Narrowing of the anterior chamber angle or the eye (between the iris and cornea)
Causes optic nerve damage and sight loss
Pathophysiology:
Occurs in anatomically pre-disposed individuals with shorter eye lengths and shallower anterior chambers
Reduced drainage of aqueous humour due to anterior chamber angle narrowing
Mediated by a pupillary block contact between the iris and the lens when the iris is in a mid-dilated position
causes the peripheral iris to bow forward blocking the drainage angle, with subsequent rapid rise in IOP.
Risk factors for AACG include:
Increasing age: particularly 6th to 7th decade of life
Female sex: women have a three times greater risk than men
East Asian ethnicity
Family history
Anatomical predisposition: including short eyeball length and hypermetropia (longsightedness)
Pupil mid-dilation can cause AACG by precipitating pupillary block in those at risk
Being in a dark room
Anticholinergics e.g. oxybutynin
SSRIs and TCAs
Pupil dilating drops e.g. tropicamide - associated with bilateral AACG
History:
Symptoms tend to develop over hours to days
Since pupil mid-dilation can trigger AACG, the patient may have been in a dark room when symptoms began or be taking medications that cause pupil dilation
Typical symptoms of AACG include:
Unilateralsevere eye pain or headache that may cause nausea and vomiting.
Profound reduction in visual acuity or visual loss
Rainbow coloured haloes around bright lights
Clinical exam:
Eye is red and hard - due to a rapid rise in IOP
Diffusely hazy cornea limiting view of the iris and pupil
A fixed, non-reactive, mid-dilated pupil
Very high IOP >30
High IOP can be confirmed by asking the patient to close their eye and gently palpating using the tips of both index fingers. An eye with very high IOP will feel ‘hard’ on palpation.
Investigations:
Gonioscopy - assessing the angle between the angle between the iris and cornea
Tonometry (Goldmann applanation) - measure IOP
Management to initiate before specialist assessment:
Oral analgesics
Anti-emetics
Patient can be laid flat - opens anterior chamber angle