optic nerve, the bundle of nerve fibers connecting the eye to the brain. This condition is a leading cause of irreversible blindness. The damage is often associated with elevated pressure inside the eye, known as intraocular pressure (IOP). Glaucoma is often called the “silent thief of sight” because the vision loss is typically so gradual that a person may not notice symptoms until significant and permanent damage has occurred.
How Glaucoma Damages the Optic Nerve
The eye constantly produces a fluid called aqueous humor. To maintain stable intraocular pressure (IOP), this fluid must drain out at the same rate it is produced through the trabecular meshwork. If the drainage system becomes less efficient, the fluid builds up, causing the IOP to rise.
The most common form, open-angle glaucoma, involves a gradual clogging of this drainage system. This chronic pressure buildup compresses the optic nerve fibers as they exit the back of the eye, causing them to die off. This loss creates corresponding blind spots in the visual field, and the resulting vision loss is permanent.
The Progression of Vision Loss
The visual experience changes as the disease progresses. Damage typically begins by creating small blind spots, known as scotomas, in the outer edges of the visual field. Since these initial changes happen in the periphery, the brain often compensates for the missing information, making the loss unnoticeable. This slow onset is why the condition is often undiagnosed until later stages.
As nerve damage continues, these peripheral blind spots merge and expand, gradually narrowing the field of view. This advanced stage is commonly described as “tunnel vision,” where the person can only see what is directly in front of them. Central vision, responsible for fine detail tasks like reading, is usually spared until the very late stages. This means a person may still read an eye chart while having severe limitations in their side vision.
The slow narrowing of the visual field means the world progressively shrinks. Objects and movement outside of the direct line of sight become invisible, limiting awareness. Only when the optic nerve has suffered extensive damage does the loss of central vision begin, leading to blurred sight and, ultimately, total blindness if untreated.
Practical Implications for Daily Living
The loss of side vision creates significant challenges for everyday tasks and safety. Mobility becomes difficult because the lack of peripheral awareness makes it hard to detect obstacles, steps, or changes in terrain. This reduced ability to scan surroundings and judge distances increases the risk of tripping, falling, or bumping into objects, especially in unfamiliar environments.
Driving is often unsafe because peripheral vision is essential for noticing approaching vehicles, pedestrians, or traffic signs. People may also experience reduced contrast sensitivity, making it harder to distinguish objects against a background or navigate in dimly lit areas. Simple adaptations can help mitigate these risks, such as utilizing high contrast colors to mark steps or doorways. Adequate, bright, and glare-free lighting is also recommended to improve visibility for tasks.