What is strabismus?
Strabismus, also known as “crossed eyes” or “wandering eyes,” is a condition in which the eyes do not line up properly and point in different directions. One eye may look straight ahead, while the other looks inward, outward, upward, or downward. This misalignment can be either constant, occurring all the time, or intermittent, occurring only on occasion. Strabismus can affect only one eye or alternate between both. The condition is common in children, but it can also appear in adults due to a variety of underlying causes.
Types of Strabismus
Strabismus is classified into several types depending on the misaligned eye’s direction and the underlying cause. The most common types are:
- Esotropia is the most common form of strabismus, in which one eye turns inward toward the nose. It is commonly known as “crossed eyes.” Esotropia can be congenital (present at birth) or acquired later in life. Infantile esotropia usually appears before six months of age and is severe, necessitating early treatment. Acquired esotropia can develop as a result of uncorrected refractive errors, such as farsightedness, in which the eyes work harder to focus, causing inward turning.
- Exotropia: Exotropia is defined as one eye turning outward, away from the nose. This type of strabismus is typically intermittent, becoming more noticeable when the person is tired, ill, or concentrating on distant objects. It may also be congenital or develop later in life. Exotropia can develop in childhood and worsen over time if not treated.
- Hypertropia: One eye is misaligned upwards, higher than the other. A problem with the eye muscles, nerves, or other structures around the eye can cause vertical misalignment. Hypertropia can cause symptoms such as double vision, head tilting, and eye strain as the brain attempts to compensate for the misalignment.
- Hypotropia: Hypotropia is the inverse of hypertropia, in which one eye turns downwards and lower than the other. This condition, like hypertropia, can result from problems with the eye muscles or nerves. Hypotropia is less common than other types of strabismus but can produce similar symptoms such as double vision and head tilting.
- Cyclotropia is a type of strabismus characterized by a rotational misalignment of the eyes. One or both eyes can rotate around the visual axis, causing the perception of tilted images. Cyclotropia can be difficult to diagnose and treat because the symptoms are often subtle, and patients may describe the world as “tilted” or “off-balance.”
Causes and Risk Factors
Strabismus can result from a variety of causes, and its progression is frequently multifactorial. Some of the main causes and risk factors are:
- Genetics: A family history of strabismus raises the risk of developing the condition. Genetic factors can have an impact on the development of eye muscles, nerves, and brain pathways that control eye movement and alignment.
- Refractive Errors: Uncorrected refractive errors, especially hyperopia (farsightedness), can result in strabismus. When the eyes must work harder to focus on an object, one of them may turn inward, resulting in esotropia. Correcting these refractive errors with glasses or contact lenses can help prevent or alleviate strabismus.
- Neurological Conditions: Neurological disorders that impair the brain’s ability to control eye movements can cause strabismus. Conditions such as cerebral palsy, Down syndrome, and brain tumors can disrupt the neural pathways that coordinate eye alignment, resulting in strabismus.
- Muscle and Nerve Abnormalities: Strabismus can result from abnormalities in the eye muscles or the nerves that control them. Cranial nerve palsy, for example, can cause the affected eye to become misaligned.
- Eye Injuries: Trauma to the eye or its surrounding structures can injure the muscles, nerves, or tissues that control eye movement, causing strabismus. This can happen right after the injury or later as scar tissue forms.
- Vision Loss in One Eye: If one eye’s vision is severely impaired or lost, the brain may stop attempting to align that eye with the other, resulting in strabismus. Cataracts, retinal detachment, and severe amblyopia are some of the possible causes.
- Congenital Factors: Some children are born with strabismus because of developmental abnormalities in their eye muscles, nerves, or brain pathways. Congenital strabismus frequently necessitates early intervention to avoid long-term vision problems.
- Medical Conditions: Certain medical conditions, such as thyroid eye disease or diabetes, can impair the eye muscles and cause strabismus. Thyroid eye disease, for example, can cause inflammation and swelling in the eye muscles, resulting in misalignment.
Symptoms and Signs
The symptoms and signs of strabismus differ depending on the type, severity, and duration of the condition. Common symptoms include:
- Misaligned Eyes: The most noticeable symptom of strabismus is visible misalignment of one or both eyes. This misalignment can be continuous or intermittent, and it may be more noticeable when the person is tired, ill, or concentrating on something.
