Corneal scarring results from damage to the clear, dome-shaped front surface of the eye, which is called the cornea. This condition occurs when the normally transparent tissue is replaced by opaque, fibrous material during the healing process. The resulting cloudiness blocks or distorts the path of light entering the eye, which can significantly impair vision. Corneal scarring is a major cause of preventable blindness around the world.
Understanding the Cornea and Scar Formation
The cornea is a complex structure composed of five distinct layers that work together to maintain clarity and focus light. These layers include the Epithelium, Bowman’s layer, the Stroma, Descemet’s membrane, and the Endothelium. The Stroma is the thickest layer, making up approximately 90% of the corneal tissue.
The Stroma achieves its transparency through a precise arrangement of collagen fibers. Damage that extends past the Bowman’s layer and into the Stroma triggers a wound-healing response. Specialized corneal cells called keratocytes transform into repair cells, known as fibroblasts and myofibroblasts. These activated cells deposit collagen fibers in a disorganized manner as they attempt to close the wound. This irregular arrangement of collagen scatters light instead of allowing it to pass straight through, resulting in the visible opacity of a corneal scar.
Primary Causes of Corneal Scarring
Corneal scarring is initiated by events that cause deep physical damage or prolonged inflammation. Infections represent a significant category. Bacterial keratitis, often linked to improper contact lens use, is common. Viral infections, such as those caused by Herpes Simplex Virus or the virus that causes shingles, can also cause deep inflammation and chronic scarring. Fungal and parasitic infections, though less common, also lead to dense, vision-reducing scars.
Physical trauma is another frequent cause of corneal damage. This includes deep corneal abrasions, lacerations from sharp objects, and the presence of foreign bodies. Chemical burns are particularly damaging; alkali substances like lye or ammonia often penetrate the corneal layers more deeply than acids.
Underlying health conditions can also contribute to the development of scars. Severe dry eye syndrome, often associated with autoimmune disorders like Sjögren’s syndrome, can cause chronic surface inflammation and breakdown. Autoimmune diseases, including Rheumatoid Arthritis and Lupus, may lead to peripheral ulcerative keratitis, where inflammation causes tissue thinning and subsequent scar formation at the edge of the cornea.
How Scarring Affects Vision and Is Diagnosed
The primary functional consequence of corneal scarring is the scattering of light, a phenomenon often described as corneal haze. Scar tissue disrupts the uniformity of collagen fibrils, causing incident light to scatter in multiple directions.
This light scattering leads to patient symptoms that depend heavily on the scar’s size and its location relative to the pupil. Central scars directly over the visual axis cause a significant reduction in visual acuity, resulting in blurred or cloudy vision. Patients may also experience glare and halos, especially when looking at bright lights in low-light conditions.
Diagnosis is performed by an eye care professional using a slit lamp microscope. This instrument projects a high-intensity beam of light, which is adjustable in width and height, across the front of the eye. The slit lamp allows the examiner to create an optical cross-section of the cornea, enabling a detailed, magnified visualization of the scar’s depth, density, and precise location within the corneal layers.
Therapeutic Options for Corneal Scars
The approach to treating corneal scars is determined by the depth, density, and location of the opaque tissue. For mild or superficial scarring, initial management often involves non-surgical methods. Specialized contact lenses, such as scleral lenses, can improve vision by creating a smooth, new refracting surface over the irregular scar. Topical medications, including corticosteroids, may be prescribed to reduce inflammation, though they cannot reverse existing deep scar tissue.
Moderate or anterior stromal scars may be treated with Phototherapeutic Keratectomy (PTK). This is a precise laser procedure that uses an excimer laser to remove thin layers of the damaged tissue. PTK effectively smoothens the corneal surface and removes superficial opacities, but it is limited to scars that do not extend too deeply into the Stroma. A recently studied off-label treatment involves the use of topical Losartan, a drug that inhibits the growth factor responsible for stimulating scar formation.
For severe or deep scarring, corneal transplantation, known as keratoplasty, is the definitive treatment. There are two main types: Deep Anterior Lamellar Keratoplasty (DALK) and Penetrating Keratoplasty (PKP). DALK is a partial-thickness procedure that removes and replaces only the damaged anterior layers of the cornea, leaving the patient’s healthy innermost layer (Endothelium) intact. Because the Endothelium is preserved, the risk of immune rejection is significantly lower with DALK. PKP is a full-thickness transplant where the entire damaged cornea is replaced with donor tissue, reserved for the deepest scars or those where the Endothelium is also damaged.