Ophthalmology Anatomy Flashcards
What is the function of tears?
- Lubricate the eye ball and keep them moist
- Flush out foreign bodies
- Have sugar and oxygen in them to help supply the cornea
What is the path of tears?
- Across cornea
- Into puncta lacrimalia – hole in the lower lid
- Cannaliculi
- Lacrimal sac
- Nasolacrimal duct which empties into the Inferior meatus of lateral wall of nasal cavity
- Then is swallowed
What is the nervous supply of the lacrimal apparatus?
CN VII Facial (parasympathetic)
- Greater petrosal nerve carries presynaptic parasympathetic nerves to synapse at the pterygopalatine ganglion.
- Postsynaptic parasympathetic fibres will be distributed to V2 and then V1, specifically the lacrimal nerve.
What makes up the uvea?
Iris, choroid and ciliary body
Explain changes in the eye for near and far vision:
- Near vision: ciliary muscles contract > suspensory ligaments relax > lens become fatter and refract less (Accomodation)
- Distance: the suspensory ligaments contract > lens becomes narrower and wider for greater refraction
What is the nerve supply for intraocular muscles?
CN III Occulomotor
What are the intraocular muscles?
- Pupillary muscles (constrictor/sphinctor pupillae and dilator pupillae)
- Muscles of ciliary body
What kind of nerve palsy does this patient have?
Right CN III Occulomotor palsy.
Down and out becuase lateral retus and superior oblique are unopposed, and eyelid is drooping (ptosis) as LPS affected
Patient complains of vertical double vision. What type of nerve palsy does this patient have, especially if she also had a head tilt?
Left CN IV Trochlear nerve palsy.
Affected side will be up and in, as superior and medially pulling muscles are unopposed. (No superior oblique muscle pulling down and out)
On examination, when looking medially on the affected eye, it will go up
This patient comes in complaining of horizontal double vision. What kind of nerve palsy do they have?
Right CN VI Adbucens palsy
Becuase medial rectus is unopposed.
On examination, weak abduction on the affected eye
What 3 things are fundamentally contained within the brain and can contribite to raised ICP?
Brain, blood and CSF. So if the brain expands or blood/CSF leaks then raised ICP can occur
What is the route of aqueous humour circulation in the eye?
- Secreted from the ciliary body
- Flows over the anterior surface of the lens
- Passes through the pupil
- Drains into the trabecular meshwork into the Canal of Schlem
What are the:
- Falx cerebri
- Falx cerebelli
- Tentorium cerebelli
All extensions of the dura mater.
- Falx cerebri: separates the two cerebral hemispheres
- Falx cerebelli: separates the two hemispheres of the cerebellum
- Tentorium cerebelli: separtes the cerebrum from the cerebellym
Dural venous sinus
Spaces between the layers of dura mater filled with venous blood
Where is the CSF predominantly in the brain and spinal cord?
In the subarachnoid space
Where is CSF produced and then absorbed?
- Produced in the choroid plexus of the ventricles
- Absorbed into the dural venous sinuses via the arachnoid granulations
Where are the third and fourth ventricles located?
- 3rd - in between the thalami (so very thin)
- 4th - Between pons/medulla and cerebellum
What connects the third and fourth ventricles?
Cerebral aqueduct (via interventricular foramen)
What is the route of circulation of CSF?
- Chroid plexus (of lateral ventricles)
- Interventricular formane > 3rd Ventricles
- Cerebral aqueduct > 4th ventricles
- Then either into central canal of spinal cord or median/lateral apertures > subarachnoid space
- Reabsorbed via arachnoid villi/granulations into superior saggital sinus
Why, anatomically, can raised ICP cause visual problems?
Becuase optic nerves are actually CNS tracts covered in meninges, so raised ICP can transmit along subarachnoid space and compress the optic nerve and central retinal vessels.
What classic clinical scenario in ICP can the oculomotor nerve become damaged?
Raised ICP can compress/stretch oculomotor nerve if medial temporal lobe expands and herniates through tentorial notch
Why does a fracutred zygoma tend to medially rotate with the eye?
Becuase the suspensoruy ligament has been displaced
Why might there be sensory loss of the skin in the mid face region following a zygoma fracture?
Due to damage of the infraorbital NVB within the infraorbital canal
What is the general sensory supply of the face?
-
CN V1 (ophthalmic nerve) supplies (purple):
- the upper eyelid
- the cornea
- all the conjunctiva (anterior structures of the eye)
- the skin of the root/bridge/tip of the nose
-
CN V2 (maxillary nerve) supplies mid-face (blue):
- the skin of the lower eyelid
- the skin over the maxilla
- the skin of the ala of the nose
- the skin/mucosa of the upper lip
-
CN V3 (mandibular nerve) supplies:
- the skin over the mandible and temporomandibular joint
The nose has a dual nerve supply, what is it?