- Double Vision: When the eyes do not align, each sends a different image to the brain. The brain may struggle to combine these images into a single, coherent picture, resulting in double vision (diplopia). This symptom is more common in adults with strabismus because children’s brains are more adaptable and can suppress the image from one eye to avoid double vision.
- Strabismus patients may tilt or turn their heads to compensate for misalignment and reduce double vision. This helps align the eyes so that the brain receives similar images from both.
- Eye Strain and Fatigue: The additional effort required to align the eyes can result in eye strain, discomfort, and fatigue. This is especially noticeable when performing tasks that require prolonged concentration, such as reading or using a computer.
- Difficulty with Depth Perception: Strabismus may impair binocular vision, which is required for accurate depth perception. Individuals with strabismus may have difficulty judging distances, such as catching a ball, driving, or navigating stairs.
- Closing One Eye: To avoid double vision, some people with strabismus may close or cover one of their eyes when focusing on something. This is especially common in bright light or when focusing on a task.
- Poor Coordination: Children with strabismus may have poor hand-eye coordination because the misalignment impairs their ability to judge distances and accurately track moving objects.
Impact on Vision and Development
Strabismus can have a significant impact on vision and overall development, particularly if it occurs during childhood. One of the most serious complications of strabismus is amblyopia, also known as “lazy eye.” Amblyopia occurs when the brain favors one eye over the other due to misalignment or poor vision in the affected eye. If not treated promptly, the brain may suppress visual input from the misaligned eye over time, resulting in underdevelopment of the visual pathways and permanent vision loss.
In addition to amblyopia, strabismus can impair depth perception and binocular vision, both of which are essential for tasks requiring accurate distance judgment and eye coordination. Individuals without proper binocular vision may struggle with activities requiring fine motor skills, such as sports, driving, or even simple tasks like threading a needle.
Strabismus has a significant social and psychological impact. Visible eye misalignment can lower a person’s self-esteem and confidence, especially in children and adolescents. Children with strabismus may face teasing or bullying from their peers, which can lead to social withdrawal, anxiety, and other emotional difficulties. Early detection and treatment are critical for minimizing the negative effects and promoting healthy visual and social development.
Importance of Early Detection
Early detection and diagnosis of strabismus are critical for avoiding long-term visual impairment and improving results. Pediatricians, optometrists, and ophthalmologists all play an important role in screening for strabismus during routine eye exams, especially in younger children. Parents should also watch for signs of eye misalignment and seek medical attention as soon as possible if any symptoms appear.
Strabismus has a good prognosis if detected and treated early on. Many people with strabismus can improve their binocular vision, eye alignment, and visual acuity with appropriate treatment. However, delayed diagnosis and treatment can result in irreversible vision loss in the affected eye, emphasizing the importance of timely and proactive care.
Diagnostic methods
An optometrist or ophthalmologist will perform a thorough eye examination to diagnose strabismus. Several diagnostic methods are used to determine the presence, type, and severity of strabismus, as well as any coexisting conditions such as amblyopia or refractive errors. Early and accurate diagnosis is critical for developing a successful treatment plan and avoiding long-term visual impairment.
Visual acuity testing
Visual acuity testing is an important part of diagnosing strabismus. This test assesses the clarity of vision in each eye separately, usually using a standardized eye chart. Alternative eye charts with shapes, pictures, or symbols can be used for young children or people who are unable to read letters. Significant differences in visual acuity between the two eyes may indicate the presence of amblyopia, which is commonly associated with strabismus. Detecting amblyopia early is critical because it can result in permanent vision loss in the affected eye if left untreated.
Cover Test
The cover test is a simple and effective way to detect strabismus and determine eye alignment. During this test, the eye care professional will cover one of the patient’s eyes while they concentrate on a specific object. To detect fixation, the uncovered eye is examined for any movement that indicates a shift. If the uncovered eye moves, it means that the covered eye was misaligned, indicating the presence of strabismus. The test is repeated with the opposite eye to determine the alignment of both eyes. The cover test determines the type of strabismus (esotropia, exotropia, hypertropia, or hypotropia) and whether the misalignment is continuous or intermittent.
