Eyes Flashcards
What is Age-related Macular Degeneration (AMD)?
The macular is part of the retina, and is vital for sharp vision….. so AMD causes central vision loss
Dry AMD –> Geographic atrophy
Wet AMD –> Neovascular (excessive growth of blood vessles under the retina)
What is the difference in effect on the eye when given Pilocarpine or Atropine
Pilocarpine = Muscarinic agonist…. so miosis of the eye
Atropine = Muscarinic antagonist…. so mydriasis of the eye
How does latanaprost (xalatan) work?
A prostaglandin-analogue that reduces intra-ocular pressure via the uveosclereal outflow
How does Mydriasis occur?
Sympathetic innervation from the superior cervical ganglion causes the stimulation of radial (dilator) smooth muscle
Caused by NA binding to (a)1 adrenoceptors
How does Miosis occur?
Parasympathetic innervation of the ciliary ganglion, with post-ganglionic innervation of the sphinteric (constrictor) muscle
Stimulated by Ach binding to M3 receptors
The parasympathetic NS has a high basal tone, so is more active at rest than the sympathetic….so the pupils are small(ish) at rest
What’s the difference between open-angle and closed-angle glaucoma?
Open-angle –> Obstruction of aqueous humour through the trabecular meshwork and Canal of Schlemm
Closed-angle –> Block of AH from the posterior to anterior chamber due to a narrowing between the iris and cornea
Common in east-asian and inuit populations
What are the 2 types of iris smooth muscle?
And what do they do?
Radial –> Dialator
Sphincteric –> Constrictor
So they control the size of the pupil, and so how much light reaches the retina
Who is the most at risk of glaucoma?
Those with a family history of it
Very short-sighted people
Diabetic
African/Afro-Caribbean
Older
In a healthy eye, how does aqueous humour flow?
It is produced by the ciliary body, then flows from the posteriour chamber through the iris and into the anterior chamber
Then through the trabecular meshwork/Canal of schlemm and into the vein. Can also exit through the uveoscleal outflow
How would you treat eye problems caused by allergies?
H1 antagonists
Mast Cell Stabilisers –> Sodium cromoglycate)
Glucocorticoids –> Bad in the long run (possible glaucoma)
What is glaucoma?
Damage of the optic nerve, usually caused by raised intra-ocular fluid pressure (over >24 mmHg)….causing the loss of peripheral vision
This is determined by the rate of formation and drainage of aqueous humour
What is the main contraindication for muscarinic antagonists in the eye?
In closed angle glaucoma –> Due to them impairing the drainage of aqueous humour
What are cycloplegics?
Muscarinic antagonists that paralyse ciliary muscle…..and so block accommodation
What is Mitomycin C?
A powerful agent that prevents scarring in the eye (post surgery) by inhibiting the multiplication of cells which produce scar tissue
How would you treat ‘Wet’ AMD?
Photodynamic therapy (Verteporforin) to remove leakly blood vessels
Vascular Endothelial cell Growth-Factor (VEGF) inhibitors (eg, pegaptanib)
How/where is aqueous humour formed?
Formed in the ciliary body epithelium, driven by the active transport of Na+/HCO3- out of the cell
Stimulated by (B) agonists and carbonic anhydrase
Inhibited by (a) agonists
(a) 1 –> Vasoconstrictors
(a) 2 –> Decrease in cAMP production…causing less NA release
