Abnormality of eyeball position

Abnormality of Eyeball Position(Strabismus)By: HendriI11108051Under normal binocular viewing conditions, the image of the object of regard falls simultaneously on the fovea of each eye (bifoveal fixation), and the vertical retinal meridians are both upright. Either eye can be misaligned, so that only one eye at a time views the object of regard. Any deviation from perfect ocular alignment is called "strabismus.

physiologyMotor AspectIndividual Muscle Functions

Function of the ocular musclesMuscles Primary actionSecondary actionLateral rectusabductionnoneMedial rectusadductionnoneSuperior rectuselevationadduction, intorsionInferior rectusdepressionAdduction extorsionSuperior obliqueintorsionDepression, abductionInferior obligueextorsionElevation, abductionField of actionThe position of the eye is determined by the equilibrium achieved by the pull of all six extraocular muscles. 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 field of action of a muscle is the direction of 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 (Sherrington'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 synergistic for one function may be antagonistic for another.

Yoke Muscles (Hering's Law)For movements of both eyes in the same direction, the corresponding agonist muscles receive equal innervation (Hering's law). The pair of agonist muscles with the same primary action is called a yoke pair. Sensory AspectSensory Fusion & StereopsisSensory 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 localize 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 stimuli that strike sufficiently close to the corresponding point in the other eye. This region of fusible points is called Panum's area.Fusion is possible because subtle differences between the two images are ignored, and stereopsis, or binocular depth perception, occurs because of the cerebral integration of these two slightly dissimilar images.

Strabismus testThe Hirschberg testTo determine the type and degree of Strabismus use a small penlight and direct it toward the eyes. The reflected point of light will reveal the type and degree of Strabismus. Normal eyes will have the light in the center of the pupils. Note that 1 mm displacement (Positive or negative angle Kappa) is considered .

The Cover-uncover testIn some cases latent Strabismus, heterophioria, is present, the eye will normally be kept straight by fusion. To discover the latent deviation cover one eye with some translucent material through which you can detect any movement of the eye.If there is movement of the eye when the occluder is removed then there is latent Strabismus. The latent deviation will be revealed with either eye covered.

Krimsky TestTo measure deviation angle in strabismus person. The way is to place a prism in a middle light reflex in cornealThe light is put 33 cm in front of patient, and the prism that put

Esotropia (Convergent Strabismus)Infantil Esotropia Infantile esotropia is usually manifest by age 6 months but may present later in the first yearThe cause, therefore, is not related to the refractive error or dependent upon a paretic extraocular muscleNystagmus, manifest or latentThe most common refractive error is low to moderate hyperopiaTreatment: surgicalParetic Esotropiaparesis of action of one or more extraocular musclesAbducens palsyTreatment: surgicalExotropia (Divergent Strabismus)

Intermittent ExotropiaThe onset may be in the first yearProgresive Primary sign is closing one eye bright lightThere is no correlation with a specific refractive errorTreatment:using minus lens and surgeryConstant ExotropiaMay be present at birth or later in lifeIf there is poor vision in one eye, the deviation can become largeHipertropiaTreatment: surgicalThank You