• Question: How does laser eye surgery work, and why doesn't it blind you, because I've been told lots of times not to look directly at lasers because they blind you, but surgery makes it better?

    Asked by maddiet to Mark, Matthew, Mike, Paul, Sabina on 13 Mar 2014.
    • Photo: Sabina Hatch

      Sabina Hatch answered on 13 Mar 2014:

      A specific type of laser is used called an exciplex laser. This laser was found to be able to cut organic tissue with high accuracy but without damaging the surrounding tissue with heat. So not all lasers are the same. It has to be carefully focused so that it targets a specific part of your eye, and it uses a very short wavelength that targets the surface instead of deep into the eye. This means it can remove small sections of your cornea and reshape it to improve your eyesight.

    • Photo: Mike Lee

      Mike Lee answered on 13 Mar 2014:

      Do not look at lasers. They can damage your eye very badly and can make you go blind. Laser eye surgery works by cutting out parts of the eye so needs very precise equipment to avoid cutting out the wrong parts.

    • Photo: Paul Coxon

      Paul Coxon answered on 13 Mar 2014:

      I’m not sure I should really answer this, since I wear glasses, but I’ll give it a go…

      Light rays entering the eye pass through the cornea, and lens where they are bent (or ‘refracted’) and focussed, and then fall onto a special part of the retina called the yellow spot. This part of the retina is responsible for receiving light signals and creating a clear picture of the observed object.

      In people with poor vision, either long-sighted or short-sighted (like me), the rays don’t fall on this yellow spot, but either in front or behind it, making the image appear blurred.

      Laser surgery is used to correct where the rays of light land, bringing them onto the yellow spot, by changing the shape of the cornea and controlling the path the light takes through the eye.

      To treat shortsightedness, the centre of the cornea is slightly flattened. This reduces its refractive power and the amount by which the light is bent. To treat long-sightedness, the laser carves the cornea to make it more curved in the centre to increase its refractive power, which increases the amount by which the light is bent. Both these treatments allow the light rays to fall exactly on the yellow spot.

      There are many different kinds of lasers. Not all of them produce bright intense beams like you see in James Bond films. The lasers used in eye surgery are specially designed for the task, and operated by trained professionals. Here, excimer lasers are used which produce light in the UV part of the spectrum. This UV light directly breaks molecular bonds in the cornea without causing burning and damaging the surrounding tissue.

      Medical lasers are the only ones you should ever look at. The cheap laser pointers found in classrooms and lecture theatres are often poorly made, and can produce a very intense beam. Many injuries have been reported from people looking into high-powered lasers pointers bought online.

      In my department at work we are only allowed to use red low power Class II lasers, all others are banned for safety reasons.

    • Photo: Mark Jackson

      Mark Jackson answered on 16 Mar 2014:

      I actually had the laser eye surgery, so I can tell you my personal experience…

      First they numb your eye with drops, so you won’t feel any pain. Then you sit in a chair with the laser-machine on your face, with the doctor operating it. You are told to keep staring at a target straight ahead. The doctor controls the laser – which is not a big scary laser but only a very small one, which you can barely see – to cut open a ‘flap’ in the surface of your eye. This is less scary than it sounds, you don’t feel any pain, only smell something like burning hair. He then raises up the flap, uses the laser to zap some of the lens material in your eye, then lowers the flap. These aren’t random zaps of a laser: they are very carefully controlled to re-focus the lens in your eye in order to improve your vision. The doctor places bandages over your eyes, and for about four hours you feel like you have sand in them, but then it goes away and you feel fine. Twenty-four hours later you return and the doctor looks at the result: mine were fine and needed nothing further. My eyes weren’t perfect after that, but they were vastly improved over their previous condition.

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