Session 5: The Eye Flashcards
How is a meibomian cyst different from a stye?
A meibomian cyst is due to a blocked tarsal gland which lie posterior to the eyelash. A stye is an infection of the sebaceous gland situated at the base of the eyelash
the glands secrete an oily material that readily forms a cystic swelling if their drainage is blocked
Explain 2 different causes of a drooped eyelid?
- damage to the sympathetic fibres from the superior cervical ganglion (control the superior tarsal muscle) will cause partial ptosis
- Damage to the oculomotor nerve will lead to a greater degree or complete ptosis. Is also associated with deviation of the eyball to down and out position.
What are the effects of lacrimation of a damaged orbicularis oculi?
Upon contraction (blinking) tears are swept across the eye from the lateral part to the medial part - allows lubrication and removal of potential foreign bodies. Damage to orbicularis oculi may compromise the ability to close the eye and affect ability to lubricate and protect surface of eye. Paralysis of this muscle will result in lack of protection of cornea which will dry out and ulcerate.
A patient has ptosis, a dilated pupil and an eyeball that is deviated down and laterally what is the cause?
Lesion of oculomotor nerve. Innervates levator palpebrae superioris and motor innervation to 4 of the extraocular muscles. Parasympathetic fibre which innervate the pupil causing it to constrict travel alongside the oculomotor nerve.
What is Horner’s Syndrome?
Injury to the sympathetic fibres to the eye would cause a partial ptosis and a constricted pupil and there would be no deviation of the eyeball.
During examination of the normal eye, which side of the fundus would you find the ‘blind spot’?
The blind spot lies on the nasal side of the fundus. It is where fibres of the optic nerve pass through the retinal layers - optic disc.
Optic disc is also the point of entry of the retinal artery.
IF a patient complains of double vision on lateral gaze of his right eye which nerve is likely to be affected?
Abducens which supplies lateral rectus.
Why is the central artery to the retina termed as an end artery?
its the only arterial supply to the retina. It is a branch of the ophthalmic artery. A blockage before the central retina artery divides into small branches can cause instant, painless loss of vision due to ischaemia of all tissues distal to the site of blockage.
Explain why thrombophlebitis of the facial veins my spread into the interior of the cranial cavity?
Facial vein is connected to the cavernous sinus via the ophthalmic vein. Usually the blood drains inferiorly but because the facial vein has no valves, blood may pass in the opposite direction and may enter the cavernous sinus. With secondary thrombus formation blood clots may pass into the intracranial venous system
why might a lesion of the ophthalmic division of the trigeminal nerve be dangerous to the eye?
Will result in the cornea being insensitive to touch and so dust or grit will not be felt.
Therefore after anaesthetizing an eye its most important to cover the patient’s eye to prevent injury from foreign material.
What does ecchymosis mean?
Black-blue discolouration (bruise) produced by extravasation of blood into subcutaneous tissues.
Which division of the common carotid artery supplies the area of the skin of the forehead above the eye?
The superficial temporal artery and the terminal branches of the ophthalmic artery supply the skin above the forehead.
in which layer of the scalp would you find the blood vessels supplying it?
The dense connective tissue between the skin and epicranial aponeurosis.
If the wound runs deep and involves the aponeurosis the occipto frontalis muscle pulls and creates tension that causes the wound to gape.
Why is it that following a blow to the head, bleeding as a result of the injury can pass forward into the orbital region (causing a black eye) but does not track into the subtemporal or occipital regions?
A blow to the head can cause bleeding from the blood vessels in the dense CT and from the small blood vessels in the loose CT layer (UNDERNEATH the aponeurosis)
Blood within the loose CT layer can teack freely under the aponeurotic layer. The margins of the aponeurosis relate to where it inserts into the bone.
Laterally it is continuous with the temporalis fascia. Posteriorly the occipitalis muscle attaches to the occipital bone and mastoid process. So blood in loose CT layer cannot pass into subtmporal and occipital regions.
Can pas into oribital region because frontalis muscle inserts anteriorly by merging with the skin and not to bone.
