The cornea is a transparent avascular structure but can still be a cause of eye redness when affected by various conditions. The typical appearance is dilated inflamed conjunctival blood vessels around the limbus, often described as ciliary injection or limbal blush. Symptoms of corneal disease usually include pain, photophobia, lacrimation (excess tear production) and sometimes visual blurring and/or glare. Although a detailed examination of the cornea requires slit-lamp biomicroscopy, many conditions can be diagnosed by close inspection with a pen-torch light (especially with the additional use of topical fluorescein).
Corneal abrasions are generally from the ocular surface being scratched, commonly from finger nails, plants and paper. Symptoms include significant pain, photophobia, watering and occasionally reduced vision.
Assessment involves instillation of a topical anaesthetic which usually dramatically improves the foreign body discomfort. The diagnosis is facilitated by additional use of topical fluorescein dye which stains any part of the cornea devoid of epithelium. The corneal abrasion is therefore highlighted using a white or cobalt blue light, the latter wavelength illuminating the fluorescein.
Unless relatively minor, an urgent referral is required for an ophthalmological assessment, especially in contact lens wearers where the chance of infection may be higher. Sub-tarsal foreign bodies under the upper eyelid should be ruled out (see "Upper And Lower Eyelid Eversion" section).
The vast majority of abrasions heal quickly over a few days. Topical antibiotics reduce the risk of secondary corneal infection (microbial keratitis) and applying a pressure dressing over the closed eyelids often reduces discomfort. In a small number of individuals the healed corneal epithelium is fragile and prone to be rubbed off by the eyelids; this is known as recurrent erosion syndrome.
Corneal Foreign Body
Various foreign bodies eg metal, wood, glass may get embedded into the cornea. There may be a relevant history such as striking metal or stone without wearing eye protection. Metal foreign bodies tend to be surrounded by a rust ring within 24-48hrs but vegetable matter eg wood often carries a greater risk of microbial keratitis (secondary corneal infection).
Superficial foreign bodies may be removed, after instillation of a topical anaesthetic, using a cotton bud moistened with saline. If the foreign material is more embedded then a small gauge needle may be required. The fragment is “flicked” out using the needle which is carefully held from the temporal side of the affected eye. The resulting corneal defect is treated as for any corneal abrasion. Failure to completely remove the foreign body, deeper fragments or any suggestion of associated infection requires referral.
Dendritic Corneal Ulcer
A dendritic ulcer results from a corneal infection secondary to the Herpes Simplex Virus (HSV) type 1. This is a DNA virus which commonly infects children and young adults, often initially manifesting as a non-specific upper respiratory tract illness. Subsequently HSV type 1 lies dormant in the trigeminal nerve and activation of the virus can result in infection of the corneal epithelium.
Patients often present with a red eye, photophobia and blurred vision. Fluorescein can be used to highlight areas where some of the infected corneal epithelium has shed off. This is typically in a fine branching pattern, hence the term dendritic keratitis or ulcer.
This condition may be self limiting within a few weeks but treatment should be initiated to limit corneal scarring which may threaten vision. A topical anti-viral agent eg acyclovir is usually the most effective therapy. Even brief exposure to topical steroids can significantly worsen the dendritic ulcer and therefore must be avoided. Referral to a specialist is necessary as occasionally it is helpful to reduce the viral load by careful removal (“debridement”) of the infected corneal epithelium. Occasionally oral anti-viral agents are recommended for frequent recurrent episodes.
- A diagnosis of dendritic corneal ulcer should only be made in a contact lens wearer once acanthamoeba keratitis (which can look similar) has been ruled out.
Bacterial keratitis is a sight threatening condition which can develop rapidly over several hours. Common risk factors for bacterial keratitis include contact lens wear, corneal trauma and contaminated topical medications. Typically the corneal epithelial integrity is disturbed, making the eye vulnerable to spread of infection into the deeper corneal tissue.
Patients tend to present with a rapid onset of pain, photophobia, redness and reduced vision. Bacterial corneal ulcers typically have a variably sized defect in the corneal epithelium which can be highlighted using fluorescein dye. In addition there is usually a pale inflammatory infiltrate present in the deeper corneal tissue; this may be visible as a whitish opacity using a pen torch to illuminate. Common causative agents include Staphylococcus aureus, Streptococcus pneumonia and pseudomonas aeruginosa, the latter being the most frequent organism in contact lens wearers.
Bacterial keratitis is considered an ophthalmic emergency and immediate referral is required. Corneal scrapes to obtain specimens for gram stain and culture are required before initiation of treatment. Contact lens cases and solutions are also cultured if available. Initial intensive broad spectrum antibiotic eye drops are commenced, with later modification of therapy depending on clinical response and microbiology results.
Other differential diagnoses, such as acanthamoeba keratitis or fungal infection, should be considered if the cornea is failing to improve despite adequate antibiotic therapy.