The Orbit and Eye - 1 Flashcards
Which 2 holes lie within the sphenoid bone?
The optic foramen and the superior orbital fissure.
What is the roof of the orbital cavity formed by?
It is formed by the orbital process of the frontal bone.
On the lateral side what is the wall of the orbital cavity formed by?
It is formed by the zygomatic bone.
In the floor of the orbit, what is the dominant bone?
The maxilla.
Which bones form the medial part of the orbital cavity?
The small lacrimal bone, part of the ethmoid bone and an insignificant contribution from the palatine bone to the posterior portion of the medial wall of the orbital cavity,
Describe the medial and lateral walls of the orbital cavity.
The medial wall lies in the sagittal plane. The lateral wall diverges outwards as it is traced forwards.
Taking a cross-section of the eyelids, what can we see going from the outside to the inside?
We can see:
- skin
- sphincter muscle called obscularis oculi
- fibrous tarsal plates
- conjunctiva
There is no subcutaneous fat beneath the skin of the eyelids.
Where are the eyelashes found?
They are found at the edge of the eyelids.
What are the tarsal plates for?
Tarsal plates are made of fibrous tissue and they function to stiffen the lids.
Describe the inferior and superior tarsus.
The inferior tarsus is attached to the lower orbital margin and the superior tarsus is larger.
What is adherent to the deep surface of the tarsal plates?
Conjunctiva.
How are the tarsal plates attached to the orbital margin?
Palpebral fascia form an orbital septum. This orbital septum attaches each of the tarsal plates to the orbital margin.
What is the path of the fibres of the levator palpebrae superioris muscle?
The fibres enter the upper eyelid and they attach to the upper part of the tarsal plate. They also extend beyong the tarsal plate and they can intermingle with the fibres of the orbicularis oculi muscle further anteriorly.
What 2 types of fibres are found in levator palpebrae superioris?
There are voluntary fibres and involuntary fibres.
The voluntary fibres are supplied by the 3rd cranial nerve.
The involuntary fibres are supplied by the sympathetic neurones.
What happens when the voluntary and involuntary fibres of the levator palpebrae superioris muscle act together?
They raise the upper eyelid.
What is the function of the medial and lateral palpebral ligaments?
They attach the tarsal plates to the sides of the orbit.
Describe the medial palpebral ligament.
This is strong and lies in front of the lacrimal sac.
What is the medial lacrimal sac?
This is the apparatus that collects tears.
What are the 2 types of glands that are found in the lids?
Ciliary glands and lacrimal glands.
Where are the ciliary glands?
They are placed immediately behind the roots of the eyelashes.
What happens when the ciliary glands become infected?
They form a red swelling on the lid margin called a stye.
Where are the tarsal glands found?
They are found on the deep surface of the tarsal plates.
Where do the ducts of the tarsal glands open onto?
They open onto the the lid margin.
Where do the sensory nerves to the upper lid come from?
They come from the ophthalmic division of the trigeminal nerve.
Which branches of the opthalmic division of the trigeminal nerve go to the upper lid?
- palpebral branch of the lacrimal
- supraorbital
- supratrochlear
- infratrochlear
Which nerve supplies the lower lid?
The infraorbital nerve which is a branch of the maxillary division of the trigeminal nerve.
What is the orbicularis oculi?
This is a large muscle that surrounds the eye and it consists of several parts.
What are the 3 parts of the orbicularis oculi muscle?
- orbital part
- palpebral part
- lacrimal part
Describe the orbital part of the orbicularis oculi muscle.
- large and wide
- fibres arise from the medial palpebral ligament and the surrounding bone, fibres sweep around the forehead, temple and cheek and return to the medial point of origin.
Describe the palpebral part of the orbicularis oculi muscle.
- smaller than orbital part
- arises from medial palpebral ligament
- loops around the eye
- found entirely within the eyelids
Describe the lacrimal part of the orbicularis oculi muscle.
- this is small
- arises from the bone behind the lacrimal sac
- passes laterally into the eyelids.
