Anatomy and physiology of strabismus Sensory and motor adaptation to strabismus

1. Srabis
musMohamed Abdelzaher MD, FRCS

2. • Line passing between Object of fixation &
Fovea.
• Line passing through the centre of refractive media of the
eye
• Angle between visual axis &
optic axis (Normally +5
degrees)

3. • Perfect ocular alignment in
absence of any stimulus for
fusion (Uncommon)
• Tendency of the eye to deviate
when fusion is blocked (Latent
squint)
• Manifest deviation in which the
visual axes do not intersect at
point of fixation (Manifest squint)

4. • Monocular
movement

5. • Binocular, simultaneous, Conjugate (in the same direction) ocular
movement
• Binocular, simultaneous, Disjugate (in opposite direction) ocular
movement

6. • Lateral & medial orbital walls form an angle 45º with
each other
• Orbital axis forms an angle of 22.5º(23º)
• When the eye is in the 1ry position (eye is looking
straight ahead at a fixed point on the horizon with
the head erect),the visual axis forms an angle of
23º with the orbital axis.

7. Origin Insertion Action
Medial Rectus Annulus of Zinn
5.5 mm behind nasal
limbus
Adduction
Lateral Rectus Annulus of Zinn
6.9 mm behind temporal
limbus
Abduction
MRLR

8. Origin Insertion Action
Superior Rectus Annulus of Zinn
7.7 mm behind superior
limbus
1ry: Elevation
2ry: Adduction
3ry: Intorsion
Inferior Rectus Annulus of Zinn
6.5 mm behind inferior
limbus
1ry: Depression
2ry: Adduction
3ry: Extorsion
IR
SR

9. • Insertion of rect:
❖ MR >> 5.5 mm
❖ IR >> 6.5 mm
❖ LR >> 6.9 mm
❖ SR >> 7.7 mm
from limbus

10. • When the globe is abducted 23º, the visual
and orbital axes coincide.
• In this position it has no subsidiary actions
and can act only as an elevator.
• This is therefore the optimal position of the
globe for testing the function of the superior
rectus muscle.
• If the globe were adducted 67º, the angle
between the visual and orbital axes would be
90º.
• In this position the superior rectus could only act
as an intortor.

11. Origin Insertion Action
Superior Obliqe
Supero medial to the
optic foramen
Posterior, upper,
temporal quadrant of the
globe
1ry: Intorsion
2ry: Depression
3ry: Abduction
Inferior Oblique
Small depression behind
orbital margin at lacrimal
sac
Posterior, lower,
temporal quadrant of the
globe
1ry: Extorsion
2ry: Elevation
3ry: Abduction
SO passes forwards through the trochlea
(FUNCTIONAL ORIGIN) 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.

12. • When the globe is Adducted 51º, the visual
coincides with the line of pull of the muscle.
• In this position it has no subsidiary actions
and can act only as an depressor.
• This is therefore the optimal position of the
globe for testing the function of the superior
oblique muscle.
• If the globe were abducted 39º, the angle
between the visual and SO would be 90º.
• In this position the superior oblique could only
act as an intortor.
51º
39º

13. ❖ SO >> Intorsion
❖ SR >> Intorsion
❖ IO >> Extorsion
❖ IR >> Extorsion

14. •Lateral rectus: Sixth cranial nerve (abducent nerve –
abducting muscle).
•Superior oblique: Fourth cranial nerve (trochlear
nerve – muscle associated with the trochlea)
•All other EOMs: Third, Oculomotor nerve

16. • SO is the only depressor when the
eye is adducted
• SR is the only elevator when the eye
is abducted

17. • Muscles moving the eye in opposite
directions in the same eye.
• e.g. MR & LR of the same eye

18. • Muscles moving the eye in same directions in
the same eye.
• e.g. SR & IO of the same eye

19. • Pair of muscles conjugately
moving the eyes in same
direction.
• e.g. MR of right eye &
LR of the left eye

20. •Increased innervation to an extraocular muscle
(e.g. right medial rectus) is accompanied by a
reciprocal decrease in innervation to its
antagonist (e.g. right lateral rectus).

21. • During any conjugate eye movement, equal
and simultaneous innervation flows to the
yoke muscles

22. • In order to Avoid Diplopia, the CHILD adapts by 2 mechanisms:
• Active inhibition by the visual cortex of the image from one eye when both eyes are open

23. • In order to Avoid Diplopia, the CHILD adapts by 2 mechanisms:
• Non-corresponding retinal elements acquire a common subjective visual direction,
i.e. fusion occurs in the presence of a small angle manifest squint; the fovea of the
fixating eye is paired with a non-foveal element of the deviated eye.

24. • Adoption of Abnormal Head Posture (AHP) to maintain Binocular Single Vision (BSV).
• Components:
• To compensate Horizontal deviation

25. • To compensate Vertical deviation
• To compensate Torsional deviation

26. • Intorsion
• Depression
• Abduction

27. • Two dissimilar images e.g. a bird & a cage
• Two similar images each of which is incomplete in
one small different detail e.g, 2 rabbits, one
lacking a tail & the other lacking a punch of flowers
• The ability to obtain an impression of depth by the
superimposition of two pictures of the same object
which have been taken from slightly different angles.

28. • To detect suppression, BSV & ARC

29. • Test for stereopsis
• Measured in second of arc