The Adnexa of the Eye
Horner's syndrome (often iatrogenic) is due to the sympathetic supply being interrupted, what are its symptoms (name 4)?
- Constricted pupil (miosis), constricted by oculomotor n. - Droopy upper eyelid (ptosis) as tarsal smooth muscle lost sympathetic innervation - Prominent third eyelid as orbitalis m lost sympathetic innervation - Sunken eye (the impression that the eye is sunk in due to a narrow palpebral aperture rather than true enophthalmos)
Which 2 structures can be found within the superficial muscular fascia?
- Levator palpebrae superioris, raiser of the upper eyelid - Lacrimal gland
Observe the rotation of the globe around 3 perpendicular axes
- Medial and lateral recti rotate the globe around a dorsoventral axis - Dorsal and ventral recti rotate the globe around a mediolateral axis - Dorsal and ventral obliques account for the differences in the optic and orbital axes, ensuring smooth elevation/depression of the globe under the action of the dorsal and ventral recti.
Name the extrinsic muscles of the eye.
- Medial, lateral, dorsal and ventral rectus - Ventral and dorsal oblique - Retractor bulbi
As well as the lacrimal gland, what other glands contribute to the lacrimal fluid?
- Nictitans (3rd eyelid) gland - 1/3 aqueous portion - Meibomian (tarsal) gland - fatty component
What does the periorbita blend with at the orbital rim?
- Periosteum at the orbital margin and on the medial and dorsal walls of the orbit. - Dense connective tissue of the eyelids, the orbital septum, which extends into the musculofibrous layer of the lid and forms a tarsal plate which stiffens the edges of the upper and lower eyelids.
What are the muscular components of the musculofibrous layer of the eyelid?
- Tarsal m - Aponeurosis of levator palpebrae superioris - Orbicularis oculi
Which nerves innervate the extrinsic muscles of the eye?
- Trochlear nerve - dorsal oblique - Abducent nerve - lateral rectus (ABDUCTS the eye) and part of the retractor bulbi - Oculomotor nerve - Dorsal rectus, medial rectus, ventral rectus, ventral oblique and part of the retractor bulbi
Describe the pathway of tears through the lacrimal apparatus, beginning at the lacrimal gland.
1. Lacrimal gland 2. Lacrimal ducts 3. Dorsal fornix 4. Conjunctiva sac 5. Washed over eye by 3rd eyelid and upper + lower eyelid 6. Held around lacrimal caruncle 7. Two (dorsal and ventral) lacrimal puncta 8. Upper and lower canaliculus 9. Lacrimal sac 10. Naso-lacrimal duct 11. Floor of nasal cavity
Name 8 adnexa (structures which surround or attach to the globe).
1. Orbit 2. Eyelids (protective) 3. Conjuctiva 4. Orbital fascia (connective tissue that holds the eye in place and surrounds muscles) 5. Lacrimal apparatus (secretes components of the tear film and keeps the eyes moist) 6. Extrinsic muscles (move the eye in different directions) 7. Nerves (sensory and motor innervation) 8. Blood vessels (nourish the eye and remove waste products)
Which 3 conical layers surround the eyeball?
1. Periorbita - thick, collagenous, white layer 2. Superficial muscular fascia - thin and fatty 3. Deep muscular fascia - in contact with the surface of the eye
What does the third eyelid arise from?
A fold from the ventromedial aspect of the conjunctiva - inner (bulba) and outer (palpebral) conjunctiva (nictitating conjunctiva).
What is the third eyelid supported by?
A t-shaped piece of cartilage Helps to spread tears across the eye.
Why is it important to know the structure of the orbit walls?
Affects diseases and surgical approach/access
What is the lining of the anterior cornea called?
Anterior cornea epithelium
Where is the retractor bulbi located?
Around the whole posterior of the eyeball, encircling the optic nerve.
What is the lining of the anterior sclera called?
Bulba conjunctiva
Which animals have an incomplete bony orbital rim?
Carnivores and pigs The orbital rim is complete in herbivores and humans.
