Visual symptoms are very common following both ischemic and hemorrhagic stroke. These complaints have a tendency to receive the label “blurred” or “blurry” by both patients and healthcare providers, but an important part of accurate diagnosis and increasing the chance of improving these symptoms for the patient involves understanding what the problem is. Not all “blurry” vision after a stroke is actually “blurry”! Over time, I have found that visual deficits following a substantial brain injury tend to fall into one of the following categories. While scores of neurological conditions can result in these visual syndromes, for our purposes we will keep the focus on stroke.
Diplopia, or double vision, occurs when more than one image of an object is being visualized by the patient. This occurs most commonly because the eyes are not aligning properly to fixate on a visual target, and as a result of failing to converge at a specific point, mixed visual information is presented to the brain. When a patient has experienced a stroke, most often I find that the injury was in the brainstem, as there are centers controlling eye movements in this location. Double vision can also occur if there is an injury to one of the cranial nerves controlling eye movement closer to the eye itself, even if the brainstem is not injured.
Visual aura often is described as “blurry vision” by patients, but is much more complex than this description would suggest. Stroke patients may experience temporary visual illusions, such as the visualization of distorted surroundings, blurring of a crescent-shaped area or a larger section in a person’s visual world, flashing lights, wavy lines, development of “tunnel vision,” or any other number of transient visual symptoms. Fortunately, visual aura is very benign and treatable in most cases. Patients may be concerned that episodes of visual aura are TIAs, or transient ischemic attacks, that may represent the start of another stroke. I have seen people who have been taking warfarin or other big-gun anticlotting therapy for years because of “TIAs,” but when we get down to it turns out to be visual aura.
- Homonymous Hemianopia occurs when a visual field is distorted or absent, meaning that one half of someone’s visual world is impacted. Often patients will think they have lost vision in the right eye or in the left eye, when in reality upon testing, the eyes are fine, but the right half of the person’s visual world is absent. This typically occurs with an injury to the occipital lobe, the brain’s visual processing center. Put simply, the right occipital lobe processes visual information in the left field of vision, and the left occipital lobe processes the right field. A stroke impacting the right occipital lobe may result in loss of vision in the left visual field. The MRI brain (figure 1) was obtained from a young postpartum woman with a left occipital infarction with hemorrhagic conversion, which resulted in loss of vision in her right visual field.
Visual Hallucinations occur when a patient detects objects or movement that is not actually present. This can occur for a variety of reasons, involving either the brain or the eye. Charles Bonnet Syndrome is the name given to visual loss followed by the brain “filling in” missing visual information in the form of hallucinations. I have seen cases where the hallucinations are pleasant (a cuddly appearing kitten), and cases where they are disturbing (large insects). If visual hallucinations are present after a stroke, I always think it is worth performing an electroencephalogram (EEG) during the hallucination to better exclude seizure activity in the area of injury.
Oscillopsia is present when a patient perceives that objects at rest are “swaying” back and forth when movement is not actually present. This can occur with brainstem or cerebellar stroke, but I have seen it in other locations as well. Patients without stroke may experience this visual phenomenon with benign paroxysmal position vertigo (“inner ear” vertigo, as a lot of patients describe it) or with migraine as well.
Cortical Blindness typically involves injury to both occipital lobes. Patients lack vision, even though the eyes may be healthy. This can be devastating for patients, as these are typically patients who have always relied on vision who abruptly become blind without warning since stroke is usually of sudden onset. I attended an event in 2013 (Dining in the Dark) in which a nice dinner was served to us as we wore blindfolds. Have you ever considered how heavily you might depend on your vision to get through simple tasks, such as a meal? It gave me tremendous appreciation for what patients with cortical blindness after stroke must experience – to have vision one day, and for it to be gone the next is difficult to imagine. To make things even more challenging, some patients with cortical blindness develop Anton Syndrome, which involves blindness without the recognition that blindness exists. Now can you imagine everything around you seeming real, but none of what you are visualizing is actually there?
Finally, there is vision that is truly blurry. Regardless of the stroke’s location, patients often complain that their glasses prescription does not seem correct any longer. They may obtain a new prescription after the stroke, only to find that it is no longer accurate six weeks later. A neuroophthalmologist (this is a neurologist or an ophthalmologist who specializes in visual problems after a brain injury) can be helpful here, but it takes patience from both patient and physician as symptoms tend to fluctuate.