AH&N- The Eye

Question 1

What are the contents of the bony orbit?

Answer 1

Extra-ocular muscles
Eyelids
Nerves (optic, oculomotor, trochlear, trigeminal & abducens)
Blood vessels: ophthalmic artery & superior & inferior opthalmic veins
Any space not occupied is filled with orbit fat, cushions the eye & stabilises the extraocular muscles.

Question 2

What are the pathways into the orbit?

Answer 2

Optic canal: transmits the optic nerve & opthalmic artery
Superior orbital fissure: transmits the lacrimal, frontal, trochlear, oculomotor, nasociliary & abducens nerves & carries superior opthalmic vein.
Inferior orbital fissure: transmits the maxillary nerve, inferior opthalmic vein & sympathetic nerves.
Minor openings: nasolacrimal canal on medial wall drains tears from eye to nasal cavity.
Supraorbital foramen and infraorbital canal: carry neurovascular structures.

Question 3

What are the two most common fractures of the bony orbit?

Answer 3

Orbital rim fracture: fracture of the bones forming the outer rim of the bony orbit, usually occurs at the sutures joining the maxilla, zygomatic and frontal.
Blowout fracture: partial herniation of the orbital contents through one of its walls. Usually occurs via blunt force trauma to the eye. The medial and inferior walls are the weakest with the contents herniating into the ethmoid & maxillary sinuses respectively.

Question 4

What does a fracture of the bony orbit cause?

Answer 4

Any fracture of the orbit will result in intraorbital pressure, raising the pressure in the orbit, causing exophthalmos (protrusion of the eye). There may also be involvement of surrounding structures e.g.haemorrhage into one of the neighbouring sinuses.

Question 5

Name the 7 extraocular muscles.

How can they be functionally divided?

Answer 5

Levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, inferior oblique & superior oblique.
Responsible for eye movement: recti & oblique muscles
Responsible for superior eyelid movement: Levator palpebrae superioris

Question 6

What is superior tarsal muscle?

Answer 6

It is a small portion of the Levator palpebrae superioris which contains a collection of smooth muscle fibres, and is innervated by the sympathetic nervous system.

Question 7

What are the attachments, actions and innervations of the Levator palpebrae superioris?

Answer 7

Attachments: originates from the lesser wing of the sphenoid bone, immediately above the optic foramen. It attaches to the superior tarsal plate of the upper eyelid (thick plate of connective tissue).
Actions: elevates the upper eyelid
Innervation: oculomotor nerve and sympathetic nervous system (superior tarsal muscle).

Question 8

What is Horners syndrome?

Answer 8

Refers to a triad of symptoms produced by damage to the sympathetic trunk in the neck:
Partial ptosis (drooping of the upper eyelid)- due to denervation of the superior tarsal muscle.
Miosis (pupillary constriction)- due to denervation of the dilator pupillae
Anhydrosis (absence of sweating)- on the ipsilateral side of the face, due to denervation of the sweat glands.
HS can represent serious pathology, such as a tumor of the apex of the lung (pancoast tumour), aortic aneurysm or thyroid carcinoma.

Question 9

What is the difference in path between the recti and oblique muscles of the eye?

Answer 9

Recti have a direct path from origin to attachment on sclera, oblique have an angular approach to eyeball

Question 10

Where do recti muscles of the eye characteristically originate from?

Answer 10

The common tendinous ring.

Question 11

What are the attachments, actions and innervation of superior rectus?

Answer 11

Attachments: originates from the superior part of the common tendinous ring & attaches to the superior & anterior aspect of the sclera.
Actions: primarily elevation but comtributes to addiction & medial rotation.
Innervation: oculomotor nerve

Question 12

What are the attachments, actions and innervations of the inferior rectus?

Answer 12

Attachments: originates from the inferior part of the common tendinous ring and attaches to to inferior and anterior part of the sclera.
Actions: primarily depression but contributes to adduction & lateral rotation.
Innervation: oculomotor nerve

Question 13

What are the attachments, actions and innervation of medial rectus?

Answer 13

Attachments: originates from the medial part of the common tendinous ring & attaches to the anterio-medial aspect of the sclera.
Actions: adducts the eyeball
Innervation: oculomotor nerve

Question 14

What are the attachments, actions and innervations of the lateral rectus?

Answer 14

Attachments: originates from the lateral part of the common tendinous ring & attaches to the antero-lateral aspect of the sclera.
Actions: abducts the eyeball
Innervation: abducens nerve

Question 15

What are the attachments, actions and innervations of the superior oblique muscle?

Answer 15

Attachments: originates from the body of the sphenoid bone, it’s tendon passes through a trochlear and attaches to the sclera of the eye, posterior to the superior rectus.
Actions: depresses, abducts & medially rotates the eyeball.
Innervation: trochlear nerve

Question 16

What are the attachments, actions and innervation of the inferior oblique?

