A cataract is a clouding of the eye’s lens that impairs vision, making it blurry or dim. When this condition is caused by exposure to specific types of energy, it is known as a radiation cataract. This form develops due to the damaging effects of radiation on the lens’s sensitive cells, leading to a gradual loss of its transparency.
Sources of Cataract-Inducing Radiation
Exposure to ionizing radiation is the primary cause of these cataracts. Medical treatments are a significant source of this exposure. Radiotherapy for cancers of the head, neck, or brain can deliver a substantial radiation dose to the eyes, even with modern shielding. Diagnostic imaging procedures using X-rays, like fluoroscopy, also contribute to exposure, especially for the medical personnel performing them.
Occupational exposure presents a risk for several professions. Interventional radiologists and cardiologists are exposed to scatter radiation from daily work with X-ray equipment. Workers in the nuclear industry also face potential exposure. Airline pilots and astronauts are exposed to higher levels of cosmic radiation, which increases their long-term risk.
Ultraviolet (UV) radiation from the sun is another factor in cataract development, as prolonged exposure can damage proteins within the lens. Historically, studies of atomic bomb survivors in Japan provided definitive evidence linking a single high-dose exposure of ionizing radiation to the subsequent development of cataracts.
How Radiation Damages the Eye Lens
The human lens is composed of a capsule, lens fibers, and a single layer of epithelial cells on its front surface. This layer is responsible for the growth and maintenance of the entire structure. The cells are most actively dividing in a region near the lens’s edge, known as the germinative zone at the equator.
Ionizing radiation is particularly damaging to actively dividing cells. When radiation passes through the eye, it can directly damage the DNA within these epithelial cells or create free radicals that cause cellular injury. The lens has a limited ability to repair this damage or clear away affected cells, so the damaged cells fail to differentiate properly into healthy, transparent lens fibers.
Instead of integrating seamlessly into the lens, these damaged cells migrate toward the back surface of the lens. There, they accumulate and begin to form an opacity that scatters light instead of focusing it, leading to the characteristic cloudiness of a cataract. While it was once thought a specific threshold dose was required, some analyses suggest there may not be a safe level of exposure and that risk may increase with any amount of radiation.
Diagnosis and Clinical Characteristics
Diagnosing a radiation cataract begins with a patient history to identify past exposure to significant sources of ionizing radiation. An ophthalmologist will then conduct a comprehensive eye examination. The primary tool for this diagnosis is the slit-lamp biomicroscope, which provides a highly magnified, three-dimensional view of the eye’s structures, including the lens.
Radiation exposure typically causes a specific type of cataract known as a posterior subcapsular cataract (PSC). This term describes an opacity that forms on the rear surface of the lens, directly under its containing membrane, or capsule. In its early stages, it may appear as small, iridescent dots or vacuoles at the back of the lens. As it progresses, it often forms a more dense, plaque-like opacity that can significantly interfere with vision, especially when reading or in bright light.
A distinct feature of radiation cataracts is the latency period between exposure and the appearance of a clinically detectable opacity. This period is not immediate and can range from several months to many years, depending on the dose of radiation received. Generally, a higher radiation dose is associated with a shorter latency period, while lower doses may not result in a cataract for decades.
Treatment and Prevention
The treatment for a visually significant radiation cataract is the same as for any other type of cataract: surgery. The most common procedure is phacoemulsification. During this operation, a surgeon makes a small incision in the eye, uses an ultrasonic probe to break the cloudy lens into small pieces, and removes them from the eye. The surgeon then inserts a clear, artificial intraocular lens (IOL) to replace the natural lens.
Preventing radiation cataracts involves minimizing exposure to the eyes. For medical professionals, this includes using protective equipment such as wraparound leaded glasses, thyroid collars, and ceiling-suspended leaded-glass shields during procedures that involve radiation. For patients undergoing radiotherapy, modern techniques like intensity-modulated radiation therapy (IMRT) help to shape the radiation beams more precisely, sparing sensitive structures like the lens.
For the general public, the most relevant preventive measure is protection from UV radiation. Wearing sunglasses that block 100% of both UVA and UVB rays is an effective strategy to reduce the risk associated with sun exposure. Limiting unnecessary medical imaging when possible is another sensible precaution.