Session 9: Self-Study Flashcards
Outline the process by which aqeuous humour is produced and drained; how might its drainage be impeded?
Ciliary process -> posterior chamber -> anterior chamber via the pupil -> canal of Schlemm via the irido-corneal angle and the trabecular meshwork -> venous circulation.
Can be impeded by either degeneration of the trabecular meshwork or by a narrow irido-corneal angle.
Why is it not possible to lose a contact lens behind the globe of the eye?
Because the conjunctivae reflects off the sclera to line the inner surface of the eyelid.
What is papillooedema and how is it caused?
Swelling of the optic disc due to raised intracranial pressure.
Patients may report blurring of vision, increased size of blind spot, peripheral or complete visual field loss.
Why do patients report blurring of vision in both eyes in papilloedema?
Because the optic canal is continuing with the meningens so raised ICP leads to swelling of the optic discs. This means that both will be exposed to the same degree of external pressure.
How is papilloedema different from optic disc cupping?
Optic disc cupping is due to increased intra-ocular pressure and leads to a decreased optic disc to optic cup ratio.
Papilloedema causes (depending on its severity) a swelling of the optic disc and make its margins blurred. Raised ICP does not cause cupping.
(The optic cup is usually a central depression of the optic disc)
Outline what happens in the accommodation reflex. What is presbyopia?
Pupil constriction
Focus of both eyes
Contraction of the ciliary muscles causing the suspensory ligament to be less taught and fattens the lens.
In presbyopia the lens is more rigid and can’t fatten as easily.
Outline the direct and consensual light reflexes. Include the relevant nerves and anatomical structures.
Light is shone into left eye. Sensory afferents from left retina (CN II) goes to the brainstem and the pretectal nucleus. Here the pretectal nucleus is connected with both the left and right Edinger-Westphal nuclei. Parasympathetic fibres from the EDW leaves the brain stem (both left and right) and run as part of the CN III. It passes via the ciliary ganglion and then to reach the sphincter pupillae of the iris.
The direct light reflex will be the constriction of the left eye where light has been shone into.
The consensual light reflex will be the constriction of the right eye.
A patient presents to her GP with a lump in her left eyelid. She is diagnosed with a Meibomian cyst.
What is a meibomian cyst and how does this differ from a stye?
Meibomian cyst is due to a blocked meibomian gland (tarsal) within the tarsal plates of the eyelid. These are usually deep to styes.
A stye is an infection of a sebaceous gland situated at the base of the eyelash.
Explain why these specific clinical signs have arisen.
Prolapse of the contents of the orbit into the maxillary sinus. Ocular muscles become trapped (especially inferior rectus). This prevents elevation of the eyeball so when the patient tries to look up they won’t be able to.
There’s reduced sensation to touch over his right cheek because the infraorbital nerve (maxillary branch of trigeminal nerve) (via infraorbital foramen) has been damaged which supplies sensory.
Two weeks later the patient attends an outpatient follow-up appointment for a review by opthalmology. His diplopia has resolved but he reports excessive tearing of the right eye with the tears constantly running over his lower eye lid (epiphora).
Why do you thin he has developed epiphora?
This injury can lead to injury of the lacrimal canaliculi and the nasolacrimal duct.
If there is any impeding to drainage of tears there can be overspill and excessive tearing.
This should be referred to a specialist.
During fundoscopic examination of the normal eye:
Which side of the fundus (nasal or temporal) would you find the blind spot?
Nasal side
During fundoscopic examination of the normal eye:
What structure gives rise to the blind spot?
The optic disc.
Why is the central artery to the retina termed an end artery, what are the consequences should this become occluded?
Because it is the only arterial supply to the inner retinal area.
An obstruction here can cause instant, painless loss of vision.
Explain how an infection involving the orbit or mid-area of the face could spread into the interior of the cranial cavity.
Vein draining the orbits like the ophthalmic veins have anastomotic links with the facial vein but also with the cavernous sinus.
This can lead to intracranial infection.
Why might a lesion of the ophthalmic division of the trigeminal nerve be dangerous to the eye?
The ophthalmic division of the trigeminal nerve provides sensation to the conjunctiva and the cornea. This means that latent varicella zoster from chicken pox can be reactivated and involve the ophthalmic division. This can be sight threatening.
Right eye is affected. Abducens nerve is paralysed causing lateral rectus not able to abduct the eye.
It can be vasculopathic, tumour or general increased intracranial pressure.