Answer 16

Attachments: originates from the anterior aspect of the orbital floor. Attaches to the sclera of the eyes, posterior to the lateral rectus.
Actions: elevates, abducts & laterally rotates the eyeball.
Innervation: oculomotor nerve

Question 17

What are the symptoms of oculomotor nerve palsy?

Answer 17

Affected eye is displaced laterally by the lateral rectus & inferiorly by the superior oblique. (Down & out)

Question 18

What are the symptoms of trochlear nerve palsy?

Answer 18

Paralyse the superior oblique muscle.

Patient will complain of diplopia (double vision) & may develop a head tilt away from the site of the lesion.

Question 19

What are the symptoms of abducens nerve palsy?

Answer 19

Paralyse the lateral rectus muscle. The affected eye will be adducted by the resting tone of the medial rectus.

Question 20

Name the three layers of the eyeball?

Answer 20

Fibrous layer
Vascular layer
Inner layer

Question 21

Describe the structure and function of the fibrous layer.

Answer 21

Outermost layer, consists of sclera (85%) and cornea which are directly continuous with each other.
Main function: provide shape and support deeper structures

Question 22

Describe the structure and function of the vascular layer.

Answer 22

Lies underneath the fibrous layer.
Choroid: layer of connective tissue & blood vessels, provides nourishment to outer layers of retina.
Ciliary body: 2 parts: ciliary muscle and ciliary processes. The ciliary muscle consists of a collection of smooth muscle fibres, they are attached to the lens of the eye by the ciliary processes. The ciliary body controls the shape of the lens & also contributes to the formation of aqueous humor.
Iris: diameter altered by smooth muscle fibres within the iris, innervated by the autonomic nervous system. Situated between the lens & cornea

Question 23

What are the two cellular layers of the retina?

Answer 23

Neural layer: consists of photoreceptors. Located posteriorly and laterally in the eye.
Pigmented layer: lies underneath the neural layer & is attached to the choroid layer. Acts to support the neural layer & continues around the whole surface of the eye.

Question 24

What is the non visual retina?

Answer 24

Anteriorly the pigmented layer continues but the neural layer does not.

Question 25

What is the optic part of the retina and how can it be viewed?

Answer 25

Posteriorly and laterally both the neural and pigmented layer are present.
Can be viewed during opthalmoscopy.
Centre of the retina is marked by the macula- yellowish & highly pigmented. Macula contains a depression (fovea) which has a high concentration of light detecting cells. This area is responsible for high acuity vision.
Area that the optic nerve enters the retina is known as the optic disc- no light detecting cells.

Question 26

Where is the lens located? How is the shape of the lens changed? What happens to it with old age?

Answer 26

Anteriorly between the vitreous humor and the pupil.
Shape of the lens is altered by the ciliary body, changing its refractive power.
In old age the lens can become more opaque.

Question 27

What are the two fluid filled chambers of the eye?

Answer 27

Anterior chamber: between cornea and iris
Posterior: between iris and ciliary processes
The chambers are filled with aqueous humor, nourishes and protects eye, produced constantly & drains via the trabecular mesh work, an area of tissue at the base of the cornea near the anterior chamber.

Question 28

What is glaucoma? What are the 2 clinical classifications?

Answer 28

An increase in intra-ocular pressure, secondary to and increased amount of aqueous humor.
This eventually compresses the retinal arteries, damaging the retina & leading to loss of vision. 2 clinical classifications:
Open angle: outflow of aqueous humor through the trabecular meshwork is reduced. Causes a gradual reduction of the peripheral vision until the end stages of the disease.
Closed angle: where the iris is forced against the trabecular meshwork, preventing any drainage of aqueous humor. It is an opthalmic emergency, which can rapidly lead to blindness.

Question 29

Describe the Vasculature of the eyeball.

Answer 29

Primarily opthalmic artery, branch of the internal carotid artery immediately distal to the cavernous sinus.
Branches of opthalmic artery:
Central artery supplies internal surface of retina, occlusion will quickly result in blindness.
Venous drainage: superior and inferior opthalmic veins, drain into the cavernous sinus.

Question 30

What is papilloedema?

Answer 30

Swelling of the optic disc, visible during opthalmoscopy.
Swelling occurs secondary to raised intra-cranial pressure. The high pressure within the cranium resists venous return from the eye. This causes fluid to collect in the retina, producing a swollen optic disc.

Question 31

What are the boundaries of the bony orbit?

Answer 31

Roof(superior wall): formed by the frontal bone & the lesser wing of the sphenoid. The frontal bone separates the orbit from the ️anterior cranial fossa.
Floor(inferior wall): formed by the maxilla, palatine & zygomatic bones. The maxilla separates the orbit from the underlying maxillary sinus.
Medial wall: formed by the ethmoid, maxilla, lacrimal & sphenoid bones. The ethmoid bone separates the orbit from the ethmoid sinus.
Lateral wall: formed by the zygomatic bone & greater wing of the sphenoid.
Apex: located at the opening to the optic canal, the optic foramen.
Base: opens out into the face & is bounded by the eyelids, orbital rim.