Common Types of Visual Impairments

Students with non-correctable vision problems have visual impairments. Depending on the severity of the condition, the following terms may be used in the special education or regular education school environment. To qualify as a visually impaired student, certain criteria must be met, like low visual acuity, visual field limitation, progressive eye disease, or cortical visual impairment.

Partially Sighted: A visual impairment that adversely affects a student's educational performance even when corrected to the extent possible.

Low Vision: If someone's vision is between 20/70-20/160 and cannot be corrected, the student has moderate to low vision.

Legally Blind: From 20/200-20/400 is legally blind with severe low vision. From 20/400-20/1000 is profound visual impairment, and is very close to total blindness.

Totally Blind: The lack of light perception is known as total blindness or total visual impairment.

The most common types of visual impairments are simple refractive errors. These include nearsightedness, farsightedness, and astigmatism. In nearsightedness images are focused in front of the retina, making far away images appear blurry. Farsightedness results from an image being focused behind the retina, which means the child will have trouble focusing on objects that are close up. Astigmatism results from curvature of the cornea, which keeps light rays from focusing properly in one area of the retina. This condition results in the inability to focus on objects far or near. Fortunately, refractive errors are correctable. Many children use glasses and enjoy clear vision. These students will have no need for special services unless the refractive error is not correctable for some reason.

Amblyopia:

Amblyopia is also known as lazy eye. Children with a lazy eye may or may not be perceptible. Sometimes a lazy eye visibly turns in or out, but sometimes there is no outward sign. Amblyopia causes the eye to have reduced acuity due to the poor positioning of the eye and weak muscles. The treatment is commonly a patch over the normal eye that makes the lazy eye work harder. Surgical corrections are also common.

Retinitis Pigmentosa:

This is a degenerative condition that is inherited. Retinitis pigmentosa results in a loss of peripheral vision, and eventually the student is left with a severe visual impairment.

Retinopathy of Prematurity:

This condition is common in children who were premature babies that required high concentrations of oxygen at birth. Scarring and detachment of the retina can result from this condition.

Strabismus:

In this condition, both eyes are unable to gaze at an object at the same time. Strabismus is caused by a muscle imbalance.

Cortical Visual Impairment:

Cortical visual impairment is not a problem with the eye itself, but with the visual cortex area of the brain. These children may also have other developmental delays or cerebral palsy. Vision may change throughout the day, depending on the health, mood of the child, or his environment.

1. http://www.nhbvi.com/Agenda/Goal1/Book1/commoncauses.html

2. http://www.childrenshospital.org/az/Site2100/mainpageS2100P0.html

3. http://en.wikipedia.org/wiki/Low_vision