People can have retinal or brain damage or malformation and cannot see {blindness}| [Hull, 1990]. Peripheral retinal processing allows subconscious navigation.
restored sight
If blind people have restored sight, they can see but not well. Children with unused eyes see light spots after applying pressure to eyeball.
space
Senses can carry information about space and time. Vision impairment causes brain reconnections to other sense regions. Input and output shape plastic brain [Sur and Leamey, 2001] [Simpson, 1988] [Teuber et al., 1960] [Teuber, 1960] [Von Senden, 1960].
space: touch or sound
If touches or sounds substitute for vision, it seems that sense qualities vaguely become more like visual sense qualities [Bach-y-Rita, 1995] [Dobelle, 2000] [Normann et al., 1996] [Schmidt et al., 1996].
space: touch
Skin-vibrator arrays (Tactile Vision Substitution System) can represent camera images. People can learn images and place them in 3D space, so they use depth perception as well as form perception. Tongue electrode arrays can replace vestibular system [Bach-y-Rita and González, 2002].
space: sound
Sound pitches and timing can substitute for spatial dimensions [Meijer, 2002]. Blind people perceive objects by sound echoes. Blindfolded people can learn echo navigation rapidly.
People can be unaware that they cannot see {Anton's syndrome} {blindness denial}. They deny that they are blind [Ramachandran, 2004].
Eye lenses can have protofibrils, which can develop into plaques {cataract, eye}|.
Infection or tear-duct blockage can cause eyes not to receive enough tears {dry eye}|, primarily in older people.
In older people, vitreous humor can thicken and pull away from retina, and neurons can cause flashes in front of eye {flasher, vision}|. If new flashers appear, go to ophthalmologist. If you receive head blows, vitreous humor can rub retina, causing flashes {stars, vision}.
In older people, vitreous humor can thicken and make denser filaments, which can appear as floating objects in front of eye {floater, vision}|. If new floaters appear, go to ophthalmologist.
Optic nerve can have damage {glaucoma}|.
causes
High intraocular pressure (IOP), eye injury, inflammation, tumor, advanced cataract, advanced diabetes, and steroid drugs can damage optic nerve.
types
Primary open-angle glaucoma (POAG) affects three million in USA. Eye-drainage canals clog, and inner-eye pressure increases. It has no symptoms and is gradual. It has easy treatment.
Blocked drainage canals can cause acute angle-closure glaucoma {narrow-angle glaucoma}. When pupil enlarges too much or too quickly, outer iris edge bunches up over drainage canals. Iris cannot open wide. Symptoms include headaches, eye pain, nausea, colors around lights at night, and blurred vision. Surgery can remove small region at outer iris edge.
Normal-tension glaucoma (NTG) {low-tension glaucoma} {normal pressure glaucoma} has optic nerve damage with almost normal intraocular pressure from 12 mm Hg to 22 mm Hg.
Older people can have macula focal-area degeneration {age-related macular degeneration} (AMD) {macular degeneration}|. In first macular-degeneration stage {dry stage, macular degeneration}, tissues thin. In next stage {wet stage, macular degeneration}, blood vessels grow and hemorrhage or leak behind macula, forming scar tissue. Anti-oxidant vitamins and minerals slow dry form. Laser treatments and photodynamic therapy can seal leaking blood vessels.
People can not see one quarter of visual field {quadrantanopia} [Horton and Hoyt, 1991].
Sunlight on snow can cause temporary blindness, eye watering, and double vision {niphablepsia} {snow blindness}.
Eye can turn away from nose {walleye}|, or cornea can be white or opaque.
People can have agnosia for colors {color-blindness}| [Meadows, 1974] [Nordby, 1990] [Zeki, 1990].
Males can interchange long-wavelength and middle-wavelength cones {double color-blindness} {Nida-Rümelin inversion}.
Eye refraction can be correct {emmetropia}, neither near-sighted nor far-sighted.
Far-sightedness {hyperopia} {hypermetropia} {far-sightedness} {presbyopia} results if eye length is too short. Hyperopia usually develops soon after birth. One person in three is hyperopic.
Near-sightedness {myopia}| {near-sightedness} results if eye length is too long. Myopia usually develops in early teens. One person in five is myopic. Near-sightedness makes reds more prominent.
4-Medicine-Disease-Kinds-Organ-Nerve
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Date Modified: 2022.0225