Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Visual impairment wikipedia , lookup
Blast-related ocular trauma wikipedia , lookup
Diabetic retinopathy wikipedia , lookup
Eyeglass prescription wikipedia , lookup
Dry eye syndrome wikipedia , lookup
Visual impairment due to intracranial pressure wikipedia , lookup
Strabismus: Defination:it is misaligment of visual axis. Misaligment may be in any direction –inward,outward,up, or down.the amount of deviation is angle by which the deviating eye is misaligned.strabismus present under binocular viewing condition is manifest strabismus ,hetrotropia ,or tropia.a deviation present only after binocular vision has been interrupted (ie, by occlusion of one eye) is called latent strabismus, hetrophoria, or phoria. Physiology 1.motor aspects each of the six extraocular muscles plays a role in positioning the eye about three axes of rotation .the primary action of a muscle is the principal effect it has on eye rotation .lesser effects are called secondary or tertiary actions.the precise action of any muscle depends on the orientation of the eye in the orbit and the influence of the orbital connective tissues,which regulate the direction of action of the extraocular muscles by acting as their functional mechanical origins(the active bulley hybothesis). The medial and lateral rectus muscles adduct and abduct the eye,respectively,with little effect on elevation or torsion.the vertical rectus and oblique musclesdebre have vertical rotation and torsional functions. In general terms,the vertical rectus muscles are the main elevators and depressors of the eye,and the obliques are mostly involved with torsional positioning.the vertical effect of the superior and inferior rectus muscles is greater when the eye is abducted.the vertical effect of the obliques is greater when the eye is adducted. Field of action The position of the eye is determined by the equilibrium achieved by the pull of all six extraocular muscles.the eyes are in the primary position of gaze when they are looking straight ahead with the head and body erect.to move the eye into another direction of gaze,the agonist muscle contracts to pull the eye in that direction and the antagonist muscle relaxes.the filed of action of a muscle is the directionof gaze in which that muscle exerts its greatest contraction force as an agonist,eg,the lateral rectus muscle undergoes the greatest contraction in abducting the eye. Synergistic & antagonistic muscles(sherringtion’s law) Synergistic muscles are those that have the same field of action.thus,for vertical gaze,the superior rectus and inferior oblique muscles are synergists in moving the eye upward. Muscles synergistis for one function may be antagonistMuscles synergistis for one function may be antagonistic for another .for example , the superior rectus and inferior oblique muscles are antagonists for torsion ,the superior rectus causing intorsion and the inferior oblique muscles are antagonists for torsion, the superior rectus causing intorsion and the inferior oblique extorsion.the extraocular muscles, like skeletal muscles, show reciprocal innervations of antagonistic muscles (Sherrington’s law).thus, in dextroversion(right gaze), the right medial and left lateral rectus muscles are inhibited while the right lateral and left medial rectus muscles are stimulated. Yoke Muscles(Hering’s Law) For movements of both eyes in the same direction, the corrponding agonist muscles receive equal innervation(Hering Iaw). reciprocal innervations of antagonistic muscles (Sherrington’s law).the pair of nsieagonist muscles with the same primary action is called a uoke pair.the right Iateral rectus and the left medial rectus muscles are a yoke pair for right gaze.the right inferior rectus and the left superior oblique muscles are a yoke pair for gaze downward and to the right. The neuromuscular system of an infant is immature so that it is not uncommon in the first few months of life for ocular alignment to be unstable.Transient esodeviations are most common and may be associated with immaturity of the accommodation-convergence system Gradually improving visual acuity together maturation of the oculomotor system allows a more stable ocular alignment by age 2 months.Any ocular misalignment after this age should be investigated Development of Binocular Movement 2.Sensory Aspects Binocular Vision In each eye, whatever is imaged on the fovea is seen subjectively as being straight ahead.thus, if two dissimilar objects were imaged on the two foveas,but the dissimilarities would prevent fusion eye,the image in each eye is actually slightly different from that in the other.Sensory fusion and stereopsis are the two different physiologic processes that are responsible for binocular vision. Sensory Fusion & Stereopsis Sensory fusion is the process whereby dissimilarities between the two images are not appreciated. On the peripheral retina of each eye, there are corresponding points that in the absence of fusion Iocalize stimuli in the same direction in space. In the process of fusion, the direction values of these points can be modified.thus each point of the retina in each eye is capable of fusing that strike sufficiently close to the corrsponding point in the other eye. Thes region of fusible points is called Panum’s area. Sensory changes in Strabismus Up to