Session 5 - Diseases of the eye Flashcards
What controls the corneal reflex?
Afferent fibres
- Opthalmic branch of the trigeminal nerve
Efferent fibres
- Temporal and zygomatic branches of the facial nerve
- Contraction of the obicularis oculi causing the eye to blink
What happens if there is damage to the facial nerve?
Dirt can cause corneal abrasions that result in sudden pain and excessive tears
This can lead on to CORNEAL ULCERATION
What is mydriasis?
Mydriasis is dilation of the pupil, sometimes referred to as a ‘Blown pupil’.
o Under-activity of PSNS -> Lack of innervation to Sphincter Pupillae
o Over-activity of SNS -> Increased innervation to Dilator Pupillae
Raised intracranial pressure is a possible cause of mydriasis.
What does aqueous humour usually drain into?
The scleral venous sinus
How does glaucoma form?
Drainage of aquous humour less than production, fluid builds up in the enterior and posterior chambers of the eye.
How can blindness result from glaucoma?
Fluid builds up in anterior and posterior chamber of the eye
Pushes lens back until it compresses vitreous humour. This presses choroid against the retina, compressing blood vessels and causing retinal cells to die. Cells at edge of focal point die first, leading to tunnel vision
What is presbyopia?
As people age their lenses become harder and more flattened. These changes reduce the focusing power of the lenswes a condition known as presbyopia.
How can retina detachment occur?
Intraretinal space separates the layers of the retina in the developing embryo. As develops, the layers fuse, obliterating the space.
However, pigment cell layer becomes firmly fixed to the choroid, attachment to the neural layer is not firm.
A blow to the eye may cause detachment of the retina.
What will a person with retinal detachment complain of?
Flashes of light or specks floating in front of the eye.
What is a coloboma?
The absence of a section of the iris. Causes include - Birth defect - Penetrating or non-pentrating injuries to the eyeball - Surgical iridectomy
What is a hyphema?
Haemorrhage within the anterior chamber of the eyeball, usually resulting from blunt force trauma to the eyeball.
Anterior chamber is tinged ried, but blood soon accumulates. The initial haemorrhage usually stops in a few days and recovery is good.
What is Horner’s syndrome (broadly) and what is it caused by?
Absence of sympathetically stmulated functions on the ipsilateral side of the head, due to interruption of cervical sympathetic trunk
Give four of the main symptoms of Horner’s syndrome
Miosis
Ptosis
Vasodilation
Anhydrosis
What is miosis in Horner’s syndrome?
Constriction of the pupil
Parasympathetically stimulated sphincter pupillae of the pupil is unopposed
What is ptosis caused by in horner’s syndrome?
Paralysis of smooth muscle fibres interdigitated with the aponeurosis of the levator palpebrae superiorisis that collectively constitute the superior tarsal muscle
What is vasodialtion caused by in horners syndrome?
Redness and increased temperature of the skin
Loss of sympathetic tone
What is exopthalmos?
Protrusion of the eye, causing the eyelids to part more than normal so that the whites of the sclera are visible all around the cornea and iris. Bilateral - Grave's disease Unilateral - Aneurysm - Haematoma
How does raised ICP cuase eye damage?
o Optic nerve is surrounded by meninges with CSF in the subarcachnoid space
o Increase in CSF pressure may compress the optic nerve compress blood vessels supplying retina blindness
o Vein is occluded before the artery, leading to oedema of the retina (Papillodema)
What is redeye and how is it caused?
The eye may appear bloodshot. This may result from trauma, infection, allergy or increased pressure in the eye. Severe coughing spells or recurrent vomiting may cause a patient to have a conjuctival haemorrhage.
What is a meibomian cyst?
Blocked Tarsal Gland, which lies behind the eyelash within the eyelid.
What is a stye?
Infection of the Sebaceous Gland at the base of the eyelash.
