Glaucoma

Glaucoma

·        Usually due to outflow obstruction: damage to the trabecular meshwork overlying the channel of schlemm ® ­resistance to flow ® ­ steady state intraocular pressure ® ¯vascular perfusion of the neural tissue ® blindness

·        Classification:

o  Primary:

§  Open angle (chronic)

§  Closed angle (acute)

o  Secondary: eg iritis, trauma, blood in the eye, etc

Primary Open-angle Glaucoma

·        Epidemiology:

o   Leading cause of preventable blindness

o   Risk factors: age, near-sightedness, African/Asian ancestry, family history, past eye injury, a history of severe anaemia or shock, steroid medication

o   Most common sort, gradual impairment of aqueous drainage, insidious loss of sight

o   2% of over 50 years

o   1 in 7 risk if primary relative has it

·        Presentation:

o   Central field defect – arcurate shape with macular sparing

o   Cupping of the disk due to ischaemic atrophy of the nerve fibre layer

o   Bullous keratopathy – oedema of the cornea

·        Screen with tonometry (measuring intra-ocular pressure), test visual fields.

·        Is diagnosed by cupping of the optic disk: not by ­intra-ocular pressure. 17% of people with glaucoma have „normal‟ IOP.

·        Pathology: 

o   ­Resistance to outflow (pathogenesis not clearly understood) ® ­aqueous humour ® ­intra-ocular pressure (normal is < 22 mmHg)

o   Leads to damage to ganglion nerve cell axon (final output) at the optic nerve head. Due to vascular insufficiency as nerves exit the eye

o   Affects peripheral bundles preferentially: spares papillo-macular bundle

·        Treatment: Medication, laser treatment to enlarge the drain (trabeculoplasty)

Primary Closed-angle Glaucoma

·        Iris is pushed forward and acutely occludes the trabecular meshwork ® ¯drainage

·        Rare but vision threatening

·        Unilateral, acute visual loss, pain, nausea and vomiting, dilated, non-reactive pupil

·        Precipitating factors: long sited (narrow anterior chamber, narrow iridocorneal angle), and when pupil dilated for a long time (dim light)

·        Can be congenital

·        Once resolved, put hole through iris (iridotomy): no further obstruction possible

Secondary Glaucoma

·        Secondary open angle glaucoma: Outflow system is obstructed mechanically by debris (ie gunge up trabecular meshwork). Rare. Eg Haemolytic glaucoma, lens protein glaucoma

·        Secondary closed angle glaucoma: Can be due to neovascularisation „zipping up‟ the angle, secondary to ischaemic eyes (eg diabetes, central retinal vein occlusion)