The cornea, the transparent dome at the front of the eye, must maintain clarity and shape for light to focus correctly onto the retina. Corneal striae are fine lines or folds that form within the deeper, innermost layers of the cornea when this clarity or shape is disturbed. Their presence suggests the corneal tissue has been subjected to mechanical stress, typically from swelling or pressure changes.
Defining Corneal Striae
Corneal striae are linear creases occurring in the posterior region of the cornea, involving the deepest layer, Descemet’s membrane, and the adjacent posterior stroma. Descemet’s membrane is a resilient layer that acts as the basement membrane for the corneal endothelium, the cells responsible for keeping the cornea dehydrated. These lines are typically oriented vertically or obliquely and are translucent, meaning they do not look like dense, white scars. Striae are usually invisible to the naked eye and are detected during a specialized eye examination using a slit lamp. This distinct appearance helps clinicians differentiate striae from other surface irregularities or opaque scars affecting superficial corneal layers.
Primary Causes of Striae Formation
The formation of corneal striae results from the mechanical folding or wrinkling of Descemet’s membrane and the posterior stroma. This folding is a direct consequence of either fluid accumulation within the cornea, known as corneal edema, or increased intraocular pressure. Normally, endothelial cells regulate hydration by pumping excess fluid out of the tissue. When these cells are damaged or overwhelmed, fluid builds up in the stroma, causing the cornea to swell and thicken. As the cornea swells, Descemet’s membrane is stretched and forced to buckle, creating the visible striae, which represent the cornea’s response to internal stress.
Associated Conditions and Severe Forms
Corneal striae are not a disease but a sign pointing toward an underlying medical condition, which can be transient or chronic. Several distinct forms of striae are associated with specific pathologies.
Vogt’s Striae (Keratoconus)
Vogt’s striae are deep, vertical folds in the posterior stroma, considered a hallmark sign of keratoconus. They appear in the area of maximum corneal thinning and protrusion and are used to diagnose and monitor the progression of this disorder.
Acute Hydrops
Striae are closely associated with sudden, severe swelling events, such as acute hydrops, which occurs in advanced keratoconus. Hydrops involves a rupture in Descemet’s membrane, allowing fluid to rapidly enter the cornea and cause significant edema.
Haab’s Striae (Congenital Glaucoma)
Haab’s striae are found in eyes with primary congenital glaucoma, a condition where high intraocular pressure in infancy causes stretching and tearing of Descemet’s membrane.
Post-Surgical Striae
Striae can also be observed temporarily after eye surgery, particularly LASIK, where folds in the corneal flap (macrostriae) can develop due to improper positioning or healing.
Treatment Approaches and Visual Impact
Corneal striae indicate a physical irregularity that can significantly impact vision quality, especially if they are large or located near the center of the visual axis. The tissue folding creates an irregular surface, leading to distorted or blurred vision that standard eyeglasses often cannot correct. The primary goal of management is not to treat the striae directly, but to resolve the underlying cause of the edema or pressure. For acute edema, treatment focuses on reducing fluid accumulation using topical medications like hypertonic saline drops. In chronic conditions like keratoconus, treatments such as corneal collagen cross-linking stiffen the tissue to prevent further deformation, while special rigid contact lenses can be used to smooth the surface and improve vision.