A US doctor is trying to pioneer a laser treatment that changes patients\' eye colour. Dr Gregg Homer claims 20 seconds of laser light can remove pigment in brown eyes so they gradually turn blue. He is now seeking up to $750,000 (£468,000) of investment to continue clinical trials. However, other eye experts urge caution because destroying eye pigment can cause sight problems if too much light is allowed to enter the pupil. Stroma Medical, the company set up to commercialise the process, estimates it will take at least 18 months to finish the safety tests. \'Irreversible\' The process involves a computerised scanning system that takes a picture of the iris and works out which areas to treat. The laser is then fired, using a proprietary pattern, hitting one spot of the iris at a time. When it has hit every spot it then starts again, repeating the process several times. \"The laser agitates the pigment on the surface of the iris,\" Dr Homer - the firm\'s chairman and chief scientific officer - told the BBC. \"We use two frequencies that are absorbed by dark pigment, and it is fully absorbed so there is no danger of damage to the rest of the eye. \"It heats it up and changes the structure of the pigment cells. The body recognises they are damaged tissue and sends out a protein. This recruits another feature that is like little pac-men that digest the tissue at a molecular level.\" After the first week of treatment, the eye colour turns darker as the tissue changes its characteristics. Then the digestion process starts, and after a further one to three weeks the blueness appears. Since the pigment - called melanin - does not regenerate the treatment is irreversible. Lasers are already used to remove the substance in skin to help treat brown spots and freckles. Safety concerns Other eye experts have expressed reservations. Artwork of a section through a healthy human eyeball Dr Homer said his treatment only removes pigment from the eyeball\'s surface \"The pigment is there for a reason. If the pigment is lost you can get problems such as glare or double vision,\" said Larry Benjamin, a consultant eye surgeon at Stoke Mandeville Hospital, in the UK. \"Having no eye pigment would be like having a camera aperture with a transparent blade. You wouldn\'t be able to control the light getting in.\" Dr Homer said that he only removes the pigment from the eye\'s surface. \"This is only around one third to one half as thick as the pigment at the back of the iris and has no medical significance,\" he said. He also claimed patients would be less sensitive to light than those born with blue eyes. He reasoned that brown-eyed people have more pigment in the other areas of their eyeballs, and most of it will be left untouched. \"We run tests for 15 different safety examination procedures. We run the tests before and after the treatment, and the following day, and the following weeks, and the following months and the following three months. \"Thus far we have no evidence of any injury.\" Testing in Mexico Dr Homer originally worked as an entertainment lawyer in Los Angeles, but gave up full-time practice in the mid-1990s to study biology at Stanford University in California. He said he filed his first patent for the laser treatment in 2001. But it was not until 2004 that he began carrying out experiments on animals at a hospital facility. To fund his research he used his own savings, attracted investments from venture capital funds and secured a government grant. Dr Homer said he has raised $2.5m to date. Tests on humans initially involved cadavers, and then moved on to live patients in Mexico in August 2010. \"From a regulatory perspective it is easier,\" Dr Homer said, \"and I can speak Spanish fluently so I can closely monitor how everyone is doing.\" Seventeen people have been treated so far. All are very short-sighted. They have been offered lens transplants in return for taking part. Dr Homer said the work is checked by a board of ophthalmology experts to ensure it is up to standard. The new funds will be used to complete safety trials with a further three people. Stroma Medical then intends to raise a further $15m to manufacture hundreds of lasers and launch overseas - ideally within 18 months. A US launch is planned in three years\' time, because it takes longer to get regulatory approval there. Stroma Medical believes the treatment will be popular; its survey of 2,500 people suggested 17% of Americans would want it if they knew it was completely safe. A further 35% would seriously consider it. There is also evidence of a growing desire to alter eye colour overseas - a recent study in Singapore reported growing demand for cosmetic contact lenses.