Background¹

The cornea is the avascular convex, slightly elliptical-shaped anterior transparent part of the globe. It is one of the sites of refraction of light entering the eye and provides a clear medium through which the light can travel. It is limited at its periphery by the corneal limbus, where the transparent cornea stops and the opaque sclera starts. It is intimately related to the conjunctiva via its epithelium which is continuous (if slightly different in nature) between the cornea and the conjunctiva. Thus infections, inflammatory conditions and trauma can all potentially extend from one to the other.

This record will give you an overview of acute corneal conditions. Other related records include:

Corneal Problems - Non Acute (includes recurrent conditions)
Recurrent Corneal Erosion Syndrome
Dry Eye (keratoconjunctivitis sicca)
Contact Lenses (types and care)
Contact Lens Problems

Symptoms in corneal problems

• Pain - this occurs with any infective, inflammatory and several other corneal problems unless there is gross neuropathy in which case severe disease may cause minimal discomfort. Beware of the patient who complains of severe pain with only a very small apparent defect which you suspect to be of infective origin: this is a characteristic presentation in patients who have acquired the potentially devastating Acanthamoeba keratitis.
• Photophobia - this frequently accompanies pain.
• Reduced visual acuity - any lesion affecting the central visual axis (i.e. occurring over the pupil area) or condition distorting the shape of the cornea will affect the visual acuity. Excess lacrimation (epiphora) due to pain can also temporarily affect the vision.
• Red eye - this frequently accompanies the above symptoms.
• Systemic symptoms - it is not unusual for patients with acute corneal disease to complain of headaches, feeling slightly nauseous and feeling generally run down.

Assessment of the cornea

The cornea in primary care

See our record on Examination of the Eye for more detail about how to perform these assessments.

• Test the visual acuity of both eyes.
• Observe the cornea in plain light. Are there any areas of gross opacification?
• Check for sensation: twist a clean tissue or cotton ball to a tip and lightly touch the centre of the cornea: this should elicit a brisk and immediate response from the patient.
• Apply fluorescein stain to look for defects (if you suspect corneal perforation, perform a Seidel's test).
• If you have access to a slit-lamp, assess the cornea from the anterior (epithelial) surface, through the stroma and to the posterior (endothelial) surface by gently moving the focus backwards by a few millimeters. Look for defects (fluorescein uptake), oedema (area of haziness) and infiltrates (a well demarcated white lesion within the stroma). Vascularisation may occur over the surface or through the stroma, indicating more long-standing disease.
• Examine the rest of the globe and its adnexae. If the symptoms warrant it, do a full systemic examination (see disorders below).

Further assessment of the cornea in a specialist unit

• Pachymetry - this is the measurement of corneal thickness. It is a painless investigation involving placing a measuring probe lightly on the surface of the anaesthetised cornea.
• Specular microscopy - this is a photographic investigation that enables the corneal endothelial cells to be accurately assessed.
• Corneal topography - this is another painless investigation which maps the surface of the cornea rather like an ordnance survey map, showing the gradient at each spot and therefore highlighting asymmetries, such as are found in the dystrophic conditions for example.
• Microbiological investigations - a corneal scrape (clinic) or biopsy (theatre) may need to be done.

Infections²

Bacterial keratitis³

• Nature - infection of one or more layers of the cornea. Most bacteria can only produce keratitis once the integrity of epithelium is compromised, such as following a corneal abrasion or prolonged contact lens wear. Neisseria gonorrhoeae and Haemophilus influenzae are the exception, being able to cross intact epithelium. Risk factors include:⁴
  • Extrinsic factors, e.g. contact lens wear (especially prolonged or associated with poor hygiene), corneal trauma (accidental or surgical) and drug-related (such as contaminated medication, prolonged steroid therapy and some glaucoma medication).
  • Ocular surface disease, e.g. poor tear film.
  • Corneal epithelial abnormalities, e.g. neurotrophic keratopathy, viral keratitis.
  • Systemic disease, e.g. diabetes, debilitating disease and hypovitaminosis A.
• Presentation - redness, pain, photophobia, foreign body sensation and reduced visual acuity. There will usually be an epithelial defect ± the presence of white cell infiltrate ± oedema.
• Management - refer:
  • These patients will need intensive topical antibiotic treatment (often after microbiology cultures) ± cycloplegics.
  • Topical steroids may be added during the healing stage.⁵ A balance has to be struck between reducing corneal scarring through inflammatory suppression and the possible adverse effects (including prolonging the infection, raising the intraocular pressure and inhibiting collagen synthesis).⁴ For this reason, steroids should only be given under specialist supervision.
  • Patients with severe infection or in whom treatment compliance may be poor are admitted. A few others (e.g. this is their only functioning eye) may also be admitted.
  • When explaining your plan to the patient, tell them to discontinue any contact lens wear and to bring all their contact lens equipment (lens, storage box and cleaning solution) with them - these will be sent off to microbiology; they will be destroyed in the culturing process.

