Strabismus

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Strabismus
Neuro-ophthalmology

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Strabismus

  1. 1. STRABISMUS Dr. Joe M Das Senior Resident Dept. of Neurosurgery
  2. 2. A squint is not a sign of luck, it may indicate poor vision. Get it checked immediately. • Greek strabismos, from strabizein "to squint," from strabos "squinting, squint-eyed.“ • 7,500,000 people suffer from strabismus in the US • A worldwide estimate would be 130 to 260 million
  3. 3. • Binocular single vision (BSV) is one of the hallmarks of the human race that has bestowed on it the supremacy in the hierarchy of the animal kingdom • ~ 60% of the brain tissue and more than half of the twelve cranial nerves subserve the eyes • BSV is accomplished by a perfect sensorimotor coordination of the two eyes both at rest and during movement
  4. 4. ANATOMY
  5. 5. Anatomy • • • • • The two obliques are abductors The two recti are adductors (RAD) The two superiors are intorters (SIN) The two inferiors are extorters Each is supplied by 2 anterior ciliary arteries, except lateral rectus which is supplied only by one. • Recti muscles pull the eye in the direction of their name in the abducted position • Obliques push the eye in the direction opposite to their name in the adducted position
  6. 6. • The eye movements when tested uniocularly – Ductions (Adduction, abduction, elevation or sursumduction, depression or deorsumduction, intorsion or incycloduction, extorsion or excycloduction) • In paresis, normal ductions may be observed. This is due to the extra innervation called in to compensate for the paresis. In version, this is picked up as the extra innervation goes to the yoke muscle, which overacts
  7. 7. • The eye movements when tested binocularly – Versions – Same direction (Conjugate) – Opposite directions (Disjugate) - vergence • Dextroversion, levoversion, dextroelevation, levoelevation, dextrodepression, levodepression, sursumversion, deorsumversion, dextrocycloversion, levocycloversion
  8. 8. • Vergence – Convergence, divergence – Positive vertical divergence – right up, left down – Negative vertical divergence – Left up, right down – Incyclovergence- both intort – Excyclovergence – both extort
  9. 9. Fun fact • People blink, on average, once every 5-6 seconds. • Women blink almost twice as often as men.
  10. 10. Sherrington’s law of reciprocal innervation • EOM working in pairs – yoke, synergist, agonist • Opposing muscle – antagonist • For any movement, the synergists receive equal and simultaneous innervation. In addition, the respective antagonists are inhibited to facilitate a smooth and unobstructed movement
  11. 11. • Each fovea has a primary visual direction (the direction of its straight-ahead gaze) • The two fovea share a common visual direction • Any object imaged on the visual direction of either of the fovea would be superimposed and seen in the common visual direction, which is of neither eyes, but of an imaginary cyclopean eye
  12. 12. • One fovea as well as other areas in the retina have a corresponding point on the other retina • Objects imaged on the corresponding areas are seen binocularly single • Imaginary plane on which corresponding points are projected – horopter • A little area on either sides of horopter, which allows the sensory fusion, despite the disparity – Panum’s area of fusion  Stereopsis
  13. 13. • Normally, the two visual axes meet at the point of regard or the object of attention – orthophoria / orthotropia • If the two visual axes are not aligned to the point of regard, one eye fixates, other eye does not  Strabismus • When this tendency is overcome by the fusional vergence, the person does not manifest squint  Latent squint (heterophoria) • When the squint is present at times, and controlled at other times – intermittent squint
  14. 14. Classification • Concomitant (comitant) – when the deviations are equal in all the different gazes • Incomitant – When deviations are more in one gaze than the other
  15. 15. Concomitant • Horizontal strabismus: Exotropia (divergent) and esotropia (convergent) / Latent ones (heterophorias) – Esophoria, exophoria • Vertical tropias: Hypertropia and hypotropia – described by the hypertropic eye • Torsional – Incyclotropia / Excyclotropia
  16. 16. Incomitant • Paralytic – Neurogenic (supranuclear, nuclear / infranuclear) or myogenic • Restrictive • Spastic
  17. 17. • Hering’s law of motor correspondence: – Whenever an ocular movement is performed, simultaneous and equal amount of innervation flows to the corresponding yoke muscles in the direction of gaze • Sherrington’s law of reciprocal innervation: – Whenever an agonist receives an impulse to contract, an equivalent inhibitory impulse travels to the antagonist muscle, which actively relaxes and lengthens
  18. 18. Consequences of strabismus • Strabismus  Two fovea get two different images  Rival cortical perception  Confusion  Suppression of one image • Tries to overcome by fusion (converting tropia into phoria) • Head posturing  other image falls on the periphery of retina / blind spot • Sensory adaptations (upto 6-7 years of age) – Suppression (if in peripheral retina) – Anomalous retinal correspondence (Fovea with extrafoveal area)
  19. 19. AMBLYOPIA • Condition with u/l or b/l ↓ of visual functions, caused by form vision deprivation and / or abnormal binocular interaction, that cannot be explained by a disorder of ocular media or visual pathways itself • Caused by abnormal visual experience in early childhood
  20. 20. What is Phrenology? • Phrenology is the study of the morphology of the skull, • Developed by Franz Josef Gall (1758 – 1828). • Gall felt there was a direct link between the shape of the skull and human character and intelligence. • Gall was one of the first to consider the brain the source of all mental activities. • People with “high brows” were considered more intelligent than those with “low brows.”
