Chun-Huei Liu ( left ) Fourth-year medical student at Griffith University , Sunshine Coast , Queensland .

Professor Graham A Lee ( right ) Professor of ophthalmology at the University of Queensland , Brisbane and visiting senior consultant ophthalmologist at Mater Hospital Brisbane and Queensland Children ’ s Hospital , Brisbane , Queensland .

First published online on 5 April 2024

BACKGROUND

THE cornea is the most exposed part

of the eye . It is at risk of injury , environmental conditions , infection and UV radiation . Damage to the cornea can result in scarring , with a loss of clarity and reduction in vision . It has the highest density of nerve fibre endings of any tissue in the body , which acts as a protective mechanism . Any breaches of this ocular surface stimulate pain . Loss of this sensitivity results in increased trauma and poorer healing response . The cornea is in a continuum with the conjunctiva and in contact with the lids and anterior chamber of the eye . Thus , conditions of these structures have a direct effect on the cornea .

The accessibility of the cornea is also a benefit . With good illumination and magnification , the cornea can be examined , and conditions diagnosed and appropriately managed . The slit lamp is the ideal equipment for corneal examination ; however , this is generally more available to the ophthalmologist . Otherwise , light from an LED torch , loupes , or direct ophthalmoscope , with local anaesthetic , fluorescein stain and cobalt blue light can be

utilised to examine for most of the common corneal conditions .

This How to Treat covers the more common corneal conditions that may be encountered and aims to ensure GPs can either manage safely or make the appropriate referral for further ophthalmic review .

CORNEAL FOREIGN BODIES

CORNEAL foreign bodies ( FBs ) are

a common ocular trauma . There is a wide-ranging presentation , from superficial epithelium only to full-thickness penetration of the cornea . As such , the presenting symptoms range from mild irritation to severe pain with vision loss .

History

The timing and onset of the FB event is crucial , as recent incidents are typically easier to address because of the absence of encroaching corneal epithelium and the lack of a rust ring . The leading cause of FBs stems from a combination of inadequate use of protective eyewear and engaging in high-risk activities such as grinding , hammering , drilling and welding . In cases where the FB is metallic , it is

common to observe a small rust ring surrounding it . However , it is important to note that organic materials , such as plant or insect ( see figure 1 ), carry a higher risk of infection and necessitate referral for appropriate management . Broken sutures from previous ophthalmic surgery may be encountered and require removal by a specialist .

Examination

The location , size and depth of the corneal FB is critical for appropriate management planning . The surrounding tissue needs to be examined for rust ring , burn , infection ( see figure 1D ), oedema or scar tissue . If the pupil is peaked in shape , suspect iris incarceration from a penetrating FB . Eyelid eversion is performed to thoroughly examine the tarsal plate and upper fornix for FBs ( see figure 1C ), which if missed can cause ongoing symptoms after corneal FB removal . Topical fluorescein aids in identifying epithelial defects caused by the FB . Specifically , vertically oriented linear corneal defects suggest the presence of a tarsal plate FB . In situations where corneal perforation has occurred , a

positive Seidel test may be observed , characterised by a waterfall appearance because of the flow of aqueous humour from the wound .

Differential diagnosis

Corneal abrasion or laceration without

an FB can be challenging to distinguish , given the overlapping symptoms of discomfort . It is crucial to also consider the potential for globe perforation . If an intraocular FB is suspected from the history , for example , hitting metal against metal , urgent specialist referral is required for FB removal and prevention of intraocular infection ( endophthalmitis , see figure 2 ). Keratitis is indicated by opacity around the FB and intense conjunctival injection . Differentiating between these various conditions is facilitated by a comprehensive patient history and identifying the key signs on examination .

Investigations

In the investigation of FBs , additional diagnostic procedures are generally unnecessary unless there is a suspicion of ocular penetration , an intraocular FB , or intracranial FB . However , in certain cases , further