This article outlines the importance of history taking and identifying clinical signs and symptoms to manage patients presenting with corneal infection.
Most peri-ocular and corneal infections, especially if mild, are treated with Chloramphenicol and Fucithalmic preparations. They occur commonly, with patients frequently presenting to the optometrist, general practitioner and the hospital accident and emergency departments. Most eye infections require treatment. However, contact lens wearers should be given special consideration, as given the very nature of wearing contact lenses, introducing a foreign body onto the eye in a non-sterile manner while also inducing some degree of tissue hypoxia, increases the risk of aggressive sight threatening infections.1 With an estimated 3.7 million contact lens wearers in the UK,2 the number of people having experienced or at risk of significant corneal infection is not to be ignored.
Contact lens wear is a recognised risk factor for corneal infections.3 Even if a contact lens wearer presents with a corneal abrasion, due to a breach in their epithelium and change in their microenvironment, they are at a particular risk of subsequent infection. Poor contact lens care, such as storing contact lens cases in a moist bathroom, not changing lenses and solution as per the recommended regimen, over wearing lenses, poor hand hygiene are all the risk factors for acquiring an infection.3–4 Abnormal blinking is often seen in contact lens wearers. Incomplete blinking or a reduced blink rate can lead to contact lens drying, reduced tear exchange beneath the lens and deposit formation; these in turn contribute to corneal hypoxia and debris retention beneath the contact lens and, therefore, increase the risk of infection.5
It has been suggested that the incidence of infection between daily and monthly contact lens wearers is similar.6 However, monthly contact lens wear is more likely to be associated with severe infections and result in sight loss than daily disposables.7
There are numerous other causes of eye infection that can either stand alone, or accumulate together with contact lens wear to contribute to an increased risk of corneal infection. Trauma and surgery, particularly when the corneal surface is breached, also increases the risk of infection;8 both of these decrease the integrity of the corneal epithelium. Systemic disease, for example, diabetes and thyroid-associated orbitopathy are also linked with infection.1 Topical steroid use may suppress the immune response to infection, or be associated with increased ocular surface dryness, again compromising the corneal epithelium and, therefore, pose as risk factors which can contribute to corneal infection.5
The purpose of taking a history is to be able to ‘pre-diagnose’ the problem, even before clinical examination has taken place. In most cases, careful history taking can paint an accurate picture of what you will find on clinical examination and, therefore, it can be a very useful tool if done well.
To ensure all the potential factors that could be contributing to a corneal infection are identified, it is important to take a thorough history and not make assumptions based on previous experience, although this can help to streamline the process. The first thing to ascertain is which eye is the patient concerned about, right, left or both, and how long have they been aware of their symptoms. After this, the presenting symptoms need to be confirmed. In some cases simply looking at the patient will allow the practitioner to identify the affected eye. The eye may be red, watery and/or oedematous. The oedema may be of the eyelids or chemosis of the conjunctiva itself. In addition, there may be discharge and photophobia present. Asking about onset, duration, and how quickly symptoms have escalated will potentially allow you to determine the severity of the presenting complaint. For example, fast progressing symptoms are likely to be due to an aggressive pathogen.
Routinely, it is considered good practice to enquire if there are any factors that relieve or aggravate the patient’s symptoms. Equally, chronologically sequencing events can also help determine the cause and severity of infection. For example, if the patient knows their symptoms commenced after working in the garden following vegetative material trauma to the eye, the risk of fungal or atypical infection is increased. Alternatively, if their symptoms started after a recent history of swimming in their contact lenses, there is the possibility that acanthamoeba is the causative organism. By determining risk factors, it also allows the visual morbidity of the infection to be estimated.
Specifically for contact lenses wearers, it is important to determine the type and duration of contact lens wear. Equally, how often they wear their contact lenses must be established. How, when and where they clean their lenses must be elicited, as must how and what they use to do this. Sometimes it can be beneficial to ask the patient to describe the regimen they use to clean their lenses. If they are unable to do this satisfactorily, it may suggest they are not adhering to the best standards of contact lens care. Enquiring about previous infections the patient may or may not have suffered can help to guide the type of infection they are presenting with, particularly if they have a history of atypical infection such as fungus or acanthamoeba, which are notoriously difficult to eradicate.
