The cornea, the eye’s transparent outer layer, acts as a primary lens that focuses light to enable clear vision. Its clarity results from a highly organized cellular structure. When this structure is disrupted by injury or disease, the body’s healing response can lead to corneal fibrosis, the formation of opaque scar tissue. This process replaces clear tissue with a compromised substitute that can significantly impair vision and results from a flawed wound-healing cascade.
The Biological Process of Corneal Scarring
A healthy cornea owes its transparency to the precise arrangement of collagen fibers within its main layer, the stroma. These fibers are uniform in diameter and organized into layers, or lamellae, that minimize light scatter. This architecture allows light to pass through unobstructed. Specialized cells called keratocytes are situated between these collagen layers, playing a role in maintaining this structure.
Following an injury, this stable environment is disrupted. The healing process begins with the activation of keratocytes, which transform into repair-oriented cells known as fibroblasts and myofibroblasts. This transformation is a response to growth factors released during the injury response.
The new matrix, particularly the collagen, is deposited in a disorganized manner. Instead of replicating the cornea’s original, highly ordered structure, the new collagen fibers are irregular in size and arrangement. This disordered matrix scatters light rather than transmitting it, creating opacity. This process leads to the formation of a scar that blocks vision.
The persistence of these myofibroblasts is a determining factor in the severity of the scarring. In a well-regulated healing process, these cells would undergo programmed cell death (apoptosis) once the wound is closed. However, in cases leading to significant fibrosis, the myofibroblasts persist, continuing to produce the disorganized matrix and resulting in a permanent, vision-impairing scar.
Primary Causes and Risk Factors
Corneal fibrosis is triggered by events that initiate an aggressive healing response. Traumatic injury is a direct cause, and physical damage like a deep scratch, a cut, or exposure to harsh chemicals can breach the cornea’s protective layers and provoke scarring.
Infections are another major cause of fibrosis. Severe bacterial, fungal, or viral invasions can cause significant tissue damage, such as Herpes simplex keratitis, which is known for causing recurrent inflammation and scarring. The body’s inflammatory response to pathogens can contribute to the formation of a fibrotic scar during healing.
Complications from ocular surgery can also be a source of corneal fibrosis. Refractive surgeries like photorefractive keratectomy (PRK) intentionally remove corneal tissue, and some patients develop a subepithelial haze, a form of fibrosis. Other eye surgeries involving corneal incisions also carry a risk of abnormal wound healing.
Chronic diseases affecting the ocular surface create an environment where the risk of fibrosis is elevated. Conditions like severe dry eye syndrome or autoimmune disorders cause persistent inflammation and irritation. This long-term stress can disrupt normal cell function, making the cornea more susceptible to developing scar tissue.
Symptoms and Diagnostic Methods
The most common symptom of corneal fibrosis is a decline in vision, which patients often describe as blurry or cloudy. Individuals may also experience significant glare and halos, particularly around lights at night. Other symptoms include sensitivity to light (photophobia), a persistent feeling that something is in the eye, and in some cases, a visible white or hazy spot.
An ophthalmologist diagnoses corneal fibrosis through a physical examination using a slit-lamp. This specialized microscope provides a highly magnified, three-dimensional view of the eye’s structures. It allows the doctor to assess the size, location, depth, and density of the corneal scar to determine its impact on the visual axis.
Clinicians may use advanced imaging for more detailed information. Corneal topography creates a map of the cornea’s surface curvature, revealing distortions caused by the scar. Anterior segment optical coherence tomography (OCT) provides a high-resolution, cross-sectional image of the cornea, allowing the ophthalmologist to see the affected layers and measure the scar’s thickness to aid in treatment planning.
Management and Treatment Strategies
The management of corneal fibrosis depends on the scar’s severity and its impact on vision. For less severe cases or to manage inflammation, topical medications are used. Corticosteroid eye drops can be prescribed to reduce inflammation and inhibit scar-forming cells, while a drug called Mitomycin C is sometimes applied to prevent haze after procedures like PRK.
For superficial scars that affect vision, a laser procedure known as Phototherapeutic Keratectomy (PTK) is an effective option. This technique uses an excimer laser to precisely remove thin layers of tissue from the corneal surface. By vaporizing the scar tissue, PTK can help restore a smoother and clearer optical surface, thereby improving vision.
When fibrosis is deep and causes significant vision loss, a corneal transplant, or keratoplasty, may be necessary. Lamellar keratoplasty is a partial-thickness transplant where only the scarred layers of the cornea are removed and replaced with healthy donor tissue. This approach preserves the patient’s own healthy endothelial layer.
For the most severe scars involving the full thickness of the cornea, a penetrating keratoplasty (PK) is performed. This procedure replaces the entire central portion of the patient’s damaged cornea with a full-thickness donor cornea. The choice between a partial and full-thickness transplant depends on the depth and extent of the fibrosis.