strabismus lecture one

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Introduction : 

Introduction بسم الله الرحمن الرحيم علم فن خيل قرار متابعه ” لا يوجد علم دون تعب ... ودراسة مستمرة ... و متابعة حثيثة ” قال رسول الله صلى الله عليه و سلم : ( ان الله يحب اذا عمل احدكم عملا ان يتقنه)


DEFENITIONS VISUAL AXIS (line of vision ) : passes from the fovea through the nodal point of the eye to the point of fixation ( object of regard ) . In normal binocular single vision (BSV) the two visual axes intersect at the point of fixation , with the images from the two eyes being aligned by the fusion reflex and combined by binocular responsive cells in the visual cortex to give BSV .


DEFENITIONS ORTHOPHORIA Implies perfect ocular alignment in the absence of any stimulus for fusion which is uncommon. Orthotropia = correct position of eyes even if small heterophoria is present . HETEROPHORIA ( PHORIA ) Implies a tendency of the eyes to deviate when fusion is blocked (latent squint ). Or ocular deviation kept latent by the fusional mechanism . Slight phoria is present in most normal individuals and is overcome by the fusion reflex.


DEFENITIONS Heterophoria Heterophoria refers to a muscular imbalance between the two eyes that leads to misalignment of the visual axes only under certain conditions. This is in contrast to orthophoria, muscular balance with parallel visual axes. Heterophoria is typified by initially parallel visual axes and full binocular vision.


DEFENITIONS The following forms are distinguished analogously to manifest strabismus: Esophoria: latent inward deviation of the visual axis. Exophoria: latent outward deviation of the visual axis. Hyperphoria: latent upward deviation of one eye.


DEFENITIONS Hypophoria: latent downward deviation of one eye. Cyclophoria: latent rotation of one eye around its visual axis. Epidemiology: This disorder occurs in 70–80% of the population. The incidence increases with age.

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Hypophoria: latent downward deviation of one eye. Cyclophoria: latent rotation of one eye around its visual axis. Epidemiology: This disorder occurs in 70–80% of the population. The incidence increases with age.

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Etiology and symptoms: Heterophoria does not manifest itself as long as image fusion is unimpaired. Where fusion is impaired as a result of alcohol consumption, stress, fatigue, concussion, or emotional distress, the muscular imbalance can cause intermittent or occasionally permanent strabismus. This is then typically associated with symptoms such as headache, blurred vision, diplopia and easily fatigued eyes .

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Diagnostic considerations: Heterophoria is diagnosed by the uncover test. This test simulates the special conditions under which heterophoria becomes manifest (decreased image fusion such as can occur due to extreme fatigue or consumption of alcohol) and eliminates the impetus to fuse images.

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In contrast to the cover test, the uncover test focuses on the response of the previously covered eye immediately after being uncovered. Once uncovered, the eye makes a visible adjustment to permit fusion and recover binocular vision.

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Heterophoria requires treatment only in symptomatic cases. Convergence deficiencies can be improved by orthoptic exercises. The patient fixates a small object at eye level, which is slowly moved to a point very close to the eyes. The object may not appear as a double image. Treatment:

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Prism eye glasses to compensate for a latent angle of deviation help only temporarily and are controversial because they occasionally result in an increase in heterophoria. Strabismus surgery is indicated only when heterophoria deteriorates into clinically manifest strabismus.

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HETEROPHORIA It can be either esophoria or exophoria . When fusion is insufficient to control the imbalance the phoria is described as decompensating and is often associated with symptoms of binocular discomfort or double vision ( diplopia ). HETEROTROPIA It implies a manifest deviation in which the visual axes do not intersect at the the point of fixation. Or deviation that is manifest and not kept under control by the fusional mechanism . The images from the two eyes are misaligned so that either double vision is present or more commonly in children , the image from the deviating eye is suppressed at cortical level .

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failure of the normal development of binocular fusion mechanisms. oculomotor imbalance secondary to differences in refraction of the two eyes Why squint in childhood ?

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failure of fusion , for example secondary to poor vision in one eye . weakness of muscles . restriction of muscles . damage to nerve supply . Why squint in adult ?

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Horizontal deviation ( latent or manifest ) is the most common form of strabismus . A vertical deviation almost invariably reflects abnormal ocular motility . Upward displacement of one eye relative to the other is termed hypertropia and a controlled upward imbalance a hyperphoria . Downward displacement is termed a hypotropia and controlled imbalance a hypophoria .

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Is a line passing from the posterior pole through the center of the cornea . Because the fovea is usually slightly temporal to the anatomical center of the posterior pole of the eye , the visual axis does not usually correspond to the anatomical axis of the eye . Anatomical axis = pupillary axis ANATOMICAL AXIS

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Is the angle subtended by the visual and the anatomical axes and is usually about 5 degrees . The angle is positive when the fovea is temporal to the center of the posterior pole resulting in a nasal displacement of the corneal reflex and negative when the converse applies . ANGLE KAPPA

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A large angle kappa may give the appearance of a squint when none is present ( pseudo- squint ) and is seen most commonly as a pseudo- exotropia following displacement of the macula in ROP where the angle may significantly exceed + 5 degrees .

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