Case 1.   Blurry Vision
The patient was sitting watching television when his vision suddenly went "blurry and cloudy" for about 4 minutes and then returned to normal over the next 10 minutes.  He wasn't convinced that anything had really happened, but then later on that evening he had another episode. This time he tried checking one eye at a time, and discovered that his right eye was fine, but that the vision in his left eye was "blurry."  He called 911 because he remembered seeing something about this kind of problem on a Brain Attack poster in his doctor's waiting room.
Diagrams
 

Expert Note Case 1.
Blurry Vision
Diagrams


This patient experienced a typical episode of transient monocular blindness (amaurosis fugax).  Many patients describe a blackout, a cloud or a "gray fog" that obscures vision in one eye, or in part of one eye. Occasionally it may be likened to "a shade falling over the eye." Usually the attacks are very brief, lasting about 1- 5 minutes, and are followed by full restoration of vision. Some patients have many repeated attacks, but others have only one or a few.

Two major mechanisms are proposed to explain this type of TIA.  (1) A tiny piece of thrombus formed on an ulcerated plaque at or near the carotid bifurcation, or a piece of the underlying plaque itself, breaks off and enters the ophthalamic artery and finally lodges in a retinal arteriole.  Ophthalmoscopic observation of the retinal vessels during actual episodes of transient monocular blindness has shown bits of whitish material (small emboli) temporarily blocking the retinal arteries.  (2) A low perfusion state resulting from ICA stenosis (and probably temporary formation of thrombus that further blocks the vessel) causes regions far from the site of stenosis (like the retina) to become briefly ischemic.

There can be a number of reasons for a transient loss of vision in one eye, such as inflammation of the arteries that supply the eye.  However, in older patients the cause is often carotid occlusive disease, produced by significant atherosclerosis and plaque erosion in the extracranial carotid.  In such a patient, transient monocular blindness may be a warning that a stroke is in the offing. Patients like this should therefore be evaluated immediately.