- runs behind the lacrimal apparatus therefore function will be clearer when studying the lacrimal apparatus.
What does the conjunctive line?
The conjunctiva lines the deep surface of the eyelids and the exposed surface of the eye.
What is the conjunctiva continuous with?
With the anterior epithelium of the cornea.
What are fornices?
Above and below where the palpebral parts of the conjunctiva are reflected onto the eyeball, there are recesses called fornices.
In what condition is the conjunctiva maintained at all times?
The conjunctiva remains moist at all times.
What is the palpebral fissure?
This is the elliptical space between the 2 lids.
What is the palpebral fissure named at its extremities?
The medial and lateral canthus.
Which 2 structures lie in the medial canthus?
- a small red mass called the lacrimal caruncle
- a semilunar fold called the plica semilunaris
- this is all that remains of the 3rd eyelid
Where does the lacrimal gland lie?
It mainly lies in the orbit but there is a small palpebral part that extends into the upper lid.
How many ducts open into the upper fornix?
About 12 or so ducts open into the upper fornix.
What is the lacrimal fluid produced by and what is its path?
Lacrimal fluid is produced by the lacrimal gland and and it flows towards the medial end of the conjuctival sac.
What is the name of the small duct within the medial end of each eyelid?
The lacrimal canaliculus.
What it the name given to the opening of each of the lacrimal ducts?
The opening of each of the ducts is called the lacrimal punctum.
What does the lacrimal punctum open at?
It opens at a swelling or lacrimal papilla on the medial end of each lid margin.
What structures are tears drawn through?
They are drawn through the lacrimal canaliculi and into the lacrimal sac.
Where does the lacrimal sac lie?
It lies in a cavity in the medial wall of the bony orbit.
From the lacrimal sac what is the is the path of the tears?
Tears drain downwards through the nasolacrimal duct and then into the cavity of the nose.
What type of fibres initiate secretion of the lacrimal gland?
The parasympathetic fibres.
What happens when there is contraction of the orbicularis oculi muscle?
Because the orbital part and the palpebral part lie on either side of the lacrimal sac which lies on the medial side of the orbit, contraction of the orbicularis oculi muscle squeezes the lacrimal sac.
When are tears drawn into the lacrimal sac?
Tears are drawn into the sac as the muscle relaxes.
Where do tears go from the lacrimal sac?
Tears go to the nasolacrimal duct which opens onto the lateral wall of the nose.
What is the palpebral part of the orbicularis muscle responsible for?
It is responsible for gently closing the eyes during sleep and when blinking.
What is the function of the orbital part of the orbicularis oculi muscle?
The orbital extends beyond the eyelids and it screws up the eyes for added protection.
What are the 3 coats the wall of the eye is composed of?
- Outer layer – sclera and retina
- Middle layer – choroid
- Inner layer – Retina
What is the outermost layer of the wall of the eye?
The cornea – this is transparent in front and dense and white behind.
What is the cornea continuous with at its margin?
It is continuous with the conjunctiva at its margin.
What is present on the front of the cornea?
A layer of epithelium.
What is present on the posterior surface of the cornea?
A posterior limiting lamina. This is elastic.
What happens to the posterior limiting lamina at its periphery around the posterior margin of the cornea?
This breaks up into bundles with tiny spaces between them and it becomes a permeable structure called the pectinate ligament of the iris.
What is the significance of the permeable pectinate ligament of the iris?
These spaces allow aqeous humour from the anterior chamber of the eye to pass into the venous sinus in the sclera.
This system allows aqueous humour to be filtered back into the venous system.
What happens if there is a blockage of the system that drains the anterior chamber of the eye?
Blockage of this system produces a marked increase in fluid pressure in the eye and this leads to a damage to side and this condition is known as glaucoma.
Describe the sclera.
It is dense.
Where does the optic nerve enter the sclera?
The optic nerve enters the sclera about 3mm to the nasal side of the posterior pole of the sclera.
