LONDON — Doctors at a London eye hospital are warning against the dangers of nerf guns, after at least three people reportedly suffered serious injuries from getting hit in the eye.

CBS reports that nerf guns are toys that shoot soft foam projectiles. Legitimate replacement bullets are recommended and widely available, but generic ones are cheaper. They're also harder, and have more potential to cause injury.

Nerf video tutorials abound online, with some giving instructions on how to modify the toy gun to make it shoot faster and farther.

According to three cases reported in the British Medical Journal, patients who were hit in the eye reportedly complained of blurred vision and pain.

Doctors soon discovered their eyes were inflamed, and blood was pooling in the anterior chamber. Both the cornea and retina had also developed swelling.

Fortunately, after being given eyedrops, their sight returned to normal after a few weeks.

Such eye trauma may not always lead to permanent vision loss, but could result in a long-term condition like glaucoma. Experts recommend wearing safety glasses to minimize the danger.