UNDERSTANDING STRABISMUS (CROSSED EYES OR SQUINT): TYPES, COMPLICATIONS AND TREATMENT
What is Strabismus?
Strabismus, or squint eyes, happens when one eye turns in a different direction from the other eye. This misalignment of the eyes is also known as crossed eyes.
A consequence of strabismus is that it negatively affects depth perception and it also causes problems with binocular vision. Having a squint eye can happen in both adults and children.
Worldwide, strabismus occurs in about 0.14% to 5.65% of children. Strabismus occurs in approximately 4% of adults.; it is a common eye condition in those over 60 years of age.
Normal Eye Alignment and 3D Vision
It is important that the eyes are correctly aligned to judge 3D depth perception. In order to enable vision, light enters the eye and then passes through the cornea and lens, which bend and focus the light rays onto the retina; the signals are then transmitted to the brain, where the image is interpreted.
To correctly form an image of an object, the eyes need to function together, so the object should be centered in each eye. Misaligned eyes cause a loss in depth perception (stereopsis). In children, this is because the brain ignores the image coming from the misaligned eye. However, in adults, the presence of strabismus may lead to double vision.
Different Types of Strabismus
There are several types of squints that occur based on which way the eye turns and the direction in which the eye deviates. Strabismus can also be classified based on whether it is constant or not and when symptoms first appear.
Based on Direction
Horizontal Strabismus
- Esotropia/Convergent Strabismus (inward turning of the eye)
- Alternating esotropia – Happens in both eyes but not at the same time.
- Accommodative/Refractive esotropia – Seen in those with hypermetria (farsightedness). This condition can be corrected with glasses.
- Non accommodative esotropia – When the Strabismus angle is unchanged with glasses, it is called non accommodative esotropia.
- Near esotropia – Strabismus occurs only when the person looks at close objects.
- Exotropia/Divergent Strabismus (outward turning of the eye)
- Sensory exotropia – This happens in one eye, which has weaker vision than the other.
- Alternating exotropia – Strabismus occurs in each eye but at different times.
- Unilateral exotropia – This happens when one eye turns outwards all the time while the other eye is unaffected.
- Consecutive (secondary) exotropia – In this condition, the eyes become misaligned after surgical intervention to treat esotropia.
Vertical Strabismus
- Hypertropia (upward turning of the eye) – This condition is more common in childhood.
- Hypotropia (downward turning of the eye) – Similar to hypertropia, hypotropia is more often diagnosed in children than in adults.
Based on Timing
Whether strabismus is constant or intermittent is an important factor in diagnosis.
- Constant: Eyes are misaligned all the time.
- Intermittent: Eyes are misaligned only sometimes.
Based on Onset
- Infantile/Congenital Strabismus – Also known as newborn strabismus, this occurs in children younger than 6 months of age, resulting in a squint.
- Acquired Strabismus – This occurs in individuals who are older than 6 months of age.
What Causes Strabismus?
Multiple factors can lead to strabismus. These can be listed as follows: There are many reasons why a person may have strabismus.
- Muscle weakness or imbalance in the eyes – Several muscles hold the eye in place and allow it to move. Any weakness or stiffness in these ocular muscles can lead to eye misalignment.
- Farsightedness or hyperopia – Hyperopia can lead to strabismus as the affected eye tries to focus.
- Uncorrected refractive errors (nearsightedness, astigmatism) – Refractive errors can cause an affected eye to be squint.
- Certain medical conditions – Some medical conditions, such as hypertension, diabetes, thyroid problems, and neurological disorders like stroke and brain tumors, can cause strabismus.
- Retinoblastoma – Strabismus may be a symptom of this rare eye cancer usually found in children.
- Increased intraocular pressure - This can be a complication of eye surgery that leads to a person becoming cross-eyed.
What Causes Strabismus in Newborns?
- Congenital conditions – Some congenital conditions like Down syndrome and cerebral palsy can result in a child born with crossed eyes strabismus in newborns.
- Family history – Inherited gene mutations can be a cause of strabismus in newborns.
Strabismus Symptoms
There are several symptoms of strabismus described below:
- Double vision (diplopia) or blurry vision - A person may see two images of an object or have unclear blurred vision.
- Tilting of the head (in some cases)
- Crossed eyes
- Squinting of eyes
- Eye strain or headaches
Signs of strabismus may happen at any age but often occur before a child is 6 years old.
Strabismus vs. Pseudostrabismus
Strabismus can be differentiated from pseudostrabismus (false strabismus) by an ophthalmologist who can examine the eyes and perform tests. One such test is to cover one eye and see how the other eye responds. Another test entails seeing where light hits the surface of the eye. In pseudostrabismus, the light will reach the center of each eye, while this is not the case for strabismus.