Hirschberg Test (Coronal Light Reflex Test)
The Hirschberg test, also known as the corneal light reflex test, is another method for determining eye alignment. In this test, a small light is shone into the patient’s eyes and its reflection on the corneas is observed. A person with properly aligned eyes will have the light reflex centered in both pupils. If one eye is misaligned, the light reflex will be off-center, indicating the presence of strabismus. The Hirschberg test is especially useful in infants and young children, who may not cooperate with more complex testing.
Prism Coverage Test
The prism cover test, a more advanced version of the cover test, involves placing a prism in front of one eye to measure the degree of strabismus. The prism alters the image perceived by the eye, and the amount of movement required to align the eyes is measured in prism diopters. This test provides a precise measurement of the angle of deviation, which is critical for treatment planning, especially if surgery is an option.
Binocular Vision Assessment
Assessing binocular vision is critical in diagnosing strabismus and determining the extent to which the brain uses both eyes simultaneously. The Worth 4 Dot test or the synoptophore can be used to assess the patient’s ability to combine images from both eyes into a single, cohesive image. The Worth 4 Dot test involves showing the patient a pattern of four dots, and the patient’s perception of the dots can determine whether one eye is suppressed or binocular vision is intact. The synoptophore, on the other hand, enables a more detailed evaluation of eye alignment and fusion at various angles and distances.
Refraction Assessment
A refraction test is performed to determine whether refractive errors like myopia (nearsightedness), hyperopia (farsightedness), or astigmatism are contributing to the development of strabismus. This test is typically performed after administering cycloplegic eye drops to temporarily paralyze the eye’s focusing muscles, allowing for a more accurate measurement of the refractive error. Correcting significant refractive errors with glasses or contact lenses can be an important part of treating strabismus.
Ocular Motility Testing
Ocular motility testing evaluates the eye’s range of motion as well as the coordination of the extraocular muscles that control eye movement. The eye care professional will instruct the patient to follow a target with their eyes in various directions to detect any movement limitations or nystagmus (involuntary eye movements). This test helps to determine whether strabismus is caused by a problem with the eye muscles or the nerves that control them.
Fundus Examination
A fundus examination, also known as ophthalmoscopy, allows an eye care professional to examine the eye’s interior surface, which includes the retina, optic disc, and blood vessels. This examination is necessary to rule out other ocular conditions that could be causing strabismus, such as retinal diseases, optic nerve abnormalities, or structural issues within the eye.
Neurological Examination
In some cases, especially when strabismus is acquired rather than congenital, a neurological examination may be required to rule out any underlying neurological conditions that may be interfering with eye alignment. This examination may include neuroimaging studies, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans, which provide detailed images of the brain and orbits.
Stereopsis Testing
Stereopsis, or depth perception, is a crucial part of binocular vision. Stereopsis testing assesses a patient’s ability to perceive three-dimensional depth using both eyes simultaneously. Stereopsis is commonly assessed using tests like the Randot Stereotest and the Titmus Fly Test. Patients with strabismus frequently show reduced or absent stereopsis, indicating impaired binocular vision.
Strabismus Management: Key Approaches Explained
Strabismus treatment is a multidisciplinary approach that aims to correct eye alignment, improve visual function, and prevent long-term complications like amblyopia (lazy eye). Treatment options differ depending on the type, severity, and underlying cause of the strabismus, as well as the patient’s age and overall health. Early intervention is critical for achieving the best results, especially in children, because the visual system is more adaptable during early development.
Corrective Lenses
Corrective lens prescription is one of the first steps in treating strabismus, especially when refractive errors are present. Glasses or contact lenses can correct underlying refractive errors like myopia, hyperopia, or astigmatism, which may be causing the strabismus. In some cases, especially with accommodative esotropia (where the eye turns inward when focusing), corrective lenses can significantly improve eye alignment without requiring additional treatment. Bifocal lenses may also be prescribed if the patient’s strabismus occurs when he or she focuses on nearby objects.
