Protecting Your Eyes From Ionizing Radiation Exposureshielding is one of the three basic radiation safety principles. Time, distance and shielding are the primary means of eliminating or reducing ionizing radiation exposure.
Shielding should be used wherever it is necessary to reduce or eliminate radiation exposure. There are a variety of types of lead shielding options, the focus of this article will be on radiation eye protection and the use of lead glasses.
Appropriate shielding placed between the source of radiation and the worker, radiation is attenuated and exposure may be completely eliminated or reduced to an acceptable level. Lead acts as a barrier to reduce x-ray’s effect by blocking or bouncing particles through a barrier material. Attenuation is the result of interactions between x-ray and matter that include absorption and scatter. Much like lead aprons which are commonly found in x-ray rooms in hospitals, lead glasses reduce radiation exposure and protect the lens of the eye.
Occupational Radiation Exposure Limits
Exposure limits have been established by the Nuclear Regulatory Committee (NRC) and set to a level where apparent injury due to ionizing radiation during a normal lifetime is unlikely. This limit is called the “maximum permissible exposure” and medical personnel should be aware of their occupational radiation dose. These occupational radiation exposure limits have been established to help minimize the amount of radiation a worker receives annually by monitoring their occupational radiation dose and keeping them under the established limits. “The exposure limit for the whole body (5,000 mrem) is lower than that for a single organ because all organs and tissues are exposed in whole body exposure, while only a single organ is involved in the single organ exposure limits¹.”
Lens of Eye (LDE) Radiation Exposure Limit
The occupational exposure limit for the lens of the eye (LDE) is 15,000 millirem or 0.15 Sieverts. The Lens of Eye Dose Equivalent (LDE) 10 CFR 20.1003 “applies to the external exposure of the lens of the eye and is taken as the dose equivalent at tissue depth of 0.3 centimeter (300 mg/cm²).”
The U.S. Nuclear Regulatory Commission has requirements regarding personal monitoring devices. Many medical personnel are required to wear an individual monitoring device to measure the dose to the whole body as well as one at an unshielded location closer to the eye to provide an accurate reading of the lens dose equivalent. Wearing lead glasses will help ensure the lenses of the eyes are properly protected from ionizing radiation thereby reducing your risk of developing cataracts.
“Radiation workers who operate x-ray machines, fluoroscopy units, certain unsealed and sealed radioisotopes or are exposed to other sources of gamma or high energy beta radiation are generally required to wear one or more dosimeters².”
Eye Protection: Reducing Tissue Reactions
Tissue reactions, previously referred to as deterministic effects or non-stochastic effects, describe a cause an effect relationship between radiation and some side-effects. There is a threshold dose, once exceeded, the severity of an effect increases with dose. Examples of tissue reactions include skin erythema, which can occur shortly after radiation exposure. Late tissue reactions, particularly those involving the lens of the eye, such as cataracts, can develop long after the initial radiation exposure, but still can be traced back to the original exposure.
Two separate studies published in 2010 reported that interventional cardiology personnel have an increased risk of developing cataracts, a clouding or opacity of the eye that hinders vision. In a recent study, Radiation Cataract Risk In Interventional Cardiology Personnel (October of 2010), Vano et al tested 116 exposed interventional cardiologists, nurses, and technologists for radiation cataracts and compared them to 93 unexposed control personnel. Thirty-eight percent of the cardiologists, with a cumulative median lens dose of 6.0 Sieverts, developed cataracts, compared with 12 percent of the controls. Twenty-one percent of the other medical personnel, who were exposed to a cumulative median lens dose of 1.5 Sieverts, developed radiation-associated lens changes attributed to ionizing radiation exposure.
The second study, Risk For Radiation-Induced Cataract For Staff In Inventional Cardiology: Is there reason for concern? (November 2010), examines the prevalence of radiation-associated lens opacities among interventional cardiologists and nurses and to correlate with background radiation exposure. The results of the study demonstrated a dose dependent increased risk of posterior lens opacities for interventional cardiologists and nurses when radiation protection tools are not used. Although, a study of a larger cohort is needed to confirm these findings, the results suggest ocular radio-protection should be used.
Radiation Eye Protection
Our eyes are one of our most valuable organs, without properly functioning eyes even the most routine tasks can become extremely difficult to complete. “Eyes are delicate and precious” says Dr. Andrew Lwach, spokesperson for the American Academy of Ophthalmology. When working near and around ionizing radiation it is important to protect your eyes from potential exposure by wearing lead glasses. Radiation safety glasses, commonly referred to as lead glasses, are designed to protect the lens of the eye by reducing the amount of radiation that is permitted to pass through the leaded glass lenses.
According to a study, Comparing Strategies For Operator Eye Protection In The Interventional Radiography Suite, published in November of 2010, the “use of leaded glasses alone reduced the lens dose rate by a factor of five to 10.” The operator lens radiation dose rate was recorded with a solid-state dosimeter with nonleaded and leaded (0.75mm lead equivalent) eyeglasses. Lens dose measurements were obtained in right and left 15 degree anterior obliquities with the operator at the upper abdomen and during digital subtraction angiography (two images per second) with the operator at the patient’s groin.
Today, lead glasses come in a wide-variety of styles and configurations including wraparound, goggles, fit over, economy, plastic, metal, and designer frames. For example, metal frames are available with frontal (lens) and lateral radiation(side shields) protection offering 0.75mm and 0.35mm lead (Pb) equivalency respectively.
The industry standard 0.75mm lead equivalency SCHOTT SF6 radiation safety glass lenses provide protection from harmful radiation exposure. The lenses have been tested (CE Certified for Radiation Reducing Eyewear) at 100 kV and have a nominal lead equivalence of 0.75mm Pb and the side shields offer a nominal lead equivalence of 0.35mm Pb at 100 kV. Lead glasses are an essential piece of personal protective equipment that will help reduce the amount of radiation exposure to your eyes.