Pain, photophobia and reduced-vision red flags

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Redness is a sign shared by disorders of very different severity. A comfortable eye with normal vision and no concerning exposure is assessed differently from an eye with deep pain, light sensitivity or lasting visual loss. Begin by identifying the patient's actual change in function: can they read usual text, recognise faces or see normally with each eye separately? Ask whether blur clears after blinking or cleaning discharge. Sustained reduction from baseline, especially when paired with pain or a corneal finding, requires more than symptomatic treatment.

The first action depends on mechanism. Chemical exposure requires immediate irrigation while help is arranged. A suspected penetrating or open-globe injury requires protection from pressure and urgent transfer; an embedded object should not be removed in a community examination. These priorities come before a detailed diagnostic work-up. For other red-eye presentations, measure acuity, inspect pupils and the cornea, examine eye movements and look for relevant lid or orbital changes within the limits of training and equipment.

History can sharply change urgency even before all examination findings are available. Contact-lens use raises concern for microbial keratitis. Recent intraocular surgery or injection makes pain and visual deterioration particularly concerning for endophthalmitis. Severe eye pain with headache and nausea suggests acute angle closure, while fever, proptosis and impaired eye movement suggest orbital disease. A previous episode of uveitis or a bottle of steroid drops at home should not encourage automatic retreatment. The immediate goal is a timely, accurate assessment of the currently threatened structure.

Key points

Measure visual acuity in each eye with usual correction when feasible, but never delay chemical irrigation or another immediate protective action.
Pain, photophobia and persistent blur should not be explained away by a familiar diagnosis of conjunctivitis or dry eye.
Ask about lenses, trauma, chemicals, recent surgery or injections, immunosuppression and current eye drops early in the assessment.
A corneal infiltrate, abnormal pupil, hypopyon or relative afferent pupillary defect materially increases concern.
Tonometry and pressure on the eye are inappropriate when an open-globe injury is suspected.
Communicate urgency and practical transfer arrangements directly rather than relying on a routine referral letter for a threatened eye.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Surface infection or injury

Microbial keratitis, chemical exposure and trauma can damage the corneal surface and deeper tissue. Lens wear and exposure history help identify urgent possibilities early.

Intraocular disease

Inflammation, acute pressure elevation or infection can cause redness with pain and impaired vision. Recent surgery or injection makes an intraocular infectious process particularly concerning.

Orbital pathology

Infection or other disease behind the orbital septum can affect eye movement and optic function. Proptosis, movement restriction and systemic symptoms shift attention beyond the conjunctiva.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Nociception and tissue injury
The cornea is densely innervated, so epithelial damage can produce substantial pain. Deep inflammation and pressure-related stress can also generate severe ocular or referred discomfort.
2
Light-sensitive inflammation
Corneal injury and iris or ciliary inflammation can make light uncomfortable. Photophobia gains diagnostic importance when combined with pain, pupil change or persistent visual impairment.
3
Loss of optical or neural function
Corneal opacity, intraocular inflammation, pressure injury or optic dysfunction can reduce vision through different mechanisms. Measuring function helps reveal severity that surface appearance may underestimate.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Corneal danger pattern

Pain, photophobia, a white opacity or fluorescein-staining defect suggests corneal disease, especially with contact lenses, water exposure or trauma.

Intraocular danger pattern

Persistent visual decline, an abnormal pupil, ciliary redness or a hypopyon suggests deeper pathology; recent surgery or injection makes infection an immediate concern.

Pressure-related emergency

Severe ocular pain with headache, nausea, corneal haze and a poorly reactive mid-dilated pupil supports acute angle closure and needs emergency ophthalmic treatment.

Orbital or traumatic danger

Proptosis, painful or limited eye movements, systemic illness, an injury mechanism or an afferent pupil defect suggests disease beyond uncomplicated conjunctival inflammation.

Red flags requiring action

Pain with marked photophobia or sustained reduction in visual acuity requires urgent assessment for corneal or intraocular disease.
A contact-lens wearer with a painful red eye or corneal opacity needs same-day emergency ophthalmic assessment.
Severe eye pain with headache, nausea, corneal haze or an abnormal pupil may indicate acute angle closure.
Pain and deteriorating vision after intraocular surgery or injection raise concern for endophthalmitis and require immediate ophthalmic contact.
Proptosis, restricted or painful eye movements, fever or reduced vision suggests disease behind the orbital septum and requires urgent hospital assessment.
High-velocity injury, an embedded object or suspected globe rupture requires protection without pressure and emergency assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Visual acuity in each eyeFirst step
Why
Quantify the functional deficit and support clear communication.
Interpretation and limitations
Record usual correction and whether a pinhole changes acuity when practical; inability to complete the chart still permits documentation of gross visual function without delaying urgent care.
02
Pupil and eye-movement examination
Why
Identify neurological, pressure-related or orbital warning findings.
Interpretation and limitations
A fixed or irregular pupil, an afferent defect, proptosis or restricted movements needs urgent interpretation in the full clinical context.
03
Corneal examination and fluorescein when appropriate
Why
Identify an opacity, epithelial lesion or important alternative diagnosis.
Interpretation and limitations
Use within competence and avoid manipulating a suspected open-globe injury; an infiltrate or significant epithelial defect should trigger a corneal assessment pathway.
04
Tonometry and specialist slit-lamp assessment
Why
Assess pressure and structures that cannot be judged externally.
Interpretation and limitations
Measure pressure only when safe and appropriately trained; suspected globe rupture contraindicates pressure measurement, and unavailable equipment must not delay referral.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Microbial keratitis

Pain, photophobia and a focal corneal lesion suggest an infectious corneal process. Contact-lens use or a relevant exposure strengthens the need for urgent assessment.

