Why does foreign body in the eye cause red eye?

Red Eye is a very common presentation of Foreign Body in the Eye. The conjunctiva is the thin clear layer over the white of the eye and inside the eyelids. When dust, an eyelash, grit or another particle rubs it or the cornea, local blood vessels become more visible. Tearing, a foreign-body sensation, blinking, pain and light sensitivity can occur at the same time.

A red eye has several possible causes, including infection, allergy and dryness. Redness after an eye injury deserves attention because a retained particle or corneal scratch can keep irritating the surface.

Avoid rubbing the eye, as this can cause further scratching. Wash your hands, remove contact lenses, and gently rinse with clean water or sterile saline if a loose particle may be present. Blink while rinsing. Do not use tweezers, cotton buds or sharp objects to remove material, and do not try to remove anything that appears stuck in the eye.

Rest the eye and avoid contact lenses until symptoms have resolved and a clinician has advised they can be worn. Keep the other eye uncovered; covering both eyes can make it harder to move around safely.

Get urgent assessment for a change in vision, severe pain, persistent redness after rinsing, worsening swelling, discharge, light sensitivity, nausea with eye pain, or trouble keeping the eye open. Seek immediate help for chemicals, a high-speed injury, an embedded object, or a cut to the eye. Continue rinsing after chemical exposure while arranging emergency care.

Ask whether the eyelid has been checked for hidden material, whether there is a corneal abrasion, which pain relief or drops are appropriate, and when you may return to contact lenses or work requiring eye protection.