Floaters and flashes of light

Floaters are moving spots, threads, cobwebs or rings that drift across the vision, caused by opacities in the vitreous casting shadows on the retina. Flashes (photopsia) are brief lights, arcs or lightning streaks caused by traction on the retina or by neurological events. Most floaters are benign, but new floaters and flashes, especially with a field defect, can indicate retinal tear, retinal detachment or vitreous haemorrhage.

Anatomy and mechanisms. With age the vitreous gel liquefies and collapses; posterior vitreous detachment separates it from the retina, usually between ages 45 and 70, causing floaters and flashes. Strong adhesions can tear the retina, allowing fluid beneath it (rhegmatogenous retinal detachment). Migraine aura and occipital lesions cause bilateral, geometric, shimmering lights.

Classification. Ocular (posterior vitreous detachment, retinal tear, retinal detachment, vitreous haemorrhage, vitritis, posterior uveitis, asteroid hyalosis, myopic vitreous degeneration) and neurological (migraine aura, occipital lesions, optic neuritis, seizures).

Key distinctions. Monocular flashes in one position of the eye or with eye movement suggest vitreoretinal traction. Binocular, zigzag, expanding lights lasting 20 to 30 minutes suggest migraine aura. A curtain or shadow across the field suggests retinal detachment.

History. Onset (acute or gradual), laterality, number and character of floaters (new, increasing, shower of black dots, cobweb, ring), flashes (frequency, position, trigger by eye movement), curtain or shadow, blurred vision, headache, aura.

Also ask about previous eye disease, myopia, previous eye surgery or injury, family history of retinal detachment, diabetes, hypertension, bleeding disorders, anticoagulants, inflammatory disease, HIV, and previous retinal lesions.

Drug history. Anticoagulants and antiplatelets (vitreous haemorrhage), miotic drops (pilocarpine: retinal detachment risk), and drugs causing visual phenomena (digoxin, sildenafil).

Examination. Visual acuity, pupils (relative afferent defect indicates detachment or macular involvement), confrontation fields, anterior segment (cells, pigment, Shafer sign: pigment in the vitreous), intraocular pressure.

Dilated fundus examination with indirect ophthalmoscopy and scleral depression (tears, detachment, haemorrhage, Weiss ring), Amsler grid, and a neurological examination when neurological causes are suspected.

Red flags

• Sudden onset of new floaters, especially a shower of floaters or a cobweb
• New flashes, particularly with floaters
• A curtain, shadow or field defect, or reduced central vision
• Floaters or flashes after eye surgery, injury or in high myopia
• Family history of retinal detachment, or previous detachment in the other eye
• Anticoagulation, diabetes with proliferative disease, or sickle cell disease
• Pain, redness or photophobia with floaters (uveitis)
• Immunosuppression or HIV with floaters (retinitis)
• Floaters with headache, neurological symptoms or papilloedema

Special groups. Children: trauma, retinopathy of prematurity, toxocariasis, and leukaemia. Pregnancy: hypertension related retinal disease and diabetic retinopathy progression. Older adults: posterior vitreous detachment and age related macular degeneration. Region specific: toxoplasmosis, onchocerciasis, cytomegalovirus retinitis and tuberculosis.

Vitreous and retinal

• Posterior vitreous detachment (common, benign), vitreous syneresis, asteroid hyalosis
• Retinal tear (horseshoe tear), retinal break, lattice degeneration, retinal detachment (rhegmatogenous, tractional, exudative)
• Vitreous haemorrhage (diabetic retinopathy, retinal tear, retinal vein occlusion, trauma, sickle cell disease, macroaneurysm, age related macular degeneration)
• Vitritis and posterior uveitis (sarcoid, tuberculous, syphilitic, toxoplasmic, cytomegalovirus, endogenous endophthalmitis), pars planitis
• Retinal vein occlusion, retinal vasculitis, retinoblastoma and lymphoma, choroidal melanoma
• Myopic vitreous degeneration, Stickler syndrome, cataract surgery related, laser, and trauma

Neurological and other

• Migraine aura, occipital lobe lesions and seizures, optic neuritis, temporal lobe lesions
• Drug effects (digoxin), photopsia from carotid disease, retinitis pigmentosa, and cancer associated retinopathy
• Entoptic phenomena (blue field entoptic phenomenon, floaters of tear film), eye rubbing, and functional

Reasoning. Same day dilated retinal examination for any new floaters or flashes. Repeat examination at 2 to 6 weeks when the first is normal, because tears and detachment can develop after the posterior vitreous detachment.

First line. Visual acuity, pupils, fields and dilated fundus examination with scleral depression.

Targeted tests.