Structures that normally keep the gland of the third eyelid hidden may lax so that the gland protrudes, what is this condition called?
Cherry eye Particularly common in bulldogs.
What hairlike structures are found mainly on the upper eyelid and what is their function?
Cilia (eyelashes), they prevent particulate matter from entering the eye. They are usually more prominent and numerous on the upper than on the lower lid; conspicuous cilia are absent from the lower lid of carnivores.
Describe the blood supply to the eye, beginning from the common carotid artery.
Common carotid a. --> external carotid a. --> maxillary a. --> external opthalmic a.
What is the orbit?
Cone shaped (tapers caudally towards the optic foramen) cavity on the lateral surface of the skull, which houses the adnexa and globe.
What are the canthi?
Corners of the eye Medial and lateral ends/angles of the palpebral fissure, where the upper and lower eyelids meet. Singular, canthus.
Small ciliary and sebaceous glands are associated with the roots of the cilia, what happens if one of these glands gets blocked?
Develop a hordeolum (stye)
Where do the dorsal oblique and dorsal rectus lie in relation to each other?
Dorsal rectus superficial to dorsal oblique
Where is the lacrimal gland located within the superficial muscular fascia?
Dorsolaterally
What structures can be found within the deep muscular fascia?
Extraocular muscles
Which nerve innervates the orbicularis oculi muscle?
Facial nerve
The globe, "eyeball", is housed in the orbit in lots of protective __.
Fat If an animal is starving it is one of the last bits of fat to go. An emaciated animal will have a sunken eye appearance due to this fat being lost.
In which species is the lower eyelid more mobile?
In many birds, lizards and amphibians
Which blood vessel supplies some of the deeper structures of the eye?
Internal opthalmic a.
What is the function of the trochlear cartilage?
It changes the direction of the dorsal oblique muscle
What is distinct about the pupil of a cat's eye in bright light?
It is a vertical slit
Where is the trochlear cartilage located?
It is embedded in the dorsomedial wall of the periorbita
What is the condition called in which dogs, cats and horses have a deficiency in the aqueous part of tears?
Keratoconjunctivitis sicca (dry eye) Can result in conjunctivitis, corneal ulceration and scarring. Greek keras, kerat- 'horn', sick means 'dry'.
What is the fleshy mound called in the medial aspect of the eye?
Lacrimal caruncle Latin caruncula, from caro, carn- 'flesh'. It contains sebaceous (oil) and sudoriferous (sweat) glands, and holds tears in a 'moat' around it, helping to keep the eye moist. It bears a few fine hairs in the large species.
What does lacrimal fossa refer to?
Lacrimal fossa can refer to: - Fossa for the lacrimal gland on the frontal bone - Fossa for the lacrimal sac on the lacrimal bone
In the horse, where does the medial palpebral ligament attach to on the skull?
Lacrimal tubercle (palpable)
Precisely, which nerves innervates the lateral canthus?
Maxillary division of the trigeminal nerve
Where is the third eyelid located?
Medial aspect of the eye, between the lacrimal caruncle and the eyeball.
Where does the medial palpebral ligament attach?
Medial canthus --> nasomaxillary suture
The orbit walls are entirely bony in humans/primates, but they are only osseous where in domestic species?
Medially and dorsally
Where are the palpebral ligaments located?
Medially and laterally to the eye Only the medial palpebral ligament is well defined.
What do the meibomian glands (tarsal glands) secrete?
Meibum This is an oily substance that prevents evaporation of the eye's tear film. It is the fatty component of tears and provides surface tension for the watery secretions. Deep to the tarsus and opening onto the edge of the lid by a row of tiny openings is a series of tarsal glands.
What are the functions of the adnexa?
Moisture, protection (light, heat, trauma) and movement
What is the inner layer of the eyelids called?
Mucous membrane, palpebral conjuctiva
What is the middle layer of the eyelids called?
Musculofibrous layer
Do humans and primates have a retractor bulbi?
No
Are the tarsal plates well developed in the dog?
