Information Update – New dose limit for the lens of the eye

What are cataracts?
A cataract is clouding of the lens of the eye, which impedes the passage of light.
There are three predominant forms of cataract depending on their anatomical location in the lens:•••cortical cataracts are formed in the cortex of the lens, which is the outside edge of the lens;
nuclear refers are found in the central portion of the lens; andposterior subcapsular cataracts (PSC) are formed at the back of the lens. It is called"subcapsular" because it forms beneath the lens capsule, which is a small "sac," or membrane,that encloses the lens and holds it in place.

What are the known causes of cataracts?
Most cataracts are related to ageing, although occasionally children may be born with the condition,or cataract may develop after an injury, inflammation or disease.
The risk factors for age-related cataract include prolonged exposure to ultraviolet radiation, diabetes,
tobacco use and drinking of alcohol.
Exposure to ionizing radiation can cause cortical cataracts and posterior subcapsular cataracts.

What is the prevalence of cataracts?
In the economically developed countries, the prevalence of cataracts roughly doubles with each 10years of age after the age of 50. The prevalence rates in the USA for cataracts with age and race isshown in the figure [1].

The prevalence in developing countries also increases with age. However, cataracts in many
developing countries occur earlier in life than in developed countries, and cataracts are more common.
For example, in an Indian study, visually significant cataract occurred 14 years earlier than in acomparable study in the United States [2].

According to the latest assessment [3], cataracts are responsible for 51% of world blindness, which
represents about 20 million people. Although cataracts can be surgically removed, in many countries
barriers exist that prevent patients to access surgery. As people in the world live longer, the number ofpeople with cataracts is anticipated to grow. Cataract is also an important cause of low vision in bothdeveloped and developing countries [3].

How are cataracts treated?
The only treatment for cataracts is surgical removal. This involves removing the opacified lens, and aplastic lens is inserted. Surgery is normally performed when the cataracts begin to affect the quality oflife or interfere with the ability to perform normal daily activities of the individual.

Why has the dose limit for the lens or the eye for workers been reduced?
The previous limit on equivalent dose to the lens of the eye of 150 mSv in a year was based on a dosethreshold of 0.5–2 Gy for single acute (or brief) exposure and 5 Gy for protracted exposure fordetectable opacities and 5 Gy for single acute (or brief) exposure and 8 Gy following fractionated orprolonged exposure for visual impairment (cataract) [4]. However, some of the earlier
epidemiological studies, on which this limit was based may not have had sufficient follow-up to
detect either radiation-induced lens changes or visual disability requiring cataract surgery. In addition,better techniques for detecting, quantifying, and documenting early radiation-associated lens changes,
as well as better dosimetry, may have been factors that contributed to the more recent findings ofradiation-induced cataracts at low exposures.
In ICRP Publication 118 [5], ICRP presented its review of recent epidemiological evidence regarding
the induction of deterministic effects and concluded that there were some deterministic effects,
particularly those with very late manifestation, where threshold doses were or might have been lower
than previously considered [5, 6].
The ICRP concluded: “For cataracts in the lens of the eye induced by acute exposures, recent studies,
where formal estimates of threshold doses have been made after long follow-up periods, indicate
values of approximately 0.5 Gy with 90–95% confidence intervals including zero dose. This is lower
by a factor of 10 than deduced in earlier studies. Those studies generally had short follow-up periods,
failed to consider the increasing latency period as dose decreases, did not have sufficient sensitivity todetect early lens changes using the various techniques employed, and had relatively few subjects withdoses below a few Gy. For fractionated and protracted exposures, values of approximately 0.5 Gy
have been similarly deduced from recent studies. However, the evidence pertaining to the latter
exposures mainly refers to opacities rather than cataracts impairing vision because the follow-up times
are shorter in those studies. For chronic exposure over several to many years, much of the evidence
refers to minor lens opacities. Nonetheless, there is no indication that the threshold accumulated doses
are higher in this scenario. These are no established mitigators of lens radiation injury leading toopacities or cataracts, but lens replacement is a well-established surgical procedure.”

What is meant by a threshold dose?
The IRCP defines the threshold dose for practical purposes as the dose resulting in a 1% incidence ofthe specified reaction in the tissue or organ [6].

