Subepithelial infiltrates (SEIs) are an immune reaction occurring within the cornea, the clear, dome-shaped front surface of the eye. The cornea is normally transparent, allowing light to pass through to the retina. SEIs represent a localized accumulation of inflammatory cells, which is the body’s defensive response to a trigger, most commonly an infection. These infiltrates are physical evidence of the immune system working to clear a threat from the corneal tissue.
Defining Subepithelial Infiltrates
The cornea is composed of five distinct layers, the outermost being the epithelium, which serves as the protective surface. Subepithelial infiltrates are located directly beneath this epithelium, typically residing in the superficial or anterior stroma. They sometimes involve Bowman’s layer, a thin membrane just below the epithelium.
These infiltrates are not foreign particles or infectious organisms, but rather a collection of the body’s immune cells. They are primarily composed of white blood cells, such as lymphocytes and macrophages, which migrate from surrounding blood vessels. This migration is triggered by chemical-signaling molecules released in response to an irritant or pathogen. The visible, often grayish or white, pinhead-sized spots are physical evidence of the immune system mounting a defense.
Common Causes and Associated Conditions
The most frequent cause of subepithelial infiltrates is a previous viral infection, particularly those related to Adenovirus. This virus is responsible for epidemic keratoconjunctivitis (EKC), a highly contagious condition. In EKC, SEIs often appear as the active viral phase resolves, typically one to three weeks after the infection onset. The infiltrates are considered a post-infectious immune phenomenon, where the body reacts to viral antigens trapped within the corneal tissue.
Non-infectious, or sterile, causes can also lead to SEIs. Contact lens wear is a common factor, where inflammation may result from bacterial byproducts or hypersensitivity to lens solutions. In these cases, the infiltrates are often smaller, more peripheral, and associated with less severe pain. Other inflammatory conditions, such as staphylococcal blepharitis, or post-surgical inflammation following procedures like PRK, can similarly induce SEI formation.
How Subepithelial Infiltrates Affect Vision
The presence of subepithelial infiltrates directly interferes with the cornea’s function of maintaining clarity for sharp vision. The collection of immune cells creates a localized area of cloudiness, or opacity, in the transparent tissue. When light enters the eye, these opaque spots cause the light rays to scatter instead of passing straight through to the retina.
This light scattering causes the most common visual symptoms associated with SEIs. Patients often experience decreased visual acuity, especially if the infiltrates are located over the central visual axis. They may also report significant glare and halos around lights, particularly at night. Other accompanying symptoms include photophobia, or sensitivity to light, and a foreign body sensation resulting from the inflammatory state of the eye.
Treatment and Management Approaches
Managing subepithelial infiltrates requires careful assessment to distinguish between an active infection and a post-infectious immune response. If the infiltrates cause significant visual impairment or discomfort, the standard approach involves topical corticosteroid eye drops. These anti-inflammatory medications suppress the immune response, reducing the inflammatory cells forming the infiltrates.
Corticosteroid use must be closely monitored due to potential side effects, including increased intraocular pressure (IOP) and, with long-term use, cataract formation. If the underlying cause is a viral infection like Herpes Simplex, steroids can worsen the disease, making accurate initial diagnosis paramount. Less potent steroids or non-steroidal anti-inflammatory agents may be used for less severe cases or as step-down therapy. Supportive treatments, such as lubricating eye drops, are also recommended for comfort.
Long-Term Outlook and Scarring
Subepithelial infiltrates are often persistent, lingering for weeks or months after the initial trigger has resolved. Resolution involves the body slowly clearing the accumulated immune cells from the corneal tissue. Although many SEIs resolve completely without leaving a trace, they can recur if topical corticosteroid treatment is withdrawn too quickly.
The inflammatory process carries a risk of permanent corneal scarring, which appears as faint hazing in the tissue. Scarring is more likely if the initial inflammation was severe or if the condition was left undertreated. If scarring occurs centrally, it can cause long-term vision issues requiring further intervention. Consistent follow-up care is necessary to monitor resolution and manage potential long-term visual consequences.