The main causes are trauma, infection and disease.
Improper contact lens use, or traumatic abrasions, or injury to the superficial epithelium, usually heal without a scar. Abrasions, or injuries that damage subsequent layers (Bowman’s and the stromal layers), can result in the formation of corneal scars.
If a corneal ulcer penetrates the Bowman’s and the stromal layer, scars can form.
Eye infections can be bacterial, fungal, viral, or parasitic. If an infection penetrates the Bowman’s and the stromal layer, scars can form.
Epithelial dystrophy is a type of corneal disease that causes corneal erosions, which can result in corneal scarring.