Pseudoestropia is the most prevalent form of pseudostrabismus and occurs when a child’s eyes appear to be crossed or squint but not misaligned. This can be due to the child having prominent epicanthal folds or a flat nasal bridge.
Complications of Strabismus
If left untreated, strabismus can have the following complications:
- Amblyopia ("lazy eye") – This leads to vision loss due to the brain favoring one eye. This occurs in half of children who have strabismus and are not treated.
- Difficulty perceiving depth (3D vision) – This condition can cause problems for children trying to learn while in school. Adult strabismus can have consequences for daily life, for instance, causing difficulty when a person is driving a car.
- Decreased self-esteem and, in some cases, social anxiety and depression may occur in individuals who suffer from strabismus.
Diagnosis of Strabismus
An ophthalmologist can diagnose strabismus by completing a series of eye exams. These can be listed as follows:
- Hirschberg test/Corneal light reflex test- For newborns, a light is shone in the eyes, and the doctor looks to see where the light reflects on the eyes.
- Cover test - For older children, vision tests also include testing of each eye individually while the other is covered. The child is asked to read out numbers and letters while each eye is covered in turn.
- Cycloplegic refraction test- This can be done to assess if a child has strabismus. Doctors use eye drops in this test to stop the eyes from overfocusing, which helps the doctor test for refractive errors.
- Visual acuity tests- These are an important part of a comprehensive eye exam and give an idea of how sharp your vision is and the extent to which misaligned eyes affect your sight.
- Ocular motility testing- This test is done to evaluate eye movements in different directions. The coordination of the eyes and speed of movement are evaluated while tracking a moving object.
Treatment Options for Strabismus
- Eyeglasses or contact lenses: These correct underlying vision problems that are due to refractive errors.
- Prism lenses: These are lenses that are designed to bend the light in such a way as to alleviate double vision. This is a squint eye treatment option for adults.
- Vision therapy: Eye exercises to improve eye coordination and alignment.
- Eye patching: This helps strengthen the weaker eye (for amblyopia), which can also help strabismus and improve the eye’s condition. This treatment is usually for children who have squint eyes.
- Botox injections: Botulinum toxin can be used to temporarily weaken overactive eye muscles (in some cases), but there is a risk of having a droopy eyelid from the procedure.
- Orthoptics: These are exercises that the person can do to help their eyes and correct a squint. It is often done pre-surgery and post-surgery.
Strabismus Surgery
Surgery may be necessary in some cases of strabismus and is done to adjust the position of eye muscles for permanent realignment and to restore binocular vision.
What to expect after surgery:
After your squint surgery, someone needs to drive you home and stay with you for at least 24 hours. The doctor will prescribe eye drops, and you can take painkillers like nonsteroidal anti-inflammatories.
Precautions and recovery:
Recovery after strabismus surgery can take some time. Your eyes can take up to 12 weeks to heal. Hence, it is important to follow your doctor’s advice.
What not to do after strabismus surgery:
Do not drive until your doctor says it is okay to do so. Also, avoid swimming or going into a sauna or hot tub for 14 days after the procedure.
Complications/side effects of surgery:
As in all surgeries, there are risks, which include;
- Bleeding
- Misalignment reoccurring
- Double vision
- Drooping eyelids
- Scarring
- Infection – Signs of eye infection after strabismus surgery include eye pain that gets worse, vision that deteriorates, fever, redness, swelling, and discharge.
Innovations in Strabismus Treatment
There have been a few innovations in the treatment of strabismus, such as the following:
- 3D computer modeling for pre-surgical planning – Advances in bioprinting and modeling are useful for surgeons’ training.
- Adjustable sutures for fine-tuning after surgery – Being able to adjust sutures post-operatively is beneficial. The adjustable sutures are more effective than fixed sutures.
- Vision therapy advancements using computer games and virtual reality – Virtual reality may be a useful tool for helping treat strabismus.
Living with Strabismus
- Coping strategies for daily activities:
Squint eye exercises, such as pencil push-ups, may help with strabismus. It is also important to get regular eye checkups. The specialist can check if the chosen treatment is helping your condition and can give further advice on the next steps.
You can also find information on the American Association for Pediatric Ophthalmology and Strabismus (AAPOS) website and look online for community support groups which can help with coping strategies.
FAQs
What is the best age for Strabismus Surgery?
The best age for corrective surgery is before the age of 6.
How Successful is Strabismus Surgery in Adults?
The surgery is successful for most adults, with about 80% of patients having their eye alignment corrected.
Amblyopia vs. Strabismus: What's the Difference?
Amblyopia is linked to a problem in the brain, where the affected eye and brain lack coordination, while strabismus is linked to the eye itself being misaligned.
Does Strabismus go away With Glasses?
It depends on the cause of strabismus. Prescription glasses can fix strabismus if the condition is due to long-sightedness or near-sightedness. However, other causes of strabismus may require different treatments.
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