The Red Eye

Identify the Risk Factors

The first step in approaching a patient and reaching a successful diagnosis is identifying risk factors for particular diseases. We are taught early on in medical school that obtaining a thorough history is paramount. An accurate history is no less true in ophthalmology than it is in primary care. Although a brief history may suffice in some cases, it should never be overlooked. Moreover, when the presentation and clinical findings do not agree with the obtained history, it is important to take a step back and reevaluate what the patient has or more likely has not told you. These omissions in history may be inadvertent or intentional, but often, they require more specific questioning in order to obtain the whole clinical picture. A prime example is the patient with a corneal ulcer from topical anesthetic abuse; these patients frequently do not disclose their use of these medications to their provider.

Important questions to ask patients presenting with red eye include any recent illnesses particularly upper respiratory illnesses, close contacts with an infection and accompanying red eye, trauma, contact lens wear, contact with animals/pets, exposure to chemicals/irritants, other systemic symptoms such as joint pain or skin rashes, and other systemic diseases such as autoimmune disorders. A thorough review of any prior ocular surgery including eyelid procedures is warranted. Similarly, it is also important to review any prescribed or homeopathic ocular medications that the patient has used or is currently using.

Onset and Duration of Disease

Understanding the duration of the red eye can help in narrowing the differential diagnosis. Is the red eye acute or chronic? Does the patient have recurrent episodes of red eyes? Do the symptoms wax and wane throughout the day?

In general, acute (hours to days) and subacute (days to a few weeks) causes of red eye are more likely to have a single identifiable cause. Examples include foreign bodies on the cornea or conjunctiva, corneal abrasions and erosions, acute viral or bacterial conjunctivitis, and microbial keratitis from a bacterial etiology. Some examples of intraocular conditions causing acute red eye include angle-closure glaucoma and uveitis. Most of these acute and subacute conditions do not pose significant diagnostic challenge; the cause is usually determined following an appropriate history and examination.

Chronic (greater than several weeks’ duration) and recurrent red eye conditions can be more difficult to diagnose. A careful history is important, particularly when a patient has seen multiple providers and received multiple treatments over many months or longer. For instance, a patient who has had multiple ocular surgeries and remains on numerous topical ocular medications may present with complaints of chronic redness, irritation, and foreign body sensation. Many patients may also have systemic diseases such as thyroid disease, hypertension, diabetes mellitus, depression, and seasonal allergies (just to name a few) that may impact the ocular surface either directly or indirectly as result of medications used to treat the condition. It may take time to review the patient’s whole past ocular history and past medical history, but the multiple conditions and risk factors must be identified and considered in terms of potential contribution to the overall end result of redness.

Laterality

It is not so important which eye is red, but it is more important to know whether the redness is unilateral or bilateral. If it is bilateral, did it present in both eyes simultaneously or did it start in one and spread to the other? Or alternatively, does the redness alternate between the two eyes? Again, a careful history is key in elucidating the underlying etiology for the redness. For instance, both eyes that are simultaneously and intermittently involved may point toward ocular surface disorders such as dry eye syndrome or blepharitis. A unilateral intermittent red eye may more likely occur with episcleritis or pingueculitis.

Another example of the importance of laterality is the red eye seen in patients with floppy eyelid syndrome. These patients may have a unilateral chronic red eye, and further questioning may reveal a preferential sleeping position on the side of the red eye. Owing to the laxity of the eyelids, the eyelids inadvertently open during sleep causing irritation to the ocular surface.

Pain

In addition to a thorough history of the present problem and the past medical and ocular history, two key symptoms can help to clarify the severity of the disease and the urgency for evaluation and management. Those key symptoms are the presence or absence of pain and whether or not there is an associated change or loss of vision. For instance, a simple conjunctival hemorrhage alone should not produce an affirmative response to either of these questions. If the response is affirmative to either question, another condition may exist.

The majority of causes of red eye are associated with only mild to moderate irritation. Patients with ocular surface diseases such as dry eyes and blepharitis will complain of mild burning, itching, irritation, or foreign body sensation. Similarly, episcleritis, pinguecula, and pterygia, even small retained foreign bodies in the conjunctiva or cornea, should only cause mild to moderate discomfort. If a patient has moderate to severe pain or pain that wakes them at night frequently, a more serious etiology should be considered. Although severe pain often occurs with a simple corneal abrasion, it may also indicate more vision-threatening pathologies such as infectious corneal ulcer, uveitis, scleritis, and acute angle-closure glaucoma.

Vision Loss

Vision loss is another important differentiating symptom in addition to pain. Unlike pain, this symptom can also be confirmed with visual acuity testing. If vision has been affected, the underlying etiology is most likely one in which the cornea is involved (e.g., corneal ulcer or infiltrates) or an intraocular process causing associated external inflammation (e.g., iridocyclitis, endophthalmitis, and acute angle-closure glaucoma). Conjunctivitis alone typically does not affect visual acuity. Decreased visual acuity also helps to indicate the severity of the underlying disease process. For instance, punctate epithelial erosions are often seen in patients with dry eyes. In mild cases, visual acuity is most likely not affected. However, for some patients with severe dry eyes, particularly those with an underlying autoimmune etiology such as Sjögren syndrome, diffuse punctate epithelial erosions on the cornea can lead to a decline in visual acuity.