Laser pointers may damage vision

THE TRIBUNE


SCIENCE & TECHNOLOGY
Friday, August 6, 2010, Chandigarh, India


Laser pointers may damage vision
K.S. Parthasarathy



AS Dr.Timothy B L Ho, Firmley Park Hospital NHS Foundation Trust, Surrey, UK entered his house one evening, his seven year old son flashed a laser pointer on his face. The eye injury, he suffered, was not apparent immediately.
Four days later, he developed an area of partial alteration of his field of vision His son found the device, a gift from a drug company, on his father’s desk. Laser pointers which are common place now can damage vision if handled carelessly.
“My vision took several months to recover and initially I was very worried”, Dr Ho wrote in The British Medical Journal, (BMJ, 29 June 2010), when Drs Ziahosseini, Doris and Turner published in the BMJ, a laser injury case suffered by a teenager.
He bought a green diode laser pointer over the internet and shone the laser beam into his eyes while playing with it. He had no previous medical or ophthalmic problems. Tests confirmed disturbance of his retinal pigment epithelium; it took two months to improve his clearness of vision.
In yet another instance, while on the school bus, a friend attempted to determine whether a laser pointer would cause pupillary constriction (Arch Ophthalmol, Nov 1999). She made an 11 year old girl to stare at an activated laser pointer for several multi-second exposures with the right eye. The victim immediately noted decreased vision. It took many months to recover her vision; long term effects of the injury are unknown.
Retinal injuries from lasers may be caused by ablative, thermal or photochemical mechanisms. These depend on power, wavelength, exposure time and size of the pupil (BMJ, 27 May 2010). Normally, the adverse impact may be transient; they may disturb the retina and the interconnecting layers and may induce clinical conditions causing loss of sight later.
Laser pointers costing a few dollars are available in curio shops, electronic stores or office supply shops. You may buy them directly or through mail order or by placing orders with internet outlets. Children may use them as toys.
Most laser pointers used while presenting lectures operate in the visible light region of wavelengths between 600 to 670 nanometre (one-thousandth of a millionth of a metre, nm). They are low powered, battery operated, hand-held devices and are cheaper than those operating at green light of wavelength 532 nm.
The response of the eye depends on wavelength with a peak at about 550nm. It decreases as either end of the spectrum is reached. If laser pointers are compared at the wave lengths of 670 nm, 635 nm and 532 nm at the same power level, the brightness as eye perceives it will be nearly in the ratios of 1:10:30.When the laser beam is closer to the eye’s peak response, it can produce adequate visual stimulus at lower power levels.
If you want to buy a laser pointer choose only one that is labelled Class II and operates with a wavelength between 630 nm and 680 nm. Maximum output should be less than 5 milliwatts.
Before you use a laser pointer, read the caution or danger sticker carefully. Never point the laser at another person. Do not point a laser pointer at mirror-like surfaces. A reflected beam can act like a direct beam on the eye. Never look directly at the laser beam. Never view a laser beam using a binoculars or a microscope.
Lastly, you must not gift a laser pointer to a child. You may regret later. Laser pointers are not toys.
The writer is Raja Ramanna Fellow, Department of Atomic Energy

CT scanning: safety issues

The Committee on Medical Aspects of Radiation in the Environment (COMARE), UK, has just now published its report on the impact of personally initiated X-ray computed tomography (CT) scanning for the health assessment of asymptomatic individuals. Every one must be read this, as it is a scholarly assessment of a powerful medical imaging tool.




Science and technology Janaury 4, 2008, Chandigarh, India


CT scanning: safety issues
K.S. Parthasarathy

ON December 19, the Committee on Medical Aspects of Radiation in the Environment (COMARE), UK, published a report on the impact of personally initiated X-ray computed tomography (CT) scanning for the health assessment of asymptomatic individuals. Everyone must read this 83-page report (www.comare.org.uk/documents/COMARE12thReport.pdf) which comprehensively deals with the safety issues of CT scanning.