age 7 or 8,the brain usually develops responses to abnormal binocular vision that may not occur if the onset of sttabismus is later. These changes include diplopia, suppression, anomalous retinal correspondence, and eccentric fixation. A.DIPLOPIA If strabismus is present, each fovea receives a different image. The objects image on the two foveas are seen in the same direction in space. This process of localization of spatially objects to the same location is called visual confusion .the object viewed by one of the foveas is imaged on a peripheral retinol area in the other eye. The foveal image is localized straight ahead, while the peripheral image of the same object in the other eye is localized in some other direction. Thus, the same object is seen in two places(diplopia). B.SUPPRESSION Under binocular viewing conditions, the images seen by one eye become predominant and those seen by the other eye are not perceived (suppressipon). Suppression takes the form of a scotoma in the deviationg eye Only under binocular viewing conditions. (A scotoma is an area of reduced vision within the visual field; surrounded by an area of less depressed or normal vision.) c.Amblyopia: prolonged abnormal visual experience in a child under the age of 7 years may lead to amblyopia (reduced visual acuity in the absence of detectable organic disease in one eye).the three clinical causes of amblyopia due to visual deprivation e.g congenital cataract, strsbismus or unequal refractive error (anisometropia). D .Anomalous retinal correspondance. ARC is a sensory adaptation that occurs in strabismus under binocular viewing conditions. E.Eccentric fixation: In eyes with suffeciently severe amblyopia, an extrafoveal retinal area may be used for fixation under monocular viewing conditions. It is always associated with severe amblyopia and unstable fixation. The eccentric fixation point is often not displaced in a dircetion appropriate to the direction of strabismus (eg, the nasal retina in esotropia). Gross eccentric fixation can be readily identified clinically by occluding the dominant eye and directing the patient’s attention to a light source held directly in front. An eye with gross eccentric fixation will not point toward the light source but will appear to be looking in some other direction. More subtle degrees of eccentric fixation can be detected by an ophthalmoscope that projects a small fixation target onto the retina. EXAMINATION HISTORY A careful history is important in the diagnosis of strabismus. A.FAMILY HISTORY Strabismus and amblyopia are frequently found to occur in families. B.AGE AT ONSET This is an important factor in long-term prognosis. The earlier the onset of strabismus, the worse the prognosis for good binocular function. C.TYPE OF ONSET The onset may be gradual, sudden, or intermittent. D.TYPE OF DEVIATION The misalignment may be in ang direction. It may be greater in certion positions of gaze, including the primary position for distance or near. E.FIXATION One eye may constantly deviated, or alternating fixation may be observed Visual Acuity Visual acuity should be evaluated even if only a rough approximation or comparison of the two eyes is possible. Each eyeis evaluated by itself, since binocular testing will not reveal poor vision in one eye. For the very young ptarget. The target should be as small as the child’s age, interest, and level of alertness allow . fixation is described as being normal if it is centrally(foveally) fixated and maintained while the eye follows a moving object. One technique for quantitatively measuring visual acuity in younger children is forced-choice preferential looking. By the age of 2.5-3 years, it is possible to perform recognition visual acuity testing using the Allen pictures By age 4 years, many children will understand the Snellen tumbling ‘’E’’game and the HOTV recognition test. By age 5 or 6 years, most children can respond to snellen alphabet visual acuity testing. At this age, single optotype snellen acuity has normally developed fully, but snelles acuity to a line of multiple optoypes (linear acuity) may not develop fully for another 2 years. Determination of Refactive Error. In children Cyclorefraction using cycloplegic agent to know the refractive errors by retinoscopy. Inspection : Whether the strabismus constanttermi tant, alternating or nonalternating and variable or constant also asociated ptosis any abnormal head position . Determination of Angle of strabismus (Angle of Deviation) a-prism and cover tests : cover tests consist of four parts:(1)the cover test, (2)the uncover test, (3)the alternate cover test, and (4)the prism cover test. B.Objective Tests 1.Hirschberg method. 2.Prism reflex method (Krimsky test). Ductions (Monocular Rotations) Disjunctive Movements A.Convergence B.Divergence Sensory Examination A.Stereopsis Testing B.Suppression Testing C.Fusion Potential OBJECTIVES &PRINCIPLES OF THERAPY OF STRABISMUS Timing of treatment in children Medical treatment A.Treatment of Amblyopia 1.Occlusion therapy a.Initial stage b.Maintenance stage 2.Atropine therapy B.Optical Devices 1.spectacles 2.Prisms c.Botulinum Toxin D.Orthoptics Surgical Treatment(Figure 12-6) A.Surgical Procedures 1.Resection and recession 2.Shifting of point of muscle attachment 3.Faden procedure B.Choice of muscles for surgery C.Adjustable sutures