A scratch on the cornea's surface caused by a damaged lens, trapped foreign bodies, or improper handling. A scratch on the cornea's surface caused by
Contact Lens–Related Complications - StatPearls - NCBI - NIH trapped foreign bodies
The most frequent reason for lens discontinuation, causing stinging, burning, or a "gritty" sensation.
Swelling of the cornea, typically due to a lack of oxygen from overwearing lenses or a poor fit.