Anatomy of the eye
Card Set Information
Anatomy of the eye
Vet Med - Module 8
What is the orbit?
The bony cavity on the side of the head, with medial, dorsal and variable lateral margins, that houses the eye.
What terms are used to describe the topography of the eye: rostral/caudal or anterior/posterior?
How many tunics of the eyeball are there? What are these?
3 - external fibrous tunic, middle vascular tunic, and internal nervous tunic
What is the function of the external fibrous tunic?
It gives shape to the eyeball and has a protective function
What are the two parts of the external fibrous tunic?
The cornea and sclera
Where do the cornea and sclera meet?
At the limbus
What is type of tissue is the cornea made up of and how is this arranged to suit its function?
The cornea is made up of connective tissue. They are arranged in layers to allow them to be transparent.
What happens if fluid builds up between the layers of CT in the cornea?
Oedema occurs and the eye takes on a foggy/blueish appearance
True or false: the cornea contains blood vessels?
False - this would interfere with the transmission of light
What structures are the anterior/posterior epithelium of the cornea continuous with?
Anterior - conjunctival epithelium
Posterior - anterior surface of iris
Which reflex occurs when the anterior corneal epithelium/conjunctival epithelium is stimulated?
How does the cornea receive nutrients?
From the anterior surface of the iris (which is continuous with the posterior epithelium of the cornea)
What is the basement membrane of the cornea called?
If you stain a corneal ulcer and it shows a central non-staining area, why must this ulcer be treated immediately?
As the non-staining area is the decemet's membrane and this is the last barrier to penetration of the cornea
What colour is the sclera?
What is the sclera also an attachment point for?
Ocular muscles anterior to the equator
What is the name of the thin membranous covering separating the eyeball from retrobulbar fat? And what is its function?
Vagina Bulbi - allows eyeball free movement within the socket
What three parts make up the vascular tunic?
The choroid, ciliary body and iris
Where are the choroid, ciliary body and iris located?
Choroid - lines sclera from optic nerve to limbus
Ciliary body - thickening of tunic area at level of limbus
Iris - projects into cavity behind cornea
What are the functions of the vascular tunic?
Vascular supply, suspends lens and controls shape of lens and pupil
Where do vessels enter the eyeball? What structure do they accompany?
They enter at the posterior pole and equator, accompanying the optic nerve.
What is the function of the tapetum lucidium?
This is a reflective area that sends light back through the retina
Which muscles control pupil size?
Smooth sphincter (constrictor, parasympathetic) and radial (dilator, sympathetic) muscles
What structures may be present in horses and ruminants that project from the dorsal border across the pupil?
What area of the retina contains receptors and why?
Only the posterior 2/3 contains receptors as the anterior 1/3 cannot be reached by light
What type of receptor cells are present in the retina?
Rods and cones
Which receptor cells are responsible for black and white/colour vision? And day/night vision?
Rods - black and white, night
Cones - colour, day
Describe the path light takes to get to receptor cells
Light must pass through a layer of ganglion cells and bipolar cells before hitting the light receptors
Which cranial nerve enters the eye?
The optic nerve (CN II)
What is the macula?
The area of greatest receptor cell density and therefore greatest resolution
What substance fills the anterior and posterior chambers of the eye?
What type of cells produce aqueous humor?
Ciliary process cells
Why must drainage of aqueous humor equal its production? What condition results from a failure to drain aqueous humor?
Production of aqueous humor is continuous and therefore drainage must also be continuous. Glaucoma, although this is much less prevalent in domestic species than humans.
What is cataracts?
Opacification of the lens - if the lens becomes opaque then light cannot travel through it, cannot reach receptors and vision decreases
What shape is the lens for looking at objects far away/close up?
Far away - wide and thin
Close up - thick and fat
What is the vitreous body?
A gel-like mass that maintains contain between retina and choroid
What are the different methods of imaging the eye?
Opthalmoscope - direct visualisation
Ultrasound - cheap, simple, allows assessment of retina
CT and MRI may be useful for orbital disease
What components are part of the adnexa of the eye?
Orbit, orbital fasciae, ocular muscles, eyelids, conjunctiva, lacrimal apparatus
Which bones make up the orbit?
Frontal, lacrimal and zygomatic bones
Which species have an orbital ligament?
Carnivores and pigs
List the different ocular muscles
Dorsal, ventral, medial and lateral rectus muscles. Dorsal and ventral oblique muscles. Retractor bulbi muscle.
What is the other term for true eyelids?
Where do the upper and lower eyelids meet?
At the commissures
True or false: the third eyelid is a true eyelid?
False - it is a fold of conjunctiva supported by T-shaped cartilage
What type of muscle usually retracts the third eyelid?
What does the lacrimal apparatus produce?
Lacrimal fluid (tears) for protection and corneal nutrition
Which glands are part of the lacrimal apparatus?
Lacrimal gland and gland of the third eyelid
Which muscle draws the eye back caudally?
Retractor bulbi muscle
Which muscle does not originate in the area of the optic canal? Where does it originate?
Ventral oblique muscle - it originates from the ventromedial orbital wall
What is the purpose of the trochlea for the dorsal oblique muscle?
Acts as a pully to change the direction of the draw muscle
What is the presumed function of the oblique muscles?
To resist axial rotation of the eyeball during movement
What nerves innervate the ocular muscles?
Oculomotor - dorsal, medial, ventral rectus muscles. Ventral oblique and part of retractor bulbi.
Trochlear - dorsal oblique
Abducens - lateral rectus, retractor bulbi
What is deviation of one eyeball called?
What is the preposed function of the tapetum?
To reflect light back into the retina to increase sensitivity of the eye in low light conditions