What is the new dose limit for the lens of the eye for occupational exposure?
In 2011, the ICRP has recommended that the occupational dose limit for equivalent dose for the lensof the eye be reduced from 150 mSv in a year to 20 mSv in a year, averaged over defined periods of 5years, with no single year exceeding 50 mSv.
The recommended dose limit for the lens of the eye for occupational exposure was incorporated into
the revised International Basic Safety Standards during the most recent revision [7].

Has the dose limit for the lens or the eye for the public been reduced?
ICRP did not recommend reducing the dose limit for public exposures to the lens of the eye, as theCommission judged that the existing limit was adequately protective. It is considered to be highly
improbable that any member of the public would receive a dose to the lens of the eye over a lifetimein excess of the nominal threshold of 0.5 Gy from a licensed practice considering: application of theeffective dose limit of 1 mSv/year; the low likelihood of the lens of the eye being preferentially
exposed for any significant period; and optimisation of protection below the equivalent dose limit for
the lens of the eye.
The dose limit for equivalent dose for the lens of the eye for members of the public remains
unchanged at 15 mSv in a year.

What categories of workers may be affected the new dose limit?
There are a number of workers where the doses to the lens of the eye can exceed the new dose limit if
appropriate protective actions are not taken. Examples include:••••••

Medical specialists operating image guided equipment in interventional cardiology andinterventional radiology;
Medical specialists performing some tasks in nuclear medicine;Workers involved in some tasks in the decommissioning of nuclear facilities;
Workers in nuclear facilities using glove boxes;
Workers that carry out some tasks in fuel cycle facilities;
Industrial radiographers.

What actions need to be taken by employers?
Employers have prime responsibility for radiation protection and safety of workers. Employers areresponsible for carrying out a safety assessment to identify those workers at risk of receiving doses tothe lens of the eye that may exceed the new dose limit.

Examples of such employers are managers of hospitals that perform image guided interventional
radiology; managers of nuclear facilities processing fuel; managers of companies involved indecommissioning of nuclear facilities; and managers of industrial radiography companies.
Actions to optimize protection of workers against high doses to the lens of the eye, in order ofpriority, rely on:••••Engineered controls such as shielding to reduce exposure of the eyes;
Administrative controls such as written rules to control exposure in normal operations;
Personal protective equipment such as protective glasses. Glasses made of Perspex may besufficient for those workers where the exposure is primarily due to beta radiation. Protective
glasses containing lead can be used to protect against scattered X rays;
Information, instruction and training for workers on any changes to the radiation protection
program to reduce doses.

When considered necessary, appropriate dosimeters are to be provided to workers to measure the doseto the lens of the eye to verify compliance with the dose limit.

What action is for regulatory bodies?
Regulatory bodies in Member States are responsible to establish and enforce compliance with the newdose limit. Regulatory bodies will need to ensure that the appropriate changes are made to national
regulations to establish the new dose limit for the lens of the eye.

References:[1]

USA Department of Health and Human Services, The National Institutes of Health, National Eye
Institute: Cataracts, https://nei.nih.gov/eyedata/cataract[2]

Brian, G., Taylor, H., Cataract Blindness – Challenges for the 21st Century, Bulletin of the World HealthOrganization, 79 (2001) 249-256.

[3]

World Health Organization, Prevention of Blindness and Visual Impairment, World Health Organization
website, (2015). http://www.who.int/blindness/causes/priority/en/index1.html[4]International Commission on Radiological Protection, 1990 Recommendations of the International
Commission on Radiological Protection, ICRP Publication 60, Ann. ICRP 21 (1-3) (1991).

[5]International Commission on Radiological Protection, ICRP Statement on Tissue Reactions / Early andLate Effects of Radiation in Normal Tissues and Organs – Threshold Doses for Tissue Reactions in aRadiation Protection Context, ICRP Publication 118, Ann. ICRP 41 (1/2) (2012).

[6]

International Commission on Radiological Protection, The 2007 Recommendations of the International
Commission on Radiological Protection, ICRP Publication 103, Ann. ICRP 37 (2-4) (2007).

[7]

EUROPEAN COMMISSION, FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED
NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOURORGANIZATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTHORGANIZATION, UNITED NATIONS ENVIRONMENT PROGRAMME, WORLD HEALTHORGANIZATION, Radiation Protection and Safety of Radiation Sources: International Basic SafetyStandards, IAEA Safety Standards Series No. GSR Part 3, IAEA, Vienna (2014).