By Chris Crowe
 LASIK eye surgery is now becoming more and more common for anyone who wishes to improve their eyesight. However, PRK surgery, or photorefractive keratectomy, was in the past the most common type of laser surgery performed on the eyes for vision problems and is still used today. Here is a quick guide to the similarities and differences between the two types of surgery.
The Corneal Flap
As you are probably aware, LASIK surgery requires the creation of a corneal flap under which the laser does its job to correct any aberrations in vision. This is one of the main differences between LASIK and PRK, as no flap is created in the PRK procedure.
During PRK surgery, a flap is created by using a blade and then alcohol is used to scrape the flap away from the eye's surface. This means that only the area to be treated will then be exposed. This type of surgery is usually more appropriate for patients who have thinner corneas.
During LASIK the flap is kept as a way to reduce any complications such as the |
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By john mce
 We've all had some fun with optical illusions, staring blankly at pictures for 5 minutes until a rabbit turns into a duck, or a Jackson Pollack style painting slowly morphs into a forest scene, or more often than not nothing happens at all and you've been gazing dumbly at a set of squiggly lines and splodges for God knows how long.
However do these optical illusions have any other value than brief entertainment? Can they be used to improve people's perception?
Primarily we have to define which type of optical illusion we are referring to as there are three; literal optical illusions, physiological illusions and cognitive illusions. The latter plays on unconscious inferences and assumptions about the world that are embedded into our minds and therefore can dictate our perception because of what we expect to see.
Physiological illusions are typified by exposure to excessive stimuli such as bright lights or movement. These cause an imbalance in the viewer's visual channels, resulting in altered observation. Finally, literal optical illusions create images that differ from the actual objects and components that |
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