Glaucoma is a collection of eye conditions that progressively damage the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. This damage often results in vision loss and is usually associated with abnormally high pressure within the eye. The internal pressure builds up when the fluid that circulates inside the eye cannot drain properly. Because the visual changes can be subtle initially, glaucoma is sometimes referred to as the “silent thief of sight,” progressing unnoticed until significant damage has occurred.
Vision Loss Progression
The most common form, Primary Open-Angle Glaucoma (POAG), begins with a gradual and painless loss of peripheral vision. This process is so slow that the brain typically compensates for the missing visual information, meaning a person rarely notices the vision loss in its earliest stages. The initial blind spots occur in the periphery, allowing the condition to advance significantly before it is detected.
As the disease progresses and more of the optic nerve fibers are destroyed, the field of vision gradually constricts. This creates the appearance of “tunnel vision,” where only the central vision remains. By the time a patient notices this distinct visual effect, a substantial amount of the optic nerve has already been permanently damaged. Vision loss caused by this chronic form is irreversible, underscoring why routine eye examinations are important for early detection.
Acute Symptoms of Glaucoma
A different type of glaucoma, called Angle-Closure Glaucoma, presents with sudden, painful symptoms. This condition is caused by an abrupt blockage of the eye’s internal drainage system, leading to a rapid and severe spike in intraocular pressure. A person experiencing this acute attack will often report severe eye pain and an intense headache around the eye or forehead.
The visual disturbance is immediate and noticeable, often described as a sudden blurring or haziness of vision. The intense pain and high pressure can trigger systemic reactions, resulting in symptoms such as nausea and vomiting. An acute angle-closure attack is a medical emergency because the extremely high pressure can cause permanent vision loss within a matter of hours.
Physical Signs of the Condition
One common experience is seeing halos or rainbow-colored rings around bright lights, particularly at night. This visual effect is caused by swelling of the cornea, the clear front surface of the eye. The swelling occurs when the internal eye pressure is suddenly elevated.
In acute cases, the eye itself can look visibly red or bloodshot due to the rapid pressure increase. The eye may also feel noticeably tender to the touch. The pupil in the affected eye may appear mid-dilated and unreactive to light, a sign noted during an examination.
The Underlying Eye Damage
The visual symptoms described are a direct result of physical damage to the optic nerve, which connects the eye to the brain. This nerve damage is usually caused by sustained or sudden high pressure, but it can occur even with normal eye pressure in some cases. The increased pressure pushes against the nerve fibers as they exit the back of the eye, the optic disc.
This pressure causes the nerve head to physically change its shape, a process known as “cupping.” As the delicate nerve fibers die, the central indentation, or cup, of the optic disc gets progressively larger and deeper. This change is measured by doctors using the cup-to-disc ratio. This hollowing-out corresponds directly to the visual field loss, as the damaged nerve tissue can no longer transmit visual signals.