- Result of any kind of chronic superficial irritation.
- Usually deposited in the epithelium (sometimes anterior stroma).
- Origin: proliferation and centripetal migration of melanocytes that would normally remain in the limbus
- Usually associated with corneal vascularisation
- Aetiology:
- Excessive exposure: macroblepharom, facial nerve palsy.
- Irritation: medial entropion, distichiasis.
- Tear film abnormalities.
- Chronic immune stimulation.
**Exception: corneal sequestration in cats.