Prisms
Prism lenses are another non-surgical option for managing strabismus. Prisms are used in glasses to change the way light enters the eye, reducing the amount of effort required to align the eyes and helping to prevent double vision. Prisms are especially useful for patients with mild to moderate strabismus, where the misalignment is not severe enough to require surgery.
Occlusion Therapy
Occlusion therapy, also known as patching, is frequently used in conjunction with other treatments, particularly in children who have amblyopia due to strabismus. The stronger eye is covered with a patch for several hours each day, forcing the brain to rely on the weaker, amblyopic eye. This improves visual acuity in the affected eye and promotes the formation of neural pathways associated with that eye. Occlusion therapy is typically most effective when started early in life, when the visual system is still developing.
Vision Therapy
Vision therapy, also known as orthoptics, is a series of eye exercises that aim to improve eye coordination, focusing ability, and binocular vision. These exercises are usually done under the supervision of an optometrist or orthoptist and may include activities like eye-tracking, focusing, and the use of specialized equipment such as computer programs or prism lenses. Vision therapy is especially effective for treating intermittent exotropia (when the eye turns outward on occasion) and improving binocular vision in patients who have had strabismus surgery.
Botulinum Toxin Injections
Botulinum toxin (BOTOX) injections can be used as a temporary treatment for eye misalignment, particularly in adults with acquired strabismus. The toxin is injected into the overactive eye muscles, causing temporary paralysis while the opposing muscles strengthen and correct the alignment. Botox injections are frequently used as a supplement to other treatments or as a test run before pursuing more permanent surgical options.
Strabismus Surgery
Many patients, especially those with significant or persistent strabismus, may require surgical intervention. Strabismus surgery involves repositioning the eye muscles to align the eyes. To achieve better alignment, you can weaken, strengthen, or reposition the muscles. In children, the procedure is typically performed under general anesthesia, while adults are given local anesthesia.
Several surgical techniques exist, including:
- Recession: This procedure involves moving the insertion of an eye muscle further back on the eye, weakening its action. It is most commonly used to treat esotropia.
- Resection: This technique shortens an eye muscle to strengthen its action. It is frequently combined with recession on the opposing muscle to achieve balanced alignment.
- Adjustable Sutures: In some cases, the surgeon uses adjustable sutures during surgery to fine-tune the eye alignment after the patient awakens from anesthesia. This technique is especially useful in adult patients, as it allows for more precise control over the final alignment.
Strabismus surgery is generally safe and effective, but some patients may require additional procedures to achieve the best results. Postoperative care typically consists of the use of eye drops or ointments to prevent infection and inflammation, as well as follow-up visits to monitor healing and determine the surgery’s success.
Ongoing Monitoring and Follow-up
Strabismus management is a continuous process that necessitates regular follow-up visits to assess progress and adjust the treatment plan as needed. Children undergoing strabismus treatment should be closely monitored to ensure that amblyopia does not return and binocular vision continues to improve. Adults with strabismus may also require regular evaluations, especially if they have had surgery or are wearing prisms or other corrective devices.
In some cases, additional therapies, such as ongoing vision therapy or part-time occlusion therapy, may be required to maintain treatment benefits and avoid regression. The goal of ongoing care is to help the patient achieve and maintain good visual function, cosmetic alignment, and quality of life.
Trusted Resources and Support
Books
- “Strabismus and Amblyopia: Clinical Management and Basic Aspects” by Guntram Kommerell: This comprehensive text provides detailed information on the diagnosis and management of strabismus and amblyopia, making it an invaluable resource for clinicians and patients alike.
- “Crossed and Lazy Eyes: A Parent’s Guide to Strabismus and Amblyopia” by Jonathon M. Holmes: Written for parents, this book offers practical advice and guidance on understanding and managing strabismus and amblyopia in children.
Organizations
- American Association for Pediatric Ophthalmology and Strabismus (AAPOS): AAPOS is a leading organization dedicated to the treatment and research of pediatric eye conditions, including strabismus. They offer resources, specialist directories, and patient education materials.
- Strabismus and Amblyopia Support Group: This online community provides support and resources for individuals and families affected by strabismus and amblyopia. It offers a platform for sharing experiences, finding treatment options, and connecting with others who face similar challenges.
