Strabismus

» How Do the Eyes Work Together?

In normal vision, both eyes focus on the same point. The brain then combines these two images to create a three-dimensional picture, giving us depth perception. If one eye deviates, the brain receives two different images. In a small child, the brain ignores the image from the deviating eye and only processes the image from the normal, well-seeing eye, resulting in the loss of depth perception. In adults, strabismus typically causes double vision because the brain is accustomed to seeing images from both eyes and cannot ignore the image from the deviating eye.

» Amblyopia (Lazy Eye)

During childhood, if both eyes are parallel, good vision development occurs. The brain perceives the image from the well-seeing eye but ignores the image from the lazy eye. This condition is seen in nearly half of children with strabismus. Treatment for amblyopia should be conducted before the age of 8-10 years, as it becomes difficult to treat afterward. Several treatment methods exist. One involves covering the good eye to strengthen the vision in the lazy eye. Another method involves sessions using CAM devices in special clinics, where the child is asked to color, draw, or solve puzzles over rotating lines. A third method involves using atropine-based eye drops in the healthy eye to force the other eye to work. If treatment is delayed, amblyopia becomes permanent. Generally, the earlier amblyopia is treated, the better the outcome. For this reason, children should undergo eye examinations during infancy and at least once a year afterward.

» Causes of Strabismus

The exact cause of strabismus is unknown. Six muscles attached to each eye’s exterior control its movements. Two muscles in each eye pull it left or right, while the other four move it up or down at certain angles. To maintain parallel eyes and focus on a specific target, all muscles must work together in balance. For both eyes to move together, the muscles in both eyes must function in harmony. The brain controls the eye muscles.

• Children with cerebral palsy (who experienced oxygen deprivation during birth);
• Down syndrome;
• Hydrocephalus;
• Brain tumors are more prone to strabismus.

Cataracts or eye injuries can also impair vision and lead to strabismus.

» Symptoms of Strabismus

The primary symptom of strabismus is an eye that does not look straight. Sometimes, children close one eye in sunlight or tilt their heads to use both eyes together.

» How Is Strabismus Diagnosed?

Strabismus is diagnosed through an eye examination. It is recommended that all children undergo a vision test before the age of four. If there is a family history of strabismus or amblyopia, earlier testing may be warranted. Babies’ eyes often appear crossed, which usually resolves as they grow. A broad and flat nasal bridge and a fold of skin at the nasal side of the eyes can create the appearance of crossed eyes. However, this pseudo-strabismus condition disappears as the child grows. In cases of true strabismus, the condition does not improve. An ophthalmologist can distinguish between true and pseudo-strabismus.

» How Is Strabismus Treated?

The goals of strabismus treatment are:

• To preserve vision;
• To align the eyes;
• To restore binocular vision, or depth perception.

After a complete eye examination, the ophthalmologist will determine the appropriate treatment. In some cases, glasses may be recommended for your child. The deviation may be completely or partially corrected with glasses. In addition, surgery may be necessary to align the eyes or remove a cataract if present. Strengthening the lazy eye often requires covering the healthy eye.

» Common Types of Strabismus

Esotropia (Inward Deviation): This is the most common type of strabismus in infants. Children with esotropia cannot use both eyes together. In most cases, early surgery can align the eyes. During surgery for esotropia, the tension in one or both eyes’ muscles is adjusted. Tight inner muscles are repositioned backward, allowing the eyes to turn outward. Sometimes, the external muscles are shortened to increase tension and correct the strabismus. Surgery does not necessarily need to be performed on the deviating eye. Surgery on the other eye can also correct the deviation.

Accommodative Esotropia: This type is more common in hyperopic (farsighted) children aged two years and older. The child may adjust their eyes to see objects up close, but this focusing effort (accommodation) causes the eyes to cross. Glasses reduce the focusing effort, correcting the deviation. Sometimes, bifocal lenses are needed for near work. Eye drops, ointments, or special lenses called prisms may also be used to align the eyes.

Exotropia (Outward Deviation): Another common type of deviation occurs when the child looks at distant objects. Exotropia can occur when the child is daydreaming, ill, or tired. In bright sunlight, the child may squint one eye.

» How Is Strabismus Surgery Performed?

In eye surgery, the eyeball is never removed. To reach the eye muscles, a small incision is made in the white covering of the eye. Based on the type of deviation, specific muscles are adjusted. Surgery may be planned on one or both eyes. When strabismus surgery is performed on children, general anesthesia is required. Local anesthesia can only be used in adults. Recovery is quick, and patients can resume normal activities within a few days. Glasses or prisms may be needed after surgery. In some cases, a second surgery may be required later. Early surgery in children with constant strabismus yields better results. Therefore, if surgery is needed, it should be considered before school age. As with any surgery, there are risks associated with eye muscle surgery. These include infection, bleeding, excessive scarring, and other rare complications that could lead to vision loss. Strabismus surgery is generally an effective and safe treatment for aligning the eyes but cannot replace glasses or amblyopia treatment.

» Injections

To reduce the effect of a muscle, a special drug called botulinum toxin can be injected. This causes the opposing muscle to work more intensely. Although the drug’s effect typically wears off after 5-10 weeks, some cases may achieve permanent results. In some instances, repeated injections may be necessary, but they are generally less effective than surgery.