A red eye is an eye that appears red due to illness or injury. Most frequently, it is injection and prominence of the superficial blood vessels of the conjunctiva, which may be caused by disorders of these or adjacent structures. Unilateral or single red eye means only one eye is affected.
Most common diseases
Meibomian Cyst
It usually presents as an acute onset of unilateral eyelid oedema, with a red and painful eye. [evidence.nhs.uk]
[…] eyelid oedema, with a red and painful eye. [evidence.nhs.uk]
Orbital cellulitis (an infection involving the deep soft tissue surrounding the eyeball, located posterior to the orbital septum) usually presents as an acute onset of unilateral [evidence.nhs.uk]
Foreign Body in the Eye
[…] protection Symptoms Typically unilateral Irritation/foreign body sensation/pain Lacrimation Blurred vision Red eye Signs Foreign body adherent to ocular surface Linear corneal [college-optometrists.org]
Aetiology Patient often gives history of foreign body entering eye wind blown high velocity (hammering, grinding) DIY and gardening Predisposing factors Lack of suitable eye [college-optometrists.org]
Keratitis
In the hospitalized patient with a unilateral red eye, always suspect herpes simplex keratitis. [infectiousdiseaseadvisor.com]
Answer and interpretation History: Painful red eye, altered vision, foreign body sensation, photophobia, tearing; usually unilateral Skin (e.g., eyelid) vesicular rash may [lifeinthefastlane.com]
eye Photophobia Signs of keratitis (marginal) Ulcer (stromal infiltrate with overlying epithelial loss) which may be round or arcuate, single or multiple, unilateral or bilateral [college-optometrists.org]
Conjunctivitis
The following "red flags" point to other more serious diagnoses, such as keratitis ( inflammation of the cornea ), iritis, or angle closure glaucoma : Unilateral red eye Changes [dermnetnz.org]
The following "red flags" point to other more serious diagnoses, such as keratitis (inflammation of the cornea), iritis, or angle closure glaucoma: Unilateral red eye Changes [dermnetnz.org]
It is usually unilateral. it is the commonest cause of red eye (1) conjunctivitis in children is predominantly bacterial, with nontypeable H. influenzae being the most common [gpnotebook.co.uk]
Eyeball Injury
An extreme eye injury can cause a globe rupture where the eyeball can split open. This can be due to trauma directly on the eye or around the eye. Watch this episode of A State of Sight with Isaac Porter, MD to learn more about this injury and the eye surgery options to help save the eye and restore vision.[…] [eyeporter.com]
Uveitis
Symptoms [ 11 ] Acute anterior uveitis Usually unilateral. Pain, redness and photophobia are typical. Eye pain is often worse when trying to read. [patient.info]
Patients with unilateral anterior uveitis have ocular ache in the affected eye if light is shined in the unaffected eye (true photophobia), which is uncommon in conjunctivitis [merckmanuals.com]
Differential diagnosis Any cause of a red eye or visual disturbance should be included in the differential diagnosis. [patient.info]
Anterior Uveitis
Conjunctivitis causes watering and discharge from the eye ACUTE ANTERIOR UVEITIS (IRITIS) Presentation * Painful red eye – usually unilateral. * Photophobia and watering of [redorbit.com]
Sudden onset Photophobia Ocular pain Eye redness Non-granulomatous Severe inflammation potentially resulting in: Hypopyon Anterior chamber fibrin Rarely: Papillitis Vitritis [eyewiki.org]
DIAGNOSIS Acute anterior uveitis Supporting points • Unilateral eye pain with photophobia and redness with excessive tearing for duration of 5 days. • Circumcorneal congestion [slideshare.net]
Cluster Headache
Usually unilateral. Deep stabbing pain around the temple or the eye. [diffen.com]
Cluster headaches Deep stabbing pain around the temple or the eye, which is usually on one side (unilateral) Stuffy or runny nose Tearing or redness in eyes, droopy eyelids [belmarrahealth.com]
Stuffy or runny nose Tearing or redness in eyes, droopy eyelids Migraine Moderate to severe, throbbing head pain. [diffen.com]
Acute Angle Closure Glaucoma
Often, closed angle glaucoma presents acutely as a painful red eye. Reference: (1) European Glaucoma Society (EGS) 2008. [gpnotebook.co.uk]
Frequently associated symptoms include eye redness, headache (classically unilateral and periorbital), nausea, vomiting, and photophobia.[3] Rarely, acute ACG can present [tamingthesru.com]
The condition is frequently bilateral and its incidence increases with age. 90% of acute attacks are unilateral (2). [gpnotebook.co.uk]
Central Corneal Ulcer
4 More common complaints include redness, pain, pain with eye movements (suggestive of associated scleritis), blurred vision, photophobia and tearing. [ophthalmologymanagement.com]
Presentation - acute unilateral/bilateral exacerbations characterised by decreased visual acuity, with variable pain and redness (there may be none). [patient.info]
Although PUK can be bilateral and extensive, it's more often unilateral or asymmetric in its presentation, and the pathology is limited to one sector of the peripheral cornea [ophthalmologymanagement.com]