Lecture 8, Squint - New PDF

 Eye movement is one of the most complex functions of the body.  It is controlled by three out of the twelve cranial nerves: EXTRAOCULAR  Oculomotor “III” MUSCLES  Troclear “IV”,  Abducent “VI”  With numerous internuclear and...

 Eye movement is one of the most complex functions of the body.  It is controlled by three out of the twelve cranial nerves: EXTRAOCULAR  Oculomotor “III” MUSCLES  Troclear “IV”,  Abducent “VI”  With numerous internuclear and supranuclear connections..  The eye can rotate around three axes: ① Vertical axis:  On which the eye moves horizontally (Adduction and Abduction). AXES OF EYE ② Horizontal axis: MOVEMENTS  On which the eye moves vertically (Elevation and Depression). (FICK’S AXES) ③ Antero-posterior axis:  On which the eye performs torsional movements (Intorsion and extorsion)  ① LATERAL RECTUS ② MEDIAL RECTUS ③ SUPERIOR ④ INFERIOR RECTUS RECTUS Apex of orbit, Annulus of zinn ORIGIN: (common tendentious ring)  Antero-lateral  Antero-medial  Anterior-  Anterior- INSERTION: sclera sclera superior sclera inferior sclera NERVE Abducent N. (6th) Oculomotor N. (3rd) SUPPLY:  Abduction  Adduction  Elevation  Depression ACTION:  Adduction  Adduction  Intorsion  Extorsion ⑤ SUPERIOR OBLIQUE ⑥ INFERIOR OBLIQUE  Apex of orbit (Between SR & MR)  Floor of the orbit, behind lacrimal ORIGIN: Rolls around trochlea (Physiological sac origin) INSERTION:  Posterolateral sclera  Inferior postero-lateral sclera NERVE SUPPLY:  Trochlear N. (4th)  Oculomotor N. (3 rd)  Depression  Elevation ACTION:  Abduction  Abduction  Intorsion  Extorsion  Superior Rectus: The main elevator of abducted eye.  Inferior Rectus: The main depressor of abducted eye.  Inferior Oblique: The main elevator of adducted eye.  Superior Oblique: The main depressor of adducted eye. SUMMARY All EOM originate from Apex of orbit  IO (floor of orbit) All EOM insert into anterior sclera  SO, IO (Posterior) EXCEPT  SO (4th) All EOM supplied by Oculomotor N. (3rd)  LR (6th)  DUCTION (MONOCULAR EYE MOVEMENT)  The main action of the LR muscle. ABDUCTION:  It can be also achieved by contraction of SO and IO muscles.  The main action of the MR muscle. ADDUCTION:  It can be also achieved by contraction of SR and IR muscles.  In the primary position both SR and IO muscles assist in elevation of eye. ELEVATION:  In abduction: SR muscle is the main elevator.  In adduction: IO muscle is the main elevator.  In the primary position both IR and SO muscles assist in depression of eye. DEPRESSION:  In abduction: IR muscle is the main depressor.  In adduction: SO muscle is the main depressor. SUMMARY ABDUCTION: LR (1ry), SO, IO (2ry) ADDUCTION: MR (2ry), SR, IR (2ry) SR, IO ELEVATION: In adducted eye (IO), In abducted eye (SR) IR, SO DEPRESSION: In adducted eye (SO), In abducted eye (IR) SR, SO INTORSION Superiors are intortors IR, IO EXTORSION Inferiors are extortors  VERSION (BINOCULAR EYE MOVEMENT) = NINE CARDINAL POSITIONS OF GAZE Achieved by coordination of movements of both eyes through internuclear and supranuclear connections.  Looking straight ahead with both eyes. PRIME POSITION:  It is achieved by using the tone of all extraocular muscles.  Looking to the right. DEXTROVERSION:  Achieved by contraction of LR muscle of right eye & MR muscle of left eye.  Looking to the left. LEVOVERSION:  Achieved by contraction of MR muscle of right eye & LR muscle of left eye.  Upward movement of both eyes together. ELEVATION:  Achieved by contraction of SR and IO muscles of both eyes.  Downward movement of both eyes together. DEPRESSION  Achieved by contraction of IR and SO muscles of both eyes. DEXTRO-  Looking up and to right ELEVATION: DEXTRO-  Looking down and to right. DEPRESSION: LEVO-ELEVATION:  Looking up and to left. LEVO-  Looking down and to left. DEPRESSION::  EOM work together in pairs  Complementary (Yoke) → Pulling the eyes in the same direction  Opposites (Antagonists) →Pulling the eyes in opposite directions EXTRAOCULAR MOTILITY  Achieved by contraction of the MR muscles of both eyes.  Usually seen in near reflex accompanied by accommodation and miosis.  Can be measured by meter angle or prism diopter. CONVERGENCE  Meter angle:  Degree of eye convergence when we look at a onemeter distance.  Each one-meter angle is equivalent to about 4 prism diopters. DIVERGENCE  Achieved by contraction of the LR muscles of both eyes  Main target of the near reflex. ACCOMMODATION  Associated convergence is termed Accommodative Convergence (AC) (A) AC/A ratio = Constant  Certain amount of accommodation is usually associated with a parallel IN NEAR REFLEX amount of accommodative convergence  So AC/A is always a constant value. NEAR POINT OF  The nearest point on which the eye can converge. CONVERGENCE  It normally ranges from 8-10 centimeters  COORDINATED USE OF THE 2 EYES TO PRODUCE  Its development starts at 3-6 months of age leading to maintained A SINGLE VISUAL binocular fixation. MENTAL  Squint should not be diagnosed before the age of six months. IMPRESSION  At 9 years, full maturation of binocular vision is achieved, after which it can’t be disturbed.  