It is also important to ask every contact lens patient if they own glasses. Any patient presenting with an infection should be told they must not wear contact lenses until the problem has fully resolved. An infection may mean they fall below the level of vision required for driving and would invalidate their insurance if they drive without their prescribed refraction. If an infection, for example, causing a corneal ulcer were to be located on the visual axis, the achievable visual acuity may also be reduced from the patient’s usual level. A summary of the most useful questions to ask patients presenting with an eye infection is provided in Table 1.
Signs of infection
Having taken a comprehensive history from the patient, an equally thorough examination of both eyes must be performed. Care needs to be taken so as not to risk spreading infection from the affected to the unaffected eye. In some infections, for example, bacterial conjunctivitis, transfer of infection to the practitioner, colleagues and other patients must also be avoided and, therefore, it is important to wash hands both before and after examining patients. Do not use the same cotton bud or any item that comes into contact with the eye on the fellow eye of the patient or other patients. Observe the patient to determine if they exhibit reduced vision or visual acuity, signs of pain, conjunctival injection, photophobia, epiphora and discharge.
When examining a patient, using the slit lamp will give the most detailed view using adequate magnification and resolution. Instilling fluorescein and using a Wratten filter can detect any disturbance to the corneal epithelium. Evert the eyelids and look for foreign bodies and also check for signs of papillitis. Determining the exact location of a corneal ulcer is helpful. If the ulcer is small in size and located away from the visual axis, the long term effects are likely to be less severe than if it is located over the pupil on the visual axis, as the resulting scarring is likely to obscure their vision and result in glare and reduced visual acuity.
When to refer to the eye casualty
If an eye infection is suspected, practitioners should have a low threshold for considering referral or discussion with the local eye casualty for a second opinion and treatment. Although many practitioners are participating in minor eye condition schemes through local arrangement, any patient that causes concern or if the practitioner feels uncertain, should be referred. All eye departments offer the capacity to give immediate and specific treatment to patients they confirm have an infection. They also have the facilities to perform tests to isolate the causative organism. These include both bacterial and viral swabs, along with corneal scrapes. The samples taken can be sent to the microbiology laboratory for analysis, which may identify the causative organism and give specific drug sensitivities; this will guide the choice of drug treatment. Similarly, positive organism culture provides advice on drug resistance and again this will enable the practitioner to target treatment more effectively. Another advantage about referring infections to eye casualty is that they have the capacity to follow patients up and ensure treatment has been effective.
Treatment type and mechanism of action
Chloramphenicol is a broad spectrum antibiotic, commonly used as an eye drop to treat conjunctivitis and ulcers. It can easily be bought as an over-the-counter preparation by patients. It exerts bacteriostatic effect by inhibiting protein synthesis. It does this by binding to the 50s subunit of bacterial ribosomes, thereby inhibiting peptidyl transferase and, therefore, preventing peptide bond formation and as a consequence the formation of proteins.9 However, it does not provide cover against Pseudomonas aeruginosa.
Pseudomonas aeruginosa is gram-negative, aerobic coccobacillus bacterium. It is a versatile opportunistic human pathogen, found in soil and water.10 It can cause corneal infection when the ocular surface is compromised. The risk of infection increases when people do not wash their hands properly and when patients wash their contact lenses or cases in water. It can also colonise contact lens cases, so a history of durable contact lens use is particularly important, as this may be the cause of infection. Pseudomonas aeruginosa infections can be treated with an array of agents targeting gram-negative bacteria and these include Ofloxacin and Gentamicin. However, the first line treatment is Ofloxacin or any of its derivatives due to reduced epithelial toxicity.