No, they are known as vestigial tarsal plates.
Which nerve causes constriction of the pupil?
Oculomotor nerve
Which nerve innervates the levator palpebrae superioris?
Oculomotor nerve
Precisely, which nerves innervates the medial canthus?
Opthalmic division of the trigeminal nerve
Which muscle closes the eye and what is its innervation?
Orbicularis oculi, facial n.
What does the periorbita divide?
Orbital and extraorbital structures in the domestic species Divided by the bony socket in primates.
Which structure completes the orbital ring in carnivores and pigs?
Orbital ligament
What is the fibrous component of the musculofibrous layer of the eyelid?
Orbital septum/tarsal plate
What is the lining of the inside of the eyelid (posterior eyelid) called?
Palpebral conjunctiva
What is the opening between the eyelids called?
Palpebral fissure
Name 3 other words that mean 'eyelid'
Palpebral, tarsal and blepharon
What is the normal fusion of the eyelids at birth in carnivores known as?
Physiological ankyloblepharon (an-ky-lo-bleph-aron) Gk, agkylos, crooked + blepharon, eyelid. This is necessary because at birth the lacrimal apparatus is immature.
What terms are used instead of 'caudal' and 'rostral' to describe the eye?
Posterior and anterior
The third eyelid has an associated gland, the gland of the third eyelid, what is its function?
Produces 1/3 aqueous portion of the tear film. The other 2/3 is produced by the lacrimal gland (fatty component of the tears - meibum - produced by meibomian glands).
What is the purpose of the nictitating membrane?
Protection and moisture It is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten the eye while maintaining visibility. It offers further protection for animals that have protruding eyes.
What is the function of the retractor bulbi?
Protective mechanism for animals whose eyes stick out.
Where do the extrinsic muscles of the eye insert?
Sclera (equator)
What is the external layer of the eyelids called?
Skin
What keeps the third eyelid retracted?
Smooth muscle (m. orbitalis) under sympathetic influence.
Embryonically, what do the eyelids originate from?
Surface ectoderm As does the lens, cornea and conjunctiva.
The tarsal muscle (muscle of the eyelid) is smooth muscle, is it under sympathetic or parasympathetic innervation?
Sympathetic. If you lose sympathetic innervation (Horner's syndrome) the eyelids partially close, giving the appearance of a sunken eye.
Which two structures is the medial palpebral ligament sandwiched between?
Tendon of levator nasolabialis and angularis oculi vein
What is the function of the lateral and medial palpebral ligaments?
Tether the canthi of eyelid This enables the eye to open quickly as an elongated fissure and stops the eye from begin a small round opening that would be created by the orbicularis oculi. This elongating action is also reinforced by the retractor anguli oculi lateralis and levator anguli oculi medialis.
What is an alternative name for the third eyelid?
The nictitating membrane (from Latin nictare, to blink)
What is the conjunctiva fornix?
The potential space between the lids and the eyeball is known as the conjunctival sac, and their dorsal and ventral extremities are the fornices.
What is the conjunctival sac?
The potential space between the lids and the eyeball.
The extrinsic muscles of the eye originate near the optic foramen, except for which one?
Ventral oblique - originates in the medial wall of the orbit
Where do the ventral oblique and ventral rectus lie in relation to each other?
Ventral oblique superficial to ventral rectus
Where does the periorbita form the wall of the orbit in carnivores?
Ventrolaterally, where there is no bone.
Can the orbital ligament be palpated?
Yes
Do the internal and external ophthalmic arteries anastomose?
Yes
Is the palpebral conjunctiva, bulba conjuntiva and anterior cornea epithelium continous?
Yes - you cannot lose a contact lens!
Where does the orbital ligament attach?
Zygomatic process of facial bone and facial process of zygomatic bone
In carnivores what forms 2/3 of the orbit floor laterally and ventrally?
Zygomatic salivary gland Equivalent to dorsal buccal gland in large animals. It is not common but a salivary mucocele/sialocele could potentially affect the eye too.
