Eye Anatomy PDF

Special sense 3 R D Y E A R  ElGhazawy | Special Sense Anatomy 1  ElGhazawy | Special Sense EYE Eye is one of the organs of special sense which carries visual information...

Special sense 3 R D Y E A R  ElGhazawy | Special Sense Anatomy 1  ElGhazawy | Special Sense EYE Eye is one of the organs of special sense which carries visual information & provides us with the sense of sight. It is kept within a bony cavity in the skull (orbital cavity). Protective mechanisms of the eye: 1. Posterior ⅔: Protected by eye orbit 2. Anterior ⅓: By eye lids 3. Tear film: Moistens & protects cornea & conjunctiva The Bony orbit Definition: It is a four-sided pyramid with the apex pointing posteriorly. Boundaries: It has apex, base, four sides: roof, floor, lateral and medial walls. (1) Apex: Lies at the posteromedial end of the orbital cavity. It is near the medial end of the superior orbital fissure. (2) Base: It is the orbital opening. (3) Roof: Is mainly formed by the orbital plate of the frontal bone (separating the orbit from the anterior cranial fossa). (4) Lateral Wall: Is mainly formed by the orbital surface of greater wing of sphenoid. (5) Floor: The orbital surface of the maxilla (separating the orbit from the maxillary sinus). (6) Medial Wall: Lacrimal Bone, orbital plate of the ethmoid bone (separating the orbit from the ethmoidal air sinuses). 2  ElGhazawy | Special Sense Portas and special features of the bony orbit - The roof: Lacrimal fossa for the lacrimal gland at its anterolateral angle. Trochlear fossa for the trochlea of the superior oblique muscle at its anteromedial angle. Optic canal close to the posterior end of the roof. - The lateral wall: Superior orbital fissure, between the lateral wall and the roof posteriorly Inferior orbital fissure, between the lateral wall and the floor posteriorly. - The floor: Infraorbital groove and canal which end on the surface of the skull at the infraorbital foramen. Lacrimal groove for the lacrimal sac. - The medial wall: anterior and posterior ethmoidal foramina at its junction with the roof.. 3  ElGhazawy | Special Sense Anatomy of the Extraocular Muscles There are 7 extraocular muscles: o one acts on the upper eyelid: levator palpebrae superioris o and the remaining six (4 recti + 2 oblique) act on the eyeball. Levator Palpebrae Superioris (L.P.S.) Attachments: Arises from the posterior part of the roof of the orbit. Ends in an aponeurosis which inserts into the: The skin of the upper eyelid. The superior tarsus (this part of L.P.S. is formed of smooth, involuntary muscle fibers called superior tarsal muscle). The superior conjunctival fornix. N. Supply The striated part of the muscle is supplied by the oculomotor N. The smooth part is supplied by the cervical sympathetic derived from the carotid nerve plexus. Actions The muscle is the elevator of the upper eyelid. Clinical Anatomy: Injury to the cervical sympathetic nerve to the head produces Horner’s syndrome: ptosis, miosis, anhidrosis and enophthalmos. 4  ElGhazawy | Special Sense The Four Recti Muscles These are: superior, inferior, medial and lateral recti muscles which are disposed around the eyeball according to their names. Attachments and General Features: 1. All arise from the common tendinous ring o which is attached around the optic canal and the medial part of the superior orbital fissure. 2. All are inserted by expanded tendons o into the sclera 6 - 7 mm behind the corneoscleral junction, anterior to the coronal equator of the eyeball. 3. All form a muscular cone around the optic N. and the posterior part of eyeball. o The apex of the cone is represented by the origin of the muscles at the tendinous ring and its base is represented by the insertion of the muscles into the sclera. 5  ElGhazawy | Special Sense The Two Oblique Muscles Superior Oblique: Attachments: Arises from the roof of the orbit superomedial to the optic canal. It ends in a tendon which passes through a fibrotendinous trochlea attached to the trochlear fossa of the frontal bone; the tendon passes posterolaterally to insert into the sclera posterior to the coronal equator of the eyeball. Inferior Oblique: Attachments: Arises from the floor of the orbit lateral to the nasolacrimal groove. It ascends posterolaterally to insert into the lateral part of the sclera posterior to the coronal equator of the eyeball Nerve Supply of the Extraocular Muscles This could be remembered by the famous equation (LR6,SO4,O3) which means that: lateral rectus is supplied by the abducent N (LR6), superior oblique by trochlear. N (SO4) and other extraocular muscles including (L.P.Superioris) are supplied by oculomotor. N (O3). 6  ElGhazawy | Special Sense Actions of the Extraocular Muscles A. Actions of the Individual Muscles on the Eyeball : 1) Medial rectus : Adduction. 2) Lateral rectus : Abduction. 3) Superior rectus : Elevation, adduction, intorsion. 4) Inferior rectus : Depression, adduction, extorsion. 5) Superior oblique : Depression, abduction, intorsion. 6) Inferior oblique : Elevation, abduction, extorsion. B. Compound Actions of the Six Extraocular Muscles: 1) Adduction : Medial rectus (assisted by superior and inferior recti). 2) Abduction : Lateral rectus (assisted by superior and inferior oblique muscles). 3) Elevation : Superior rectus + inferior oblique. 4) Depression : Inferior rectus + superior oblique. (reading and downstairs) 5) Intorsion : Superior rectus + superior oblique. 6) Extorsion : Inferior rectus + inferior oblique. Muscles act Abducted eye Mid position Adducted eye (L. rectus, S.O + I.O) (Neutral) (M. rectus, S.R + I.R) Elevation Superior rectus Superior rectus + Inferior oblique inferior oblique Depression Inferior rectus Inferior rectus + Superior oblique superior oblique Intorsion Superior rectus + superior oblique Extorsion Inferior rectus + inferior oblique 7