Managing the Red Eye Patient–A Diagnosis You Can’t Afford to Miss

Eye health evaluations are an important part of comprehensive primary and urgent care medicine.  Many of my patients visit their primary care provider or an urgent care facility when they have a red eye. More than 80% of all acute cases of conjunctivitis are reported to be diagnosed by non-ophthalmologists including internists, family medicine physicians, pediatricians, and nurse practitioners.⁴

Physician associates/assistants (PAs) are playing an increasing role in providing primary and urgent health care than ever before and this includes care for the eyes.  The PA profession is one of the fastest-growing healthcare careers, thanks in part, to a global shortage of primary care doctors. PAs need to know how to diagnose and manage a patient presenting with a red eye.

The Right Tools for the Job

Diagnosing the red eye’s cause is often difficult without proper equipment.  Many times, primary care providers prescribe antibiotic eyedrops for red eyes thinking it’s bacterial conjunctivitis.  When I see this patient, the diagnosis may be an inflamed eye, viral conjunctivitis, or high eye pressure–none of which require antibiotics.  Delayed or inappropriate treatment can result in further ocular complications, sometimes even permanent eye and vision defects. 

Differential Diagnosis of Red Eye

Viral Conjunctivitis

One of the more common causes of red eye is viral conjunctivitis.  Viral conjunctivitis can be difficult to diagnose even among seasoned eyecare professionals.  When one considers viral conjunctivitis, adenoviral conjunctivitis (sometimes called “pink eye”), may come to mind. However, other viral infections can cause conjunctivitis such as herpes simplex, herpes zoster, or COVID-19.^5. 

There are characteristic features that allow for proper diagnosis. A corneal dendritic ulcer may accompany herpes simplex conjunctivitis.  Patients with herpes zoster typically report unilateral burning pain, allodynia, and headache along the oph­thalmic (V1) branch of the trigeminal nerve.⁶ Herpes zoster conjunctivitis typically accompanies a vesicular rash on the upper eyelid and forehead on one side of the face.⁶ Adenoviral conjunctivitis should be suspected when the patient has a recent systemic adenoviral infection. 

There are adenoviral testing kits to confirm if the suspected conjunctivitis is adenoviral conjunctivitis.  Antibiotic eyedrops rarely would benefit viral conjunctivitis for obvious reasons.  A slit lamp microscope is essential to check for sight-threatening corneal infiltrates and/or ulcers that can accompany viral conjunctivitis. 

Allergic Conjunctivitis

Another common cause of red eye is allergic conjunctivitis.  Allergens from a variety of sources, including an allergic response to one’s natural bacterial flora, can cause inflammation and injection of the conjunctival tissue.  Antibiotic eyedrops would have no direct benefit for allergic conjunctivitis. 

Over-the-counter allergy eyedrops are often effective for low-grade allergic conjunctivitis or to reduce the risk of a flare-up with daily use.  For moderate to severe cases, it is unlikely that over-the-counter allergy eyedrops would resolve the patient’s signs and symptoms.  Steroid-based eyedrops are often needed for moderate to severe allergic conjunctivitis.  Potential side effects of steroid medications such as elevated eye pressure and possible corneal complications from the inflammation should be closely monitored with tonometry and slit lamp exam. 

Disorders of the Anterior Segment

Inflammation of the anterior segment of the eyes besides conjunctivitis may also result in a patient presenting with a red eye. This includes anterior uveitis, episcleritis, and scleritis. Anterior uveitis encompasses inflammation of the iris and/or ciliary body and is one of the most common types of ocular inflammation.⁷

Anterior uveitis is defined by the presence of cells or cellular aggregates that are visible in the anterior chamber during examination.⁸  This cellular material is typically detected using slit lamp microscopy.   It would be difficult to make a diagnosis of anterior uveitis without the aid of a slit lamp.  It’s critical to determine if cells in the anterior chamber are present in the red-eye patient to make the diagnosis of anterior uveitis. 

Anterior uveitis can be caused by a wide variety of systemic and non-systemic conditions.  Blood work and other testing may need to be ordered to determine the cause of the ocular inflammation, if not known.  

Disorders of the Sclera

Episcleritis is an acute unilateral or bilateral inflammation of the episclera, the thin layer of tissue between the conjunctiva and sclera.⁹ Most episcleritis cases are idiopathic, but 26% to 36% of patients have an associated systemic disorder responsible for the pathological process and development of episcleritis.⁹ When a systemic condition is suspected due to a positive review of systems, laboratory, and radiographic testing should be completed.⁹ Supportive treatment with refrigerated artificial tears is a common recommendation.⁹  

For those patients who require prescription medication, a mild topical corticosteroid eyedrop may be prescribed.⁹  These patients will need to be monitored especially for possible steroid-induced ocular hypertension.  

Scleritis is an ocular inflammation affecting the scleral tissue.   Scleritis tends to result in more pain and is often more challenging to treat than conjunctivitis or episcleritis.  Scleritis can be idiopathic or caused by infectious or noninfectious conditions.¹⁰ However, the most associated systemic associations with scleritis are rheumatoid arthritis and systemic vasculitic conditions.¹⁰   Topical corticosteroid eyedrops may be all that is needed for mild cases.  Oral NSAIDs, oral corticosteroids, or injectable corticosteroids are often required for moderate to advanced cases.   Immunosuppressive agents and biologics are also possible treatment options.  

The Rest

Many other conditions may result in a red eye including, but not limited to, severe ocular hypertension, subconjunctival hemorrhages, keratitis, corneal ulceration, contact lens overwear, corneal abrasions, dry eye syndrome, and eyelid disorders.  Most of these eye problems require specialized equipment and expertise that may not be readily available when patients present to their primary care provider or an urgent care facility.  

Think Twice Before Prescribing Antibiotics for Red Eye

Prescribing an antibiotic eyedrop for most of the conditions discussed in this article is unlikely to help.  Delaying proper diagnosis and treatment can result in worsening of the condition.   This can lead to further patient discomfort and additional ocular complications.  It is imperative that if a patient presents with a red they be referred to an eye clinic if you’re unsure of the diagnosis.   A red eye accompanied by vision loss, intense pain, photophobia, or symptoms that persist for an extended period should be seen by an eye specialist immediately.