Acute angle closure

Pain, headache, nausea, corneal haze and pupil abnormality can reflect abrupt pressure elevation. This combination requires emergency treatment rather than a routine red-eye prescription.

Uveitis or scleritis

Inflammation of intraocular or scleral structures can cause a painful photophobic eye and visual change. Slit-lamp and other specialist examination distinguish the affected tissue.

Endophthalmitis

Pain and declining vision after an intraocular procedure are concerning for infection within the eye. A hypopyon further increases concern but is not required before referral.

Orbital or globe injury

Abnormal eye movement, proptosis, an afferent defect or a dangerous injury mechanism suggests deeper disease. Protecting the eye and arranging emergency assessment take priority.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Chemical injuryIrrigate before completing the assessmentFirst stepA chemical has entered the eye and ongoing exposure may continue tissue damage.

1PreferredStart copious irrigation immediately using clean water if the preferred clinical fluid is not already available.
2Continue for at least twenty minutes while urgent assessment is arranged, removing a contact lens only if doing so does not delay flushing.
3In clinical care, irrigate until ocular-surface pH is normal and check again after stopping: NHS Highland recommends testing at completion, five minutes later and again after twenty minutes. Repeat irrigation if pH becomes abnormal. Examine the fornices for retained particles within competence and give the receiving service the substance, exposure time and treatment already delivered.

02Threatened visionArrange emergency ophthalmology with a focused handoverPain, photophobia, visual reduction or a significant corneal, pupil or postoperative finding is present.

1Record what can be assessed promptly, including acuity, onset, lenses, recent procedures and current topical medication.
2Contact the urgent eye service directly and state the suspected corneal, pressure-related or intraocular threat rather than simply describing a red eye.
3Arrange a safe route to assessment and avoid driving when visual function is affected; do not postpone contact while awaiting non-essential investigations.

03Possible globe injuryProtect from pressure during urgent transferPenetrating injury, a high-velocity mechanism or examination raises concern for an open globe.

1Avoid pressing on the eye, measuring intraocular pressure or attempting to remove an embedded object.
2Use a rigid protective shield where available and minimise manipulation while arranging emergency ophthalmic care.
3Communicate the mechanism, time, available visual assessment and any anticoagulant use so the receiving team can prepare appropriately.

04Lower-risk findingsReassure only after documenting the safety criteriaExamination supports a benign cause with preserved function and no dangerous exposure or finding.

1Explain the likely diagnosis and why the current findings support a less urgent management plan.
2Give specific instructions about new pain, photophobia, visual change or worsening redness, with a route to timely reassessment.
3Arrange review when symptoms persist or the expected course fails to occur, instead of repeatedly extending empirical treatment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Irreversible visual loss

Delay in treating infection, pressure elevation or severe injury can damage transparent tissue or neural structures. The opportunity to preserve vision may narrow rapidly.

Loss of structural integrity

Corneal melting or traumatic rupture can compromise the globe. Pressure and unnecessary manipulation can add harm when the eye wall is already weakened or open.

Harm from an incorrect treatment

Steroids may aggravate infection, and a routine antibiotic may delay recognition of non-infectious emergencies. Diagnostic uncertainty should guide escalation rather than indiscriminate topical prescribing.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Ensure the urgent referral has a practical destination and timeframe; a recorded referral without a workable assessment route does not protect vision.
Document pre-treatment vision where feasible, while noting when an immediate action such as irrigation appropriately came first.
Advise patients receiving outpatient care to seek help earlier for worsening pain, photophobia, a corneal white spot or any continuing visual decline.
Review the response to an initially benign diagnosis and reconsider it when the clinical course or new symptoms contradict the original assessment.
After specialist treatment, ensure the patient understands which medicines continue, the next review date and who to contact if symptoms recur.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Severity is not redness alone

A minimally red eye can harbour important posterior, neurological or early infectious disease, while a painless subconjunctival bleed can look striking. Function and mechanism guide prioritisation.

Photophobia requires clinical context

Mild light sensitivity may accompany surface irritation, but marked or new photophobia with pain or visual change increases concern for corneal or intraocular inflammation.

Recent intervention changes probability

Pain and declining vision after intraocular surgery or injection should prompt immediate contact with the treating or emergency eye service because endophthalmitis requires rapid assessment.

An antibiotic is not a referral substitute

A routine topical prescription cannot address acute angle closure, a penetrating injury or the full treatment needs of a corneal ulcer. Match the response to the threatened structure.

11Common pitfallsFrequent interpretation and management errors.

01
Completing a detailed history or waiting for saline before starting irrigation after a chemical splash.
02
Applying pressure, using tonometry or removing an embedded object when an open-globe injury is possible.
03
Assuming contact-lens-related redness is ordinary conjunctivitis because discharge is present or pain is initially mild.
04
Allowing transient symptom relief from anaesthetic or old steroid drops to replace an assessment of ongoing corneal or intraocular disease.
05
Giving vague advice to return if worse without specifying that visual change and photophobia require prompt reassessment.