2020–2021 BCSC Basic and Clinical Science Course™
11 Lens and Cataract
Chapter 5: Pathology
The lens is extremely sensitive to ionizing radiation; however, up to 20 years may pass after exposure before a cataract becomes clinically apparent. This period of latency is related to the dose of radiation and to the patient’s age; younger patients are more susceptible because they have more lens cells that are actively growing. Ionizing radiation in the x-ray range (0.001–10.0-nm wavelength) can cause cataracts in some individuals in doses as low as 2 Gy in a single fraction. (A routine chest x-ray equals 0.01-Gy exposure to the thorax.) A single computed tomography (CT) scan of the brain may expose the lens to as much as 2.5–5 cGy (100 cGy = 1 Gy).
The first clinical signs of radiation-induced cataract are often punctate opacities within the posterior capsule and feathery anterior subcapsular opacities that radiate toward the equator of the lens. These opacities may progress to complete opacification of the lens.
Exposure of the eye to infrared (IR) radiation and intense heat over time can cause the outer layers of the anterior lens capsule to peel off as a single layer. Such true exfoliation of the lens capsule, in which the exfoliated outer lamella tends to scroll up on itself, is seen today only in rare cases. Cortical cataract may be associated with this condition, in which case it is known as glassblower’s cataract (Fig 5-16). (See the section Pseudoexfoliation Syndrome later in this chapter.)
Figure 5-16 Infrared radiation may cause cortical changes, for example, this glassblower’s cataract.
(Courtesy of James Gilman, CRA, FOPS.)
Experimental evidence suggests that the lens is susceptible to damage from ultraviolet (UV) radiation. Epidemiologic evidence suggests that long-term exposure to sunlight is associated with an increased risk of cortical cataracts, perhaps more frequently in men than women. Although sunlight exposure accounts for only approximately 10% of the total risk of cortical cataract in the general population in temperate climates, this risk is avoidable. Because exposure to UV radiation can lead to other morbidity, clinicians should encourage their patients to avoid excessive sunlight exposure. Lenses sold in the United States must conform to the American National Standards Institute (ANSI) requirements aimed at reducing UV transmission. Using prescription corrective lenses and non-prescription sunglasses decreases UV exposure by more than 80%, and wearing a hat with a brim decreases ocular sun exposure by 30%–50%.
Klein BE, Lee KE, Danforth LG, Schaich TM, Cruickshanks KJ, Klein R. Selected sunsensitizing medications and incident cataract. Arch Ophthalmol. 2010;128(8):959–963.
Modenese A, Gobba F. Cataract frequency and subtypes involved in workers assessed for their solar radiation exposure: a systematic review. Acta Ophthalmol. 2018;96(8):779–788.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.