1. Introduction and Glaucoma Flashcards
Draw the Visual Pathway
Insert Image
What constitutes the visual pathway?
Optic nerve to the chiasm, where fibres from the nasal retina cross over to opposite side
Optic tract from chiasm to the lateral geniculate nucleus, synapse
Optic radiation from the LGN to the occipital cortex
What is Bitemporal Hemianopia, and what causes it?
Bitemporal Hemianopia = where vision is missing in the outer half of both the right and left visual field
Pressure on chiasm (pituitary tumour) causes bi-temporal hemianopia
What are the two broad categories of visual loss causes?
- Physiological
2. Pathological
Give some examples of physiological causes of visual loss.
Uncorrected Refractive Error.
Myopia, hypermetropia, presbyopia, glasses, contact lenses, refractive surgery.
What are the two categories of Pathological Visual Loss? Which is more common?
Chronic (more common)
Acute
Name the 5 most common treatable causes of chronic visual loss and briefly give their treatment.
Cataract - Surgery
Glaucoma (POAG) – Drops, laser surgery
Age related Macular Degeneration (ARMD) - Sometimes anti-oxidents, anti-vegf, laser)
Diabetic retinopathy (Good DM control, BP+Lipids, laser, surgery)
Name the preventable causes chronic visual loss
Glaucoma
Diabetic retinopathy
Possible dry ARMD (if early detection)
What are the main causes of Acute Loss of Vision? What are they all accompanied by?
• Acute Angle Closure Glaucoma • Temporal • Corneal ulceration • Endophthalmitis • Acute uveitis (All are accompanied by a PAINFUL loss of vision)
In whom is Glaucoma Common (give stats)?
Elderly, 2% over 40yo, 5% over 80yo
What are the clinical features of Glaucoma?
Optic nerve cupping
Peripheral visual field loss What
Most have elevated ocular pressure
Most patients have open angle glaucoma
Uncommonly they may have acute angle closure glaucoma
Most patients have primary glaucoma (some is secondary to other conditions)
Describe the clinical course of Glaucoma.
Asymptomatic in early stages Progressive + irreversible if not detected + treated at early stage • Silent • Slow (5-10 years) • Progressive • Irreversible
Describe the Pathogenesis of Primary Open Angle Glaucoma
Optic nerve damage caused by:
- Elevated IOP
- Reduced ocular vasculature perfusion pressure
How does elevated intraorbital pressure contribute to the development of POA Glaucoma
Reduced drainage of the aqueous humour through the trabecular meshwork drainage angle
What causes reduced ocular perfusion pressure?
- Low blood pressure, esp diastolic
* Peripheral vasospasm
What tests are used to detect the onset of glaucoma?
Visual Field Test
Nasal Step Test
How are a patients visual fields tested?
Humphrey’s Visual Field Test (detects + monitors progression)
What is the average IOP amongst >40yo’s?
16mmHg
What is considered a normal disc ratio?
0.2 (cup to disc)
What is considered a glaucomatous disc ratio?
0.7
What are the goals of glaucoma treatment?
- Reduce IOP (by 33%)
2. Preserve Visual Field
What is the overall mechanism of glaucoma treatment?
Reduce production of aqueous humour
Increase outflow of aqueous humour
Which eyedrops are considered 1st line in glaucoma? MOA?
Prostaglandin Analogues
Increase Aqueous Humour
Which eyedrops are considered 2nd line in glaucoma? MOA?
Beta adrenergic blockers
Reduced Aqueous Humour secretion
Which eyedrops are considered 3rd line in glaucoma? MOA?
Carbonic Anhydrase Inhibitors (CAI)
Reduce Aqueous Humour Secretion
What are the side-effects of Beta Adrenergic Blocking Eyedrops?
Respiratory S/E • Bronchospasm • Reduced exercise tolerance Cardiovascular S/E • Bradycardia • Hypotension Other S/E’s • Depression • Lethargy • Impotence
What are the side-effects of Carbonic Anhydrase Inhibitor Eyedrops?
- Peripheral Paraesthesia
- General malaise, depression , weight loss
- G.I. Upset – altered taste, nausea, diarrhoea
- Renal & Metabolic – Hypokaliemia, acidosis, calculi
- Aplastic anaemia, agranulocytosis, Stevens Johnson syndrome
What are the side-effects of parasympathomimetic eyedrops?
Miosis – poor night vision, visual acuity
Accommodative Spasm
Which eyedrops agents may be used in glaucoma in an emergency? What are the consequences?
Alpha adrenergic agonists
Reduces secretion
Increases Outflow
Pilocarpine
Reduced outflow
Usually used in emergencies/acute cases
Highly toxic but very effective
Name and describe the surgical intervention used in POA glaucoma?
Trabeculectomy • Drainage by a plastic tube • Scleral Flap • Peripheral Iridectomy • Suturing Conjunctiva to form bleb
What is the name given to the acute form of glaucoma? What causes it?
Acute Angle Closure Glaucoma
Caused by an acute closure of the aqueous humour drainage angle
Can be precipitated by use of dilating eyedrops
What are the symptoms of Acute Angular Closure Glaucoma?
Often has mild brief self-resolving prior episodes
Sudden onset very severe unilateral eye pain / unilateral frontal headache / nausea and vomiting
Loss of vision
Coloured haloes around white lights (corneal oedema)
Dilated pupil and unreactive to light
Red eye
IOP >40mmHg
Acute closure of aqueous humour drainage angle
Can be precipitated by use of dilating eyedrops
What are risk factors associated with AAC Glaucoma?
More common in hypermetropes (long sighted)
Uncommon in young patients
Can be precipitated by use of dilating eyedrops
How should acute angle closure glaucoma be managed?
Refer to Eye A & E
Topical ocular anti hypertensives (beta blockers and prostaglandin analgoues)
IV acetazolamide 500mg
Topical miotics (pilocarpine)
Peripheral YAG laser iridotomy within 36 hours
Prophylactic YAG laser iridotomy to fellow eye also
Glaucoma without an elevated IOP is associated with what?
Migraines and Raynaud’s phenomenon
How is Intraocular Pressure Measured?
Using a Goldmann tonometer
Prisms in the tip of tonometer split the contact meniscus into 2 semi circles
Tip of tonometer applies pressure to the cornea - this can be increased or decreased manually
