Ординатура / Офтальмология / Английские материалы / Textbook of Visual Science and Clinical Optometry_Bhattacharya_2009

Anatomy of Appendages of the Eyeball 41

responsible for associated pain in retrobulbar neuritis in extreme movements of the eyeball.

e.Superior rectus is the longest extrinsic muscle of the eyeball.

f.Inferior oblique is the only muscle which arises from the anterior part of the orbit.

g.All the extrinsic muscles of the eye are provided with fascial check ligaments which are intimately blended with the perimuscular sheath and Tenon’s capsule for controlling their delicate movements.

TENON’S CAPSULE (OR FASCIA BULBI)

It is a fibrous membrane which covers the eyeball from the limbus to the optic nerve. So, the cornea remains uncovered by this membranous capsule. The Tenon’s capsule is attached to the eyeball, in front at the limbus, to the extrinsic muscles and to the sclera by fine trabeculae. The posterior surface of this capsule is in close contact with the orbital pad of fat. The lower part of the Tenon’s capsule is very thickened to form a hammock to support the eyeball. This thickened part is called suspensory “ligament of Lockwood”. The Tenon’s capsule is pierced by:

i.Anteriorly – 6 extrinsic muscles

ii.Posteriorly – Optic nerve, ciliary nerves and arteries

iii.At the equator – Vortex veins.

LEVATOR PALPEBRAE SUPERIORIS

It arises by a short tendon from the apex of the orbit, above and in front of the optic foramen. It’s tendinous origin is blended with the origin of the superior rectus.

INSERTION

It ends in a membranous aponeurosis to insert as following slips;

i.Anterior slip—Main insertion is at the skin of the upper eyelid by passing through the orbicularis fibres.

ii.Central slip— Upper margin and anterior lower third of tarsal plate of upper eyelid

42Textbook of Visual Science and Clinical Optometry

iii.Posterior slip— Superior fornix of the conjunctiva

iv.Medial horn/slip— To the medial palpebral ligament

v.Lateral horn/slip— It separates the orbital and palpebral part of the lacrimal gland and is attached to the lateral palpebral ligament.

NERVE SUPPLY

Oculomotor (IIIrd Cranial) nerve. Superior division of the IIIrd nerve innervates the muscle usually by traversing through the medial side of the superior rectus muscle.

ACTION

It elevates upper eyelid.

Anatomy of the Orbit 45

separates ethmoidal air cells in the upper half of the fossa and middle meatus of the nose in the lower half. Inflammation of the ethmoidal sinus spreading to orbit is also very common probably due to thinness of the medial wall.

FLOOR

It is the shortest of the orbital walls and separates maxillary sinus from the orbit.

LATERAL WALL

It is most exposed to external injuries. However, it is the thickest of the orbital walls providing protection from external injuries. Lateral to it lies temporal fossa and middle cranial fossa from anterior to posterior.

ORBITAL CONTENTS

•Eyeball

•Optic nerve

•Extrinsic muscles

•Lacrimal apparatus

•Adipose tissue

•Fascia bulbi (or Tenon’s capsule)

•Nerves and vessels which supply the above structures.

SUPERIOR ORBITAL FISSURE (SPHENOIDAL)

It is a comma-shaped fissure between greater and lesser wings of the sphenoid bone. It is located between the roof and the lateral wall of the orbit. It is the largest communication between the orbit and the middle cranial fossa. The superior orbital fissure is divided into lateral and wider medial parts by the common tendinous ring. The lateral rectus arises from both margins of the fissure from this common tendinous ring. Structures passing through the superior orbital fissure are (Fig. 3-2):

46 Textbook of Visual Science and Clinical Optometry

a.Through the annulus, i.e. between the two heads of the lateral rectus muscle (from above downwards)

i.Superior division of the oculomotor nerve

ii.Nasociliary nerve

iii.Inferior division of the oculomotor nerve

iv.Abducens nerve.

b.Through the narrow lateral portion, i.e. above the annulus

i.Lacrimal nerve

ii.Frontal nerve

iii.Trochlear nerve

iv.Superior ophthalmic vein

v.Recurrent lacrimal artery.

c.Through the wider medial portion – rarely, inferior ophthalmic vein.

INFERIOR ORBITAL FISSURE (SPHENOMAXILLARY)

It is a fissure between greater wing of the sphenoid and the maxilla. It is located between the floor and the lateral wall of the orbit. Structures passing through it are (Fig. 3-2);

i.Infraorbital nerve

ii.Zygomatic nerve

iii.Communication between the inferior ophthalmic vein and the pterygoid plexus.

OPTIC FORAMEN (OPTIC CANAL)

It is a canal formed by the two roots of the lesser wing of the sphenoid and communicates the apex of the orbit with the middle cranial fossa. The optic canal is separated from the wider medial part of the superior orbital fissure by a bar of bone. It is funnelshaped with the orbital end being the mouth of the funnel. Structures passing through it are (Fig. 3-2);

i.Optic nerve with its sheath, i.e. meninges

ii.Ophthalmic artery embodied in the dural sheath of the optic nerve

iii.Sympathetic plexus from the ophthalmic artery.