It implies the perception of images of two eyes simultaneously even if GRADE I dissimilar images. SIMULTANEOUS  Objects outside corresponding retinal points aren’t fused but seen PERCEPTION: simultaneously.  Objects falling onto corresponding retinal points are fused when they GRADE II are similar in size, sharpness, and brightness. FUSION:  So, in unequal images e.g. aniseikonia, blurred images e.g. ametropia, or unclear images e.g. cataract, no fusion occurs. GRADE III  Fusion of slightly discrete retinal images (little differences seen by each STEREOPSIS (DEPTH eye) falling onto corresponding retinal points. PERCEPTION): Synoptophore  DEVIATION OF THE VISUAL AXES RELATIVE TO EACH OTHER COMITANT NON-COMITANT  Latent  Paralytic  Manifest  Restrictive APPARENT TRUE ESODEVIATION EXODEVIATION  Small IPD  Large IPD  High myopia  High hypermetropia  Epicanthus  Hypertolerism   Type of squint which:  There is limitation of movement  Angle of deviation differs with direction of gaze.  Caused by muscle paralysis or paresis: DEFINITION AND ① Muscle: Due to orbital disease, muscle disease, or trauma ETIOLOGY ② Nerve: Due to pressure from tumors, aneurysms, trauma, infection of the meninges, cavernous sinus, or orbit ③ Nucleus: Due to thrombotic, hemorrhagic disorder. The main predisposing factor is uncontrolled DM, hypertension, or atherosclerosis. ① Limitation of movement ⑤ Nausea, Vertigo, Uncertain gait CLINICAL ② Eye Deviation ⑥ Abnormal head posture PICTURE ③ Binocular diplopia ⑦ Sensory anomalies ④ False projection ① LIMITATION OF MOVEMENT LR  Limited Abduction. MR  Limited Adduction. SR  Limited Elevation of Abducted eye. IR  Limited Depression of Abducted eye. SO  Limited depression of Adducted eye. IO  Limited elevation of Adducted eye. ② OCULAR DEVIATION = MANIFEST SQUINT  2RY ANGLE OF DEVIATION IS LARGER THAN 1RY  The amount of neural stimulus needed for the paretic eye to fixate is very high and according to Hering’s Law, equal amount of stimulus will supply the normal eye leading to more deviation ③ BINOCULAR DIPLOPIA ① Iridodialysis UNIOCULAR ② Irregular astigmatism DIPLOPIA ③ Subluxated lens ④ Incipiant cataract ① Squint ② Significant aniseokonia  Binocular diplopia is the main presentation in a paralytic squint, in which the patient sees double vision with both eyes, especially in the field of action of the paralyzed muscle. It may be: HORIZONTAL VERTICAL BINOCULAR DIPLOPIA UNCROSSED IN ESOTROPIA CROSSED IN EXOTROPIA CONFUSION   If normal eye is closed and the patient is asked to point at object in field ④ FALSE of action of paretic muscle he will point behind it PROJECTION  Object location is projected according to amount of nervous energy exerted ⑤ NAUSEA, VERTIGO, UNCERTAIN GAIT  To avoid the field of action of paretic muscle & diplopia, the head takes a position that decreases the need for eye movement.  Face Turn: Right/Left  Head Tilt: Right/Left  Chin Position: Elevation/Depression  To avoid the field of action of the paretic muscle and diplopia, the head takes a position that decreases the need for eye movement.  Face Turn (Right/Left): To compensate for horizontal movement ⑥ ABNORMAL weakness HEAD  Head Tilt (Right/Left): To compensate for torsional movement POSTURE weakness  Chin Position (Elevation/Depression): To compensate for vertical movement weakness.  Anomalous retinal correspondence ⑦ SENSORY  Suppression ANOMALIES  Amblyopia  Eccentric fixation  CLINICAL PICTURE OF ABDUCENT CLINICAL PICTURE OF TROCHLEAR PALSY PALSY LIMITATION OF MOVEMENT Limited abduction Depression of adducted eye EYE DEVIATION Esotropia Hypertropia BINOCULAR DIPLOPIA Uncrossed diplopia Vertical diplopia FALSE PROJECTION False orientation False orientation NAUSEA, VERTIGO Uncertain gait Uncertain gait Head tilt and face turn to the ABNORMAL HEAD POSTURE Face turn to the same side normal side, chin depression SENSORY ANOMALIES If Tropia)  Etiology: (Excess accommodation)  High hypermetropia  High AC/A ratio (Angle is larger at near  Treatment: (Inhibiting accommodation)  Full correction of hypermetropia ① ACOOMODATIVE:  Reading glasses or bifocal if high AC/A ratio  Treatment of amblyopia  Characterized by:  Starts within 6 m (often hereditary).  Usually associated with cerebral palsy, birth trauma, and CNS infection.  Usually alternating, large, and stable angle. ② CONGENITAL  Cross fixation: in which the patient uses his right eye to see objects in the left field while suppressing his left eye and uses his left eye to see objects in the right field while suppressing his right eye.  Treatment: Surgical alignment: recession of both medial recti after elimination of amblyopia, and correction of refractive errors.  The deviation is 2ry to poor vision in one eye -> no fusion.  Causes:  Corneal opacities.  Macular lesion ③ SENSORY  Anisometropia  Unilateral Cataract  Optic atrophy  Injuries  Treatment: surgical after correction of the cause.  Cause: Due to surgical over-correction of exotropia. ④ CONSECUTIVE  Treatment: surgical.  ETIOLOGICAL TYPES OF EXOTROPIA ① Primary (Alternating): the most common ② Accommodative ③ Congenital ④ Consecutive ⑤ Sensory