The cornea is the clear, dome-shaped tissue at the front of the eye that focuses incoming light. Its transparency is maintained by deturgescence, the active removal of fluid. Corneal edema, or swelling, occurs when this balance is disrupted, causing the cornea to absorb too much fluid. This excess fluid buildup leads to a loss of clarity, much like looking through a fogged pane of glass.
How to Recognize Corneal Edema
A common sign of corneal swelling is noticeable blurring or haziness of vision, often worse immediately upon waking up. This temporary increase in blurriness occurs because fluid accumulates when the eyes are closed during sleep, and tear film evaporation is absent. Vision typically improves throughout the day as the eye remains open.
Another common symptom is seeing colored halos or rings around light sources, particularly at night, caused by the swollen corneal tissue scattering light. Patients may also experience increased sensitivity to light (photophobia) and a feeling of discomfort or grittiness. In severe cases, the swelling can cause tiny fluid-filled blisters, called bullae, to form on the corneal surface, which may rupture and lead to sharp pain.
The Underlying Reasons for Swelling
Corneal edema results from an imbalance between fluid entering and fluid being pumped out of the cornea. The crucial element maintaining corneal dehydration is the innermost layer of cells, the endothelium. The endothelium acts as a metabolic pump to actively remove fluid from the cornea’s central layer, the stroma. When these endothelial cells are damaged or depleted, the pump fails, causing fluid to rush in, swelling the cornea and clouding vision.
Chronic, progressive failure of the endothelial pump cells is a primary cause, with Fuchs’ Endothelial Dystrophy being the most common genetic condition. This inherited disorder causes the gradual degeneration and loss of endothelial cells over time, often leading to noticeable symptoms after age 50. As the cell count drops, the remaining cells are unable to compensate, resulting in chronic edema that worsens and affects vision throughout the day.
High intraocular pressure (IOP), such as that seen in glaucoma, can overwhelm or damage the endothelial cells. The excessive pressure mechanically stresses the pump cells, hindering their ability to remove water. Another frequent cause of endothelial cell loss is a complication following intraocular surgery, such as cataract removal. While modern surgical techniques minimize this risk, any surgery within the eye can result in some loss of these non-regenerative cells, potentially leading to postoperative edema.
Other causes of swelling are acute or secondary to external factors or infections. Prolonged or improper contact lens wear can induce corneal hypoxia (oxygen deprivation), which stresses the corneal layers and leads to temporary edema. Acute trauma or injury, such as a blunt force impact, can directly damage the endothelial layer. Furthermore, certain viral infections, like herpes simplex virus, cause inflammation (keratitis), triggering an immune response that damages the fluid-regulating cells.
Treatment and Management Options
The first step upon noticing any symptoms of corneal swelling is to seek a prompt and comprehensive evaluation from an eye care professional, such as an ophthalmologist. An accurate diagnosis of the underlying cause is necessary, as management strategies differ significantly depending on whether the issue is acute or chronic. If the swelling is associated with contact lens use, immediate discontinuation of the lenses is required.
Medical management for mild to moderate edema focuses on drawing fluid out of the cornea using osmotic agents. This is achieved with hypertonic saline solutions, such as 5% sodium chloride drops or ointments, which create an osmotic gradient across the corneal surface. This gradient draws excess water out of the swollen cornea and into the tear film, temporarily restoring clarity. If the underlying cause is high intraocular pressure, treatment also includes medication to lower the pressure inside the eye and prevent further endothelial damage.
Surgical intervention is required for chronic or severe edema that no longer responds to drops or when vision loss is significant. The most common procedure for endothelial dysfunction is Endothelial Keratoplasty, which selectively replaces the diseased inner cell layer with healthy donor tissue. Descemet’s Stripping Endothelial Keratoplasty (DSEK) and Descemet’s Membrane Endothelial Keratoplasty (DMEK) are two variations of this procedure. DMEK offers faster visual recovery and better final visual acuity due to the thinner graft. A full-thickness corneal transplant, known as Penetrating Keratoplasty (PK), is reserved for cases where all layers of the cornea are damaged.