Halos around lights

Halos are coloured or white rings seen around lights, usually at night. They arise when light is scattered by corneal oedema, lens opacity, or optical aberration.

Mechanisms. Corneal epithelial oedema (raised intraocular pressure, contact lens overwear, endothelial failure) scatters light into rings with blue inside and red outside. Lens changes (early cataract, cortical and posterior subcapsular opacities) and tear film irregularity also produce halos. Optical aberrations after refractive surgery and multifocal lens implants cause halos and glare.

Classification. Acute (angle closure, corneal oedema, drug effect), chronic or recurrent (cataract, corneal dystrophy, dry eye, post-surgical, intermittent angle closure), and physiological (pupil dilation at night in uncorrected refractive error).

Key distinctions. Halos with a painful red eye, headache, nausea and reduced vision indicate acute angle closure. Halos worse in the morning with blur that clears indicate corneal oedema. Halos with glare and gradual loss of vision indicate cataract.

History.

• Onset (sudden or gradual), laterality, duration, timing (evening, dim light, morning).
• Eye pain, redness, headache, nausea or vomiting, blurred vision, glare.
• Contact lens use and wearing time, previous eye surgery (laser refractive surgery, cataract surgery, multifocal implants), eye drops.
• Previous intermittent episodes (precipitated by dim light, reading, stress), hyperopia, family history of glaucoma or angle closure, dry eye symptoms, and drug history.

Drug history. Topiramate, sulphonamides and other drugs that precipitate angle closure, anticholinergics, tricyclic antidepressants, selective serotonin reuptake inhibitors, antihistamines, decongestants, sympathomimetics, mydriatic drops, digoxin (yellow halos), amiodarone, and sildenafil (blue tinge).

Examination.

• Visual acuity with pinhole, pupils (mid-dilated fixed pupil in acute closure), cornea (microcystic oedema, haze, Descemet folds, guttata).
• Anterior chamber depth (shallow; van Herick test), conjunctival injection (ciliary flush), intraocular pressure (applanation).
• Gonioscopy by ophthalmology, lens (cataract grade), fundus (optic disc cupping and haemorrhage), and tear film.

Red flags

• Halos with severe eye pain, red eye, headache, nausea or vomiting (acute angle closure)
• Reduced vision with cloudy cornea or fixed mid-dilated pupil
• Recent mydriatic drops, new topiramate or other precipitating drug
• Previous episodes of halos with brow ache in dim light (subacute angle closure)
• Contact lens wearer with pain
• Sudden bilateral halos with a new drug (topiramate, bilateral closure)
• Corneal infiltrate or ulcer

Special groups. Pregnancy: avoid oral carbonic anhydrase inhibitors in the first trimester when possible. Older adults: angle closure, cataract and endothelial disease. Region specific: primary angle closure is more frequent in East and South East Asian populations.

Angle closure and pressure related

• Acute primary angle closure, subacute and intermittent angle closure, chronic angle closure
• Secondary angle closure (drug induced, lens induced, uveitic, neovascular, ciliary body swelling)
• Open angle glaucoma with high pressure, congenital glaucoma

Corneal

• Corneal oedema (contact lens overwear, endothelial dystrophy, bullous keratopathy, post-surgical, trauma, hydrops)
• Keratitis, corneal scarring, keratoconus, dry eye and tear film instability
• Epithelial basement membrane dystrophy, Fuchs endothelial dystrophy

Lens

• Early and established cataract (cortical, posterior subcapsular), posterior capsule opacification, lens subluxation
• Intraocular lens related optical effects (multifocal, monofocal edge glare, dysphotopsia)

Refractive and other

• Uncorrected myopia, astigmatism and hyperopia, post laser refractive surgery
• Pupil size effects in dim light, vitreous opacities
• Drug induced (digoxin, amiodarone, phosphodiesterase inhibitors), migraine, functional

Reasoning. Exclude angle closure first when there is any pain or redness. If the eye is quiet, assess the cornea, lens and refraction.

