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Strabismus may be classified as either constant or intermittent, based on the frequency with which an eye deviates. When an eye deviates all of the time, Strabismus is classified as constant. If, on the other hand, an eye deviates only some of the time, Strabismus is classified as intermittent. Intermittent cases of Strabismus usually result from some other physical condition, such as sickness or stress. Treatment is available for both classifications of Strabismus. There are also various sub-classifications of Strabismus, which determine the type of treatment that may be needed.

Bilateral, Unilateral and Alternating Strabismus

Strabismus may be classified according to the laterality of the eyes. Strabismus may be classified as bilateral, unilateral or alternating. If both are eyes converge or diverge, at the same time, Strabismus is bilateral. If only one eye converges or diverges, Strabismus is said to be unilateral. If convergence or divergence alternates between the eyes, such that one eye is able to focus on an object while the opposite eye is askew, Strabismus is said to be alternating. In many cases, both eyes deviate, but only one eye appears to be askew.

Congenital and Acquired Strabismus

Strabismus may be classified according to the time at which the conditions onsets When strabismus is developed during infancy, it is called congenital. When strabismus develops in adults, it is called acquired. Research has not been able to determine the reason for Congenital Strabismus. Congenital Strabismus may develop Amblyopia, which is referred to as lazy eye. Amblyopia is a naturally occurring condition in which the brain ignores any input from a deviated eye. Amblyopia in infancy causes problems in the ability to perceive depth. Early treatment of Strabismus or Amblyopia greatly reduces the chance of developing depth perception problems.

Acquired Strabismus in an adult, who otherwise had proper alignment of the eyes before the onset, is likely to cause double vision, which also known as diplopia. This is in contract to orthotropia, which is characteristic of eyes that are properly aligned. With orthotropia, the brain is able to fuse the two different objects seen by each eye into one three dimensional object. Orthotropia is also characterized by a high degree of depth perception. Acquired Strabismus is typically caused by injury to the eye orbit or injuries to the brain, such as with a stroke or head injury. Loss of vision from Acquired Strabismus usually results in a gradual development of an exotropia condition, rather than Amblyopia. Exotropia is the condition where the eye turns outward, away from the nose. Vision is already developed in adult brains and an adult brain will not compensate for deviation as children’s brains do. In other words, the adult brain is already developed and trained. It is not able to ignore images acquired by a strabismic eye.

Esotropic, Exotropic and Hypertropic Strabismus

Strabismus may be classified according to the direction in which the eye turns. Eyes that turn inward characterize Esotropic Strabismus, the most common form of Strabismus. The symptoms of Esotropic Strabismus are usually visible by 6 months and the condition will only worsen with age.

Accommodative Esotropia is a form of Esotropia that develops in farsighted children, almost exclusively after 6 months of age. The condition is termed accommodative since it relies upon the degree of accommodation necessary for a farsighted child to bring an object into focus. The degree of accommodation is proportional to the degree of farsightedness. In some children, an over-convergence of the eyes is necessary to bring an object in focus. This over-convergence is Accommodative Esotropia. Eyeglasses are usually able to correct this condition

Eyes that turn outward, away from the nose, characterize Exotropic Strabismus. The degree of turn is typically greater in children as they focus on more distant objects since focusing on close objects forces their eyes to converge. Unlike children with other types of Strabismus, bright sunlight tends to make exotropic children squint. While some children may benefit from eyeglasses or prisms, most children require surgery to correct the misalignment.

Hypertropic Strabismus is characterized by a vertical misalignment where an eye turns up or down in relation to the other eye. It is common for medical professionals to regard the condition relative to the upwardly skewed eye. Hypertrophic Strabismus may exist along with other types of Strabismus.

Pseudostrabismus

Pseudostrabismus is a false appearance of Strabismus. Strabismus is usually falsely anticipated when the patient has a flat, wide bridge of the nose and a fold of skin in the corner of the eye that makes the eye appear to be turned inward (esotropic). Pseudostrabismus is typically found in infants and children. As children age, the systems of Pseudostrabismus disappear since the bridge of the nose tends to narrows and eliminate any folds in the corner of their eyes. Strabismus may be differentiated from Pseudo Strabismus as early as 6 to 9 months.