Session 5 - Group work questions Flashcards
How is a meibomian cyst different from a stye?
Meibomian cyst is due to a blocked tarsal gland which lies just posterior to the eyelash within the lids. A stye is an infection of a sebaceous gland situated at the base of an eyelash. The glands secrete an oily material that readily form a cystic swelling if their drainage is blocked.
What two nerves can be damaged to cause ptosis?
The oculomotor nerve or sympathetic nerve fibers
What are the effects on lacrimation of damaged obicularis oculi?
The obicularis oculi is the sphincter of palpebral fissure. Upon contraction, tears are forced from the lateral aspect of the fissure where they are secreted by the lacrimal gland. Damage to the muscle causes the eyelid to fall away from the eye. A stagnant pool of tears will then form in the lower fornix, which wll eventually spill over the paralused lower lid. Infection may occur in this pool and the resultatnt conjunctiviitis will increase the secretion of tears with further weeping. APralysis of the obicularis oculi will result in the lack of protection of the cornea which will dry out and ulceratie.
A patient presents with ptosis, a dilated pup and an eyeball that looks down and laterally. Explain.
Ptosis is due to sympathetic or oculomotor cranial nerve problems, The dilated pupil may be due to loss of parasympathetic control/
Damage to oculomotor nerve and parasympathetic nerve fibers.
Which side of the fundus would you normally find the blind spot in a normal eye?
It lies on the nasal side of the fundus. Blind spot is where the fibres of the optic nerve pass through the retinal layers. Pale are seen on fundoscopy as the optic disc
Patient cannot turn his right eye to the right side. What nerve is affected?
ABducent nerve which supplies the lateral rectus.
Why is the central artery to the retina called an end artery?
Only arterial supply to the retina. Thrombosis before it divides can cause instant blindness due to ischaemia of all tissues distal to the blockage.
Explain why thrombophlebitis of the facial veins may spread into the interior of the cranial cavity?
Facial vein has connection with the cavernous sinus through the opthalmic vein. Usually the blood in the facial vein drains inferiorly, but the valveless facial vein may allow blood to enter cavernous sinus. In patients with thrombophlebitis of the facial, inflammation of the vein with secondary thrombus formation may pass into the intracranial system
What is the cavernous sinus?
A venous channel of the dura mater covering the brain
Why might a lesion of the opthalmic division of the trigeminal nerve be dangerous to the eye?
A lesion of the ophthalmic division will result
in the cornea being insensitive to touch
and so specks of dust or grit will not be
felt in the eye. This quickly leads to
corneal ulceration and scarring which if not
controlled may cause blindness. It is for
this reason that after anaesthetizing an
eye, it is most important to cover the
patient’s eye to prevent collection of more
foreign material.
What is ecchymosis?
The term refers to the discouloured patch produced by extravasation of blod into the subcutaneous tisues
Which division of the common carotid artery supplies the area of the skin of the forehead above the eye?
Superficial temporal artery which is one of the terminal branches of the external carotid, the other being the maxillary artery. The terminal nbranches of the opthalmic artery also supply the skin of the forehead above the eye.
In which layer of the scalp would you find blood vessels supplying it?
The blood vessels of the scalp run in the dense subcutaneous layer between the skin and the epicranial aponeurosis. The way they are held by the connective tissue means that they tend to remain open when severed/lacerated - thus, bleeding from the scalp is profuse
Blood and fluid collecitng in the epicranial aponeurosis does not track into the subtemporal or the occipital regions of the skull, but passes forward into the orbital region
Tracking of fluid into the subtemporal region is
prevented because the epicaranial aponeurosis is
continuous with the temporal fascia which is
attached to the zygomatic arch. Tracking into the
occipital region is prevented because the occipitalis
muscle is attached to the occipital bone and the
mastoid process. Thus fluid enters the orbital
region and collects in the upper eyelid because
the frontalis muscle inserts into the skin and
subcutaneous tissue and does not attach to the
bone; some fluid may also enter the lower eyelid.
