The Cornea, Lens and Intra-Ocular Pressure Flashcards
What is the cornea?
Avascular transparent structure that separate anterior chamber from tear film
What are the 3 main roles of the cornea?
Maintain transparency
Ocular protection
Refract light
Describe the epithelium of the cornea
5-7 cell layer thick non keratinized stratified squamous layer.
Cells migrate from basal layer to surface then sloughed off into tar film
How is corneal oedema seen?
Visible lines in the stroma
What happens to endothelial cell number with age?
Falls
What nerve supplies the cornea?
Opthalmic branch of the trigeminal nerve –> via long ciliary nerve
What can trigger an infection of the cornea?
Disruption of the epithelial surface caused by:
Trauma Contact lens wear Dry eyes Pre-existing corneal disease Systemic conditions - immunocompromised
What symptoms would a patient with infective keratitis present with?
Severe pain
Red eye
Epiphora - excess eye watering
possible reduced visual acuity
Photophobia
Mucus discharge
What would you expect to see on examination if you suspect infective keratitis?
White deposits in cornea - corneal infiltrate
Hypopyon - pus collect in anterior chamber
Anterior chamber may show cells and flare - leucocytes and protein respectively due to leaky blood vessels
What is the aqueous humour pathway?
Ciliary processes in ciliary body –> iris and anterior surface of lens –> pupil –> through iridocorneal angle –> trabecular meshwork –> Canal of Schlemm –> episcleral vessels –> systemic venous circulation
What is the unconventional drainage route for aqueous humour?
Uveaoscleral route - drain into root of iris and ciliary muscle –> scleral vascular system
10-20%
How is intraocular pressure measured?
Force needed to flatten corneal surface using tanometer - pressure at which green lines match
Must correct for corneal thickness
What is the normal intraocular pressure?
11-21mmHg
What does ocular hypertension put you at higher risk of?
Developing glaucoma
Which autonomic receptors control intra-ocular pressure?
Adrenergic - alpha 2 and beta 2
Cholinergic have little direct effect
What effect does alpha 2 have on intraocular pressure?
Reduce IOP by reducing aqueous production
May increase uveoscleral outflow
What effect does beta 2 have on intraocular pressure?
Increase IOP by increasing aqueous production
What drug classes are used to target intraocular pressure?
Beta-blockers Alpha antagonists Prostaglandin analogues Carbonic anhydrase inhibitors Parasympathomimetics
Give examples of beta blockers and their MoA for intraocular pressure
Timolol, Carteolol
Reduce aqueous humour - block beta 2 receptors
Give examples of alpha agonists and their MoA for intraocular pressure
Apraclonidine, brimonidine
Reduce production of aqueous and slight increase in drainage
Give examples of prostaglandin analogues and their MoA for intraocular pressure
Latanoprost, Bimataprost
Increase uveoscleral outflow of aqueous humour
Give examples of carbonic anhydrase inhibitors and their MoA for intraocular pressure
Dorzolamid, Brinzolamide
Reduce production of aqueous humour by decreasing fluid transport in ciliary body
Give examples of parasympathomimetics and their MoA for intraocular pressure
Pilocarpine
Increase outflow by ciliary muscle contraction causing trabecular meshwork to open
What topical preparations are used in raised IOP?
Cosopt - timolol and dorzolamide
What is the main function of the lens and how powerful is it?
Refraction
Refractive power less than cornea
How does the lens change refractive power?
Changes shape (accommodation)
How does the lens change shape?
Ciliary body contract –> pull suspensory ligaments –> flatten lens –> less refraction
vice versa if ciliary body relax
What is presbyopia?
Lens’ ability to accomodate diminish with age
What causes presbyopia?
Atrophy of ciliary muscle
Loss of lens elasticity
How do inner lens fibres vary from outer lens fibres?
Inner fibres older and much harder then newer fibres on outside
How does a lens maintain transparency?
Fibres are tightly packed and highly organised
What is a cataract?
Loss of transparency of the lens
What is the most common cause for cataracts?
Increasing age
Why is early detection of cataracts crucial in newborns?
To salvage best vision possible
What are common causes of cataracts in younger patients?
Trauma
Drugs - steroids, amiodarone, allopurinol
Systemic disease - Diabetes, myotonic dystrophy, neurofibromatosis type 2
What are general symptoms of cataracts?
Painless loss of vision
Diplopia
Loss of red reflex
Difficulty with every day tasks
What is the most common technique for cataract surgery?
Phacoemulsification
What is the management for infectious keratitis?
Topical broad spectrum quinolone
What is the prognosis for infectious keratitis?
Usually good
Risk of long term visual disability in:
Elderly, contact lens wearer, fungal disease
What happens in a cataract lens?
Disruption of lens fibres leading to protein aggregation and deposition in the lens
Causes clouding, light scattering and vision obstruction
What complications are associated with phacoemulsification?
Rupture of posterior capsule Infection Inadequate correction for refractive error Haemorrhage Posterior capsule opacification
What is a congenital cataract?
Inherited cataract
Cataract secondary to intrauterine infection - rubella
What can happen in congenital cataracts aren’t removed?
Lead to nystagmus and amblyopia
What are children who have surgery for a congenital cataract within their first year of life at risk of?
High risk of glaucoma
What are the ADR’s associated with latanoprost?
Iris turn brown
Risk of uveitis and keratitis
Longer eyelashes
What are the CI for latanoprost?
Uveitis
Pregnancy
What are the ADR’s associated with Timolol?
Irritated, red, dry eye
Bronchospams
Bradycardia
What are the CI’s for timolol?
Asthmatics
Heart block
What are the ADR’s for Dorzolamide (carbonic anhydrase inhibitors)?
N&V
Headache
Dizzy
What are the CI’s for carbonic anhydrase inhibitors?
Renal impairment
What are the ADR’s associated with sympathomimetics (brimonidine)?
Dry eye
Postural hypotension
What are the ADR’s associated with parasympathomimetics (pilocarpine)?
Blurred vision
Constricted pupil
Sweating
Bradycardia
What the are CI’s associated with sympathomimetics?
Angle closure glaucoma
On MAOI’s
What are the CI’s associated with parasympathomimetics?
Uveitis
