A stromal scar is a type of tissue damage within the eye, specifically affecting the cornea. It can directly interfere with vision, leading to various visual impairments from mild blurriness to severe vision loss, depending on its characteristics and location.
What is a Stromal Scar?
The cornea is the transparent, dome-shaped front surface of the eye, acting as a protective barrier and playing a large role in focusing light onto the retina. It consists of multiple layers, and the stroma is the thickest of these, accounting for about 80-85% of the cornea’s total thickness. This layer is primarily composed of highly organized collagen fibrils, arranged in flattened layers called lamellae, along with keratocytes and proteoglycans. This precise arrangement gives the cornea its transparency.
A stromal scar, also known as corneal fibrosis or haze, is a physical alteration within this stromal layer. It appears as a cloudy or opaque area, disrupting the cornea’s normal clarity. Unlike the healthy, organized collagen in the stroma, the scar tissue is made up of disorganized collagen fibers and other extracellular matrix components. This abnormal arrangement scatters light rather than allowing it to pass through clearly, leading to reduced transparency and affecting vision.
How Stromal Scars Form
Stromal scars develop as a consequence of the eye’s healing response to various injuries, infections, or diseases that affect the corneal stroma. Common causes include direct trauma to the eye, such as scratches or foreign bodies, which can create deeper wounds. Infections, whether bacterial, viral, or fungal, can also lead to significant damage and subsequent scarring if they penetrate beyond the superficial layers of the cornea. Inflammatory conditions, sometimes associated with systemic diseases, can similarly trigger the scarring process.
When the stromal layer is damaged, the body initiates a wound healing cascade. This process involves the transformation of normal keratocytes into repair cells called fibroblasts and myofibroblasts. These transformed cells then produce new extracellular matrix components, including collagen. While normal corneal healing aims to restore transparency, scarring occurs when newly formed collagen is laid down in a disorganized manner, resulting in opaque tissue. This fibrotic response can also involve inflammatory cells that promote scar formation.
Impact on Vision and Eye Health
The presence of a stromal scar can have varying impacts on an individual’s vision and overall eye health, largely depending on its characteristics. A scar located centrally, directly in the path of light entering the eye, will cause more significant visual impairment than one situated peripherally. The size and density of the scar also play a role; larger and denser scars block more light and cause more pronounced symptoms.
Individuals with stromal scars experience blurred vision or a general haziness, as the opaque tissue scatters incoming light. Glare, especially from bright lights, and increased light sensitivity (photophobia) are also common symptoms. In severe cases, extensive or deep stromal scarring can lead to substantial vision loss, potentially resulting in blindness if left untreated. Beyond visual symptoms, some individuals may experience discomfort or notice a visible change in the appearance of their eye due to the opaque area on the cornea.
Managing Stromal Scars
Managing stromal scars begins with a thorough eye examination to diagnose the scar and assess its characteristics, such as size, depth, and location. For mild scars or those located away from central vision, non-surgical approaches may be sufficient. Prescription glasses or rigid gas permeable (RGP) contact lenses can help correct the irregular astigmatism and refractive error caused by the scar, thereby improving vision. Anti-inflammatory eye drops, such as corticosteroids, may be prescribed to reduce associated inflammation and help with symptoms.
For more significant or visually impactful stromal scars, surgical interventions are considered. Phototherapeutic keratectomy (PTK) is a laser procedure that uses an excimer laser to remove superficial scar tissue and smooth the corneal surface. For deeper or more extensive scarring, corneal transplantation, also known as keratoplasty, may be necessary. This procedure involves replacing the damaged corneal tissue with healthy donor tissue.
Depending on the scar’s depth, a full-thickness or partial-thickness transplant may be performed. Emerging therapies, including corneal stromal stem cells, are also being explored for their potential to reduce fibrosis and regenerate transparent stromal tissue, aiming to prevent or minimize scarring.