The report noted that in UK, some commercial CT services market CT scanning of the asymptomatic individual directly to the public as a form of preventative medicine to give individuals some peace of mind!

We are not far behind. Advertisements extolling the virtues of CT scanning have started appearing in India also.

CT scans promise greater diagnostic accuracy and an increased range of clinical applications; there is also the potential for greater radiation doses to individuals, from interventional techniques and from changes of practice within X-ray computed tomography (COMARE, 2007).

According to COMARE, a typical CT scan with an effective dose of 10 mSv is associated with a predicted average risk of fatal cancer induction of 1 in 2000 over a lifetime. (mSv is a unit of biologically effective radiation dose. A chest x-ray test exposes the patient to a dose of 0.02mSV)

The harm associated with a medically necessary CT scan is below that considered to be unacceptable, compared to the spontaneous fatal cancer risk of approximately 1 in 4.

“If 100,000 people undergo a CT scan every five years from age 40 to 70 years, receiving an effective dose of 10 mSv from each scan, then the estimated impact is approximately 240 excess fatalities…….. For scanning at higher frequencies (every two years or annually) this increases to 600 and 1200 fatalities, respectively.” COMARE cautioned.

The risk from repeated scans is unacceptable. Physicians must consider the use of alternative techniques using lower doses of ionising radiation or non-ionising radiation.

In any country, medical radiation exposure constitutes the major part of the radiation exposure from artificial sources of radiation. COMARE considered the detriment caused by radiation from the CT scan and also the subsequent psychological effects and potential physical detriment from further investigations.

Commercial CT services should provide comprehensive information regarding dose and risk of the CT scan, as well as rates of false negative and false positive findings. False negatives will lead to wrong feeling of good health, while tests that provide false positives may cause psychological trauma followed by more diagnostic tests.

The committee clarified that “it may not be possible to give an asymptomatic person a complete ‘all clear’ after a scan….It is also not clear whether CT imaging detects some cancers (eg lung) that are not as clinically as aggressive as those identified following presentation with symptoms”. Some cancers may be present at the individual’s death and would not have been life-threatening.

COMARE recommended that any individual displaying symptoms and requesting a CT scan from a commercial service should not be scanned and should be referred back to their physician.

The report considered in detail scanning of whole-body and three specific anatomical regions.

COMARE asserted that it is not possible to optimise exposure parameters for CT scans of the whole of the body. Services offering whole body CT scanning of asymptomatic individuals should discontinue to do so. CT should not be used to assess spinal conditions, body fat and osteoporosis in asymptomatic individuals (COMARE Press release, December 19)

COMARE concluded that there is no evidence that CT scanning for lung conditions is of benefit. However, cardiac CT scanning has been shown to have value for predicting cardiovascular risk and similarly CT colonography has the potential to detect small lesions. Both cardiac CT scanning and CT colonography should only be carried out in certain asymptomatic individuals.

The report recommended that CT scanning should only be undertaken on individuals with intermediate risk identified by a comprehensive cardiovascular risk assessment, unless the referral is by a cardiac specialist.

In view of the safety significance of CT scan units, they are subjected to licensing by the Atomic Energy Regulatory Board (AERB). It is illegal to operate a CT scan unit in India without obtaining a licence issued by AERB

Dr K.S. Parthasarathy is former Secretary, AERB

The first report on how India achieves nuclear safety

The article is a summary of the first National report for the Convention on Nuclear Safety submitted by India in September 2007 to the fourth Review Meeting of Contracting parties to be held in April 2008

K.S.Parthasarathy





Date:13/12/2007 URL: http://www.thehindu.com/thehindu/seta/2007/12/13/stories/2007121350101500.htm Sci Tech



The first report on how India achieves nuclear safety

It lists important safety improvements at each power station, starting with Tarapur

The average capacity factor for the Indian nuclear reactors for 2005-06 was 74 per cent

Among other measures, reduction of radiation doses to workers is notable

Recent debates on the Indo-US agreement for cooperation concerning the peaceful use of nuclear energy compelled the media to look at nuclear power more benignly. Members of the public realised for the first time that nuclear power has a role to play in the energy mix of the country. Those who have concerns on nuclear safety, must read the first ‘National Report for the Convention on Nuclear Safety (September 2007),’ to find out how India achieves nuclear safety . (Please see www.aerb.gov.in or www.dae.gov.in for the text of the report.)