Viral keratitis

• Nature - the most common culprits are the herpes simplex virus (HSV), causing herpes simplex eye infections, and the varicella zoster virus (VZV), causing herpes zoster ophthalmicus. These can cause damage at all layers of the cornea and the surrounding structures, either through direct viral invasion or as a result of secondary inflammation.
• Presentation
  • HSV: primary infection is very mild and usually occurs in early childhood, characterised by a viral-type upper respiratory tract infection and slight rash. Secondary infection varies from superficial dendritic ulcers to deep stromal involvement. The patient presents with typical features of corneal problems (see above). There is often decreased corneal sensation.⁶ Triggers for viral reactivation include UV light, trauma, cold, menstruation and psychological stress.
  • VZV: years to decades after the primary varicella infection (chickenpox), there is the development of an influenza-type illness, neuralgia, macular-papular rash over the distribution of the ophthalmic branch of the trigeminal nerve (occasionally crosses this barrier). Keratitis develops in about 65% of these patients (Hutchinson's sign: cutaneous involvement of the tip of the nose suggests an increased likelihood of ocular complications). Precipitating factors include physical trauma, surgery, immunosuppression and systemic illness.
• Management - refer in both cases, as degree of corneal involvement needs to be carefully assessed to determine the need for (usually) topical antivirals ± cycloplegia (HSV),⁷ systemic antivirals (VZV), topical steroids (in some cases of deep HSV) and to monitor for complications (such as necrosis, ulceration/perforation, scarring). Immunosuppressive drugs such as ciclosporin A are new alternatives to corticosteroid use in select HSV patients.⁸ Most patients also benefit from lubricants.⁶ Whilst it is best practice to refer the patient with suspected HSV, in the case of a well-established case of recurrent infections in an individual living in a rural area, treatment may exceptionally be started in the community where there is an agreed written plan with the local specialist.⁹

Fungal keratitis (keratomycosis)

• Nature - rare but potentially devastating infection most commonly caused by Aspergillus and Fusarium species and typically seen in agricultural settings or where an injury occurred involving organic matter such as wood or plants. Candida keratitis is seen in AIDS patients. Other susceptible patients are debilitated individuals and those with pre-existing corneal disease.⁵
• Presentation - similar symptoms to bacterial keratitis but onset very gradual and less severe. May be diagnosed following non-response to treatment of 'bacterial' keratitis.
• Management - refer. The cornea is scraped and topical antimycotic therapy initiated (although doubt has been cast as to the effectiveness of current available therapies)¹⁰. The treatment may last many weeks and unresponsive cases may require systemic treatment or even a therapeutic penetrating keratoplasty (corneal transplant).

Protozoal keratitis

• Nature - the most feared is the Acanthamoeba species - a ubiquitous free-living protozoan found in air, water (fresh, salty, tap, swimming pools and hot tubs) as well as dust, soil or sewage. It largely survives freezing to boiling temperatures and the chlorination of swimming pools. Contact lens wearers are at risk (although anybody can be infected). It can cause a devastating, sight-threatening infection.
• Presentation - this ranges from asymptomatic to a foreign body sensation, reduced visual acuity and extreme pain (disproportionate to mild clinical findings). Punctate or dendritiform defects may be present with small, white satellite lesions.
• Management - refer. Topical amoebicides will be used in association with topical steroids. In severe cases, a therapeutic penetrating keratoplasty may be needed to preserve the globe.

Other infectious keratitis

• Luetic interstitial keratitis - stromal inflammation associated with, amongst others, syphilis infection.
• Microsporidial keratitis - bilateral diffuse keratitis or unilateral deep keratitis seen in the immunocompromised.
• Infectious crystalline keratopathy - a rare indolent infection associated with the herpes simplex virus, acanthamoeba keratitis, Strep. viridans and long-term topical steroid therapy.

Trauma¹¹

Go to our record on Eye Trauma for further information.

