How do bacterial corneal infections usually begin after an eye injury?

Bacterial corneal infections typically begin following an injury to or a breakdown of the cornea’s surface.1

The corneal epithelium—the eye's outer surface layer—serves as a vital barrier against pathogens. Because very few bacteria possess the ability to penetrate these intact surface layers, infection generally cannot occur unless that protective barrier is compromised by trauma, such as a scratch or abrasion, or other forms of surface breakdown. Once this barrier is breached, bacteria can invade the underlying tissue, potentially leading to severe ulceration and a risk of eye perforation.21