Measures explained

The 208 page report explains the measures taken by India to implement the Convention on Nuclear Safety, the first international legal instrument dealing directly with the safety of civilian nuclear power plants. The Fourth Review Meeting of the Contracting Parties scheduled to be held in April 2008 will examine the report along with 13 others including those from Canada, France, Russia and U.S. The international peer review is unique to the nuclear industry.

The report highlights the steps taken to implement Articles 6 to 19 (Chapter 2 titled ‘Obligations’). It lists important safety improvements at each power station starting with the Tarapur Atomic Power Station (TAPS) which began its operation in 1969. The comprehensive safety review and implementation of safety up-gradations for continued operation of TAPS-1 and 2 are notable.

The report gives graphically the electrical power generated by each reactor in India and its availability and capacity factors. Nuclear Power Corporation of India Limited (NPCIL) deserves congratulations for consistent performance for the past few years.

The average capacity factor for the Indian nuclear power reactors for 2005-06 was 74 per cent. India must compete with other countries now. The U.S. recorded an average capacity factor of 89.6 per cent in 2006 for 105 reactors with 29 reactors exceeding 95 per cent. The comprehensive safety assessments carried out after major events such as the accident at Three Mile Island in the U.S. and that at Chernobyl in the former Soviet Union are very informative. NPCIL implemented the recommendations arising from these assessments.

Following the pressure tube failure incident at the Pickring-2 reactor in Canada, India introduced a major programme to ensure the integrity of the pressure tubes in Indian Pressurized Heavy Water Reactors by enhancing the design as well as in-service-inspection and rehabilitation technologies.

The thoroughness with which AERB reviewed the fire incident at Narora in March 1993 and the tsunami incident at Kalpakkam in December 2004 and ensured implementation of its recommendations is reassuring.

Seismic re-evaluation of old generation reactors, enhanced inspection of certain systems and components, ageing management and reduction of radiation doses to workers are notable.

The directive prescribing ‘formal and elaborate retraining and re-licensing of all the frontline operating staff and the station management personnel’ following a safety-related incident at the Kakrapar Atomic Power Station reflects the no-nonsense attitude of AERB

The report describes the legislative and regulatory framework including the Atomic Energy Act 1962 and the rules framed under it and other legal instruments such as Indian Electricity Act 2003, Environment (Protection) Act 1986 etc.

It highlights the functions and responsibilities of AERB, the Board’s organisational structure and its position in the government which ensures administrative and financial independence in its functioning.
Forum member

AERB participates in the activities of the International Atomic Energy Agency (IAEA).

It is a member of the forum for the CANDU senior regulators with six other countries operating pressurized heavy water reactors. AERB and the US Nuclear Regulatory Commission have held several meetings on safety related topics.

The Board has a cooperation agreement with the French Directorate General of Nuclear Safety and Radiation Protection and the Federal Nuclear and Radiation Safety Authority of Russia.

The measures India takes to comply with other Articles covering the responsibilities of the licensee, financial and human resources, capabilities and limitations of human performance, quality assurance, assessment and verification of safety, radiation protection, siting, design and construction and emergency preparedness are very comprehensive.
Acronyms, jargon

The report contains some tongue-twisting acronyms and incomprehensible jargon (defendable as the report is meant for scientists and engineers!); it also contains a wealth of useful information patiently collected, collated and interpreted from government documents, incident reports, minutes of meetings and publications.

The feedback from the review meetings will help to enhance nuclear safety in countries operating nuclear power plants.

K.S.PARTHASARATHY

Former Secretary, AERB

( ksparth@yahoo.co.uk )

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