A<unk>  is an area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that is surrounded by a field of normal – or relatively well-preserved – vision. Every normal mammalian eye has a<unk>  in its field of vision, usually termed its blind spot. This is a location with no photoreceptor cells, where the retinal ganglion cell axons that compose the optic nerve exit the retina. This location is called the optic disc. There is no direct conscious awareness of visual<unk> s. They are simply regions of reduced information within the visual field. Rather than recognizing an incomplete image, patients with<unk> s report that things "disappear" on them. The presence of the blind spot<unk>  can be demonstrated subjectively by covering one eye, carefully holding fixation with the open eye, and placing an object (such as one's thumb) in the lateral and horizontal visual field, about 15 degrees from fixation (see the blind spot article). The size of the monocular<unk>  is 5×7 degrees of visual angle. A<unk>  can be a symptom of damage to any part of the visual system, such as retinal damage from exposure to high-powered lasers, macular degeneration and brain damage. The term<unk>  is also used metaphorically in several fields. The common theme of all the figurative senses is of a gap not in visual function but in the mind's perception, cognition, or world view. The term is from Greek σκότος/skótos, darkness.
Scotoma
Tar melanosis
Apudoma
Cementoma
Ocular melanosis
Bowenoid papulosis
Melasma
Erythrasma