Blindness is frankly lack of vision. Only those who experience no light perception are considered totally blind. And few are totally without some glimmer.
Legally blind refers to vision less than 20/200 or peripheral (side) vision is 20 degrees or below. Even though you may still have some useful vision.
A vision loss may indicate that you:
- see nothing at all
- able to tell light from dark
- able to detect vague shapes
A loss of vision may concern losses that are:
- sudden or gradual
- in one or both eyes
- part or total visual field
- temporary or permanent
Gradual vision loss may go unnoticed until some event brings it to the fore.
Visually impaired refers to a loss of vision that is uncorrectable or not correctable to a normal level. Vision impairment may be caused by:
- loss of visual acuity ~ objects unclear
- incorrect eye shape ~ harder to focus on stuff
- brain doesn’t process visual information correctly
- damage to the eye ~ affects ability to receive or process visual information
- loss of visual field ~ cannot see wide area without moving eyes or turning head
You can become visually impaired anytime.
Low vision means that even with correction, performing everyday tasks are a problem. Common types of low vision:
- central vision loss ~ blur, blinds pot, peripheral is okay
- night blindness – inability to see in dimly lit environments
- blurred vision – near & far out of focus even with correction
- generalized haze ~ sensation of a film or glare over viewing field
- light sensitivity ~ normal illumination overwhelms vision causing washed out image
- peripheral (side) vision loss – inability to see beside, above & below, aka tunnel vision
Typical causes for blindness or loss of vision globally include:
- lazy eye
- sports injury
- stroke or TIAs
- chemical burns
- vitamin A deficiency
- blocked blood vessels
- eye surgery complications
- cataracts ~ eye lens clouding
- glaucoma ~ optic nerve damage
- retinoblastoma ~ form of eye cancer
- trachoma ~ type of Chlamydia infection
- optic neuritis ~ optic nerve inflammation
- optic glioma ~ slow growing benign tumors
- diabetic retinopathy ~ complication of diabetes
- retinitis pigmentosa ~ progressive retinal damage
- retrolental fibroplasia ~ premature birth complication
- Hansen’s disease (leprosy) ~ chronic bacteria infection
- onchocerciasis (river blindness) ~ roundworm infection
- macular degeneration ~ sharp central vision destruction
A couple of these losses cause only temporary blindness.
Your vision loss may only involve part of the visual field, known as visual field defects. For instance:
- diabetic retinopathy, hypertensive retinopathy, retinal detachment ~ causes small, irregular vision patches
- tumor, aneurysm near pituitary gland ~ causes inability to see the outside part of the visual field in either eye
- macular degeneration, certain optic nerve damage ~ causes loss of ability to see things in the center visual field
- stroke, tumor affecting brain’s left side ~ causes inability to see all or part of visual field on right side for both eyes
- glaucoma, certain retinal disorders (i.e. retinitis pigmentosa) ~ causes vision loss in all directions of your peripheral, center straight is all that’s visual
Many causes for blindness, vision loss or visual impairments are painless, but serious.
Some treatments have only a limited window of time to preserve the health of your sight. So any degree of sudden vision loss needs to be responded to as an emergency. In other words, go to an ophthalmologist or emergency room at once.
FYI: an ophthalmologist is a medical doctor who specializes in eye and vision health care.