Concomitant<unk>  Concomitant<unk>  – that is, an inward squint that does not vary with the direction of gaze – mostly sets in before 12 months of age (this constitutes 40% of all<unk> rabismus cases) or at the age of three or four. Most patients with "early-onset" concomitant<unk>  are emmetropic, whereas most of the "later-onset" patients are hyperopic. It is the most frequent type of natural<unk> rabismus not only in humans, but also in monkeys. Concomitant<unk>  can itself be subdivided into<unk> s that are<unk> her constant, or intermittent. ; Constant<unk>  : A constant<unk> , as the name implies, is present all the time. ; Intermittent<unk>  : Intermittent<unk> s, again as the name implies, are not always present. In very rare cases, they may only occur in repeated cycles of 'one day on, one day off' (Cyclic<unk> . However, the vast majority of intermittent<unk> s are accommodative in origin. A patient can have a constant<unk>  for reading, but an intermittent<unk>  for distance (but rarely vice versa). Accommodative<unk>  Child exhibiting uncorrected accommodative<unk>  Child exhibiting corrected accommodative<unk>  Accommodative<unk>  (also called refractive<unk>  is an inward turning of the eyes due to efforts of accommodation. It is often seen in patients with moderate amounts of hyperopia. The person with hyperopia, in an attempt to "accommodate" or focus the eyes, converges the eyes as well, as convergence is associated with activation of the accommodation reflex. The over-convergence associated with the extra accommodation required to overcome a hyperopic refractive error can precipitate a loss of binocular control and lead to the development of<unk> . The chances of an<unk>  developing in a hyperopic child will depend to some degree on the amount of hyperopia present. Where the degree of error is small, the child will typically be able to maintain control because the amount of over-accommodation required to produce clear vision is also small. Where the degree of hyperopia is large, the child may not be able to produce clear vision no matter how much extra-accommodation is exerted and thus no incentive exists for the over-accommodation and convergence that can give rise to the onset of<unk> . However, where the degree of error is small enough to allow the child to generate clear vision by over-accommodation, but large enough to disrupt their binocular control,<unk>  will result. Only about 20% of children with hyperopia greater than +3.5 diopters develop<unk> rabismus. Where the<unk>  is solely a consequence of uncorrected hyperopic refractive error, providing the child with the correct glasses and ensuring that these are worn all the time, is often enough to control the deviation. In such cases, known as 'fully accommodative<unk> s,' the<unk>  will only be seen when the child removes their glasses. Many adults with childhood<unk> s of this type make use of contact lenses to control their 'squint.' Some undergo refractive surgery for this purpose. A second type of accommodative<unk>  also exists, known as 'convergence excess<unk> .' In this condition the child exerts excessive accommodative convergence relative to their accommodation. Thus, in such cases, even when all underlying hyperopic refractive errors have been corrected, the child will continue to squint when looking at very small objects or reading small print. Even though they are exerting a normal amount of accommodative or 'focusing' effort, the amount of convergence associated with this effort is excessive, thus giving rise to<unk> . In such cases an additional hyperopic correction is often prescribed in the form of bifocal lenses, to reduce the degree of accommodation, and hence convergence, being exerted. Many children will gradually learn to control their<unk> s, sometimes with the help of orthoptic exercises. However, others will eventually require extra-ocular muscle surgery to resolve their problems. Congenital<unk>  Congenital<unk> , or infantile<unk> , is a specific sub-type of primary concomitant<unk> . It is a constant<unk>  of large and consistent size with onset between birth and six months of age. It is not associated with hyperopia, so the exertion of accommodative effort will not significantly affect the angle of deviation. It is, however, associated with other ocular dysfunctions including oblique muscle over-actions, Dissociated Vertical Deviation (DVD), Manifest Latent Nystagmus, and defective abduction, which develops as a consequence of the tendency of those with infantile<unk>  to 'cross fixate.' Cross fixation involves the use of the right eye to look to the left and the left eye to look to the right; a visual pattern that will be 'natural' for the person with the large angle<unk>  whose eye is already deviated towards the opposing side. The origin of the condition is unknown, and its early onset means that the affected individual's potential for developing binocular vision is limited. The appropriate treatment approach remains a matter of some debate. Some ophthalmologists favour an early surgical approach as offering the best prospect of binocularity whilst others remain unconvinced that the prospects of achieving this result are good enough to justify the increased complexity and risk associated with operating on those under the age of one year. Incomitant<unk>  Incomitant<unk> s are conditions in which the<unk>  varies in size with direction of gaze. They can occur in both childhood and adulthood, and arise as a result of neurological, mechanical or myogenic problems. These problems may directly affect the extra-ocular muscles themselves, and may also result from conditions affecting the nerve or blood supply to these muscles or the bony orbital<unk> ructures surrounding them. Examples of conditions giving rise to an<unk>  might include a VIth cranial nerve (or Abducens) palsy, Duane's syndrome or orbital injury.
Esotropia
Cyclotropia
Exotropia
Ocular dysmetria
Heterotopia 
Quadrantanopia
Presbyopia
Pseudomyopia