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How to accurately diagnose red eye

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Medical schools cannot be accused of overloading medical students with ophthalmology knowledge during their training; medicine is such a huge field of study, and there is so much to learn, that subjects like ophthalmology are moved down the hierarchy in terms of importance.

Additionally, ophthalmology is a field with a special device or piece of equipment for examining almost every part of the eye, so the GP in his/her consulting room may be forgiven for feeling ill-equipped on occasion to deal with the patient with the red eye that has just walked in the door.

However, with an ophthalmoscope, a torch, and a relatively simple work plan, a reasonable diagnosis can be made most of the time that can save the patient a lot of trouble if managed well.

There are a few basic principles that help differentiate more serious conditions from the more benign conditions. Generally speaking, the following indicate that the situation may be more serious:

1) One eye involved (rather than both);
2) Pain being a feature (rather than just grittiness or a foreign body sensation);
3) Photophobia or an increased sensitivity to light;
4) Pupils that have changed shape (teardrop or peaked) and that have changed size (either dilated or constricted).

When thinking about the red eye, the following conditions come to mind: Conjunctivitis, keratitis, acute glaucoma, and uveitis/iritis. Conjunctivitis is very common and affects all age groups, from babies to the elderly.

Acute glaucoma, on the other hand, is actually very rare and typically affects only older patients. Keratitis can be bilateral and, hence, less serious (adenovirus kerato-conjunctivitis) or unilateral and, hence, more serious (HZO or HSV involvement of the eye). Uveitis is associated with at least 3,000 systemic conditions, but in more than 80 per cent of cases where it occurs once only and responds well to treatment, no associated cause can be found and it is regarded as idiopathic.


A common cause of a suddenly appearing red eye is that of spontaneous subconjunctival haemorrhage. It almost always looks far more serious than it is. There is normally associated hypertension or the patient is on blood-thinning medications like aspirin or Warfarin and has recently made a valsalva manoeuvre (coughed, lifted something heavy, strained at stool, etc.).

The haemorrhage clears spontaneously and there is no specific treatment except reassurance for the patient. It’s an entirely different issue when a subconjunctival haemorrhage follows an injury.

Now the haemorrhage could be hiding an underlying scleral rupture or perforation and this requires examination of the peripheral retina to ensure that there is no serious damage beneath the haemorrhage.

Episcleritis and scleritis usually cause a sector of redness in one eye, and the two conditions have very different courses even though they may initially look quite similar.

Episcleritis is usually benign and not associated with other systemic diseases, and normally responds well to an anti-inflammatory. Scleritis can be more serious and associated with collagen vascular disorders and may affect the vision through corneal damage. Episcleritis is, fortunately, the more common of the two conditions.


A good approach in terms of treatment is to try and avoid the use of corticosteroids in the treatment of any of these conditions, unless you can be absolutely certain that there is no herpetic disease of the cornea and the patient is scheduled to see an ophthalmologist imminently.

The abuse of corticosteroids can not only lead to exacerbation of the herpes keratitis but can also lead to cataract and glaucoma.

The use of fluorescein in either strip or drop form facilitates corneal examination and makes the diagnosis more apparent and more certain. Fluorescein is taken up by areas that are denuded of surface epithelial cells and one can clearly see the shape (small and round, large and geographic, dendritic, etc.) of the lesion causing the corneal problem.


Trauma to the eye can have devastating effects, and because the ocular tissues tend to be so delicate, trauma that may go unnoticed elsewhere may have serious ocular sequelae. With physical trauma, always bear in mind that there may be other occult injuries like corneal or intra-ocular foreign bodies, blow-out fractures of the orbit, penetrating corneal, or scleral injuries that may go unnoticed unless you specifically look for them.

Chemical injuries can have devastating effects on the vision and the health of the eye, with alkaline injuries typically being far more serious than acidic injuries.

The immediate treatment is simply copious rinsing and washing of the eye and eye lids with water for 15 minutes, and arranging for the patient to be seen as soon as possible by an ophthalmologist.

Do not waste time trying to figure out if the chemical is alkaline or acidic and certainly do not try and neutralise an acid injury with an alkaline solution or vice versa. The single most important intervention in the management of a chemical injury is the first few minutes directly after the injury where the causative agents are rinsed away.

Generally speaking, with regard to the management of the red eye, if the condition does not respond to the initial treatment and if the vision is affected in any way, then it makes good sense to seek an ophthalmology opinion.

We are happy to see eye emergencies at the Wellington Eye Clinic, or an alternative is to refer the patient to the Beacon Hospital emergency department and the patient will be referred to one of the many ophthalmologists available on campus.

If in doubt about the diagnosis or treatment of a red eye, especially with discomfort or compromised vision, always refer to a specialist ophthalmologist as a priority.

Mr Arthur Cummings and Mr Richard Corkin, Consultant Ophthalmologists, Beacon Hospital and Wellington Eye Clinic, Dublin


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