许多年前,在星球大战cra的高度ze, my big brother / arch-rival had a light sabre. A plastic replica of course, but he liked to pretend. Before long we had games like "let's slash Dalya's eyes up with my laser". Our mother confiscated that toy pretty quickly, but it's ironic, isn't it, that shining lasers into my eyes all those years ago was judged to be a bad idea, yet today it's big business.
The big business I am talking about is LASIK (laser-assisted intrastromal in-situ keratomileusis). LASIK is a non-invasive surgery which allows the patient (assuming it goes well) to be freed from wearing corrective eye wear for near-sightedness, far-sightedness and / or astigmatism. This is the very idea my brother had. The only real difference lies in exactly how this should be achieved. In LASIK, a flap is cut in the thin protective layer on the front of the eye, called the epithelium, which is then gently pulled back to expose the cornea. The cornea is then re-shaped, also using the laser, to the correct refractive index to reduce blurry vision, and then the flap of epithelium is laid back on top. I suppose my brother's method was cruder but probably would have had (if the light sabre were real) a higher rate of success. His was a simple equation: no eyes = no glasses, so he planned, lovingly, to blast my eyeballs out of my head (and probably my brain stem as well), freeing me from my despised glasses.
LASIK procedures require much more subtle and complicated equations and are not always successful in eradicating the need for corrective eye wear. Some people do still need to wear glasses or contact lenses if the desired refractive index isn't achieved or if they become astigmatic due to irregular healing of the eye, but they can usually still see. A second surgery can be performed, if necessary, to rectify many of these problems, although many people still suffer dry eyes, 'star bursts' and poor night vision, and some have even more serious difficulties, which may be permanent.
The ability to see clearly relies on the light which enters the eye being accurately focused on light-sensitive cells called photoreceptors which form part of the retina at the back of each eye. The photoreceptors then transmit the information about what they are 'seeing' along the optic nerve to the brain's visual areas which, in turn, decipher the signals to re-create a picture of the world around us. So, in essence, the world we live in is what our brain makes it, and hence there is no way of knowing whether the colour blue, for example, looks the same to both you and me!
Phew, a complicated process, but think how amazing sight really is. There are so many things that can go wrong along such a complicated route. For instance, corneas are often misshapen so that light entering the eye is not focused onto the retina, but instead falls either in-front of the retina, as in short-sightedness, or behind the retina, as in long-sightedness. By adjusting the shape of the cornea, to correct the refractive index, LASIK attempts to create the perfect corneal shape, allowing optimal light capture by the retina.
I have chosen to address briefly the topic of LASIK for two reasons: firstly, perhaps a LASIK surgeon will read this and, to thank me for the publicity, will offer me a discounted rate for the surgery and, secondly, to highlight the paradoxical nature of health and disease.
Usually, cutting slits into someone's eyes is a really bad idea. In most uncontrolled situations it would probably impair vision rather than correct it. However, there are so many cases in which what should be harmful is helpful and vice versa; it just depends on the precise situation. Radiation is routinely used to treat many types of cancer, but it is also the cause of many others, like skin cancer. If you carry one gene for the disease sickle-cell anemia, you are protected against malaria, but if you have two, you can become very sick, and even die. In malarial areas, particularly in Africa, many people survive to child-bearing age because they carry one copy of the gene. But if two of these lucky disease carriers have a baby together, there is a 25% chance that it will have full-blown sickle disease, along with all of its attendant risks. On a different tack, a friend once became very ill following infection with a tropical parasite. Although she eventually recovered she was bedridden with extremely severe asthma for nearly a year. Her doctors speculated that the IgE-producing B cells responsible for removing the parasite, had been over-stimulated to the extent that they produced asthma.
Many people believe that it is good to have a balance in the life you lead. It seems that even biological phenomena follow this rule. Radiation can immortalise cells or blast them into oblivion; one disease can make sure you don't get another; the immune system can harm as it helps; just the right amount of laser beam shot into your eyes can clear up your vision, but it can clear up your toy box too!
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