First line. Visual acuity, pupils, intraocular pressure, slit lamp (cornea, chamber depth, lens), and dilated fundus examination only after angle closure risk is judged and dilation is safe.

Targeted tests.

• Gonioscopy and anterior segment optical coherence tomography for angle assessment.
• Pachymetry, specular microscopy and corneal topography for corneal disease.
• Visual field testing and optical coherence tomography of the optic nerve for glaucoma.
• Refraction and glare testing.
• Provocative darkroom tests are no longer used because of the risk of precipitating closure.
• Tear film tests (tear break up time, Schirmer test) for dry eye.
• Medication review.

Limitations. Intraocular pressure may be normal between attacks of intermittent angle closure. Shallow chamber depth is not always obvious without gonioscopy.

Acute angle closure (emergency, same day ophthalmology).

Position supine, and give:

• Acetazolamide 500 mg IV or orally (then 250 mg orally every 6 hours; avoid in sulphonamide allergy, severe renal impairment and sickle cell disease).
• Timolol 0.5 percent 1 drop (avoid in asthma, heart block and bradycardia).
• Apraclonidine 1 percent or brimonidine 0.2 percent 1 drop.
• Pilocarpine 2 percent 1 drop every 5 minutes for 3 doses once pressure is falling.

Add prednisolone acetate 1 percent 1 drop every 15 to 30 minutes for 1 hour then four times daily to reduce inflammation. Analgesia and antiemetic (ondansetron 4 mg IV, maximum 16 mg in a single dose; QT warning). If pressure remains over 40 mmHg: IV mannitol 20 percent 1 to 2 g/kg over 30 minutes. Definitive laser peripheral iridotomy by ophthalmology, with prophylactic iridotomy of the fellow eye within days. Stop the precipitating drug.

Subacute and chronic angle closure. Laser peripheral iridotomy, with clear lens extraction or cataract surgery for persistent narrow angles, and topical pressure lowering drops (latanoprost 0.005 percent 1 drop at night) when pressure remains high.

Open angle glaucoma. Latanoprost 0.005 percent 1 drop at night, or timolol 0.5 percent 1 drop twice daily, with laser or surgery by ophthalmology.

Corneal oedema. Stop contact lens wear, hypertonic saline 5 percent drops 4 times daily or ointment at night, lubricants, and management of the cause. Bandage contact lens for bullous keratopathy. Corneal transplantation (endothelial keratoplasty) for failure.

Cataract. Surgery when visual function is affected; correct refractive error; advice on night driving.

Dry eye. Preservative free lubricants (hypromellose 0.3 percent or sodium hyaluronate 0.1 to 0.2 percent, 1 drop 4 to 6 times daily), lid hygiene and, for meibomian gland dysfunction, doxycycline 100 mg orally daily for 6 to 12 weeks (avoid in pregnancy and in children under 12 years).

Refractive and post-surgical causes. Spectacle or contact lens correction, brimonidine 0.15 percent drops at night for pupil constriction (selected patients), and consider lens exchange or surgical enhancement.

Drug effects. Review with the prescriber; stop or substitute topiramate, and switch other precipitating drugs when feasible; digoxin toxicity: check digoxin level, potassium and creatinine.

Monitoring. Intraocular pressure and angle review at 1 to 2 days after acute closure and at 2 to 4 weeks after iridotomy. Annual field testing and optic nerve imaging for glaucoma risk.

Referral and escalation. Same day ophthalmology for any suspected angle closure. Routine ophthalmology for cataract, corneal and refractive causes.

Admission criteria. Acute angle closure with persistent pressure elevation, intractable pain or vomiting, or inability to arrange same day laser.

Discharge and safety netting. Return for eye pain, redness, headache, vomiting, reduced vision, or halos with brow ache. Advise on avoiding anticholinergic and sympathomimetic drugs and mydriatic drops in people with narrow angles, and encourage relatives to be screened.