Subepithelial Infiltrates: Causes, Symptoms, and Treatment

Subepithelial infiltrates, or SEIs, are a clinical finding associated with inflammation of the cornea, the clear outer layer at the front of the eye. These infiltrates can affect vision and overall eye health. Understanding their causes, symptoms, and management is important for anyone diagnosed with this condition.

What Are Subepithelial Infiltrates?

The term “subepithelial” describes the location of these infiltrates, which form just beneath the cornea’s most superficial layer, the epithelium. The ‘infiltrates’ are accumulations of inflammatory cells, primarily a type of white blood cell called lymphocytes, that gather in the anterior stroma as part of the body’s immune reaction.

During an eye exam, SEIs appear as small, distinct, and hazy or granular whitish spots, often described as ‘nummular,’ meaning coin-shaped. These infiltrates are not a disease themselves but are a physical sign of an inflammatory process. They represent the aftermath of an immune response to irritation or infection.

The presence of these cellular collections can interfere with the normal transparency of the cornea. Depending on their size, density, and location, they can scatter light as it enters the eye, leading to various visual disturbances. The number of infiltrates can range from just a few to many, and they can develop in one or both eyes.

What Causes Subepithelial Infiltrates?

The most frequent trigger for SEIs is a prior viral infection of the eye, particularly epidemic keratoconjunctivitis (EKC). EKC is a highly contagious form of ‘pink eye’ caused by adenovirus. The infiltrates are an immunopathologic response that appears seven to fourteen days after the initial infection, representing the body’s reaction to viral particles left in the corneal tissue.

Contact lens wear is another significant factor associated with SEIs. These infiltrates can arise from a sterile inflammatory reaction to the lenses, often due to overwear, poor hygiene, or a reaction to cleaning solutions. They may also appear as a residual sign after a microbial corneal infection related to contact lens use has resolved.

Beyond these common causes, SEIs can be triggered by other conditions. A reaction to topical eye medications, especially the preservatives within them, can lead to infiltrates. Other infections, such as those caused by chlamydia or herpes simplex virus, can also be culprits. Certain inflammatory conditions like Thygeson’s superficial punctate keratitis and some allergic eye diseases are also associated with SEI formation.

Recognizing the Symptoms of SEIs

The primary symptom associated with subepithelial infiltrates is a change in vision, most often described as blurry or hazy. This occurs because the collections of inflammatory cells in the cornea disrupt its smooth optical surface and scatter light, preventing it from focusing properly on the retina. The degree of blurriness often correlates with the number, density, and location of the infiltrates; those in the central visual axis tend to cause more significant issues.

Individuals with SEIs commonly report issues with glare and seeing halos around lights, particularly at night. This light scattering effect can make activities like driving in the dark difficult. Photophobia, or increased sensitivity to bright light, is another frequent complaint.

Some people may also experience a foreign body sensation or mild irritation. However, it is possible for SEIs to be asymptomatic. If the infiltrates are very small, few in number, or located in the peripheral cornea, they may not cause noticeable symptoms and are sometimes discovered during a routine eye examination.

How Are Subepithelial Infiltrates Diagnosed?

The diagnosis of subepithelial infiltrates is made by an eye care professional, such as an ophthalmologist or optometrist, during a detailed eye examination. The key diagnostic tool is the slit-lamp biomicroscope. This device provides a highly magnified, three-dimensional view of the structures at the front of the eye, allowing the doctor to closely inspect all layers of the cornea.

During the slit-lamp exam, the doctor looks for the characteristic appearance of SEIs: small, whitish, coin-shaped opacities located in the anterior stroma. The practitioner will assess the number, size, and location of these infiltrates to determine their potential impact on vision. A fluorescein dye may be used to rule out overlying defects, as SEIs themselves do not stain.

A thorough patient history is also part of the diagnostic process. The doctor will ask about recent eye infections, such as ‘pink eye,’ to check for a post-viral cause. Questions about contact lens wear habits are also important. This history, combined with the clinical findings, allows for an accurate diagnosis.

Treatment Options for Subepithelial Infiltrates

The management strategy for SEIs is tailored to the individual, depending on the severity of symptoms and impact on vision. If the infiltrates are mild and cause no visual disturbance, the course of action may be simple observation. SEIs can resolve on their own, though this process can be slow, sometimes taking months or longer.

For symptomatic cases, the primary treatment involves topical corticosteroids. These anti-inflammatory eye drops reduce the inflammation that causes the infiltrates, which can lead to a clearing of the opacities and improved vision. Steroids require medical supervision, as they can have side effects like increased eye pressure, and the dosage is tapered slowly to prevent a rebound of inflammation.

In cases of chronic or recurrent SEIs, or for patients who cannot tolerate steroids, other medications may be considered. Topical immunomodulators like cyclosporine A can be used as steroid-sparing agents to control inflammation over the long term. Preservative-free lubricating eye drops can also help soothe the ocular surface.

Addressing the underlying cause is a part of treatment. If infiltrates are related to contact lens wear, a change in lens type, wearing schedule, or hygiene routine will be recommended. For very rare and persistent cases where visually significant infiltrates do not respond to medical therapy, a laser procedure called phototherapeutic keratectomy (PTK) may be an option to physically remove the opacities.