The chemical eye burn is the true ophthalmic emergency in the foreign body context — alkali burns (from bleach, cement dust, ammonia, calcium hydroxide) cause progressive penetrating injury because hydroxide ions continue to saponify cell membranes and penetrate into the anterior chamber, potentially reaching the lens, trabecular meshwork, and ciliary body. The damage is time-dependent: irrigation started within 1 minute of alkali exposure dramatically reduces long-term corneal damage; irrigation delayed beyond 5 minutes risks permanent corneal scarring, limbal stem cell destruction, and potentially severe visual loss. The initial management priority is immediate, continuous, copious irrigation — before transport, before visual acuity measurement, before phone calls. Every GP surgery should have equipment for eye irrigation: a Morgan lens or standard IV giving set and normal saline. The target is a post-irrigation conjunctival pH of 7.0-7.4 — measured with pH paper placed in the lower fornix. If the pH does not reach neutral within 30 minutes: continue irrigation and assess for particulate chemical (cement, lime) retained in fornices — sweep the fornices with a cotton bud.

The subtarsal foreign body is one of the most frequently missed causes of persistent ocular foreign body sensation in primary care — a tiny particle of grit, metal, or plant material lodged under the upper eyelid causes relentless vertical corneal abrasions with every blink, producing a foreign body sensation that persists despite the patient believing they have 'got it out.' The characteristic clue is the vertical corneal abrasion pattern on fluorescein staining — multiple parallel vertical scratches on the superior cornea (where the tarsal plate sweeps across the cornea on blinking) rather than a single focal abrasion. Upper lid eversion is a mandatory component of any examination for ocular foreign body — the examination is not complete without it. The technique: ask the patient to look down (this relaxes the levator muscle and makes the lid more mobile), place a cotton bud or two fingers horizontally at the base (lower margin) of the upper lid at the tarsal plate, and fold the upper lid upward over the cotton bud. The inner surface of the lid is now visible and the subtarsal FB is often immediately apparent.

Fluorescein dye is an essential diagnostic tool for corneal assessment — it stains damaged corneal epithelium bright green under cobalt blue light, making corneal abrasions, ulcers, and foreign body tracks visible that are invisible in white light. The technique: moisten a fluorescein strip with a drop of saline (or tetracaine — the anaesthetic facilitates patient cooperation by reducing blepharospasm), touch the lower conjunctival fornix with the wet strip, ask the patient to blink to distribute the dye, then examine with cobalt blue light (on a standard pen torch with a blue filter, or a dedicated fluorescein examination light). The interpretation: a single bright green patch = corneal abrasion or FB site; multiple parallel vertical lines on the superior cornea = subtarsal FB; dendritic (branching) pattern = herpes simplex keratitis (not a foreign body — antiviral urgently); large diffuse staining with ring lesion = Acanthamoeba keratitis (contact lens wearers — emergency ophthalmology). GPs should be proficient in fluorescein examination — it takes 2 minutes and provides definitive diagnosis in the majority of corneal presentations.

The Seidel test is a critical sign that every GP performing eye examinations should know — if fluorescein is applied to a corneal wound and the dye streams away from the wound site in a flowing rivulet (rather than remaining pooled), this indicates that aqueous humour is leaking from the anterior chamber through the wound (positive Seidel test). This is diagnostic of a penetrating corneal injury with an open globe — the intraocular pressure is maintaining a flow of aqueous outward through the wound. A positive Seidel test is an absolute indication for emergency ophthalmology referral: do not apply any pressure to the eye, do not irrigate (unless chemical injury — in which case gentle irrigation is still appropriate), apply a rigid eye shield, and call 999. The Seidel test takes 30 seconds — applying fluorescein and examining for streaming flow under cobalt blue light is a simple but potentially sight-saving assessment.

