Anatomy of the Eye Flashcards
What are the 3 layers of the eyeball?
- Outer fibrous layer
- Middle vascular(pigmented) layer
- Inner layer
Describe the components of the fibrous coat?
- Sclera – white fibrous layer covering 5/6 of the eye
- Cornea – transparent structure forming the anterior 1/6 of the outer coat
Describe the components of the eyebeall?
- Choroid
- outer pigmented and inner vascular and invests 5/6 of the eye
- Nourishes the retina and darkens the eye. - The ciliary body
- Thickened portion of the vascular coat between choroid and iris
- Consists of ciliary ring, ciliary processes and ciliary muscles - Iris
- Thin contractile circular pigmented diaphragm with central aperture the pupil
What is the internal nervous coat?
Consists of the retina
> outer pigmented
> inner nervous
Posterior part – photosensitive
Anterior part – not photosensitive
What is the optic disc?
- Consists of optic nerve fibres
- formed by axons of ganglion cells which connect to rods and cones
- Has no receptors hence not photosensitive
Name the 3 tunics of the eye?
- The outer Fibrous coat
- inelastic coat
- transparent cornea (anteriorly)
- opaque sclera (posteriorly). - The middle vascular
pigmented coat:
- The Uvea: choroid, ciliary body and iris - The inner nervous coat
- The Retina, extends forwards to within 6 mm of the limbus.
What are the components of the outer coat?
- Sclera- opaque (white)
- Cornea - transparent
What is the sclera?
Dense fibrous tissue
- opaque + white
What pierces the sclera?
- Optic nerve
- the sclera is fused with the dural sheath of the nerve - Venae vorticosae
- ciliary arteries, nerves and veins
NB. At the lamina cribrosa is where these vessels pierce the sclera
What is the junction between the sclera and cornea called?
What is found here?
Corneoscleral junction or limbus
- scleral venous sinus is found here
What is the cornea?
Location?
Function?
The transparent cornea is largely responsible for the refraction of the light entering the eye
- It is in contact posteriorly with the aqueous humor.
Describe the blood supply of the cornea?
How is it nourished?
The cornea is avascular and devoid of lymphatic drainage
- It is nourished by diffusion from the aqueous humor and from the capillaries at its edge.
Describe the nerve supply of the cornea?
Long ciliary nerves from the ophthalmic division of the trigeminal nerve
What is the function of the cornea?
- The cornea is the most important refractive medium of the eye.
- the tear film maintains the environment for the corneal epithelial cells
Describe cornea transplants?
• Transplants: common & successful
- no blood vessels so no antibodies to cause rejection
• Nourished by tears & aqueous humor
What is the limbus?
Junction between cornea and sclera
What is the function of the limbus.
- Nourishes peripheral cornea
- Assists in corneal wound healing
- Pathway for aqueous outflow (contains trabecular meshwork and canal of schlemm)
Describe the transition zone of the limbus?
• anterior: bowman’s terminal-
Descemet’s terminal
• posterior: scleral spur / iris root
• 1.5~2.0mm width
What does the limbus look like?
• Semitransparant zone
• White sclera
What is the conjunctiva?
Where is it?
is a translucent mucous membrane which lines the posterior surface of the eyelids and anterior aspect of the eyeball (up to the edge of the cornea)
What does a normal conjunctiva look like?
Pink
Smooth
Thin
Transparent
• There are normally large deep blood vesells that run vertically
What is formed at the reflections between the eyeball and eyelid?
conjunctiva forms two sacs
- the superior and inferior fornices.
What are the functions of the conjunctiva?
- The conjunctiva helps lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland
- it also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye
What are the parts of the conjunctiva?
- Bulbar conjunctiva.
- Palpebral conjunctiva.
- Forniceal conjunctiva.
Describe the palpebral conjunctiva?
It is richly vascular, extremely thin and strongly bounded to the tarsal plate
The palpebral conjunctiva is divided into?
- Marginal
- Tarsal
- Orbital
Describe the marginal palpebral conjunctiva?
- Extends from the lid margin to about 2mm back of the lid upto the sulcus subtarsalis
- Actually a transitional zone between skin and the conjunctiva proper
- Lacrimal puncta open in the marginal zone
Describe bulbar conjunctiva?
- It is transparent and lies loose over the
underlying structures and thus can be moved easily - It is separated from the anterior sclera by episcleral tissue and tenon’s capsule
Describe the blood supply of the conjunctiva?
•Arteries supplying the conjunctiva are derived from 3 sources. They are:
1. Marginal arcade of the eyelid
2. Peripheral arterial arcade of the eyelid
3. Anterior ciliary artery
• The palpebral conjunctiva and the fornices are supplied by branches from the marginal and peripheral arcades of the artery
Describe the venous drainage of the conjunctiva?
- The veins from conjunctiva drain into the venous plexus of eyelids which in turn drain into the superior and inferior ophthalmic veins.
- A cicumcorneal zone of limbus drain into the anterior cilliary veins
Describe the lymphatic drainage of the conjunctiva?
- lateral side drain into the periauricular lymph nodes
- medial side drain the submandibular lymph nodes
Describe the nerve supply of the conjunctiva?
•BULBAR CONJUNCTIVA:
- long ciliary nerve
- Naso ciliary nerve
- Ophthalmic division of trigeminal nerve
•SUP.PALPEBRAL AND FORNICEAL CONJUNCTIVA:
-Frontal and lacrimal branches of ophthalmic division of trigeminal nerve
What are clinical conditions involving the conjunctiva?
- Conjunctivitis
- Malignant lymphoma
- Conjunctival papilloma
The middle layer (tunica media) of the eye comprises of what 3 structures?
•Choroid
•Ciliary body
•Iris
What do the structures of the middle layer of the eye make?
The choroid, ciliary body and iris together form the uveal tract
- this layer contains blood vessels
Note: Pupil is the small opening in front of it
What is the choroid?
- is the vascular layer of the eye containing connective tissues
- lying between the retina and the sclera
- It is composed of an outer pigmented layer and an inner highly vascular layer
What is the function of the choroid?
Provides oxygen and nourishment to the outer layers of the retina
What structure does the choroid help form?
The uveal tract
- along with the ciliary body and iris
What is the blood supply of the choroid?
are branches of the ophthalmic artery and enter the eyeball without passing with the optic nerve.
What is the ciliary body?
Relations?
- ciliary body is continuous posteriorly with the choroid, and anteriorly it lies behind the peripheral margin of the iris
- is composed of the ciliary ring, the ciliary processes, and the ciliary muscle