Minor mechanical injury

• Nature - this is relatively common, as fingernails, paper, foreign bodies (FBs) and an assortment of other objects can cause abrasions (and, less commonly, lacerations).
• Management - a full assessment as above should be performed. Corneal abrasions - even very large ones - heal very well and the patient should be reassured. A 5-7 day course of topical chloramphenicol ointment (provides better lubrication, and therefore comfort, than drops) and advice to take simple oral analgesia as required should do. Review if the abrasion was large ± refer if concerned. Lacerations should be referred, as they can easily mask a penetrating injury. Cover the eye with a rigid shield and make a same day referral.

Major mechanical injury

• Nature - this may range from contusion (closed injury, although there may be associated corneal epithelial abrasion) to a full thickness open injury
• Management - if the history suggests a major injury, refer for further assessment, even if there is little to be seen on examination. An apparent simple corneal abrasion may overlie iris or retinal damage.

Chemical injury¹²

• Nature - this may range from trivial to sight-threatening. The severity of the injury is proportional to the properties of the chemical, the amount of ocular surface affected and the duration of exposure (including retention of particles in the conjunctival fornices). Alkalis (particularly ammonium and sodium hydroxide) tend to penetrate deeper than acids and cause particularly severe damage.
• Management:
  • IRRIGATE - do not waste time taking a history - this can be done once irrigation is underway or after. Irrigate copiously (several litres may be required for up to 30 minutes) and test pH frequently - even after normality (about 7) has been achieved, as retained particles can lower the pH again.
  • After irrigation, take history and baseline examination - don't forget visual acuities as this may be the only point of reference if they deteriorate.
  • Refer. A white eye does not preclude referral: limbal ischaemia blanches the vessels immediately around the cornea.

Thermal injury¹²

• Nature - these may be thermal or ultraviolet (UV), the latter occurring in welders not wearing protection and when bright light is reflected off concrete and snow. The damage is usually superficial.
• Management - most can be treated as corneal abrasions (see above). Analgesia is important, particularly in the case of UV burns, which are notoriously painful. (Do not give topical analgesia to take home as this impedes epithelial healing).

Corneal foreign bodies

Also see our record on Foreign Body in the Eye.

These most commonly occur in the context of DIY work, in manual labourers and in car mechanics. They can usually simply be removed with a cotton bud under topical anaesthetic. A slit lamp and a steady hand enable removal of more deeply embedded FBs. Metallic FBs often leave a residual rust ring which should be removed then or subsequently (it should work its way more superficially after about a week). The patient should be warned that it will be more painful when the anaesthetic wears off but that the acute pain should not last more than a day. Centrally-placed FBs may result in slightly altered visual acuity for a few weeks.

Referral criteria for corneal injuries: checklist¹³

If in doubt about how to assess or manage the trauma, refer. Conditions that warrant a mandatory referral are:

• All high velocity injuries, presence of a hyphaema, distorted pupil or suspected retinal damage
• All chemical injuries
• If there is a foreign body that cannot be removed or presence of a rust ring
• Pain not relieved by local anaesthetic
• Large abrasions (>60% of the surface)
• Persistent symptoms (>72 hours), worsening symptoms or a corneal abrasion that shows no healing on daily review

Acute problems following keratoplasty^5,6

• Nature - corneal grafting (keratoplasty) is the commonest and most successful of all procedures. It can be performed as an elective procedure to improve vision, or as an emergency in the case of corneal perforation. Early post-operative complications include:
  • Wound leak
  • Raised intraocular pressure
  • Persistent epithelial defect (>2 weeks)
  • Endophthalmitis
  • Graft failure
  • Graft rejection
  • Urrets-Zavalia syndrome (iris ischaemia)
• Presentation - patients who have undergone a keratoplasty and present with any of the symptoms outlined above should be assumed to have one of the above complications until assumed otherwise. Each has a slightly different presentation: these patients will be under close ophthalmological review in the first year at least. It is worth noting that corneal graft rejection most often occurs within the first two years post procedure.
• Management - refer. Ideally, the operating surgeon should see the patient but, if they are not available (e.g. out of hours), refer to the on call ophthalmologist who will initiate the management and liaise with the team.

Recurrent or progressive conditions

There are a number of conditions that may present acutely but that are recurrent or part of a more long-term condition. These include:

• Marginal keratitis
• Rosacea-associated keratitis
• Exacerbations of exposure keratopathy
• Peripheral ulcerative keratitis

You can read more about these in our record on non-acute corneal problems.