Strabismus is a vision condition that has gone by many names; eye turn, crossed eye, lazy eye, wandering eye, wall eyed, and squint to name a few. Whichever name is most familiar to you, strabismus is a failure of the two eyes to maintain proper alignment at all times, which results in an eye turn. Strabismus is a form of binocular vision dysfunction that must be properly treated to restore both alignment and binocular vision functioning. Improper management may result in cosmetic alignment without functional improvement or worsening symptoms. In order to determine the best course of treatment, a residency-trained doctor must evaluate several aspects of the strabismus, including: direction (in, out, up, down), frequency, laterality, magnitude, causes, and the impact on binocular vision due to the strabismus.
Causes and Types of Strabismus
There are various causes of strabismus, including: mechanical restriction (ex. due to injury), paresis of a specific extraocular muscle (ex. due to diabetes), traumatic brain injury, stroke, and various systemic and ocular conditions. A strabismus can also be present from a very early age, for example an infantile esotropia. Strabismus occurs in approximately 4% of the US population. For those with a family history of strabismus the risk of strabismus can climb as high as 33%.
There are several factors that a doctor must evaluate when assessing a strabismus. Commonly, a strabismus is classified by the direction of the eye turn; in, out, up, down.
Click each item to learn more about the different types of strabismus:
This is an outward turn of one or both eyes. An exotropia may be present constantly or intermittently (sometimes), present at distance, near or both, and may affect the right eye, left eye, or both. The nature of the exotropia will determine the visual impacts of the condition. An exotropia present at near will affect reading fluency while an exotropia present at distance may affect athletic performance.
DID YOU KNOW? Patients with strabismus require specialized care by a doctor with advanced training in binocular vision.
Dr. Ryan Johnson received his residency training in binocular vision, neuro-optometry, and vision therapy at the University of California, Berkeley. He is the first optometrist in Idaho with this advanced training in these areas. He routinely manages patients with strabismus, determining how the condition has affected their visual functioning and the most appropriate treatment method for their specific type of strabismus.
This is an inward turn of one or both eyes. An esotropia can also be present constantly or intermittently, present at various distances, and affect either one or both eyes. As with any type of strabismus, it is important to differentiate the exact type and nature of esotropia as this will determine the treatment method. Among esotropias there are two that must be differentiated:
- INFANTILE ESOTROPIA
An infantile esotropia is a significant inward eye turn that appears within the first few months of life. It is important that an infantile esotropia is identified and treated early in life to provide the greatest benefit for the child.
DID YOU KNOW? The American Optometric Association recommends that all children have their first visit with the eye doctor before their first birthday.
Dr. Jill Kronberg received her residency training in pediatric optometry at the University of California, Berkeley. A comprehensive eye examination with a residency-trained pediatric optometrist can identify far more than a vision screening is able to. This allows for early diagnosis and treatment of childhood vision conditions, such as strabismus.
- ACCOMMODATIVE ESOTROPIA
Accommodative esotropia is an inward eye turn due to an uncorrected prescription. This type of esotropia occurs in early childhood and is well managed with glasses and does not require surgical correction. An accommodative esotropia is easily identified and treated during a comprehensive eye examination with a residency-trained pediatric optometrist.
DID YOU KNOW? The American Optometric Association recommends a child's second eye examination occur at three years old.
Strabismus is one of the many vision conditions that can be identified during a comprehensive eye examination with a residency-trained pediatric optometrist. During this evaluation our doctors will be able to determine how the condition has affected their visual functioning and the most appropriate treatment method for their specific type of strabismus.
- HYPERTROPIA / HYPOTROPIA
In addition to being inward or outward, an eye turn can also be upward (hypertropia) or downward (hypotropia). Vertical misalignment of the eye is especially important to identify as it can be quite symptomatic. Individuals with a vertical eye turn will often complain of double vision, headaches, blurred vision, and difficulty with vision tasks. If the eye turn in longstanding they may not notice symptoms but will instead adopt an unusual head posture; such as a head tilt.
Visual Effects of Strabismus
Strabismus affects much more than the alignment of the eyes. Vision is a complex process that involves 2/3 of the connections in the brain to produce vision, make sense of visual information (visual perception) and integrate vision with the other senses. Strabismus affects several aspects of vision, including:
- AMBLYOPIA (Lazy Eye)
Strabismic amblyopia is caused by certain types of strabismus, or eye turn. With strabismus, one eye turns in, out, up or down. When the eye is turned relative to the other it interferes with normal binocular vision functioning. As a result of this eye misalignment amblyopia develops in one eye. Along with reduced vision, the brain also develops suppression, a process by which the visual input from one eye is ignored by the brain. Suppression cannot be treated with glasses, contacts, or LASIK and instead one must restore binocular vision functioning through an active process.
- BINOCULAR VISION (Eye teaming)
The ability to use the two eyes together is a crucial visual skill. Difficulty with eye teaming results in a number of symptoms, including: double vision, headaches, eyestrain, difficulties with reading fluency, skipping or re-reading lines of text, words moving on the page, difficulty concentrating during visual tasks and fatigue. Optimum binocular vision functioning is important for both academic and athletic success.
