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Trends
THIS UNIVERSE |
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Cataract and A-bomb survivors On August 6, 1945, exactly 63 years ago, an atom bomb destroyed Hiroshima. Three days later, Nagasaki faced similar devastation. The Radiation Effects Research Foundation (RERF) at Hiroshima carries out several studies on the health status of A-bomb survivors. One such study is the effect of ionising radiation on the eye lens of the survivors.
Until now, the radiation protection specialists assumed that only high doses of radiation of two Gy cause cataracts, but new data from the A-bomb survivors suggest that the dose threshold for both minor opacities and vision limiting cataracts may be below one Gy (RERF Update Vol 19, Issue 1 2008). Gray (Gy) is a unit of radiation dose; it is equal to an energy absorption of one Joule per kilogramme. “That important finding is causing major risk assessment groups to consider re-evaluating their guidelines for permissible occupational and medical exposures to the eye”, RERF scientists claimed. Lens of the eye is like lens of a camera. Radiation causes partial opacity (cloudiness) of the eye lens. Symptoms of cataract usually appear after a latency period of several months (two to three years on average) following radiation exposure. Senile cataract which is common in old age advances with age; radiation cataract seldom does. Radiation cataract infrequently causes visual impairment. Radiation cataract possibly has a “threshold”, a certain dose value below which no effect is observed. How does radiation cataract develop? There is a transparent layer of epithelial cells on the interior frontal side of the capsule that covers the lens. This layer maintains the function of the lens by slowly growing toward the centre, achieved through cell division at the periphery (called the equator) of the lens (RERF Update, 2008). Because radiation is especially harmful to dividing cells, exposed cells at the equator are most prone to damage. The damaged cells move toward the rear of the lens before converging on the centre. Such cells prevent light from travelling straight forward, causing opacity. Study of radiation-induced cataracts in A-bomb survivors started at the Atomic Bomb Casualty Commission (ABCC), the predecessor of the Radiation Effects Research Foundation. During 1963-64, scientists found a statistically significant radiation dose response for certain type of cataracts. Later study in 1978-80 gave similar results. Some analyses gave conflicting results. Neriishi and coworkers concluded that there is radiation dose response for cataracts indicating a threshold below one Gy ( RERF Update, 2008). The authors found similar evidence in other studies. A study of children exposed during the accident at the Chernobyl nuclear power station reported a subsequent excess of cataracts. A Swedish followup study of infants treated with radium indicated excess cataracts at a dose of one Gy to the eye. A NASA study of the health of 295 astronauts predicted that relatively low doses of space radiation might predispose the crew to an increased incidence and early appearance of cataracts (RERF update, 19, 1, 2008). A recent study of Chernobyl clean-up workers reported similar results. RERF scientists thus quoted the International Commission on Radiological Protection: (ICRP,2007): “…the lens of the eye may be more radiosensitive than previously considered. In particular, among the atomic bomb survivors,…. and a group of children treated for skin hemangiomas….., there is evidence of excesses of ….. cataract at doses somewhat lower than expected. Whether ICRP may now lower the dose limits to the eye for radiation workers and members of the public or not is not clear. The RERF researchers found out that stored lens images of A-bomb survivors have great potential in cataract research, for re-evaluation and followup of the cases and for standardisation of analyses in training new researchers. RERF is starting a project to collect and store lens tissues removed from A-bomb survivors for future use. Such tissues may provide information on molecular biological changes in the formation of cataracts. Cataract studies on children of A-bomb survivors conducted during 2002-2006 are being analysed to verify whether there are trans-generational effects of radiation on the eye lens. RERF started a glaucoma prevalence study in 2006; it will conclude by September 2008; the results may be published later.
Dr K.S.Parthasarathy is former Secretary, Atomic
Energy Regulatory Board
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Trends British archaeologist Howard Carter found the mummified fetuses when he discovered Tutankhamun’s tomb in 1922. Archaeologists assume they are the children of the teenage pharaoh but their mother has not been identified. —Reuters Shakespearean theatre? The possible foundations of what is known as simply, The Theatre, were unearthed by builders excavating the site — a vacant garage — for another structure. Museum archaeologists were called to the location to make sure nothing was destroyed, and had a eureka moment. —
AP Eye-shaped camera The device might even lead to the development of prosthetic devices, including a bionic eye, they said. —
Reuters World’s smallest snake S. Blair Hedges, an evolutionary biologist at Penn State University, said the snake was found slithering beneath a rock near a patch of Barbadian forest.—
AP
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THIS UNIVERSE On my maiden visit to Leh I came across a place called magnetic hill, where the gravity plays a reverse role, that is the vehicle standing on an incline moves upwards when in neutral. Please elucidate. I do not contest your observation. But you could have easily tested whether there is magnetism involved. I am sure if you had a tennis ball or better still a football with you, you would have seen it roll in the same direction as your car — seemingly upwards. You cannot expect magnetism to work on a football. In fact, if you had a stream of water next to the road that would have also appeared to be flowing against gravity! All this, because your observation must be an illusion. Upwards or downwards is apprehended through comparison with the tilt of landscape around you. I can see that it is easy to be fooled in certain natural configurations of land. It seems that there are several places in the world where people have had the same experience as you. Next time you visit the same place in Leh, carry a football with you to confirm that magnetism is not the culprit. While using a small medium wave radio, the set gives louder and clearer reception when it is held in hand. The reception and signal strength go down when the transistor radio is kept on a wooden table or concrete surface. Why? I can only hazard a guess. When you hold your transistor in your hand, your arm acts as an antenna which is a little bigger than the one inside
the transistor. You might experiment by putting your radio in a metal plate resting on the wooden table. Let me know the result of the experiment. Readers wanting to ask Prof Yash Pal a question can e-mail him at
palyash.pal@gmail.com
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Egyptian scientists are doing DNA tests on stillborn children found in the tomb of the Pharaoh Tutankhamun in the hope of identifying their mother and grandmother, who may be the powerful queen Nefertiti, Egypt’s chief archaeologist said on Wednesday.
The theatre where “The Merchant of Venice” and “Romeo and Juliet” likely debuted and where William Shakespeare himself may have trodden the boards has likely been discovered in east London, archaeologists at the Museum of London said Wednesday.
Borrowing one of nature’s best designs, U.S. scientists have built an eye-shaped camera using standard sensor materials and say it could improve the performance of digital cameras and enhance imaging of the human body.
A U.S. scientist said Sunday he has discovered the globe’s tiniest species of snake in the easternmost Caribbean island of Barbados, with full-grown adults typically stretching less than 4 inches (10 centimeters) long.