Ofloxacin is a broad-spectrum antibiotic providing cover against gram-positive and gram-negative bacteria including Pseudomonas aeruginosa. It belongs to the fluoroquinolone family of antibiotics and is bactericidal in its action. It acts intracellularly by inhibiting DNA gyres in bacterial cells,11 preventing the DNA structure from being maintained. After instillation, Ofloxacin drops are well maintained in the tear film, meaning the pharmacokinetic and pharmacodynamic profiles for antimicrobial activity are preferable.12
In non-contact lens wearers, Staphylococcus aureus is the predominant microbe causing eye infections.1 Staphylococcus aureus is a gram-positive bacteria that has a relatively thick cell wall and for this reason prevents the crystal violet-iodine dye stain from escaping when a gram stain test is performed.13 Along with Haemophilus influenzae, Streptococcus pneumoniae and Moxarella catarrhalis, it is a common cause of bacterial conjunctivitis;14 these infections are treated by using Chloramphenicol. Table 2 summarises the media required to culture invading pathogens.
In the UK, Chloramphenicol is still a popular agent and is readily used by general practitioners and ophthalmologists. It remains the first-line agent for non-contact lens related infections and is useful for treating bacteria that are normal skin commensals such as Staphlococcus aureus. For this reason, it is still the antibiotic of choice in post-operative patients. However, it is now common practice amongst ophthalmologists to treat corneal abrasions in contact lens wearers with Ofloxacin or derivatives and not Chloramphenicol. The history of contact lens wear should always be highlighted, as this patient group is viewed differently due to their increased risk of corneal infection and risk of incurring visual morbidity.
About the authors
Dr Claire Whaley MBChB BSc (Hons) is currently working at Salisbury District Hospital as a trust grade senior house officer in ophthalmology. Prior to this she worked as an optometrist. Dr Cheryl MacGregor BM is a speciality trainee in her sixth year of ophthalmology, currently working at St Mary’s Hospital on the Isle of Wight.
- Bennett E S, Weissmann B A. (2005) Clinical Contact Lens Practice. Lippincott Williams and Wilkins
- Smolin G, Foster C S, Azar D T, Dohlman C H. (2005) Smolin and Thoft’s The Cornea: Scientific Foundations and Clinical Practice. Illustrated Edition. Lippincott Williams and Wilkins
- Bannister B, Gillespie S and Jones J. (2009) Infection: Microbiology and Management. Third Edition. John Wiley and Sons
- Yanoff M. and Duker J.S. (2009) Ophthalmology. Third Edition. Mosby, Elsevier Health Sciences
- Dart JKG, Stapleton F, Minassian D. Contact lenses and other risk factors in microbial keratitis. Lancet 1991;338:650-654
- Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JKG, Brian G et al. The incidence of contact lens microbial keratitis. Ophthalmology 2008;115:1655-1662
- Probst L E, Tsai J H. (2012) Goodman G (ed) Ophthalmology: Clinical and Surgical Principles. SLACK Incorporated
- Forrest G N, Oldach D W. (2004) Chloramphenicol. In: Sherwood L. Gorbach, John G. Bartlett, Neil R. Blacklow (eds) Infectious Diseases. Third edition. Philadelphia: Lippincott WilliansWilliams and Wilkins
- Botzenhart K, Doring G. (1993) Ecology and Epidemiology of Pseudomonas aeuruginosa. In Campa M, Bendinelli M, Friedman H (eds) Pseudomonas aeurginosa as an Opportunistic Pathogen. New York, Plenum Press
- Antibacterial activity of ofloxacin and its mode of activity, Infection; 1986; Sato K, Inoue Y, Fujii T, Aoyama H, Mitsuhashi S. Antibacterial activity of ofloxacin and its mode of action. Infection. 1986;14;(4):S226-230
- Ready I. (ed) (1995) Ocular TheraputicsTherapeutics and Drug Therapy Pensylvannia. Technomic Publishing Company, Inc.
- Freeman - Cook L, Freeman - Cook K.D, Alcamo I.E, Heymann D. L. (2006) Staphlococcus Aureus Infections. Deadly diseases and epidemics. Infobase publishing
- Lee G. and Bishop P. (2012) Microbiology and Infection Control for Health Professionals. Fifth edition. Pearson Higher Education AU.