  21. 21. Examination of a case of squint • Motor status • Sensory status
  22. 22. Motor status • Head posture • Ocular deviation • Limitations of movements or extent of versions • Fusional vergences
  23. 23. Head posture • 3 components – Chin elevation / depression – Face turn to right / left – Head tilt to right or left shoulder • Ocular torticollis: Congenital SO palsy • RSO palsy  Chin depression, face turn to left, head tilt to left shoulder
  24. 24. Measurement of interpupillary distance • Ordinary millimeter scale • Pulzone-Hardy rule • Synoptophore
  25. 25. Pseudostrabismus • A true squint is a misalignment of the two visual axes, so that both do not meet at the point of regard • An apparent squint is just an appearance of squint in spite of the alignment of the two visual axes • Apparent squint or pseudostrabismus can be due to abnormality of adnexal structures or due to abnormal relationship between the visual axis and optical axis of the eyes – Telecanthus (broad nasal bridge) / epicanthus  Pseudoesotropia – Lateral canthoplasty  Pseudoexotropia
  26. 26. Pseudo-deviations Pseudo-esotropia • • • Epicanthic folds Short interpupillary distance Negative angle kappa Pseudo-exotropia • • Wide interpupillary distance Positive angle kappa
  27. 27. Angle kappa
  28. 28. Fun facts • Eyes can process 36,000 bits of information every hour. • Only 1/6th of the eyeball is exposed to the outside world
  29. 29. Cover test • Proper fixation target – figure / letter of size 6/9 of Snellen’s -- Distance – 33 cm (near) / 6 m (distant) – Eyes appear to fixate (no apparent squint) – One appears to fixate as other deviates (apparent squint) • Cover the fixating eye  – If the other eye moves to take up fixation  Manifest squint (heterotropia) – Same eye deviates
  30. 30. • Uncover  – Covering breaks the fusion and if there is any heterophoria, the eye behind the cover deviates – If it remains deviated  latent squint with poor fusion – Speed of recovery Ξ strength of fusion – If uncovered eye reassumes fixation as the other eye deviates  Dominant uncovered eye, visual acuity unequal
  31. 31. Cover tests • Cover test detects heterotropia • Prism cover test measures total deviation • Uncover test detects heterophoria • Alternate cover test detects total deviation
  32. 32. Hirschberg’s test • Corneal reflection • In esodeviation, the corneal reflection falls more temporally and vice versa • 1 mm shift Ξ 5° deviation • If reflex falls on nasal limbus, the exodeviation is 30°
  33. 33. Hirschberg test • Rough measure of deviation • Note location of corneal light reflex • 1 mm = 5 Reflex at border of pupil = 15 Reflex at limbus = 45
  34. 34. Diplopia testing • Red and green glasses over the right and left eyes respectively • Esodeviations  Uncrossed diplopia • Exodeviations  Crossed diplopia • Esodeviation  Image falls on nasal retina  projected on temporal field  uncrossed
  35. 35. Maddox rod test • Multiple cylindrical high plus lenses stacked on top of each other • Light is seen as linear streak oriented 90° to the cylindrical ribs
  36. 36. Worth-four dot test
  37. 37. • 4 dots  Normal binocular response or anomalous retinal correspondence with manifest squint • 5 dots  Manifest deviation – Eso (uncrossed) – red on right – Exo (crossed) – red on left • 3 dots  Suppression of right eye • 2 dots  suppression of left eye
  38. 38. Medical Treatment • Treatment of Amblyopia – Occlusion therapy • Initial stage • Maintenance stage – Atropine therapy • OpticalDevices – Spectacles – Prisms • Botulinum Toxin • Orthoptics
  39. 39. Surgical Treatment • Surgical procedu res – R e s e c t io n a n d r ec e s s io n – S h iftin g o f p o in t o f m u sc l e att ac h m en t – F ad e n p ro c ed u r e • Choice of muscles for surgery • Adjustable sutures
  40. 40. Fun facts • Eyelashes have an average life span of 5 months. • The eyeball of a human weighs approximately 28 grams. • Your eye will focus on about 50 things per second.
