Reading is a complicated activity that requires coordination between the two eyes, muscle control to fixate on words while moving across a line of print and visual acuity. It also involves accommodation abilities to focus at different distances and an adequate visual field in order to see writing on a larger screen such as a power point presentation. Many of the following disorders can be corrected with eye glasses, surgery, eye patching, eye exercises or environmental adaptations.
Ocular Motor Control
There are six muscles around the eye orbit that control movement. Poor muscle coordination can cause a condition called "strabismus," where the eyes are misaligned. According to optometrist Mitchell Scheiman, author of "Understanding and Managing Vision Deficits," the three most common types of strabismus are: esotropia, where the eyes turn inward; exotropia, where the eyes turn outward, and hypertropia, where one eye turns upward. According to the FamilyDoctor.org website, normal vision needs both eyes to look in the same direction at the same time. When an eye is turned or wandering, the person will be unable to use the eyes together to read. Left untreated, a child might ignore one eye, with risk of eventual vision loss. Strabismus may be treated with surgery, glasses or by having the better eye patched to force the muscles in the weaker eye to work.
Ocular Motility Disorders
According to Regina G. Richards, author of "Classroom Visual Activities," reading requires precise eye movement skills. A child must be able to "converge" the eyes---turn both eyes to point at words with easy, smooth motions. Convergence is needed in order to maintain fixation on words long enough to read them. Difficulty doing this is called "convergence inefficiency." A child must also be able to move the eyes along a line of print using a series of precise little jumps called "saccades." Children with impaired ocular motility might skip words or lines of print and lose their place while reading.
Another important eye skill needed to read is called "accommodation." This is the ability to quickly and accurately focus on reading material located at different distances in order to copy from a blackboard to a notebook.
Visual Acuity
Most teachers notice when a student squints when looking at a black board, and parents might observe that a child can't discriminate between distant faces. These children are usually taken to an optometrist, who diagnoses myopia, or near vision. Then eye glasses are prescribed to correct the problem. Problems with hyperopia, or farsightedness, are not as obvious. Children may be able to overcome a mild case when reading by using muscular effort. However, according to Dr. Scheiman, constant effort can lead to symptoms of blurred vision, eyestrain, tearing and inability to concentrate.
Children who struggle to read should be evaluated for hyperopia, which can usually be corrected with glasses. Astigmatism is another condition that causes blurred vision both near and far away and should be ruled out when a child struggles to read.
Most adults notice that at around 40 years of age, it becomes increasingly difficult to read small print. Dr. Robert Abel, author of "The Eye Care Revolution," describes this condition, called "presbyopia," as loss of accommodation, or focusing power. Fortunately, reading glasses and improved lighting can easily help overcome vision loss associated with aging.
Visual Loss Due to Diseases
According to the American Academy of Family Physicians, the most common causes of vision loss among the elderly are age-related macular degeneration (ARMD), glaucoma, cataracts and diabetic retinopathy. All of these conditions impact reading. Cataracts, which cause the eye's lens to become cloudy, are commonly treated with surgery. ARMD causes gradual loss of central vision.
Patients may be prescribed strong reading glasses or learn to read using peripheral vision. Patients with glaucoma lose their peripheral vision and may need to use scanning techniques in order to read a full line of print or distant chart. Numerous congenital or juvenile eye disorders, such as retinitis pigmentosa and Stargardt's syndrome, also impact visual acuity and abilities to read.
References
- Common Causes of Vision Loss in Elderly Patients
- Retinitis Pigmentosa
- Stargardt's Disease
- Strabismus
- "Understanding and Managing Vision Deficits"; Mitchell Scheiman; 1997