- Tip of the nose: CN V1
- Wings of the nose: CN V2
What does the ‘blink’ corneal reflex test? What is the anatomy behind this?
“CNS connections” between CN V & CN VII
- CN V (1) carrys the afferent sensory fibres to the pons
- Then CN VII carries the efferent motor fibres back to the obicularis oculi which causes us to scrunch our eyes as reflex
What is the route for CNS sympathetic pre and post-synaptic axons for the eye?
- Descend in the spinal cord
- Exit the spinal cord in T1 spinal nerve
- Ascend within the sympathetic trunk
- Synapse in the superior cervical sympathetic ganglion
- The postsynaptic sympathetic axons then enter the internal and external carotid nerve and pass onto the surface of the internal & external carotid arteries respectively where they form a plexus to be carried to the organs of the head on the surface of the branches of ophthalmic artery into the orbit
Where is the cervical part of the sympathetic trunk?
In the the retropharyngeal space
Which cranial nerves have parasympathetic components?
CN III, VII, IX and X
Which ganglia are associated with the cranial nerves with parasympathetic components?
- CN III
- Ciliary ganglion (eye)
- CN VII
- Pterygopalatine ganglion (Lacrimal gland and nasal mucosa)
- Submandibular ganglion (submandibular adn sublingual glands)
- CN IX
- Otic ganglion (parotid gland)
Which ganglion does parasympathetic fibres of CN III Oculomotor synapse at?
Ciliary ganglion
What do the superior and inferior branches of CN III each supply?
- the superior branch: supplies SR & LPS
- the inferior branch: supplies MR, IR & IO & the ciliary ganglion (parasympathetic fibres)
What is the vestibulo-ocular reflex, and what connections does it involve?
- Turns the eyes in the opposite direction to a head movement (to stabilise the gaze on an object during head movements)
- CNS connections between CN VIII & CNs III, IV & VI
What is the oculocardiac reflex, and what connections does it involve?
- Reflex bradycardia in response to tension on the extraocular muscles or pressure on the eye
- CNS connections between CN V1 & CN X
What are the sympathetic and parasympathetic effects on the eye?
What kind of muscle fibres does levator palpebrae superioris contain?
Smooth and skeletal muscle fibres
What is the name for a non-physiologically dilated pupil?
Mydriatic pupil
What is the arranement of dilator pupillae fibres arounf the iris?
- Mobile insertion around the internal circumference of the iris
- Fixed origin around the external circumference of the iris
What is the term for a non-physiologically constricted pupil?
Miotic pupil
What is the arrangement of sphincter pupillae fibres?
- arranged encircling all around the internal circumference of the iris
What are the afferent and efferent nerves involved in the pupillary light reflex?
- special sensoruy afferent limb is the ipsilateral CN II (optic)
- the motor efferent limb is the bilateral CN III (oculomotor) - direct and consensual response
What are the 3 components of the accomodation reflex?
- 1) Bilateral pupillary constriction (CNs III)
- Focus light rays
- Prevent diverging light rays from hitting the periphery of the retina and resulting in a blurred image.
-
2) Bilateral convergence - medial rotation of both eyes (CNs III)
- Simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision
-
3) Bilateral relaxation of the lens
- Lens becomes spherical due to contraction of the ciliary muscles (CNs III)
What are the 3 different types of teas in lacrimation?
- Basal tears
- clean/nourish & hydrate the avascular cornea
- Reflex tears
- Extra tears in response to mechanical or chemical stimulation
- Emotional tears
- (happy, sad or frightened tears)
What are the afferent and efferent limbs of reflex tears?
- afferent limb of the reflex is CN V1 (the ophthalmic nerve) from the cornea/conjunctiva
- Efferent limb is parasympathetic axons originating from CN VII (the facial nerve)
What are the four neurones involved in the light reflex?
-
1st neurone: Connects the photoreceptors in retina with the pre-tectal nucleus in the midbrain via the optic nerve.
- Decussate in chiasm.
-
2nd neurone: Connects pretectal nucleus to both the ipsilateral and contralateral Edinger Westphal nuclei
- this is why a unilateral light response evokes bilateral and symmetrical pupillary constriction (the direct and consensual reflexes
-
3rd neurone: Connects the Edinger Westphal nuclei to the ciliary ganglion.
- In the orbit, the parasympathetic fibres pass in the inferior division of the third nerve to reach the ciliary ganglion (only parasympathetic fibres synapse here)
- 4th neurone: Leaves the ciliary ganglion and passes with the short ciliary nerves to innervate the sphincter pupillae
What is the near triad?
1) increased accommodation
2) convergence of the visual axes
3) constriction of the pupils.
