Students Who Are Blind or Have Low Vision

Visual impairment

  • including blindness

  • means an impairment in vision that, even with correction, adversely affects a child’s educational performance.

  • The term includes both partial sight and blindness

more commonly used term is “low vision.”

blindness

  • any person whose central visual acuity does not exceed 20/200 in the better eye with corrective lenses or a visually impaired person whose vision with best correction is 20/60 in the better eye, or with a field restriction of 105 degrees if monocular vision; 140 degrees if binocular vision

Causes of Blindness and Low Vision

Vision relies on an interaction between the eye and the brain.

  1. First, light passes through the cornea, which is the clear front layer of the eye.

    • The cornea is shaped like a dome and bends light to help the eye focus. Some of this light enters the eye through an opening called the pupil

  2. The iris, the colored part of the eye, controls how much light the pupil lets in. Next, light passes through the lens, a clear inner part of the eye. The lens works with the cornea to focus light correctly on the retina.

  3. When light hits the retina, a light-sensitive layer of tissue at the back of the eye, special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain.

  4. The brain then turns the signals into images

Optical Defects

There are three major optical defects:

  1. Myopia (i.e., nearsightedness) makes faraway objects look blurry.

  2. Hyperopia (i.e., farsightedness) makes nearby objects look blurry.

  3. Astigmatism can make faraway and nearby objects look blurry or distorted.

These are refraction errors. Refractive errors are a type of vision problem that makes it hard to see clearly. Refraction errors happen when the shape of the eye keeps light from focusing correctly on the retina.

Ocular Motility Disturbance

  • any abnormal eye alignment or difficulty controlling eye movements. These conditions involve the brain and the muscles that control eye movement

    • Strabismus is a condition where the eyes are not facing in the same direction.

    • Amblyopia is a condition in which the brain fails to process the information from one eye. This may occur because one eye is misaligned (strabismus) and incorporating that information would cause double vision.

    • Nystagmus is characterized by fast, uncontrollable eye movements.

Types of External Eye Problems

External eye problems may affect the orbit, eyelids, and cornea. Orbital problems may include protruding, recessed, or abnormally small eyeballs.

Types of Internal Eye Problems

retinopathy of prematurity (ROP).

  • is an eye disease that may occur in babies who are premature or who weigh less than 3 pounds at birth. it happens when abnormal blood vessels grow in the retina.

retinitis pigmentosa (RP)

  • a group of rare eye diseases that affect the retina, causes cells in the retina to break down slowly over time, causing vision loss.

Cortical visual impairment (CVI)

  • is a disorder caused by damage to the parts of the brain that process vision.

  • vision problems caused by their brain that cannot be explained by a problem with their eyes

Identifying Students Who Are Blind or Have Low Vision

Ophthalmologists are medical doctors who identify and treat eye problems, prescribe medication, and perform surgery.

Optometrists examine eyes for defects and problems in refraction and prescribe corrective lenses.

Opticians make or sell optical devices and instruments.

A low-vision specialist is an ophthalmologist or optometrist who specializes in assessing and treating individuals with 20/70 vision or worse.

Functional Vision Assessment

  • Functional vision is the use of any residual vision to obtain information from the environment.

Learning Media Assessment

  • learning media assessment is used to help educators and clinicians select appropriate learning media and assistive technology