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Visual acuity is the ability to see objects clearly. It is usually the only skill assessed in a school vision screening. The typical school eye chart is designed to be seen at 20 feet and measures how well or poorly the child sees at that distance.
If a problem is discovered in the screening, the child should be referred for a thorough optometric examination. Poor visual acuity is often corrected with glasses or contact lenses.
Fixation is the skill utilized to aim the eyes accurately. Static fixation is the ability to focus on a stationary object when reading a word or working a math problem. Saccadic fixation is the ability to move the eyes quickly and accurately across a page to read a line of print.
Pursuit fixation is the ability to follow a moving object with the eyes. These complex operations require split second timing for the brain to process the information received and to track the path of the moving object.
Difficulty with these eye movements can cause a child to skip words/lines or lose their place easily while reading
Accommodation is the ability to adjust the focus of the eyes as the distance between the individual and the object changes. Children frequently use this vision skill in the classroom as they shift their attention (and focus) between their book and the chalkboard for sustained periods of time. Being able to maintain focus at near for sustained periods of time is important for reading, writing and also taking tests.
Amblyopia (lazy eye) refers to poor visual acuity in one eye and is unrelated to any eye health problem. Reduced vision due to amblyopia is not correctable with lenses alone. Vision therapy may be able to improve visual acuity in a lazy eye.
Strabismus, or crossed-eyes, is a condition in which both eyes do not look at the same place at the same time. It occurs when an eye turns in, out, up or down.
Eye teaming refers to both eyes working together. Strabismus, amblyopia and difficulty with convergence can all lead to reduced eye teaming.
Signs/Symptoms of Poor Eye Teaming:
• Double vision
• Words moving around on a page
• Motion Sickness
• Difficulty catching/hitting a ball
• Decreased depth perception
• Inefficient eye-hand or eye-body coordination
• Short attention span for near work
• Closing or covering of one eye
• Excessive blinking
• Holding a book too close
• Poor handwriting
• Reduced reading comprehension Binocular Fusion (Depth Perception)
Binocular fusion refers to the brain’s ability to gather information received from each eye separately and form a single, unified image. A child’s eyes must be precisely aligned or blurred or double vision, discomfort, confusion or avoidance may result.
If that occurs, the brain often subconsciously suppresses or inhibits the vision in one eye to avoid confusion. That eye may then develop poorer visual acuity (amblyopia or lazy eye).
When reading, the eyes should aim inward at the same spot in order to fixate on print. School desk work is an example of using convergence in a classroom setting. If the eyes aim at a spot in front of or behind the print(convergence insufficiency), extra energy and effort is required to maintain fixation and double or overlapping vision may occur. Here is an example:
Field of vision is the wide area over which vision is possible. It is important that a child be aware of objects in the periphery (left and right sides and up and down) as well as in the center of the field of vision. Near central or Para-central vision is important for reading ability.
Directionality is important in understanding how similar shapes can have different meanings when they are in different orientations. Below is an example of some letters that are commonly reversed by children with poor directionality. The letters are the exact same shape, but are called a different name depending on their orientation. This can be a difficult concept because if another object, such as a chair, is turned on its side or upside-down it is still called a chair.
b d p q
Visual perception is the total process responsible for the reception and understanding of what is seen. Good visual perception is necessary for successful school achievement. Below is an example of an item from a visual perceptual skills test. In this particular test the child is asked to identify which form among the choices at the bottom matches the form on top. Other visual perceptual skills tests assess the child’s ability to identify a form from memory, identify which form is oriented in a different direction, identify a form that has a different size or orientation, identify a sequence of forms from memory, identify a figure hidden in ground and identify an incomplete form as if it were complete.
Children who can read at accelerated speeds often have a good span of recognition, allowing them to recognize and process several words at one time. Children lacking this skill may only be able to see one word or letter at a time. In order to see what this would be like, try reading a sentence or paragraph while looking through a straw.
Visualization is the ability to create mental images. Children who have vision problems may also have difficulty with visualization. This skill is important for success in sports as well as many school subjects including spelling and math.
Learning to read and reading for information require efficient visual abilities. The eyes must team precisely, focus clearly, and track quickly and accurately across the page. These processes must be coordinated with the perceptual and memory aspects of vision, which in turn must combine with linguistic processing for comprehension.
To provide reliable information, this must occur with precise timing. Inefficient or poorly developed vision requires individuals to divide their attention between the task and the involved visual abilities. Some individuals have symptoms such as headaches, fatigue, eyestrain, errors, loss of place, and difficulty sustaining attention. Others may have an absence of symptoms due to the avoidance of visually demanding tasks.
Because reading problems usually have multiple causes, treatment must often be multidisciplinary. Educators, psychologists, optometrists and other professionals must confer and work together to meet each child’s needs. The optometrist’s role is to help the child overcome the vision problems interfering with the ability to read. Once this is accomplished, the child is then more capable of responding to special education efforts aimed at treating the reading problem itself.