A squint, or strabismus, is a condition in which the eyes do not align properly. One eye turns inwards, upwards, downwards, or outwards, while the other one focuses at one spot. It can happen all the time or intermittently. This usually occurs because the muscles that control the movement of the eye and the eyelid, the extra ocular muscles, are not working together.
As a result, both eyes are unable to look at the same spot at the same time. It can also happen because a disorder in the brain means that the eyes cannot correctly coordinate. Strabismus also makes binocular vision impossible, so it is harder for the person to appreciate depth perception.
Strabismus most often occurs in babies and toddlers due to heredity or problems during physical development. Most cases in children are caused by poor communication between the brain, muscles, and nerves of the eye. However, it can also occur in adults who have suffered a stroke, head trauma, or diabetes. The condition can lead to double vision, a lack of depth perception, and even loss of eyesight if left untreated.
Read more: Blurred vision
Squint can be categorized by the direction of turned or misaligned eye:
- Hypertropia is a condition of misalignment of eyes whereby the visual axis of one eye is higher than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.
- Hypotropia is the condition where focus being on the eye with the visual axis lower than the fellow fixating eye.
- Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a ‘cross-eyed’ appearance.
- Exotropia is when one or both eyes turn outward. Exotropia may occur from time to time or may be constant and is found in every age group.
What are the types of Strabismus?
There are several forms of strabismus. The two most common are:
- Accommodative Esotropia: This often occurs in cases of uncorrected farsightedness and a genetic predisposition (family history) for the eyes to turn in. Because the ability to focus is linked to where the eyes are pointing, the extra focusing effort needed to keep distant objects in clear focus may cause the eyes to turn inward. Symptoms include double vision, closing or covering one eye when looking at something near, and tilting or turning the head. This type of strabismus typically starts in the first few years of life. This condition is usually treated with glasses, but may also require eye patching and/or surgery on the muscles of one or both eyes.
- Intermittent Exotropia: In this type of strabismus, one eye will fixate (concentrate) on a target while the other eye is pointing outward. Symptoms may include double vision, headaches, difficulty reading, eyestrain, and closing one eye when viewing far away objects or when in bright light. Patients may have no symptoms while the ocular deviation (difference) may be noticed by others. Intermittent Exotropia can happen at any age. Treatment may involve glasses, patching, eye exercises and/or surgery on the muscles of one or both eyes.
Read More: Squint eye treatment
Causes of Squint or Strabismus:
Most adults with squints have had the condition since childhood. However, strabismus can also begin in adulthood due to medical problems. Most squint results from an abnormality of the neuromuscular control of eye movement. Less commonly, there is a problem with the actual eye muscle. Squint is often inherited, with about 30 percent of children with strabismus having a family member with a similar problem.
Other conditions associated with strabismus include:
- Uncorrected refractive errors.
- Poor vision in one eye.
- Cerebral palsy.
- Down syndrome (20-60% of these patients are affected).
- Hydrocephalus (a congenital disease that results in a build-up of fluid in the brain).
- Brain tumours.
- Stroke (the leading cause of strabismus in adults)
- Head injuries, which can damage the area of the brain responsible for control of eye movement, the nerves that control eye movement, and the eye muscles.
- Neurological (nervous system) problems.
- Graves’ disease (overproduction of thyroid hormone).
Symptoms of Strabismus:
Adults with squints may experience:
- Eye fatigue.
- Double vision.
- Overlapped or blurred images.
- A pulling sensation around the eyes.
- Reading difficulty.
- Loss of depth perception.
- Inability to make direct contact while communicating or looking at people with both the eyes.
To correct the inability to focus properly, many adults with squints have to tilt or turn their heads when focusing. They are also unable to make direct eye contact with both eyes when looking at people, which can make social situations awkward.
These symptoms may have a negative impact on employment and social opportunities.
Treatment of squint or strabismus:
Treatment options include the following:
- Eyeglasses or contact lenses: Used in patients with uncorrected refractive errors. With corrective lenses, the eyes will need less focusing effort and may remain straight.
- Prism lenses: Special lenses that can bend light entering the eye and help reduce the amount of turning the eye must do to look at objects.
- Orthoptics (eye exercises): May work on some types of strabismus, especially convergence insufficiency (a form of Exotropia).
- Medications: Eye drops or ointments. Also, injections of botulinum toxin type A (such as Botox) can weaken an overactive eye muscle. These treatments may be used with, or in place of, surgery, depending on the patient’s situation.
- Patching: To treat amblyopia (lazy eye), if the patient has it at the same time as strabismus. The improvement of vision may also improve control of eye misalignment.
- Eye muscle surgery: Surgery changes the length or position of eye muscles so that the eyes are aligned correctly. This is performed under general anaesthesia with dissolvable stitches. Sometimes adults are offered adjustable strabismus surgery, where the eye muscle positions are adjusted after surgery.
What can happen if strabismus is not treated?
If the eyes are not properly aligned, the following may result:
- Lazy eye (amblyopia) or permanent poor vision in the turned eye. When the eyes are looking in different directions, the brain receives two images. To avoid double vision, the brain may ignore the image from the turned eye, resulting in poor vision development in that eye.
- Blurry vision, which can affect performance in school and at work, and enjoyment of hobbies and leisure activities.
- Increased eye strain.
- Eye Fatigue.
- Frequent Headaches.
- Appearance of Double vision.
- Poor 3-dimensional (3-D) vision.
Benefits of squint surgery:
- Improved appearance (often)
- Increased peripheral (side) vision
- Improved depth perception (sometimes)
Exercises for treatment of squint or strabismus:
Pencil push ups are simple ocular workouts that get both eyes aimed on the same fixed point. They are also known as near point of convergence exercises.
Start by holding a pencil out at arm’s length, pointing away from you. Focus your gaze on the eraser or a letter or numeral on the side. Slowly move the pencil toward the bridge of your nose. Keep it in focus for as long as you can, but stop once your vision gets blurry.
Swiss optometrist Frederick Brock developed this exercise to improve eye coordination. You’ll need a string about 5 feet long with three different coloured beads.
Secure one end of the string to a stationary point such as a handrail or the back of a chair. Space the beads out at equal distances. Hold the other end of the string tightly to your nose. You should see a consistent pattern as you shift your focus from bead to bead. The bead you are looking at will appear by itself at the intersection of two identical strings with doubles of the other beads, forming an X. Your eyes are not properly focused on the bead if you see the strings crossing in front of the bead or in back of the bead. Be sure you can get the X at all beads (except the one at the far end, which will just have the two strings coming out toward you in a V).
This is a handy exercise for Exotropia. Draw three barrels of progressive size in red lengthwise on one side of a card. Do the same thing in green on the other side.
Hold the card lengthwise and vertically against your nose so that the largest barrel is furthest away. Stare at the far barrel until it becomes one image with both colours and the other two barrel images have doubled. Maintain your gaze for about five seconds. Then repeat with the middle and smallest barrel images.
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