We clinically refer to strabismus when both eyes’ axis are not perfectly aligned, meaning, when they point in different directions. An eye may look straight ahead while the other one is looking inside, outside, up, or down. There are six extraocular muscles monitoring the movement of an eye; to be able to focus on a single image and get a three-dimensional view with depth perception, all muscles from both eyes must work together in a coordinated way. The brain is responsible for controlling these muscles through cranial nerves. Strabismus may affect vision in various ways, depending on the age at which it first manifests.
What causes adult strabismus?
Most adults with strabismus have it since their childhood, when aetiology is totally different and mostly benign. On the other hand, people who develop strabismus in adulthood generally suffer from a change in their brain, nerve or eye muscle. Here are some examples:
- Systemic health diseases such as: diabetes, thyroid (Graves’ orbitopathy), myasthenia gravis, multiple sclerosis, among other neurological disorders
- Cerebrovascular accidents (CVA)
- Brain Tumours
- Damage caused to eye muscles during any kind of eye surgery
How does adult strabismus affect vision?
When having a normal vision, both eyes are aligned and able to focus the same target. The brain combines both images of our eyes in one single three-dimensional image (3-D). We can then perceive how close or far away is something from us (the so-called depth perception).
When having a misaligned eye, two different images are sent to the brain. The brain from a small child learns to ignore the image coming from the misaligned eye. Instead of both images, it can only see the image from the dominant eye. As a result, the child loses depth perception but does not develop double vision.
Adults developing strabismus after childhood tend to experience double vision (diplopia). This occurs because the brain has already completed its development and so the adult is no longer capable (as it happens in children) to ignore the image from the misaligned eye – seeing, therefore, two misaligned images.
What are the signs or symptoms of adult strabismus?
The most obvious sign comes when people living with somebody affected by strabismus or patients themselves realise that, aesthetically, the eyes are misaligned or diverted. Regarding their vision, patients might notice, in a constant or intermittent way:
- Tiredness in or around the eyes or feeling like having a “trapped eye”.
- Changes in vision such as double vision (seeing two images instead of one), blurred vision, difficult to read or loss of depth perception.
- A constant need to tilt or turn the head to sharply focus on an image.
Is there any treatment for adults?
Yes, there is! But, before thinking about treating strabismus, it is essential to get a correct diagnosis and treat the exact cause of your strabismus, since it can mitigate or eliminate the symptoms. If this is not completely possible and strabismus persists steadily for at least 6 months after its onset, we should consider the best treatment on a case-by-case basis:
- Surgery – it is the most common treatment. Surgery can enhance or bring back eye alignment and it might also help restoring a proper vision. By intervening in extra-ocular muscles (muscles are repositioned, then decreasing or increasing their action force), the ophthalmologist seeks to improve motor coordination between both eyes. Additional surgery might be needed. This surgery is usually performed as an outpatient procedure, under general anesthesia. Surgery might be performed in one or both eyes in the same procedure. After strabismus’ surgery, the patient can go back to daily routine in a few days.
- Ocular muscle exercises – orthoptic treatment can be very useful in some types of strabismus, especially in the so-called “convergence insufficiency”. In this disease, eyes are not correctly nor steadily aligned while performing tasks such as reading or working on the computer.
- Prismatic lenses (glasses) – a prism is a wedge-shaped lens which redirects (refracts) light rays. A prism can whether be attached to normal glasses or integrate the lens itself. Prisms allow symptoms’ correction, thus nullifying double vision of small-scale strabismus.
- Botulinum toxin (Botox®) – injection this medicine into extra ocular muscles can be an extra help in surgeries – it works by paralysing the muscles responsible for preventing a correct eye alignment. Its effect may whether last a few months or improve eye alignment on a permanent basis.
Follow-ups by a specialist in Strabismus and Pediatric Ophthalmology are the most appropriate actions to take according to the experience accumulated in diagnosing and treating this disease.
American Academy of Ophthalmology – https://www.aao.org/eye-health/tips-prevention-list;
American Association for Pediatric Ophthalmology and Strabismus – https://aapos.org/patients/eye-terms