Strabismus Overview PDF

STRABISMUS Dr. Saif Ibrahim MBChB, CABophth  ANATOMY OF EXTRAOCULAR MUSCLES  They are: 4 recti, 2 oblique’s.  Recti origin: is in the apex of the orbit from a fibrous ring called "Annulus of Zinn" which surrounds the optic nerve.  Recti insertion :inserted to the glope behind the li...

STRABISMUS Dr. Saif Ibrahim MBChB, CABophth  ANATOMY OF EXTRAOCULAR MUSCLES  They are: 4 recti, 2 oblique’s.  Recti origin: is in the apex of the orbit from a fibrous ring called "Annulus of Zinn" which surrounds the optic nerve.  Recti insertion :inserted to the glope behind the limbus.  Obliques origin:  Superior oblique originates supero-medial to the optic foramen. It passes forwards through the trochlea at the angle between the superior and medial walls and is then reflected backwards and laterally to insert in the posterior upper temporal quadrant of the globe.  Inferior oblique originates from a small depression just behind the orbital rim lateral to the lacrimal sac. It passes backwards and laterally to insert in the posterior lower temporal quadrant of the globe close to the macula. ANATOMY OF EXTRAOCULAR MUSCLES  Innervations:  Medial, inferior and superior recti are innervated by oculomotor nerve.  The lateral rectus in innervated by abducent nerve (6th).  Inferior oblique: Oculomotor nerve (3rd).  Superior oblique: Trochlear nerve ( 4th) SQUINT: MISALIGNMENT OF THE VISUAL AXES  Visual axis: is the line passes from the fovea, through the nodal point of the eye, to the point of fixation. In normal binocular single vision (BSV) the visual axes of the two eyes intersect at the point of fixation, the images being aligned by the fusion reflex and combined by binocular responsive cells in the visual cortex to give BSV.  Anatomical axis: is a line passing from the posterior pole through the centre of the cornea. Because the fovea is usually slightly temporal to the anatomical centre of the posterior pole of the eye, the visual axis does not usually correspond to the anatomical axis of the eye. The angle between visual axis and optical axis is called angle of kappa (κ).  PSEUDOSTRABISMUS  Pseudostrabismus is the clinical impression of ocular deviation when no squint is present.  Epicanthal fold simulate an esotropia.  Abnormal interpupillary distance if short may simulate an esotropia and if wide an exotropia.  Angle of kappa if large positive (e.g. temporal displaced macula) give a pseudoexotropia ,if negative angle of kappa occur when fovea is situated nasal to posterior pole it give pseudoesotropia TYPES OF SQUINT:  Manifest (tropia): is a squint present when both eyes are open.  Latent (phoria): is a squint seen only when one eye is covered.  Latent squint is not seen normally when both eyes are opened, but when we occlude one eye it will deviate behind the cover, but as we remove the occluder there will corrective movement which is not seen in normal person.  Eso-= inward, Exo-= outward, Hyper-= Elevation, Hypo-= depression.  Orthophoria implies perfect ocular alignment in the absence of any stimulus for fusion; this is uncommon.  Latent strabismus (heterophoria) or phoria :implies a tendency of the eyes to deviate when fusion is blocked.  Slight phoria is present in most normal individuals and is overcome by the fusion reflex.  When fusion is insufficient to control the imbalance, the phoria is described as decompensating and is often associated with symptoms of binocular discomfort (asthenopia) or double vision (diplopia).  Types: Esophoria Exophoria Hyperphoria hypophoria ETIOLOGY: 1. Uncorrected errors of refraction:  Hypermetropia: the patient uses excessive accommodation to see clearly. As a result, excessive convergence occurs with accommodation which causes latent convergent squint.  Myopia: the patient relaxes his accommodation which results in lack of convergence and the concurrent divergent squint. 2. Congenital weakness of one or more of extra ocular muscles. 3. Secondary to ocular diseases(cataract/ retinoblastoma) EXAMINATION OF SQUINT: 1. Hirschberg test: light reflex test 2. cover-uncover test:The idea is to abolish the stimulus for binocular single vision (BSV) by covering one eye (cover test).  Ask the patient to fix object.  Each eye is covered separately.  The occluder is quickly removed and the examiner notes whether or not the eye under cover had deviated.  The examiner must also note if the eye makes a movement inwards or outwards to pick up fixation once cover is removed.  If the covered eye deviates under the cover and when the cover is removed returns to the original fixing position, latent squint is present. 3. Alternate cover test. THANK YOU