Disease processes that affect the retina and/or the optic nerve often lead to decreased or missing vision in localized areas of the visual field. These are called scotomas. While scotomas (or scotomata) are usually referred to as “blind spots,” a scotoma may be an areas of complete visual field loss (when even the brightest stimuli are not seen) or it may be an area of impaired vision or relative vision loss (when dim stimuli are missed, but bright stimuli are seen). These areas or islands of loss or impairment of vision may appear as dark, light, or blurred areas in the field of vision. The visual field may seem to have holes into which objects disappear; one second you see an object and then when you move your eyes it disappears.
Not so obvious
Surely if you have a blind spot in your visual field you would know it, you would see it. In fact every human has a blind spot in each eye, the spot representing the place on the retina where the optic nerve exits the eye, an area with no photoreceptor cells.
Why don’t you see these gaps in your visual field? We see with two eyes, and most of the time the left eye sees what’s happening in the right eye’s blind spot and vice versa. If both blind spots overlap while looking at an object the brain fills in the spot with information from the visual field around the blind spot.