A scratched eye is not a small thing

A corneal abrasion — a scratch on the clear front surface of the eye — is one of the commonest minor eye injuries. A fingernail, a branch, a corner of paper, a contact lens removed roughly, dust under a lid.

Most heal completely within twenty-four to forty-eight hours, because the corneal surface regenerates quickly. The reason to take them seriously is what happens in the minority that do not.

Why the cornea is unforgiving

The cornea has no blood supply. Blood vessels would spoil its transparency, so it is nourished by diffusion. That means the immune response to an infection there arrives slowly and weakly compared with almost anywhere else in the body — an organism that would be dealt with in hours on the skin can establish itself on a breached cornea.

And the cornea heals by scarring. A scar is opaque tissue sitting precisely where light has to pass. The eye can be entirely saved, the infection completely cured, and the vision permanently reduced because of where the scar sits.

From abrasion to ulcer

An abrasion removes the protective epithelial layer. If organisms get in before it closes, the result is microbial keratitis — an infected ulcer in the corneal tissue.

The risk rises sharply with certain circumstances:

• Contact lens wear, particularly sleeping in lenses, water contact, or overwearing. Contact lens wearers are the largest single group presenting with corneal ulcers.
• Injury by plant material — a branch, a leaf, a thorn, or a piece of wood. This carries a substantially higher risk of fungal infection, which is slower to diagnose and much harder to treat.
• Traditional remedies applied afterwards, which introduce organisms directly onto the breach.
• A dry or already unhealthy ocular surface.
• Steroid drops, which suppress the local immune response and can turn a manageable infection into a sight-threatening one.

What to watch for

An uncomplicated abrasion is painful, watery and light-sensitive, and it improves steadily from the first day.

Signs that it is not uncomplicated, and that you need to be seen the same day:

• Pain that is worsening rather than easing after the first day.
• A visible white or grey spot on the cornea.
• Vision that is reduced and not clearing.
• Increasing redness, particularly a ring of redness immediately around the cornea.
• Discharge, or a sense that there is something in the eye that will not shift.
• Marked light sensitivity persisting beyond a day.

For a contact lens wearer, the threshold is lower still: any painful red eye means the lens comes out and stays out, and you are seen the same day rather than waiting to see how it goes overnight.

What helps and what does not

Do remove contact lenses and leave them out. Do use preservative-free lubricants for comfort. Do have a foreign body removed properly if there is one. Do keep the eye clean and your hands washed.

Do not patch the eye tightly — the evidence does not support it for simple abrasions and it can make infection worse. Do not use anaesthetic drops beyond the examination itself; repeated use is toxic to the corneal surface and delays healing, and it also removes the pain that would otherwise tell you something is wrong. Do not use steroid drops. Do not apply anything traditional. Do not rub.

Recurrent erosion

A specific and often-missed sequel: some abrasions heal with the new epithelium poorly anchored, and it tears again — characteristically on waking, when the lid pulls away from a dry surface. Sudden sharp pain and watering on opening the eyes in the morning, weeks or months after an injury, is recurrent corneal erosion. It is treatable, and it is worth naming because people often endure it for years assuming there is nothing to be done.

The summary

A scratch that is improving day by day is almost certainly fine. A scratch that is getting worse, or that came from a plant, or that happened to a contact lens wearer, should be looked at today. The examination takes a few minutes and settles the question, and the cost of guessing wrong is a scar you keep.