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When Things Go Dark

Updated: Oct 4, 2021

I probably see one to two patients a week that report that their vision “went dark” for several seconds before returning to normal. There are several different reasons why this can happen. It is important for patients to notice the details of these events.

If the temporary vision loss occurs in both eyes, rather than just one eye, unusual migraines, seizures, or swollen optic nerves are usually to blame; however, this could also be a sign of an impending stroke. If the visual loss was only noticed in one eye, artery occlusions, blood clots, or a condition known as giant cell arteritis could be the cause. It is very important in these cases to have the carotid arteries evaluated for blockage. Checking the blood pressure is also a necessity.

The length of time the patient experiences darkness is also important for the physician to know. While this can be difficult for some patients to recall accurately, it can go a long way towards pinning down a diagnosis. If related to migraines, the loss of vision tends to last longer and comes on slowly, lasting as long as an hour in some cases. If vision loss lasts only seconds to minutes, it is often due to artery occlusions or blood clots interrupting blood flow to the eye.

What was the patient doing at the time of the vision loss? Temporary loss of vision can occur with changes in blood pressure medication. A drop in blood flow to the optic nerve during a sudden change in posture can also cause dimming of the vision.

If the loss of vision cannot be related to a change in medication or posture, it is important to know if the patient also notices flashes of light, zigzag lines, or prismatic colors prior to the loss of vision. This type of visual disturbance can be migraine related. Treatment will depend on the frequency and severity of the migraine. Patients are encouraged to decrease stress factors and possiblly seek relief via massage or acupuncture. Medical treatment may include simple and combination pain relievers, but should be managed by a neurologist.

Giant cell arteritis is an inflammatory condition of the medium to large blood vessels of the body. The inflammation causes narrowing of the vessels leading to constricted blood flow, particularly in the vessels of the head and eyes. The reduction in blood flow can lead to episodes of temporary vision loss over time. The threat of permanent vision loss is real, if not treated in a timely manner. Patients are usually treated by their primary care doctor with higher doses of steroid medication to control inflammation and protect the optic nerves. The steroids are usually tapered slowly over 6 months to two years, depending on the patient’s response to treatment.

Cholesterol, calcium plaques, or blood clots can also block the main artery to the eye, leading to temporary vision loss. This is known as a retinal artery occlusion. These occlusions are more common in males and in patients older than 60. Risk factors include diabetes, hypertension, and high cholesterol. Vision loss usually lasts from 1 to 15 minutes before gradually returning as the blockage breaks up and circulation comes back. Treatment of a patient with this condition is focused on decreasing the risk of stroke. Medications may be prescribed to reduce cholesterol and/or reduce blood pressure. Patients are also counseled on controlling blood sugar, losing weight if necessary, and avoiding smoking.

Temporary vision loss is a fairly common complaint heard in every doctor’s office at some point. Diagnosing and treating the conditions known to cause this can be critical to preserving the patient’s sight, as well as their life. It is important for patients to pay attention to the details of these events in order for the eye doctor to know which other specialists may also need to be involved.


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