A vision impairment refers to when you lose part or all of your ability to see (vision). The impairment must persist even with the use of eyeglasses, contact lenses, medication, or surgery.
Types of Vision Impairments
Low visual acuity means vision between 20/70 and 20/400 with the best possible correction, or a visual field of 20 degrees or less.
Blindness is defined as a visual acuity worse than 20/400 with the best possible correction, or a visual field of 10 degrees or less.
Legal blindness in the US means visual acuity of 20/200 or worse with the best possible correction, or a visual field of 20 degrees or less.
Visual acuity of 20/70 to 20/400 (inclusive) is considered moderate visual impairment or low vision.
Causes of Visual Impairment
This condition is due to the rise of normal fluid pressure inside the eyes. The type of vision is usually like a tunnel.
The intact vision remains in the center while progressively the peripheries start decreasing. The center of the tunnel reduces in size progressively till total vision is lost if left uncorrected.
A central area of woolly or cottony opacity obscures the central part of the vision.
The peripheries may be normally seen. AMD usually blurs the sharp, central vision that is needed for closely viewed activities like reading, sewing, and driving. This is a painless condition.
There is general clouding of the vision. As the whole eye lens is affected the blurring of vision may be diffuse until it is totally lost.
There may be other symptoms like photophobia – inability to see the light; diplopia – double vision etc. Cataracts are very common in older people.
Diabetes leads to damage of the smaller arteries and blood vessels at the back of the eyes over the retina.
Diabetic retinopathy is the most common diabetic eye disease and a leading cause of blindness in adults.
Usually vision impairment in diabetics begins as black spots or floating shapes that appear in the field of vision. Slowly complete vision may be lost if left unchecked.
Myopia or near sightedness or short sightedness means a person can see nearby objects clearly but distant objects appear blurred. High myopia may lead to vision impairment.
This is a genetic or inherited condition. Initially it manifests as night blindness.
As the disease progresses there may be a tunneling of vision with loss of peripheral vision followed by complete blindness.