The rust ring removal decision is one where GPs must refer rather than attempt — an iron-containing metallic FB on the cornea begins to oxidise within hours, forming an iron-oxide ring in the surrounding corneal stroma. The rust ring is not inert — it continues to release iron ions that are directly toxic to keratocytes (corneal stromal cells), causing progressive corneal stromal damage. Rust ring removal requires: a slit lamp (for precise 3D visualisation), local anaesthesia (topical), and either a sterile hypodermic needle or an ophthalmic rotary drill (burr) to mechanically debride the ring. This procedure requires ophthalmic training and equipment that is not available in primary care. GPs who identify a rust ring should refer same-day to ophthalmology or an eye casualty unit — attempting to dig out a rust ring with a hypodermic needle in primary care under a hand torch risks corneal perforation and worsening the injury.

The tangential approach for corneal FB removal is essential to avoid iatrogenic corneal perforation — the cornea is approximately 550 microns (0.55mm) thick at the centre and slightly thicker at the periphery (approximately 650 microns). A needle inserted perpendicularly into the cornea risks full-thickness penetration if it is pushed deeper than intended. The correct technique: approach the FB with the needle bevel-up (smooth concave side of the needle facing down) at a shallow tangential angle (approximately 10-20 degrees from the corneal surface), and use a gentle side-to-side sweeping motion to dislodge the FB rather than digging into the stroma. The analogy: like removing a splinter from the surface of a plum — scrape it off from the side rather than digging down. GPs who are not confident performing this technique should refer — a confident referral to ophthalmology or urgent care with a slit lamp is better than an inadvertent iatrogenic corneal injury.

Recurrent corneal erosion syndrome (RCES) is an important but frequently missed complication of corneal abrasion — it occurs in approximately 5-10% of patients who had a significant corneal abrasion, typically 2-8 weeks after the original injury. The mechanism: the new corneal epithelium that regrows over the abrasion does not form adequate hemidesmosome attachments to Bowman's membrane, making it prone to re-avulsion during sleep (particularly when the eyelid moves across the dry ocular surface during REM sleep). The patient wakes suddenly with severe eye pain — exactly reproducing the sensation of the original injury. The clue: pain awakening the patient from sleep, 2-8 weeks after an original corneal abrasion, with fluorescein showing a recurrent abrasion in the same location. Treatment: preservative-free lubricant ointment (Lacri-Lube or VitA-POS) applied at bedtime for several months — this lubricates the eyelid-corneal interface during sleep and prevents the avulsing force. Ophthalmology referral for: recurrent episodes despite ointment (anterior stromal puncture, phototherapeutic keratectomy).

The fungal keratitis risk from organic foreign bodies (plant material, soil, grain) is a serious and time-sensitive condition that differentiates plant/agricultural FB from metallic FB management — fungal keratitis (caused by Fusarium solani, Aspergillus fumigatus, Candida, and other fungi) is typically preceded by a corneal injury with organic material. The clinical presentation differs from bacterial keratitis: slower onset (days rather than hours), grey-white corneal infiltrate with feathery borders, satellite lesions, immune ring, and hypopyon. The diagnosis is confirmed by corneal scraping + microscopy and culture (specialist procedure). Treatment requires topical antifungal (natamycin 5% eye drops — not widely available in UK; voriconazole 1% or itraconazole depending on organism). Standard chloramphenicol eye drops provide no antifungal coverage. GPs who treat a corneal abrasion from organic material and find the patient returning at 48-72h with worsening symptoms (instead of the expected improvement) should suspect fungal keratitis and refer urgently to ophthalmology.

The visual acuity documentation in eye injury consultations is a medicolegal standard that cannot be overlooked — a GP who treats an eye injury without measuring and documenting visual acuity has an incomplete clinical record. If the patient subsequently develops visual loss and claims it was caused by the injury (or by inadequate treatment at the GP consultation), the absence of a documented VA measurement makes it impossible to establish whether the vision was normal at the time of the GP assessment. The documentation should state: 'VA right: 6/6 (or specific near vision equivalent). VA left: 6/6 (or specific result). Measured with [near-vision card / Snellen chart / patient's reading glasses].' If the patient was unable to cooperate with VA testing (severe photophobia, blepharospasm from the injury), document: 'VA measurement attempted — patient unable to cooperate due to blepharospasm and photophobia. Referred to ophthalmology for formal assessment.' This protects the patient and the GP.