Legal vision impairment is an important concept when describing limitations of vision for administrative hearings and legal proceedings. Understanding the overall process of vision provides a foundation for understanding the different types of vision impairment and their significance.
First, think of the eye as a camera: light enters the eye and is focused by the cornea and lens inside the eye to a point on the retina. The retina is a highly delicate tissue that lines the inside of the eye and acts very much like the film or image sensor in a camera. The individual cells in the retina, also known as photoreceptors, are activated by light and convert light energy into electrical impulses that are transmitted through the optic nerve to the brain. Just like the diaphragm inside a camera, the iris (colored part) of the iris can open or close to regulate the amount of light that gets into the eye through an opening called the pupil. The pupil normally opens wide in dim light and constricts in the presence of bright light conditions. Vision is normal when the camera works well and the brain is capable of receiving and understanding the transmission of electrical impulses coming from the optic nerve. However, a breakdown of any component in the visual pathway can cause vision impairment.
Defining legal vision impairment
Classification of legal vision impairment has significant ramifications for the individual who has decreased vision as well as government agencies who regulate activities based on the level of vision. A claimant’s medical records and eye examination by an ophthalmologist may be utilized to establish a level of vision that determines whether or not the level of vision qualifies as legal vision impairment.
The definition of legal blindness various among various governmental agencies and among countries. The most widely accepted definition of blindness is based on a presentation by Edward Jackson, A.C. Snell, and Harry S. Gradle at the Eighty-Fifth Annual Session of the American Medical Association (AMA) in Cleveland, Ohio, on June 15, 1934. The AMA adpoted the definition of blindness by these highly regarded ophththalmologists as Snellen visual acuity of 20/200 or less in the better eye with corrective glasses or the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye. While this definition is still widely held in North America, the U.S. Congress through Social Security legislation, and a number of government agencies have expanded definitions of legal vision impairment that include partial, moderate and severe impairment
Types of Vision Impairment
The most common type of vision impairment is refractive error. Refractive error is when light rays are not precisely focused on the retina. When light rays are not properly focused, the image is perceived as being blurry. The most common forms of refractive error as hyperopia (farsightedness), myopia (nearsightedness), and astigmatism. Refractive error is because of issues related to the depth and shape of the eye. Another phenomenon that can affect the ability of the eye to properly focus is presbyopia. In presbyopia, the muscles and lens of the eye became less flexible, resulting in impairment to focus when viewing objects at close range. A sufficient amount of presbyopia leads many people to wear reading glasses for proper viewing at close range. Decreased vision because of refractive error or presbyopia is usually not considered legal vision impairment since they can be corrected with eyeglasses or contact lenses.
Legal Vision Impairment
When a part of the vision sytem becomes damaged, vision loss can occur. The quality and quantity of vision loss depends on the part of the vision system that is damaged. In cases where the damage is significant, corrective lenses in the form of eyeglasses or contacts are not able to remedy the vision problem. The most common causes of vision impairment are as follows:
- Corneal scar. The cornea is the front window of the eye. A disease or injury that damages the cornea may result in failure of light to properly enter the eye. Some types of corneal problems may be treated by medication or surgery to restore its architecture and clarity.
- Anterior chamber. The portion of the eye is the space between the cornea and the iris. It is normally filled with a clear fluid known as the aqueous humor. Blood or inflammation can compromise the clarity of fluid and lead to vision impairment. Fortunately, in most cases, conditions that cause cloudiness in the anterior chamber resolve with appropriate treatment.
- Lens. The clear lens of the eye is located just behind the pupil. It is responsible for helping light rays focus on the retina. Normally, the lens is clear. A cloudy or opaque lens is referred to as a cataract.
- Retina. This delicate tissue is comparable to the film or image sensor of a camera. A variety of conditions can lead to problems involving the retina and impaired vision. Many cases of legal vision impairment are related to significant damage of the retina.
- Optic nerve. This structure is really an extension of the brain. Neurologists refer to the optic nerve as the Cranial Nerve II. Damage to the optic nerve from disease or trauma can result in permanant legal vision impairment.
The American Foundation for the Blind estimates that 10 million people in the United States are visually impaired. Vision impairment may be partial or complete. Many agencies that help people with either poartial or complete loss of vision. Significant visual loss is when vision is 20/200 or worse. This means that a person with 20/200 vision would need to be 20 feet from an object to see it as well as someone with normal (20/20) vision (corrected or uncorrected) could see from 200 feet away.
Individuals with vision impairment usually see an ophthalmologist, a physician who specializes in examining, diagnosing, and treating eyes and eye diseases. An ophthalmologist examines the eyes and tests the eyes to determine presence of any the results in impaired vision. An ophthalmologist is also qualified to advise regarding treatment options to improve or eliminate conditions that qualify as legal vision impairment.