Applied anatomy - Squint

1. Anatomy of eye and its
relevance in Squint
By
Dr Indeevar V Mishra
Aravind eye hospital, Pondicherry.

2. Muscles
Muscles
Voluntary
Recti
LPS
Obliques
Involuntary
Sphincter
pupillae
Dilator
pupillae

3. Gross Anatomy
Gross
anatomy
Orbital
Singly
innervated
Multiply
innervated
Global
Global red
singly
innervated
Gobal
intermediate
singly
innervated
Global
multiply
innervated
fibres
Global pale
singly
innervated

4. Pecularities
• Blood supply
• Innervation
No fatigue
Small motor units
Rich supply
Aerobic
metabolism

5. Tenon’s capsule ( Fascia bulbi )
•The globe is suspended within the bony orbit by a fascial system, the bulk of
which is formed by the tenon’s capsule.
• Tenon’s capsule is the condensation of the fibrous tissue that covers the globe
from the entrance of the optic nerve into the posterior aspect of the globe
extending to within 1mm of the corneal limbus.
• After that it fuses with the conjunctiva at the limbus.

6. `

7. Rectus muscle pulley system
• A reflection extending from Tenon’s capsule envelops the posterior portion of the
extraocular muscles that are extrinsic to the capsule at this position in the orbit.
• Fibroelastic sleeves consisting of dense bands of collagen , elastin and smooth
muscle surround the rectus muscles.

8. • These sleeves suspend the globe
within the orbit by structures
called as check ligaments.
• Orbital layer of the rectus
muscles has been demonstrated to
insert into the corresponding
rectus muscle pulley, rather than
on the globe.

9. • Significance – only the anterior aspect of the muscles moves during normal eye
movements into secondary gaze positions while the posterios aspects of the rectus
muscle are relatively fixed in position by the rectus muscle pulleys.
• Functional origin of the extraocular muscles is at their pulleys.
• Upward displacement of the lateral rectus pulleys and downward displacement of
the medial rectus pulleys are associated with ‘A’ pattern. Downward displacement
of the lateral rectus pulleys and upward displacement of the medial rectus pulleys
are associated with ‘V’ pattern

11. • Fascial expansions of lateral
and medial rectus muscles
are strong and are attached to
orbital tubercle on the
zygomatic bone and to the
lacrimal bone resp.
• These are lateral and medial
check ligaments.

12. • The suspensory ligament of Lockwood forms a hammock stretching below the
eyeball between the medial and lateral check ligaments and enclosing the inferior
rectus and inferior oblique muscles of the eye.
• It is a thickening of Tenon's capsule, the dense connective tissue capsule surrounding
the globe and separating it from orbital fat. The fascial sheath of the inferior rectus
muscle divides anteriorly into two layers: an upper one, which becomes part of
Tenon’s capsule, and and a lower one, which is about 12 mm long and ends in the
fibrous tissue between the tarsus of the lower lid and the orbicularis muscle.

13. • This lower portion forms part of Lockwood’s ligament.
• Attachments between Lockwood’s ligament and neighboring muscle
and fascial structures are connected to the lower lid. This makes lower
lid ptosis a potential complication of inferior rectus recession

15. • Expansion from the superior rectus
and the levator palpebrae
superioris are attached together
and ensure the movement of two
occur synergistically.
• Upward movement of the eye is
accompanied by the raising of the
upper lid.
• Levator resection for ptosis may
induce hypotropia if these
connections are not severed.

16. • Whitnall’s (superior transverse) ligament and the
superior oblique tendon in the trochlea have
common fascial attachments at the orbital rim.
• If the superior transverse ligament is weakened
inadvertently while hooking the superior oblique
tendon, thereby weakening the medial horn of the
levator muscle, ptosis of the nasal portion of the
upper lid usually results.
• Under direct vision between the nasal border of
the superior rectus and the trochlea the tendon can
be hooked.

