This last is typically the case when strabismus is present since early childhood.Results of a U.S. cohort study indicate that the incidence of adult-onset strabismus increases with age, especially after the sixth decade of life, and peaks in the eighth decade of life, and that the lifetime risk of being diagnosed with adult-onset strabismus is approximately 4%. Laterality
Strabismus may be classified as unilateral if the one eye consistently deviates, or alternating if either of the eyes can be seen to deviate. Alternation of the strabismus may occur spontaneously, with or without subjective awareness of the alternation. Alternation may also be triggered by various tests during an eye exam. Unilateral strabismus has been observed to result from a severe or traumatic injury to the affected eye. Direction and latency
Horizontal deviations are classified into two varieties, using prefixes: eso- describes inward or convergent deviations towards the midline, while exo- describes outward or divergent misalignment. Vertical deviations are also classified into two varieties, using prefixes: hyper- is the term for an eye whose gaze is directed higher than the fellow eye, while hypo- refers to an eye whose gaze is directed lower. Finally, the prefix cyclo- refers to torsional strabismus, which occurs when the eyes rotate around the anterior-posterior axis to become misaligned and is quite rare. These five directional prefixes are combined with -tropia (if manifest) or -phoria (if latent) to describe various types of strabismus. For example, a constant left hypertropia exists when a persons left eye is always aimed higher than the right.
Successful surgical correction of strabismus, for adult as well as children, has been shown to have a significantly positive effect on psychological well-being.Very little research exists regarding coping strategies employed by adult strabismics. One study categorized coping methods into three subcategories: avoidance (refraining from participation in an activity), distraction (deflecting attention from the condition), and adjustment (approaching an activity differently). The authors of the study suggested that individuals with strabismus may benefit from psychosocial support such as interpersonal skills training. No studies have evaluated whether psychosocial interventions have had any benefits on individuals undergoing strabismus surgery. Pathophysiology
The extraocular muscles control the position of the eyes. Thus, a problem with the muscles or the nerves controlling them can cause paralytic strabismus. The extraocular muscles are controlled by cranial nerves III, IV, and VI. An impairment of cranial nerve III causes the associated eye to deviate down and out and may or may not affect the size of the pupil. Impairment of cranial nerve IV, which can be congenital, causes the eye to drift up and perhaps slightly inward. Sixth nerve palsy causes the eyes to deviate inward and has many causes due to the relatively long path of the nerve. Increased cranial pressure can compress the nerve as it runs between the clivus and brain stem. Also, if the doctor is not careful, twisting of the babys neck during forceps delivery can damage cranial nerve VI.Evidence indicates a cause for strabismus may lie with the input provided to the visual cortex.