  41. 41. PARALYTIC SQUINT
  42. 42. Forced duction test • Simple and most useful method for diagnosing the presence of mechanical restriction of ocular motility. • 4% lidocaine • The eye is then moved with two-toothed forceps applied to the conjunctiva near the limbus in the direction opposite that in which mechanical restriction is suspected. • To distinguish between lateral rectus paralysis and mechanical restriction involving the medial aspect of the globe, apply the forceps at the 6- and 12-o’clock positions and move the eye passively into abduction. – No resistance  paralysis of the lateral rectus muscle. – Resistance +  mechanical restrictions do exist medially and contracture of the medial rectus muscle, conjunctiva, or Tenon’s capsule or myositis of the medial rectus muscle must be considered
  43. 43. 3rd Nerve Palsy • Complete, isolated third nerve palsy causes ipsilateral weakness of elevation, depression, and adduction of the globe, in combination with ptosis and mydriasis.
  44. 44. • (A) Left ptosis, mydriasis, exotropia, and right hypertropia in primary gaze. • (B) Absent left elevation. • (C) Reduced left depression. • (D) The left pupil shows minimal consensual response to light, with greater anisocoria.
  45. 45. Aneurysm site to cause IIIrd CN palsy
  46. 46. Complete Third Nerve Palsy • Exotropia with hypotropia, ptosis and possible dilation of pupil and accommodation palsy
  47. 47. • A characteristic feature is that the affected eye is hypotropic in upgaze but hypertropic in downgaze, because of the combined weakness of the superior and inferior rectus muscles.
  48. 48. 3rd N nuclear lesion • Specifically, there is bilateral ptosis (because the central caudal nucleus supplies both levator palpebrae muscles) and • A bilateral elevation deficit (because the superior rectus subnucleus sends fibers through the contralateral third nerve nucleus to join the opposite nerve)
  49. 49. Unilateral nuclear 3rd N palsy • Ipsilateral mydriasis • Ipsilateral weakness of the medial rectus, inferior rectus, and inferior oblique muscles • Bilateral ptosis and • Bilateral superior rectus weakness.
  50. 50. • Disruption of the superior division causes ptosis and impaired elevation • Disruption of the inferior division causes impaired depression, adduction, and mydriasis
  51. 51. Microvascular 3rd nerve palsy • Risk factors including hypertension, diabetes, hyperlipidemia, advanced age, and smoking • This disorder results from impairment of microcirculation leading to circumscribed, ischemic demyelination of axons at the core of the nerve, typically in the cavernous sinus portion where a watershed territory exists. • Most of these patients exhibit pupillary sparing, because the pupillary fibers are located peripherally, closest to the blood supply provided by the surrounding vasa nervorum.
  52. 52. AN ISOLATED DILATED PUPIL IS NEVER A MANIFESTATION OF THIRD NERVE DYSFUNCTION IN AN AWAKE AND ALERT PATIENT.
  53. 53. Treatment • The treatment of diplopia due to acute third nerve palsy may include monocular patch-ing or prisms. • Once ocular misalignment from third nerve palsy has been stable for 6 to 12 months, surgical correction can be considered. • Supramaximal lateral rectus recession (a weakening procedure that completely abolishes abduction), potentially in combination with a medial rectus resection (a tightening procedure to augment the muscle’s action).
  54. 54. • Under the right conditions, the human eye can see the light of a candle at a distance of 14 miles. • The external muscles that move the eyes are the strongest muscles in the human body for the job that they have to do. They are 100 times more powerful than they need to be.
  55. 55. 4th nerve palsy • Fourth nerve palsy presents with vertical diplopia and is commonly accompanied by compensatory contralateral head tilt. • Parks-Bielschowsky three-step test • First, hypertropia suggests weakness of the ipsilateral superior oblique, ipsilateral inferior rectus, contralateral inferior oblique, or contralateral superior rectus muscle. • Second, increased hypertropia in contralateral gaze narrows the possibilities to the weakness of the ipsilateral superior oblique or contralateral superior rectus muscles. • Third, increased hypertropia on ipsilateral head tilt further reduces the possibilities, ultimately identifying ipsilateral superior oblique weakness.
