Chapter 15
Strabismus
Fujian Provincial Hospital
Wenjie Wu MD., PhD.
Any Deviation From Perfect Ocular Alignment
Definitions
Conjugate movement: Movement of the eyes in the same direction at the same time. Ductions: Monocular rotations with no consideration of the position of the other eye.
Physiology
Sensory fusion is the process whereby dissimilarities between the two images are not appreciated. IN the process of fusion, the direction values of these points can be modified. 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.
Sensory fusion and stereopsis are the two different physiologic processes that are responsible for binocular vision.
Sensory Aspects
Sensory Fusion & Stereopsis
Physiology
Motor Aspects
Yoke Muscles: The pair of agonist muscles with the same primary action.
Physiology
Sensory Aspects
Binocular Vision: Objects imaged on the two foveas.
Sensory Aspects
Anomalous Retinal Correspondence
Physiology
Anomalous retinal correspondence is a sensory adaptation that occurs in strabismus under binocular viewing conditions. Heterotropia leads to suppression in the non-fixating eye and a shift in the visual direction of the deviated eye. This shift in visual direction offsets the amount of motor deviation and prevents the perception of diplopia. Stereopsis remains abnormal. Eccentric Fixation In eyes with sufficiently 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. 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 detected by an ophthalmoscope that projects a small fixation target onto the retina.
Because of the different vantage point in space of each eye (For one object only), the image in each eye is actually slightly different from that in the other.
Sensory Aspects
Physiology
SuppressionБайду номын сангаас
Under binocular viewing conditions, the images seen by one eye become predominant and those seen by the other eye are not perceived (suppression). Suppression takes the form of a scotoma in the deviating eye only under binocular viewings.
Heterotropia (Tropia) Strabismus: Manifest deviation of the eyes that cannot be controlled by binocular fusion. Esotropia Exotropia Hypertropia Hypotropia
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). Anomalous Retinal Correspondence
Physiology
Motor Aspects
Individual Muscle Function

Physiology
Motor Aspects
Field of Action
Physiology
Motor Aspects
Synergistic & Antagonistic Muscles Synergistic muscles are those that those that have the same field of action. Muscles synergistic for one function may be antagonistic for anther.
Definitions
Orthophoria: The absence of any tendency of either eye to deviate when fusion is suspended. Seldom Primary deviation: The deviation measured with the normal eye fixing and the eye with the paretic muscle deviating. Prism diopter: A unit of angular measurement used to characterize ocular deviation. A 1-diopter prism deflects a ray of light toward the base of the prism by 1 centimeter at 1 meter. One degree of arc equals approximately 1.7∆.
Sensory Aspects
Sensory Changes in Strabismus
Physiology
Up to age 7 or 8, the brain usually develops responses to abnormal binocular vision that may not occur if the onset of strabismus in later. Diplopia 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) Suppression Amblyopia Anomalous Retinal Correspondence
Definitions
Heterophoria(phoria): Latent deviation of the eyes held straight by binocular fusion. Esophoria Exophoria Hyperphoria