During an eye examination, a test such as cover testing or the Hirschberg test is used in the diagnosis and measurement of<unk>  and its impact on vision. Retinal birefringence scanning can be used for screening of young children for eye misalignment. A Cochrane review to examine different types of diagnosis test found only one study. This study used a photoscreener which was found to have high specificity (accurate in identifying those without the condition) but low sensitivity (inaccurate in identifying those with the condition). Several classifications are made when diagnosing<unk> . Latency<unk>  can be manifest (-tropia) or latent (-phoria). A manifest deviation, or heterotropia (which may be eso-, exo-, hyper-, hypo-, cyclotropia or a combination of these), is present while the person views a target binocularly, with no occlusion of either eye. The person is unable to align the gaze of each eye to achieve fusion. A latent deviation, or heterophoria (eso-, exo-, hyper-, hypo-, cyclophoria or a combination of these), is only present after binocular vision has been interrupted, typically by covering one eye. This type of person can typically maintain fusion despite the misalignment that occurs when the positioning system is relaxed. Intermittent<unk>  is a combination of both of these types, where the person can achieve fusion, but occasionally or frequently falters to the point of a manifest deviation. Onset<unk>  may also be classified based on time of onset, either congenital, acquired, or secondary to another pathological process. Many infants are born with their eyes slightly misaligned, and this is typically outgrown by six to 12 months of age. Acquired and secondary<unk>  develop later. The onset of accommodative esotropia, an overconvergence of the eyes due to the effort of accommodation, is mostly in early childhood. Acquired non-accommodative<unk>  and secondary<unk>  are developed after normal binocular vision has developed. In adults with previously normal alignment, the onset of<unk>  usually results in double vision. Any disease that causes vision loss may also cause<unk> , but it can also result from any severe and/or traumatic injury to the affected eye. Sensory<unk>  is<unk>  due to vision loss or impairment, leading to horizontal, vertical or torsional misalignment or to a combination thereof, with the eye with poorer vision drifting slightly over time. Most often, the outcome is horizontal misalignment. Its direction depends on the person's age at which the damage occurs: people whose vision is lost or impaired at birth are more likely to develop esotropia, whereas people with acquired vision loss or impairment mostly develop exotropia. In the extreme, complete blindness in one eye generally leads to the blind eye reverting to an anatomical position of rest. Although many possible causes of<unk>  are known, among them severe and/or traumatic injuries to the afflicted eye, in many cases no specific cause can be identified. This last is typically the case when<unk>  is present since early childhood. Results of a U.S. cohort study indicate that the incidence of adult-onset<unk>  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<unk>  is approximately 4%. Laterality<unk>  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<unk>  may occur spontaneously, with or without subjective awareness of the alternation. Alternation may also be triggered by various tests during an eye exam. Unilateral<unk>  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<unk> , 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<unk> . For example, a constant left hypertropia exists when a person's left eye is always aimed higher than the right. A person with an intermittent right esotropia has a right eye that occasionally drifts toward the person's nose, but at other times is able to align with the gaze of the left eye. A person with a mild exophoria can maintain fusion during normal circumstances, but when the system is disrupted, the relaxed posture of the eyes is slightly divergent. Other considerations<unk>  can be further classified as follows: * Paretic<unk>  is due to paralysis of one or several extraocular muscles. * Nonparetic<unk>  is not due to paralysis of extraocular muscles. * Comitant (or concomitant)<unk>  is a deviation that is the same magnitude regardless of gaze position. * Noncomitant (or incomitant)<unk>  has a magnitude that varies as the person shifts his or her gaze up, down, or to the sides. Nonparetic<unk>  is generally concomitant. Most types of infant and childhood<unk>  are comitant. Paretic<unk>  can be either comitant or noncomitant. Incomitant<unk>  is almost always caused by a limitation of ocular rotations that is due to a restriction of extraocular eye movement (ocular restriction) or due to extraocular muscle paresis. Incomitant<unk>  cannot be fully corrected by prism glasses, because the eyes would require different degrees of prismatic correction dependent on the direction of the gaze. Incomitant<unk>  of the eso- or exo-type are classified as "alphabet patterns": they are denoted as A- or V- or more rarely λ-, Y- or X-pattern depending on the extent of convergence or divergence when the gaze moves upward or downward. These letters of the alphabet denote ocular motility pattern that have a similarity to the respective letter: in the A-pattern there is (relatively speaking) more convergence when the gaze is directed upwards and more divergence when it is directed downwards, in the V-pattern it is the contrary, in the λ-, Y- and X-patterns there is little or no<unk>  in the middle position but relatively more divergence in one or both of the upward and downward positions, depending on the "shape" of the letter. Types of incomitant<unk>  include: Duane syndrome, horizontal gaze palsy, and congenital fibrosis of the extraocular muscles. When the misalignment of the eyes is large and obvious, the<unk>  is called large-angle, referring to the angle of deviation between the lines of sight of the eyes. Less severe eye turns are called small-angle<unk> . The degree of<unk>  can vary based on whether the person is viewing a distant or near target.<unk>  that sets in after eye alignment had been surgically corrected is called consecutive<unk> . Differential diagnosis Pseudostrabismus is the false appearance of<unk> . It generally occurs in infants and toddlers whose bridge of the nose is wide and flat, causing the appearance of esotropia due to less sclera being visible nasally. With age, the bridge of the child's nose narrows and the folds in the corner of the eyes become less prominent. Retinoblastoma may also result in abnormal light reflection from the eye.Strabismus correction surgery
Strabismus
Cranial nerve disease
Hypoglossia
Convergence insufficiency
Ankyloglossia
Pseudostrabismus
Trismus
Anismus