Diabetes Problems can occur at the back of the eye, for example, as a result of diabetes. These problems are treated with laser – usually an argon laser. This type of laser is used to create small burns at the back of the eye. This has the effect of reducing the complications of diabetic eye disease, which could ultimately lead to blindness. Not all people with diabetes will need this treatment. The main side-effect is sometimes people, who have extensive therapy of this sort, may not be allowed to continue to drive. Glaucoma In order to prevent and treat certain types of glaucoma, laser treatment is used. In acute glaucoma, when the eye becomes red and painful, laser treatment may be used to create a hole in the coloured part of the eye (iris). This allows fluid to flow freely between parts of the eye. This treatment is needed for both eyes, even if only one is affected, because the risk to the other eye is high. This is known as a laser peripheral iridotomy (LPI). In chronic glaucoma, lasers can be used to help the fluid drain from the eye. This is a laser trabeculoplasty and can be used instead of, or in combination with, glaucoma drugs and surgery. Cataract It\'s common to need laser after cataract surgery – usually months to years after the operation – because the bag (capsule) that holds the new lens implant in place becomes cloudy. This is called a Nd:YAG posterior capsulotomy. New techniques using lasers to remove cataracts are also being developed. Corneal laser surgery to reduce the need for glasses This is called \'laser refractive surgery’. This is the type of laser surgery that\'s commonly considered by the general public to be \'laser eye surgery\'. This is performed on people who require glasses and who wish to be able to see without them. It does not improve the health of a person’s eyes and in most cases is essentially a cosmetic operation. How does refractive laser eye surgery work? Refractive laser eye surgery changes the shape of the front surface of the eyeball – the cornea. This is the front window of the eye, which is clear and in front of the coloured part. The function of the cornea is to bend light rays and focus them onto the centre of the back of the eye (retina). The back of the eye then sends this light as a nerve impulse to the brain and the brain interprets the information. If the cornea bends the light too much and the image is focussed just in front of the back of the eye (retina) the image will be blurry. This is called being short sighted. If the cornea does not bend the light enough, the image will be focussed behind the back of the eye and the image will be blurry. This is called being long sighted. Glasses and contact lenses adjust the light rays that reach the cornea, so that they\'re focussed correctly on the back of the eye when the cornea bends and focuses them. Laser eye surgery changes the shape of the cornea which changes the way it bends the light so that it is now focussed accurately on the back of the eye. The way it changes the shape of the cornea is by \'photo-ablation\', which means that it etches out a change in corneal shape. This causes thinning of the cornea. In this way the surface of the cornea can by carved or moulded into a better shape to alter the way in which it focuses light. Before lasers Refractive surgery was invented before lasers. A procedure called a radial keratotomy was performed and occasionally is still used. The idea was to alter the shape of the cornea, so that it bends and focuses light rays accurately on the back of the eye. The way the cornea was adjusted was by making a number of shallow slits in the surface of the cornea. The slits heal over, but they have an effect on the overall shape of the cornea. Did you know? The average human cornea is approximately half a millimetre thick. What are the different types of refractive laser eye surgery? The first form of laser eye surgery was invented in about 1987 and was called photorefractive keratectomy (PRK). This is a procedure where the thin outer layer of the cornea (epithelium) is removed and the laser applied to the underlying core of the cornea (stroma). A contact lens is applied to the surface of the eye to protect it until the epithelium grows back. LASEK is a variation of PRK. LASEK stands for laser assisted sub epithelial keratectomy. In this procedure the thin outer epithelium is not removed but rather weakened and pushed aside. The laser is then applied and the epithelium spread back over the surface. LASIK is a slightly different approach. LASIK stands for laser assisted in situ keratomileusis. In this procedure a knife is used to cut open the cornea, removing about the top one third and laying it aside on a hinge – if you imagine cutting the top off a boiled egg but leaving a little shell still attached this is a good description! Once this flap has been created, the laser is applied to the stroma underneath – and the flap is put back in place. What can go wrong with refractive laser eye surgery? With any operation there may be complications. Complications or problems may be preoperative – arising before the operation, intraoperative – during the operation, or postoperative – after the operation. Some complications can also be serious. Although it\'s rare, it\'s possible to go blind in an eye as a result of a complication of laser eye surgery. Preoperative complications that may occur would be mistakes in the measurements of the cornea and glasses prescription. These measurements are used to guide the laser. If they\'re wrong, the laser will do the incorrect treatment. Also, some people are not suitable for laser treatment. If this isn\'t noticed before their surgery, they may have problems afterwards. Intraoperative complications are usually to do with the cutting of the flap in LASIK or with the laser. If the flap is accidentally cut off or cut too thick, it would not be possible to do the surgery. If the laser makes a mistake, the treatment could be a failure. Postoperative complications can be as a result of normal settling down of the operation or they can be severe problems with the surgery. It\'s common for example to have irritation of the eyes due to dryness and this can be long term (chronic). It\'s also possible for the effect of the surgery to change or even wear off over time. Severe complications that can lead to blindness are, for example, an infection on the cornea, often underneath the flap. This would require hospitalisation and intensive specialist management. In the long term, complications may arise as a result of the surgery. The cornea is weakened by the laser surgery. So, if a person had an injury, like a fall, their eye might not withstand the blow like a normal eye. In later years, the management of conditions – such as cataract and glaucoma – may be complicated due to the previous laser surgery. Anyone who undergoes laser refractive surgery must ask for the measurements of their corneas and keep this information because it will be required if they develop a cataract in later life. This information is very important – even many years later. Are there people who can not have refractive laser eye surgery? There are a lot of common minor problems that would make laser eye surgery inadvisable, for example dry eyes or blepharitis. Certain glasses prescriptions are not treatable by laser, for example long sighted people or people with high degrees of astigmatism. As people reach the age of 40, they usually start to need reading glasses. This is because of a change with the lens of the eye rather than a change in the cornea. Laser is not effective at treating this problem. Did you know? The type of laser (excimer laser) used in refractive surgery is occasionally used to treat medical conditions of the cornea, but these are rare. A lazy eye cannot be improved with laser eye surgery. What does wavefront mean? This is a sophisticated addition to the calculations used to plan the laser treatment. It is said to give a better chance of a successful outcome of laser surgery. What does femtosecond mean? A femtosecond is a short length of time – around a tenth of a second in fact. But when this term is used in relation to laser eye surgery, it refers to a specific type of laser. If this laser is used for laser eye surgery, it may give a better chance of a successful outcome.