Light rays bounce off objects and enter the human eye through the transparent covering -- the cornea -- which bends the light through the pupil. From there, the light passes through the lens and focuses on the retina. Within the center of the retina are millions of cones and rods that convert the light into impulses and send them to the brain to produce an image. Sudden loss of vision occurs when a disorder or disease interrupts any part of this process.
Eye specialists classify vision loss as "sudden" if it develops within a few minutes to a few days. Sudden vision loss can occur in a variety of ways for various reasons. Sometimes it presents as blurred vision as a result of a loss of a portion of the field of vision. The vision loss can affect both eyes or only a single eye. Other symptoms, such as pain or swelling, may accompany a sudden loss of vision. Generally, total blindness is a result of a disorder affecting the entire eye, rather than a part of it.
Many disorders and diseases that cause sudden loss of vision do so because they affect the mechanisms that allow the eye to operate. Areas of the eye that are normally transparent to allow light through may become cloudy or entirely opaque, preventing light transmission. The retina itself may have abnormalities that prevent it from sensing light properly. Finally, issues with the nerves that carry the signals from the eye to the brain can prevent the eyes from working properly.
Unfortunately, the range of variables involved in the diagnosis of sudden vision loss prevent an accurate prediction of whether vision loss will be permanent or not. For many people, the best they can hope for is a minor improvement. Ocular ischemic syndrome, for example, is incurable and treatment can provide minor relief at most. On the other hand, migraine headaches can also cause sudden vision loss or complete blindness, but the symptoms usually resolve themselves after a migraine passes. Sudden loss of vision is generally a medical emergency and calls for immediate treatment.
Infections caused by herpes or improper use of contact lenses can damage the cornea and lead to scarring. This prevents light from traveling through the eye. Contact sports injuries may cause issues such as a detached retina, which results in the eye being unable to sense light rays correctly. Swelling or blood clots can cut off the blood supply to the retina and cause similar issues. However, the most common cause of sudden loss of vision or blindness is ischemia.
If blood supply to the optic nerve becomes blocked in some way, this can damage the nerve itself. There are four classifications of ischemic optic neuropathy. Transient visual obscuration results in vision loss episodes that last a few seconds and is due to intracranial pressure. Amaurosis fugax is a brief attack of blindness that can last for several minutes. Transient bilateral visual loss affects both cerebral hemispheres and causes serious vision loss. Finally, ocular ischemic syndrome involves constant ischemic damage to the eye, causing permanent vision loss.
Some individuals may experience an increase in intracranial pressure as the result of brain trauma or altitude sickness. If left untreated, this can cause papilledema, a swelling of the optic disc. Some people may have headaches, while others may not express any symptoms at all. The associated vision loss is most often bilateral, meaning it affects both eyes. Treatment is based on the underlying cause and may involve medications that help the body absorb the excess fluid causing the pressure.
Amaurosis fugax may be better known as episodic blindness. The vision loss most often affects only one eye and lasts for less than a few minutes. People who have experienced amaurosis fugax describe the blindness as someone pulling a curtain down in front of one of their eyes. Reduced blood flow to the eye causes this rare condition, which is often a warning symptom of something more serious, such as a stroke. If the cause is a blood clot, doctors may suggest blood thinners. People with diabetes and high blood pressure are at risk of amaurosis fugax.
Migraines and seizures can place pressure on the arteries and nerves responsible for vision, causing vision loss for the duration of the attack and possibly for minutes afterward. Doctors and patients often confuse transient bilateral visual loss for transient visual obscuration, as both issues relate to cranial pressure. Individuals describe vision loss from migraines as a zigzag pattern that flickers across a person’s sightline. In some cases, the loss of vision appears as blank or flickering spots.
Rarely, those with severe carotid artery disease may experience a form of vision loss. Ocular ischemic syndrome affects men twice as much as it does women, primarily those over 65. The arteries are incapable of providing enough blood to the eye, and it begins to weaken. Generally, only a single eye is affected, though bilateral issues are possible. Pain is common, and though the vision loss occurs over a few weeks, it is almost always permanent. Thankfully, sudden vision loss occurs in only 12% of instances.
A doctor or eye specialist will perform several tests to determine the cause of a sudden loss of vision. If any eyesight remains, the doctor may have the patient read from a vision chart. If the patient is experiencing blindness, the doctor may use a tool called a slit lamp to examine the affected eye under a high level of magnification. He or she may also measure the pressure in the eye. A specialist may opt to perform an angiography, a specialized x-ray that enables the doctor to examine the veins or arteries.
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