Strabismus Dr HAN Wei The 1st Affiliated Hospital, Medical College, Zhejiang University Basic knowledge of ocular motility Extraocular muscles Not playing role in vision procedure directly, but critically important for eyeball motility and binocular vision function. Anatomy of extraocular muscles Six extra-ocular muscles for the human eye. Namely: Medial rectus m. Lateral rectus m. Superior rectus m. Inferior rectus m. Superior oblique m. Inferior oblique m. Insertion positions of four rectus m. MR: Medial rectus m. LR: Lateral rectus m. SR: Superior rectus m. IR: Inferior rectus m. Nerve innervation for extraocular m. III cranial n. Medial rectus m. Superior rectus m. Inferior rectus m. Inferior oblique m. IV (Trochlea) cranial n. Superior oblique m. VI (Abduction) cranial n. Lateral rectus m. Basic motility function of the eye ball Elevation and depression (A, B) Adduction and abduction (C, D) Intorsion and extorsion (E, F) Motility functions of right eye’s extraocular muscle Inferior oblique m. Extorsion Elevation Adduction Superior rectus m. Elevation Intorsion Adduction Lateral rectus m. Abduction Superior oblique m. Intorsion Depression Abduction Medial rectus m. Adduction Inferior rectus m. Depression Adduction Extorsion Terminology of extra-ocular muscle regarding their physiological functions Antagonist m.: Yoke m. : the muscle that counteracts the agonist (or the prime mover); lengthening when the agonist muscle contracts. e.g., medial rectus and lateral rectus m.. The contra-laterally paired extra-ocular muscles of two fellow eyes that work synergistically to direct the gaze in a given direction. Example: in directing the gaze to the right, the right lateral rectus and left medial rectus operate together as yoke muscles. Synergist m.: The muscles moving one single eye ball in the same direction as the prime moving muscle. e.g., inferior oblique m. is the synergist of superior rectus m. when the eye turns upward. Nervous innervation laws Sherrington law: A muscle will relax when its antagonist muscle (e.g., lateral and medial m.) is activated. Hering law: The yoke m. are innervated equally by nervous system in eye movement. Eye position for examination Primary position: Secondary position: With condition in which head being put vertically and straightforward and two eyes looking straightforward. The two eyes being in adduction or abduction or elevation or depression position. Tertiary position: Two eyes gazing in oblique directions (up or downward). Right Superior rectus m. Left Superior rectus m. Right Superior rectus m. Left inferior oblique m. Left superior rectus m. Left superior rectus m. Right inferior oblique m. Right superior rectus m. Left medial rectus m. Right lateral rectus m. Right medial rectus m. Left lateral rectus m. Right inferior rectus m. Left superior oblique m. Left inferior rectus m. Left inferior rectus m. Right inferior rectus m. Right superior oblique m. Right Inferior rectus m. Left Inferior rectus m. Definitions Strabismus: A condition in which the eyes are not properly aligned with each other, i.e., manifest deviation of the eyes exist. Heterophoria: A condition in which the visual axes of two eyes fail to remain parallel after elimination of visual fusional stimuli. e.g, covering one eye Classification Based on concomitancy Concomitant: Angle of squint is the same in all directions of gaze. Exotropia Esotropia Inconcomitant: Angle differs in different directions of gaze. Special types: e.g., Duane syndrome Based on etiology Functional Paralytic (secondary to traumatic or pathological lesions) Based on constancy Constant Single eye deviation Alternative deviation Intermittent Examination and diagnosis Disease and familial history Onset age Visual acuity Refraction Strabismus type Compensative head position Test for strabismus* Epicanthal fold – should be ruled out in child patients Simulated esotropia Strabismus test (1) Cover test and uncover test Alternative cover test A B Unilateral gaze (A) or alternative gaze (B) Strabismus test (2) Corneal reflex test Simple, easy method Broadly applied in clinic Strabismus test (2) Other methods Prism and cover test Perimeter arc test Maddox rod test Synoptophore test Concomitant strabismus Accommodative Complete accommodative Partially accommodative Non-accommodative First deviation angle = Secondary deviation angle First deviation angle: When the normal eye gazing target, the strabismus angle of the deviated eye. Second deviation angle: When deviated eye gazing target, the strabismus angle of the normal eye. Concomitant esotropia Most commonly seen type, closely associated with accommodation function. First angle = Second angle Usually no diplopia Normal ocular motility Intermittent in incipient stage and turn to be constant gradually. Treatment Spectacle correction for ametropia Treat amblyopia Eye position training Surgery An example of concomitant esotropia After operation, the two eyes’ position is corrected to be normal. (Lower