Approach
Current history
When taking the presenting history of red eye, it is important to consider the serious vision-threatening diagnoses along with more common causes.[1] By including key questions and noting down pertinent negative features, the differential diagnosis can be narrowed and a decision can be made on whether referral for further ophthalmological treatment is required or treatment can be given in the primary care setting.
Key questions to consider include:[18]
When did the condition start?
Is the condition unilateral or bilateral?
A foreign body or trauma is usually unilateral, whereas conjunctivitis may start as unilateral and then become bilateral.
Was the onset of the symptoms acute or gradual?
Acute onset may indicate a corneal foreign body or abrasion or foreign body trauma.
What is the patient’s visual acuity?
Is the eye painful?
The presence of reduced visual acuity or a deep aching pain within the eye, indicates a more serious underlying diagnosis, such as angle-closure glaucoma, anterior uveitis, or scleritis.[Figure caption and citation for the preceding image starts]: Anterior uveitis with posterior synechiaePrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: ScleritisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Angle-closure glaucoma: central corneal oedema with an oval-shaped mid-dilated pupil.Private collection - courtesy of Mr Hugh Harris [Citation ends].
If the patient reports a foreign body sensation, the possible diagnoses are conjunctivitis, conjunctival/subtarsal foreign body, corneal foreign body, keratitis, and corneal ulcer. If a foreign body is suspected, ask whether the patient has undertaken any recent activity that could have resulted in this and, if so, whether they were wearing eye protection. The nature of the activity will also point to potential penetrating injuries: for example, the use of mechanical saws and hammering can produce high-velocity foreign bodies, which have the ability to penetrate the surface of the globe and become intra-ocular.[Figure caption and citation for the preceding image starts]: Bacterial conjunctivitisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Viral conjunctivitisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Subtarsal foreign body: vertical corneal abrasions seen with fluorescein stainPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Corneal ulcer seen with fluorescein stainPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Dendritic ulcer seen with fluorescein stainPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Corneal foreign bodyPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Chlamydial conjunctivitisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
Contact lens users with a painful red eye should be referred for same day eye emergency assessment to avoid missing a sight-threatening complication such as microbial keratitis or corneal ulceration.[16][19]
If there is any discharge, factors that can help to identify the presence of conjunctivitis and the possible underlying aetiology are:[13][20][21]
Watery, purulent, or mucopurulent discharge; for example:
A watery discharge is seen in viral conjunctivitis
A profuse mucous discharge is seen in chlamydial conjunctivitis
A purulent discharge is seen in gonococcal conjunctivitis
A mucopurulent discharge could indicate bacterial infection.
Discharge that is worse in the morning:
May be due to allergy
Presence of itch:
Usually due to allergy
Minimal itch may be present in chlamydial conjunctivitis
History of atopy.
If the patient is photophobic, this can indicate possible underlying anterior uveitis or corneal epithelial disturbance. The systemic associations of photophobia, such as meningitis, should always be considered in an unwell patient.[22][Figure caption and citation for the preceding image starts]: Gonococcal conjunctivitisCDC Image Library/Joe Miller [Citation ends].
[Figure caption and citation for the preceding image starts]: Gonorrhoeal conjunctivitis: resulted in partial blindnessCDC Image Library [Citation ends].
Past medical and past ophthalmological history
The physician should consider whether the patient has had previous similar episodes or whether there are any underlying systemic associations of conditions known to cause red eye, such as:
Human leukocyte antigen-B27 histocompatibility complex-positive patients
Reactive arthritis
Tuberculosis, syphilis
Lyme disease
Sarcoidosis[23]
Behcet's disease
Pauciarticular juvenile chronic arthritis
Connective tissue disorders (including rheumatoid arthritis, Sjogren's syndrome, and systemic lupus erythematosus)
Granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis)
Relapsing polychondritis
Hypertension.
[Figure caption and citation for the preceding image starts]: Conjunctivitis: consequence of reactive arthritisCDC Image Library/Joe Miller [Citation ends].
Drug history
The current use of any ophthalmological medications as well as any systemic medications known to precipitate causes of red eye should be noted. These include therapeutic mydriatics and drugs with unwanted mydriatic effects such as systemic anticholinergic drugs and topiramate. Patients on anticoagulants may be predisposed to subconjunctival haemorrhage. Persistence of conjunctivitis despite topical antibiotics should prompt evaluation for a different aetiology.
