World Health Organisation (WHO) defines Low Vision as “A condition when an individual who has impairment of visual functioning even after treatment and/or standard refractive correction, and has a visual acuity of less than 6/18 to light perception, or a visual field less than 10 degrees from the point of fixation.
Causes for Low Vision
Eye diseases or conditions can cause visual impairment. Some of the more common causes of low vision include:
Macular degeneration is a disorder that affects the retina, the light-sensitive lining at the back of the eye where images are focused. The macula-the area on the retina responsible for sharp central vision-deteriorates, causing blurred vision. This can cause difficulty reading and, for some, a blurry or blind spot in the central area of vision. Both exudative and non-exudative forms of macular degeneration are age-related. They are the leading cause of blindness in people over 50.
A cataract is the thickening and clouding of part or all the crystalline lens inside the eye. This clouding interferes with light reaching the sensitive part of the eye namely the retina situated at the back of the eye, resulting in general loss of vision. Most common causes include aging, long-term exposure to the sun's ultraviolet radiation, injury, disease and inherited disorders.
Glaucoma also known as the silent killer of vision causes damage to the optic nerve, this occurs due to increasing internal pressure in the eye because of disruptions with the flow or drainage of fluid within the eye. It can also occur when the internal pressure of the eye does not increase (normal-tension glaucoma), but there is not enough blood flow to the optic nerve. There are no early symptoms in the most common form of glaucoma, but the first signs of damage are defects in side (peripheral) vision and difficulty with night vision. If diagnosed early, it can be treated with drugs, or sometimes surgery can minimize vision loss.
People with diabetes can experience day-to-day changes in their vision and/or visual functioning because of the disease. Diabetes can cause blood vessels that nourish the retina to develop tiny, abnormal branches that leak blood which can interfere with vision and with time, may severely damage the retina.
Retinitis pigmentosa gradually destroys night vision, severely reduces side vision and may result in total vision impairment. An inherited disease, its first symptom-night blindness-usually occurs in childhood or adolescence.
In amblyopia, the visual system fails to develop normally during childhood. The blurry vision that results in one or both eyes is not easily corrected with normal glasses or contact lenses alone.
Retinopathy of Prematurity (ROP)
Retinopathy of prematurity occurs in infants born prematurely. It is caused by the high oxygen levels in incubators during the critical neonatal period.
This is a vision threatening condition when the retina separates from its underlying layer. It can cause total vision impairment in the affected eye. Causes include holes in the retina, eye trauma, infection, blood vessel disturbance or a tumor. If diagnosed early, most detached retinas can be surgically reattached with vision partially or completely restored.
Acquired (Traumatic) Brain Injury
Vision can also be lost or damaged as a result of head injuries, brain damage and stroke. Signs and symptoms can include reduced visual acuity or visual field, contrast sensitivity, blurred vision, eye misalignment, poor judgment of depth, glare sensitivity, confusion when performing visual tasks, difficulty reading, double vision, headaches, dizziness, abnormal body posture and balance problems.
Low Vision Aids
These are devices which help a patient with vision disability or low vision to use their existing sight to better advantage, low vision aids increases relative size and relative distance using magnifications , some of the magnifiers are:
- Magnifiers for Near
- Telescopes for Distance
- Non optical aids
- Used only for close work
- Designed to be held close to the reading material to enlarge the image
- Includes high plus reading eyeglasses to magnify the images
- High plus lenses can be included in eyeglasses for reading
Also Known as a CCTV (Closed Circuit Television) these magnifiers provide low vision aid for a full range of visual needs, specializing in assisting individuals with macular degeneration, glaucoma, cataracts, retinitis pigmentosa, diabetic retinopathy, and other low vision causing eye diseases.