  56. 56. Bilateral 4th nerve palsy • Hyperdeviation alternates such that it is contralateral to the direction of gaze and ipsilateral to the side of head tilt.
  57. 57. Fourth nerve palsy in the setting of concomitant third nerve palsy • The failure of adduction prevents complete testing of superior oblique function. In this setting, the superior oblique can be evaluated by assessing its secondary function: intorsion of the abducted eye on attempted downgaze. The torsional movement that indicates intact superior oblique function is best appreciated by observing a conjunctival vessel
  58. 58. Treatment • Occlusion of the affected eye (or, if diplopia occurs only in down-and-contralateral gaze, occlusion of the lower half of the lens over the affected eye) can serve as a temporary measure • IO / SR recession
  59. 59. 6th nerve palsy • Weakness of the lateral rectus due to sixth nerve palsy leads to horizontal diplopia, worse to the affected side and at distance. Often, the abnormal duction is easily observed. • Nuclear sixth nerve palsy affects the ipsilateral sixth nerve as well as the interneurons destined for the contralateral medial rectus subnucleus. This lesion causes an abduction deficit of the ipisilateral eye as well as an adduction deficit of the contralateral eye; together, this is a conjugate gaze palsy.
  60. 60. Duane syndrome • 3 varieties of Duane syndrome • A paradoxic co-contraction of the lateral and medial rectus muscles • A visible retraction of the globe and narrowing of the palpebral fissure on attempted adduction – Type 1, abduction is impaired with essen-tially full adduction; – type 2, adduction is impaired with normal abduction – Type 3, adduction and abduction are reduced. • The abduction deficit in types 1 and 3 cause the patient to be esotropic on lateral gaze to the affected side, but these patients can be distinguished from those with acquired abduction deficits because they have normal alignment (rather than esotropia) in primary gaze. • Pathologic studies of patients with Duane syndrome show hypoplasia of the sixth nerve nucleus and abnormalities of the fascicle, with branches of the third nerve supplying the lateral rectus muscle. • Sporadic / familial (CHN1 gene on chromosome 2)
  61. 61. • Mobius syndrome describes congenital facial diplegia that is frequently associated with sixth nerve palsy
  62. 62. .. Mobius syndrome Signs • Bilateral sixth nerve palsies - • Primary position - 50% patient looking left straight, 50% esotropic • Horizontal gaze palsy in 50% • • Bilateral, usually asymmetrical facial palsies sparing lower face Paresis of 9th and 12th cranial nerves
  63. 63. Treatment • Occlusion / prism • Treatment of partial sixth nerve palsy may include a combined medial rectus recession and lateral rectus resection on the affected side. • In cases of complete sixth nerve palsy, the affected lateral rectus is typically left intact to preserve anterior segment circulation. Restoration of abduction on the affected side may be attempted by transposition procedures that aim to move the vertically acting rectus muscles into the horizontal plane.
  64. 64. COMBINED THIRD, FOURTH, AND SIXTH NERVE PALSY • fungal, or bacterial infection (including tuberculosis, syphilis, and Lyme disease). • Inflammatory diseases include sarcoidosis and idiopathic pachy-meningitis. • Neoplastic processes include carcinomatous and lymphomatous meningitis. • Peripheral demyelinating disorders including Guillain-Barre syndrome, the Miller Fisher variant, chronic inflammatory demyelinating polyneuropathy, and idiopathic cranial neuropathies
  65. 65. Fun facts • It's impossible to sneeze with your eyes open. • The eye of a human can distinguish 500 shades of the gray. • People generally read 25% slower from a computer screen compared to paper.
  66. 66. ‘V’ pattern deviation Signs Treatment ‘V’ pattern esotropia • • Difference between up- and downgaze is 15 or more Bilateral medial rectus recessions + downward transposition ‘V’ pattern exotropia • Bilateral lateral rectus recessions + upward transpositions
  67. 67. ‘A’ pattern deviation Signs • Treatment Difference between up- and ‘A’ pattern esotropia • Bilateral medial rectus recessions downgaze 10 or more + upward transposition ‘A’ pattern exotropia • Bilateral lateral rectus recessions + downward transposition

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