17. • It is preferable to use the limbus, a more consistent anatomical point, as the reference

18. Surgical anatomy of the inferior oblique
• Point of origin - Few millimeters behind the medial end of the inferior orbital rim just lateral to the
lacrimal fossa and proceeds posteriorly and temporally at an angle of 51 degrees with the frontal
plane passing beneath the inferior rectus (between the inferior rectus and the floor of the orbit).
• 36 mm long , average width – 9mm, shortest muscle.
• Relations –
1. The posterior extent of the inferior oblique insertion overlies a point 2 mm below and 2 mm
lateral to the macula.
2. The middle of the distal half of the muscle covers the inferior temporal vortex vein.

20. Surgical anatomy of the Superior oblique
• The superior oblique muscle has a muscular portion and a tendinous portion, both of
which are approximately 30 mm long. The muscle portion originates superiorly and nasal
to the ligament of Zinn at the apex of the orbit and becomes tendinous 10 mm before
reaching the trochlea.
• The trochlea, a cartilaginous saddle-shaped structure, is located at the junction of the
medial and superior orbital rim just posterior to the orbital rim. The trochlea acts as a
pulley redirecting the course of the superior oblique tendon. approximately 54 degrees
from the frontal plane.

21. • The muscle inserts obliquely with the
concavity forwards.
• The anterior end is 13.8 mm behind
the limbus.
• The posterior end is 18.8 mm from the
limbus.
• The width of the insertion is approx.
11mm.

23. • The tendon of the superior oblique can
telescope inward toward the apex of the
orbit approximately 16 mm during
maximum downgaze in adduction and
telescope 16 mm outward in maximum
upgaze in adduction.
• Patients with a diagnosis of congenital
superior oblique palsy, with or without a
superior oblique tendon, have in
common a superior oblique traction test
suggesting a lax or absent tendon and
are likely to have facial asymmetry, with
the larger face on the side of the paretic
or absent superior oblique.

24. Trochlear components
1) Cartilage saddle
2) A bursa-like space on the
bearing surface between the
tendon and the groove in the
cartilaginous saddle
3) A fibrillar-vascular structure
surrounding the superior oblique
tendon
4) The superior oblique tendon
5) Fibrous bands attaching the
trochlea to the bone of the orbit

26. • The rectus muscles are more or less flat narrow bands that attach themselves with
broad , thin tendons to the globe.
• The muscles originate from the Annulus of Zinn at the superior orbital fissure.
• Only the lateral rectus arises from 2 heads which join in a “V” form.
• Due to slope of the orbital roof, the origin of the superior rectus and medial rectus
is at a slightly anterior plane than the other two recti.

28. • The three recti viz :- medial , lateral, inferior are in contact with the globe for most
part.
• The superior rectus is separated from the globe by the LPS.
• The insertion lines form the spiral of Tillaux.

29. • In their extracapsular portions, the extrinsic eye muscles are enveloped by a muscle
sheath.
• This sheath is a reflection of Tenon’s capsule and runs backward from the entrance
of the muscles into the subcapsular space for a distance of 10 to 12 mm.
• At the lower aspect of the entrance, Tenon’s capsule is reduplicated. At the upper
aspect, it continues forward as a single membrane.
• The muscle sheaths of the four rectus muscles are connected by a formation known
as the intermuscular membrane, which closely relates these muscles to each other.

31. • The medial and lateral rectus muscles possess well-developed fibrous membranes
that extend from the outer aspect of the muscles to the corresponding orbital wall.
• The check ligament of the lateral rectus muscle appears in horizontal sections as a
triangle, the apex of which is at the point where the sheath of the muscle pierces
Tenon’s capsule.
• The check ligament of the medial rectus muscle extends from the sheath of the
muscle, attaching to the lacrimal bone behind the posterior lacrimal crest and to
the orbital septum behind.

35. Conjunctiva
• The bulbar conjunctiva and
anterior Tenon's capsule have
multiple, fine imbedded arterioles
and veins.
• These are branches of the anterior
ciliary circulation and of the
marginal arcades of the vessels of
the lids.
• This circulation furnishes a small
but probably significant blood
supply to the anterior segment.

37. Factors
• Sclera

38. Thank you!