Adult strabismus: causes and treatment

22/10/2024

Strabismus is an eye condition in which there is a lack of parallelism or alignment of the eyes, so that each one looks in a different direction.

It can be classified into different types. Thus, depending on its direction, strabismus can be: convergent or esotropia (the misaligned eye turns inward), divergent or exotropia (the misaligned eye turns outward), hypertropia (the misaligned eye turns upward), hypotropia (the misaligned eye turns downward). The misalignment may be constant or intermittent and can appear only during times of fatigue, fever, or distraction. It can also be classified as comitant when the misalignment remains the same in different directions of gaze or incomitant when the degree of misalignment varies depending on the direction of gaze.

Although strabismus is typically associated with childhood, it can develop at any age. It is considered congenital if it appears before 6 months of age, acquired during childhood if it starts after the age of 2–3 years, or adult-onset if it begins in adulthood.

Adult strabismus can appear as a decompensation of childhood strabismus or be secondary to other factors such as:

• Neurological diseases: Myasthenia Gravis or other neuromuscular diseases, multiple sclerosis.
• Systemic diseases: thyroid disease (thyroid orbitopathy or Graves' disease), diabetes mellitus
• Eye diseases: high myopia
• Tumours
• Cerebrovascular accidents: infarcts or cerebral haemorrhages
• Traumatic brain injuries
• Orbital fractures or trauma
• Eye surgeries: cataract surgery, glaucoma surgery, retinal detachment surgery, eyelid surgery (blepharoplasty), strabismus surgery…
• Age-related: due to laxity of the tissues involved in eye movement
• Sensory strabismus: the deviation is a consequence of poor vision in one eye

The symptoms in adults differ from those found in childhood strabismus, since in the case of children, the brain is in the stage of visual development and has greater plasticity, so it will adopt suppression mechanisms (canceling one eye) to avoid seeing double. The patient with acquired strabismus in adulthood may present clinical manifestations including:

• Diplopia or double vision: perception of two images of the same object.
• Superposition or confusion of images
• Problems with depth perception: difficulty in judging distances.
• Eye fatigue: feeling of tiredness or discomfort in the eyes.
• Headache: due to the constant effort to try to compensate for the lack of alignment of the eyes
• Loss of binocular vision: reduction in the ability of the eyes to work together, which can lead to a reduction in the effective visual field.
• Torticollis: abnormal position of the head to avoid double vision or relieve symptoms
• Low self-esteem and increased risk of anxiety/depression: due to the psychosocial impact due to the cosmetic defect that the deviation entails

In cases of childhood strabismus that is decompensated in adulthood, as well as in sensory strabismus, the patient does not usually complain of double vision, although sometimes they may report discomfort or visual fatigue.

For an adequate diagnosis of the type of strabismus, a complete ophthalmological examination by a specialist is essential, to determine visual acuity and refraction (hyperopia, myopia, astigmatism), examine the anterior and posterior segment of the eye, study ocular motility and the coordination of both eyes with the visual brain and rule out, in certain cases, the presence of systemic pathology through neuroimaging studies and assessment by other specialists.

Treatment of strabismus in adults includes different therapeutic measures, including the following:

• Optical correction: glasses or contact lenses. These can help correct or improve alignment in certain types of strabismus, such as accommodative strabismus
• Prisms: “special” wedge-shaped lenses that modify the direction of light rays and therefore the image, helping to reduce double vision. They alleviate double vision in cases with small deviations, but do not correct the underlying problem. 
• Visual therapy: specific exercises to improve ocular coordination in certain types of strabismus such as exophorias or intermittent exotropias of low magnitude with fusional convergence insufficiency
• Botulinum toxin: this is a neuromodulatory substance that temporarily paralyzes the muscles, therefore being applied to the muscles with excess activity in certain types of strabismus, such as in oculomotor paralysis
• Surgery on the extraocular muscles: it allows the restoration of ocular parallelism and the cooperation of both eyes, alleviating the symptoms, correcting torticollis and improving the cosmetic appearance.
• Treatment of the underlying cause: sometimes strabismus may require a multidisciplinary approach involving an ophthalmologist, internist, neurologist… In some of these cases, treating the primary medical condition can resolve the ocular alignment on its own.

Dr. Idoia Rodríguez Maiztegui, ophthalmologist at the Barraquer Ophthalmology Centre