Corneal dellen is a condition of the eye’s clear front surface, the cornea, characterized by a localized area of thinning or depression. This change in corneal shape is caused by severe, localized dehydration of the tissue, resulting in a characteristic saucer-shaped indentation near the edge of the cornea. It is not caused by a loss of tissue but rather a temporary change in shape due to fluid imbalance. If identified and managed promptly, the condition is usually temporary and fully reversible.
What Corneal Dellen Is and How It Develops
Corneal dellen is a disorder of tear film stability and localized moisture loss, not a primary loss of corneal layers. The condition develops when a localized elevation on the adjacent surface of the eye causes a disruption in the distribution of the tear film. This break permits rapid, localized evaporation, which leads to dehydration of the underlying corneal stroma. The stroma, which makes up the majority of the cornea’s thickness, shrinks as it loses water content, creating the thinned, depressed area.
The epithelium, the outermost layer of the cornea, typically remains intact over this dehydrated area. Because the epithelium is usually undamaged, the condition is referred to as a thinning rather than an ulceration. Patients frequently experience symptoms such as a foreign body sensation or persistent ocular irritation. Mild, localized redness, known as hyperemia, may surround the affected area, and some report slight discomfort or sensitivity to light. Diagnosis is clinical, often based on the distinctive saucer-shaped depression observed on the corneal surface.
Identifying the Underlying Causes
The primary mechanism leading to dellen formation is the localized interruption of the tear film, triggered by an adjacent elevated structure on the ocular surface. These elevations physically prevent the eyelid from spreading the tear film smoothly over the area closest to the obstruction. Ocular surface elevations include non-cancerous growths like a pinguecula or a pterygium, which are common masses of tissue near the limbus (the border between the cornea and the sclera). Other causes of elevation involve filtering blebs following glaucoma surgery, localized swelling of the conjunctiva called chemosis, or a suture granuloma.
Post-surgical factors are a frequent cause of dellen, as procedures near the limbus often create temporary or permanent elevations. Following eye surgeries like cataract extraction or pterygium removal, sutures placed near the cornea can cause localized swelling or unevenness. This uneven surface acts as a barrier, causing tears to pool or drain away from the adjacent corneal area. This stagnation and rapid evaporation precipitates the stromal dehydration and subsequent dellen formation.
Treatment Options and Expected Recovery
The objective of dellen treatment is to rehydrate the dehydrated corneal stroma and restore a stable tear film across the entire surface. Conservative management begins with the frequent application of artificial tears, gels, or lubricating ointments. Lubricating ointments are particularly helpful when applied at bedtime, as they provide a prolonged moisturizing barrier during sleep. In some cases, a pressure patch or a bandage contact lens may be applied to physically protect the area and create a moist chamber to encourage rehydration.
Addressing the underlying cause is necessary to prevent recurrence. This may involve removing irritating sutures, managing adjacent inflammatory swelling, or surgically reducing a persistent paralimbal elevation. The prognosis for corneal dellen is excellent when treatment is initiated quickly. The cornea typically rehydrates and returns to its normal contour within a few days to two weeks with conservative measures. Neglected dellen presents a risk of continued thinning, which can progress to corneal ulceration or, in severe cases, perforation of the globe.