Incidence of visual imapirment
1)Blindness affects approximately 45 million people worldwide.
2)The incidence of visual impairment increases with age because more than two thirds of persons with low vision are over the age of 65.
3)The factors that place a patient at risk for visual impairment are related not only to ocular diseases and abnormalities but also to trauma and systemic health conditions.
4) The most common causes of visual impairment in the adult population are:
a)Age-related macular degeneration
5)The incidence of these conditions increases with the average age. Medical advances that increase the survival of infants and adults with severe health problems will also contribute to the rising numbers of persons with visual defects.
6)The increasing incidence and survival of persons with traumatic brain injuries further add to the numbers of visually impaired persons in need of appropriate rehabilitation.
7)The causes of visual impairment includes systemic diseases with ocular complications, neurological insult and trauma.
Causes of visual imapirment
1)Errors of Refraction: The most common problems are the result of errors of refraction. Myopia (near sightedness), hyperopia (far sightedness), and astigmatism (blurred vision) are all examples of refraction errors that affect central visual acuity. Each of these can be serious enough to cause significant impairment. Myopia and hyperopia are the most common impairments of low vision. In these cases, glasses or contact lenses can bring vision within normal limits.
2) Glaucoma: It is a disease of the eye that is caused by a gradual degeneration of cells in the optic nerve. The loss of these cells leads to a gradual narrowing of the field of vision beginning at the periphery. There is no known cause for the most common form of glaucoma, primary open angle glaucoma, but it is commonly believed to be associated with the inability of fluid to properly drain from the eyes causing an increased intraocular pressure.
3)Cataracts: It results from a clouding of the normally slightly yellowish lens of the eye. The loss of transparency causes light to be diffused as it enters the eye which impacts the clarity of the visual image. The lens slowly develops a greenish and later a brownish tint which impedes the ability of light to pass through the lens. Symptoms of cataract include blurred vision, light sensitivity, double vision, and an apparent fading or yellowing of colours.
4)Diabetic Retinopathy: It is a visual disorder associated with diabetes that causes retinal blood vessels to leak into the retina causing macular oedema. Careful control of diabetes and regular eye exams can delay the development of the disorder. While diabetic retinopathy will often develop with no pain and minimal symptoms in its early states, it can be treated if it is diagnosed early.
5)Prenatal Causes: There are several other visual impairments that primarily affect children. Visual impairment of school-age children are often due to prenatal causes, many of which are hereditary.