- OCULOMOTOR FUNCTION (Eye Tracking)
When a strabismus is present it creates a situation where both eyes do not work efficiently. Binocular vision dysfunction makes eye tracking more difficult, especially when the individual alternates between fixating with two eyes, the right eye and the left eye. The constant changing of binocular vision status results in a constantly changing visual input, meaning the brain receives inconsistent information about the direction and speed of a moving object.
- CONTRAST SENSITIVITY (Ability to distinguish differing shades of gray)
Contrast sensitivity is an important aspect of vision. Low levels of contrast sensitivity impair mobility. Contrast sensitivity helps one judge the terrain. For someone with poor contrast sensitivity a sloped incline and a set of stairs may look the same, making it difficult to navigate through the world. Conversely, excellent contrast sensitivity helps athletes track moving objects and perform at high levels.
- DEPTH PERCEPTION (3D vision)
Depth perception is important for many reasons. For some, the ability to see depth lets them enjoy their favorite movie in 3D. For others, depth perception is important for work or hobbies. Depth perception is important for everything from driving, hitting a baseball, and threading a needle. The importance of depth perception is easily realized by covering one of your eyes. It is much more difficult and uncomfortable to move through the world while only using one eye.
- SUPPRESSION (Ignoring one eye)
Suppression is a neurological response to stress on the binocular vision system. When strabismus is present, one eye fixates (looks at the target) while the other is turned away from the target. This creates a situation where the brain begins to ignore the visual input from the turned eye. With time the brain begins to rely on the visual input from the fixating eye to eliminate double vision, eyestrain, or other symptoms. Suppression must be properly treated to restore proper binocular vision functioning.
- VISUAL-MOTOR INTEGRATION (Eye-hand coordination, gross motor and fine motor abilities)
When strabismus negatively impacts the aspects of vision just discussed, it also makes motor tasks more difficult. Many motor tasks are driven by the eyes and vision. The eyes tell the body when and how to react. People with strabismus may appear clumsy or have difficulty with athletics. It is possible for someone with strabismus to achieve some success with visual-motor tasks, however it is extremely difficult for them to achieve their full potential.
Detection of Strabismus
Strabismus is detected during a comprehensive eye examination with a doctor who has advanced, residency training in pediatric eye care or binocular vision. As there are several aspects of vision that are affected with strabismus, it is important that the comprehensive eye exam includes an assessment of these aspects of vision and vision development. These initial findings will help determine the most appropriate treatment as serve to monitor improve throughout the treatment process. That is why it is important to choose a residency-trained doctor with both the knowledge and experience of working with children and adults who have strabismus. Meet our doctors.
Treatment of Strabismus
The specific treatment protocol developed by your doctor depends on the specific type of strabismus, as well as several factors that will be evaluated during the examination, such as:
Certain types of strabismus respond extremely well to correction with glasses. In some cases correcting the refractive error is sufficient to treat the strabismus while others require specialized prism prescriptions. Prescribing prism is a specialty within eyecare that should be performed by a doctor with advanced training in binocular vision. When prescribed correctly prism can provide substantial improvements in binocular vision functioning and comfort. Incorrect use of prism may be ineffective or even worsen the symptoms. Dr. Ryan C Johnson is Idaho's first optometrist who is residency-trained in binocular vision, neuro-optometry and vision therapy. He routinely manages children and adults with strabismus.
- VISION THERAPY
Strabismus negatively impacts the ability to use both eyes together, thus it should be viewed as a form of binocular vision dysfunction. When treating strabismus it is important to recognize the effects on binocular vision, including suppression, impaired depth perception, accommodative dysfunction, vergence dysfunction, and the effects on visual integration. Treatment of strabismus is incomplete if binocular vision dysfunction is not addressed.
In-office vision therapy is used to improve binocular vision dysfunction in those with strabismus. Vision therapy effectively addresses suppression and other binocular vision deficits where glasses and surgery cannot. Vision therapy allows strabismic patients to achieve higher levels of binocular vision and positively affect visual performance.
When choosing a vision therapy program it is important to choose a program conducted under an optometrist who is residency-trained in binocular vision, neuro-optometry, and vision therapy. It is also important to choose a program that uses a research-based approach to treatment and employs licensed therapists who work one-on-one with the patient. Advanced Vision Therapy Center is Idaho's recommended vision therapy center.
For certain types of strabismus surgery is indicated to correct the misalignment. When pursuing surgery it is important to discuss the goals of the surgery. Some surgeries are designed to cosmetically align the eyes but have little effect on eye teaming or binocular vision, while others are designed to relieve the misalignment and provide an opportunity for binocular vision. When undergoing surgery it is important to remember that a strabismus is not only a mechanical misalignment of the eyes, but also a form of binocular vision dysfunction. For this reason it is often important to perform a post-operative course of vision therapy to enhance binocular vision functioning (similar to physical therapy after a surgery by an orthopedic surgeon). Stable binocular vision reduces the chances of repeat surgeries due to regression.
Whether you are a child or an adult, it is important to work with an eye care professional who specializes in pediatrics, binocular vision, and vision therapy. At Artisan Pediatric Eyecare, our team of doctors includes Dr. Jill Kronberg, Idaho's first residency-trained pediatric optometrist, and Dr. Ryan Johnson, Idaho's first residency-trained neuro-optometrist.