• B scan ultrasound when the retina cannot be seen (dense vitreous haemorrhage, cataract), wide field fundus photography, and optical coherence tomography for macular involvement.
• Fluorescein angiography for vasculitis and neovascularisation.
• Blood tests for suspected uveitis or infection: full blood count, ESR, C reactive protein, angiotensin converting enzyme, syphilis serology, interferon gamma release assay, HIV, toxoplasma serology, cytomegalovirus polymerase chain reaction (aqueous or vitreous), and chest radiograph.
• Glucose and HbA1c, blood pressure, clotting profile, and haemoglobin electrophoresis.
• Vitreous or aqueous tap for polymerase chain reaction and culture in suspected infectious posterior uveitis (by ophthalmology).
• MRI brain for suspected neurological causes; EEG for suspected occipital seizures.

Limitations. Retinal tears can be small and peripheral. Early examination may not show a tear that appears later.

Retinal tear. Same day or within 24 to 48 hours: laser retinopexy or cryotherapy by ophthalmology to prevent detachment (symptomatic tears have a high risk of progression).

Retinal detachment. Immediate ophthalmology: pneumatic retinopexy, scleral buckle, or vitrectomy (urgency greatest when the macula is still attached); positioning advice, nil by mouth before surgery, and avoidance of strenuous activity.

Vitreous haemorrhage. Ophthalmology review; sleep with the head elevated; exclude a tear (B scan if no view); laser, anti-vascular endothelial growth factor injections or vitrectomy for persistent haemorrhage or traction; control of diabetes, blood pressure and anticoagulants (do not stop anticoagulation without specialist advice).

Posterior vitreous detachment without tear. Reassurance, advice to return urgently if floaters or flashes increase or a curtain appears, and review at 2 to 6 weeks. Floaters usually become less bothersome with time (neuroadaptation). Vitrectomy or laser vitreolysis only for severe persistent symptoms.

Posterior uveitis and infectious causes. Specialist care:

• Toxoplasmosis: trimethoprim with sulfamethoxazole 160 mg/800 mg orally twice daily for 4 to 6 weeks, or pyrimethamine 25 to 50 mg daily with sulfadiazine 1 g four times daily and folinic acid 5 to 15 mg daily.
• Toxoplasmosis, sight threatening disease: add prednisolone 0.5 to 1 mg/kg daily after 2 to 3 days of antibiotics.
• Cytomegalovirus retinitis: valganciclovir 900 mg orally twice daily for 21 days then 900 mg daily (adjusted for creatinine clearance), or ganciclovir 5 mg/kg IV every 12 hours, with antiretroviral therapy.
• Syphilis: benzylpenicillin 3 to 4 million units IV every 4 hours for 10 to 14 days.
• Tuberculosis: isoniazid 5 mg/kg (maximum 300 mg), rifampicin 10 mg/kg (maximum 600 mg), pyrazinamide 25 mg/kg (maximum 2 g) and ethambutol 15 mg/kg daily for 2 months, then isoniazid and rifampicin for 4 months.
• Tuberculosis, with pyridoxine 10 to 25 mg daily and ethambutol monitoring (visual acuity and colour vision).
• Endogenous endophthalmitis: emergency intravitreal and systemic antibiotics and vitrectomy.
• Sarcoid and idiopathic uveitis: prednisolone 1 mg/kg daily (maximum 60 to 80 mg) tapered, with steroid sparing agents by specialists.

Retinal vein occlusion and vascular causes. Anti-vascular endothelial growth factor injections or laser, and systemic risk factor control.

Migraine aura. No emergency treatment. Treat attack: sumatriptan 50 to 100 mg orally at onset (not during aura alone) with ibuprofen 400 to 600 mg or aspirin 900 mg.

Prevention for frequent attacks: propranolol 40 mg orally twice daily increased to a usual 80 to 160 mg daily (maximum 240 mg daily). Avoid combined oral contraceptives with aura. Triptan contraindications: ischaemic heart disease, stroke, uncontrolled hypertension, and use of ergots or monoamine oxidase inhibitors.

Occipital seizures. Levetiracetam 500 mg orally twice daily increased every 2 weeks to a usual 1 to 1.5 g twice daily (maximum 3 g daily), or lamotrigine slowly titrated.

Optic neuritis. Methylprednisolone 1 g IV daily for 3 to 5 days under neurology and ophthalmology care.

Tumours. Urgent oncology and ophthalmology care.

Entoptic phenomena. Explanation and reassurance.

Monitoring. Review at 2 to 6 weeks for new floaters or flashes with a normal first examination. Repeat dilated examination whenever new symptoms occur. After surgery or laser: review at 1 day, 1 week and 1 month.

Referral and escalation. Same day ophthalmology for new floaters, flashes, curtain or visual loss (within 24 hours). Immediate for retinal detachment. Neurology for neurological features. Uveitis service for posterior uveitis. Retinal surgery for detachment and haemorrhage.

Admission criteria. Retinal detachment awaiting surgery (often day case), endogenous endophthalmitis, severe infectious retinitis, or neurological emergency.

Discharge and safety netting. Return urgently for a new shower of floaters, new flashes, curtain, shadow, reduced vision, or any change.