What is the optic nerve covered with when it enters the sclera?
It is covered with all 3 layers of the meninges.
What happens to the 3 layers of meninges that cover the optic nerve?
They fuse with the sclera and the nerves pass through the holes in the sclera together with the blood vessels.
Aside from the optic nerve what other nerves pierce the sclera?
The short and long ciliary nerves along with some blood vessels also pierce the sclera.
What is the middle coat of the eye formed by?
It is formed by the iris in front and the choroid behind.
The ciliary body lies between the 2
What part of the ciliary body is the iris attached to?
The iris is attached to the anterior surface of the ciliary body.
What part of the ciliary body is the lens attached to?
To the inner ciliary process.
What is the outer part of the middle coat of the eye composed of?
It is composed of the ciliary muscle.
What part of the eye does the iris lie in?
The iris lies near the front of the eye.
What lies anterior to the iris?
The cornea.
What lies posterior to the iris?
The lens.
Where is the anterior chamber of the eye?
Between the cornea and the iris.
Where is the posterior chamber of the eye?
Between the iris and the lens.
What do the anterior chamber and posterior chamber contain?
They both contain watery aqeous humour.
How are the anterior chamber and posterior chamber continuous?
They are continuous through the aperture of the iris.
Where is the aqeous humour formed?
In the anterior portion of the ciliary process.
How is aqeous humour filtered off?
It is filtered off into the venous sinus of the sclera via the anterior chamber of the eye.
What is the function of the suspensory ligament of the lens?
It raises the posterior part of the ciliary process into radial ridges.
The suspensory ligament of the lens attaches to the radial ridges.
What is the periphery of the iris connected to?
It is connected to the pectinate ligament and the anterior part of the ciliary body.
What gives the iris colour?
The iris contains pigment that gives it colour.
What is the aperture of the iris called?
The aperture of the iris is called the pupil.
What causes the pupil to vary in size?
The pupil varies in size according to the light conditions in the surrounding environment.
What happens to the pupil in a dark room?
It is dilated.
What happens to the pupil in a bright room?
It is constricted.
What kind of nervous impulses are important for dilating the pupil?
Sympathetic impulses.
What kind of nervous impulses are important for constricting the pupil?
Parasympathetic impulses.
What are the 2 kinds of muscle fibres that govern the diameter of the pupil?
- sphincter pupillae
- dilator pupillae
Describe the sphincter pupillae muscle.
- consists of circular fibres that are arranged around the pupillary margin of the iris
- activated by paraysmpathetic fibres which enter the eye through the short ciliary nerves
Describe the dilator pupillae muscle.
- composed of muscle fibres that radiate outwards from the pupillary margin of the iris.
- supplied by sympathetic neurones
- most of these arrive in the long ciliary branches of the nasociliary nerve.
Where is the ciliary muscle?
This lies within the ciliary body.
What does the ciliary muscle look like on microscopic examination?
It has radiating/ meridional fibres and circular muscle fibres as well.
Where do the radiating fibres of the ciliary muscle arise from?
They arise from the sclera spur close to the point where the sclera and the cornea join.
These fibres radiate back into the ciliary process.
What do the circular muscle fibres of the ciliary fibres form?
They form a muscular ring near the periphery of the iris.
What is the nerve supply to the ciliary muscle?
The ciliary muscle is supplied by parasympathetic fibre.
What is the shape of the lens when you are looking into the distance?
The lens is fairly flat when you are looking into the distance.
What allows the lens to maintain a flattened shape?
The suspensory ligament pulls on the periphery of the lens to maintain a flattened shape.
What happens when we have contraction of the ciliary muscle?
- the suspensory mechanism of the lens is drawn forwards.
- tha diameter of the rim to which the suspensory ligament is attached is reduced.
- the peripheral pull of the suspensory ligament on the lens is reduced
- the lens takes up its natural resting fat shape.
What is the shape of the lens when looking at an object at close quarters?
It has a thick fat state.