Examination
Examination of the eye in a primary care setting requires the use of a Snellen chart, a light source, fluorescein, and a cotton wool bud to evert the upper lid.[20] A step-wise approach can be used, with consideration of the differential diagnosis from the history.
Visual acuity should be checked in all patients, as a reduction may indicate a more serious underlying cause for the red eye.
Inspection of the lids (including under the lids) and brow should be performed to exclude peri-orbital injury. The position of the lid margins should be checked for the presence of trichiasis, an entropion, or an ectropion. If any discharge can be seen, conjunctivitis should be considered.[13] If the condition is bilateral with purulent discharge, it should be treated as conjunctivitis. A vesicular rash around the eye could indicate varicella zoster or herpes simplex infection.[Figure caption and citation for the preceding image starts]: TrichiasisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: EntropionPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: A patient with left herpes zoster ophthalmicus affecting the forehead and side of the nose (positive Hutchinson’s sign; yellow arrows). The crusted skin rashes follow the V1 dermatomal distribution and do not cross the vertical midlineImage used with permission from BMJ 2019;364:k5234 [Citation ends].
On inspection of the ocular surface and subtarsal surface, the pattern of redness (an important feature) should be assessed. Segmental injection may indicate episcleritis or the presence of a foreign body. Ciliary or limbal (junction of the cornea and sclera) injection occurs in anterior uveitis and corneal conditions. Redness that is localised and well demarcated with quiet surrounding conjunctiva is seen in subconjunctival haemorrhage, prompting the patient's blood pressure to be checked. Generalised injection, with engorgement of the deeper scleral vessels and pain on palpation of the globe, indicates the presence of scleritis.[24] The tarsal conjunctiva should be inspected for papillae (associated with allergic conjunctivitis), or follicles (associated with chlamydial conjunctivitis, drug toxicity, and viral conjunctivitis). If there is a history of a foreign body, the upper lid should be everted with a cotton wool bud to exclude a subtarsal position. If the foreign body cannot be found, and the activity during the incident may have produced a high-speed foreign body, then further ophthalmological opinion should be sought to exclude an intra-ocular position. Instilling fluorescein during inspection of the ocular surface can allow the visualisation of foreign bodies, corneal abrasions, and corneal ulcers. An area of focal corneal haze underlying a fluorescein-positive epithelial defect or the presence of a hypopyon would be concerning for corneal ulcer/microbial keratitis. If there is fluorescein staining present on the cornea, or the cornea appears cloudy (seen in angle-closure glaucoma), referral for further ophthalmological examination is advised. Rose bengal or fluorescein stain can be used in patients in whom dry eye is suspected as the underlying cause.[25][Figure caption and citation for the preceding image starts]: Dry eye (stained with fluorescein)From the personal collection of Dr Jonathan Smith; used with permission [Citation ends].
[Figure caption and citation for the preceding image starts]: Allergic (vernal) keratoconjunctivitisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Subconjunctival haemorrhagePrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: Corneal abrasion seen with fluorescein stainPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
[Figure caption and citation for the preceding image starts]: EpiscleritisPrivate collection - courtesy of Mr Hugh Harris [Citation ends].
Pupillary reactions. The physician should observe for anisocoria (unequal pupil size), and if this is present should refer for further ophthalmological assessment.[21] Using a pen torch (or equivalent light source), the direct and consensual pupillary responses should be checked. If the pupillary response is abnormal in the presence of red eye, anterior uveitis and angle-closure glaucoma need to be excluded. If the patient is photophobic on examination, further referral is also advised.[21]
Investigations
Swabs for bacterial, viral, and chlamydial culture can be taken in patients with suspected conjunctivitis. Investigation into the underlying systemic causes of red eye should be performed in a specialist clinic after a definite ophthalmological diagnosis has been given. Certain local causes of red eye including ectropion, entropion, corneal ulcer, contact lens-related red eye, corneal abrasion, corneal foreign body, scleritis, and angle-closure glaucoma should be evaluated further by an ophthalmologist. Penetrating and chemical trauma should also be evaluated by an ophthalmologist.[26]
Computed tomography imaging of the orbits should be performed if a high-velocity penetrating injury is suspected.
If acute glaucoma is suspected, intra-ocular pressure should be measured in the emergency department.
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