figure) An example of partially accommodative concomitant esotropia With spectacle, squint was partially corrected, but still existed. (lower figure) Concomitant exotropia Associated with: Central nervous biocular balancing function, Imbalance of accommodation and convergence, Anisometropia Visual impairment in one eye Intermittent early stage to constant stage. Treatment: Ametropia correction Prism spectacle Surgery An example of concomitant exotropia treated by surgery Deviation was correctly after surgery. (Figure left) An example of concomitant exotropia due to visual impairment in left eye Nonconcomitant strabismus Usually paralytic secondary to: Embryo development anomalies Trauma Inflammation Hypertension and hemorraghe & ischemia Tumor Metabolism disorder like diabetes, thyroidism, etc Symptoms Diplopia Compensation head position Deviation of affected eye First angle ＜ second angle Compromise of ocular motility Hess screen test Shift of the square denotes the muscle being paralytic. Compensation head position in paralysis of the right eye’s lateral rectus muscle An example of paralytic esotropia Lateral rectus m. of right eye paralysis. Note the 1st angle (figure right) is less than second angle (figure left) An example of paralytic vertical strabismus of right inferior rectus m. Treatment Primary diseases treatment Drug Vit B1, B12, ATP Steroid Antibiotics Botulinum A injection to relief the muscle spasm Prism Surgery Usually 6 months after onset, with deviation being stable. Differentiation of paralytic and concomittent strabismus Paralytic Concomittent Onset Suddenly Gradually Eye motility Compromised in affected m. movement direction Normal Deviation angle 2nd angle > 1st angle Equal Diplopia Yes No Compensative head position Yes No Amblyopia Definition of amblyopia: otherwise known as lazy eye, is a disorder of the visual system that is characterized by poor or indistinct vision in an eye that is otherwise physically normal. It has been estimated to affect 1–5% of the population. Etiology: The nerve pathway from one eye to the brain does not develop during childhood or the abnormal eye sends a blurred image to the brain. Category of etiology Strabismus Anisometropia (Double eye onset) Form deprivation (Imbalance of visual input) Ametropia (Most common type, due to crossing eye) (Refractive media opacity) Others (Pathological lesions) Symptoms Vision acuity loss Mild: Moderate: Severe: 0.6-0.8 0.2-0.5 less than 0.1 Abnormal fixation Crowding phenomenon Treatment (1) Early treatment. As early as possible. Critically important! Treatment effect is poor after 9 years old. Treatment (2) Ametropia correction: spectacle even LASIK, surgery for congenital cataract. Occlusion therapy Occluding normal eye, allowing amblyopic eye to develop Red light therapy Stimulating the macular function development After image therapy Depression therapy Using atropine or over- or under-correction lens Synoptophore therapy Drug (L-Dopa) Nystagmus A condition of involuntary rhythmically oscillation of the globe. According to the rhythm, it is divided into two sorts: jerky and pendular. Physiological and pathological Category: Perpetual Opticokinetic Labyrinthine Environmental Binocular vision Normal human’s vision is the matter of the coordination of the two eyes. The eyes must be capable of aligning themselves in such a manner: the retinal images of a fixated target can easily be placed and maintained on the foveae of the two eyes. Normal binocular vision is established in about 5-6 years. Binocular vision Condition of the normal binocular vision : (1) in good focus; (2) similar image size (within 5% disparity); (3) similar image shape; (4) normal eyes’ motility; (5) fusion ability and area; (6) normal neural pathways. Grade of binocular vision Simultaneous perception Fusion Ability to simultaneously percept the retinal image of the two eyes Images formed on the retina of the two eyes are combined into a single percept. Stereopsis Highest grade of binocular vision. Perception of depth and distance. Normal binocular vision Sensory aspects Corresponding retinal points Panum fusional areas Horopter Physiological diplopia Motor aspects Conjugate movement Saccadic movement Following movement Disconjugate movement Convergence Divergence Motor fusion Abnormal binocular vision Diplopia Confusion amblyopia Abnormal retinal correspondence misalignment of the two eyes in paralytic strabismus Suppression pathological strabismus Eccentric fixation amblyopia Low vision Definition of low vision (WHO 1992) Best corrected visual acuity <0.3, Semi-visual field narrower than 10 degree Treatment Etiological diseases if viable Visual aid instruments Telescope Magnifier Electronic apparatus like CCTV, computer display Low vision aid products Questions State refractive components of the eye’s optical system. The category of myopia and the clinical management? The classification of the concomittent strabismus and the clinical management?