Cataract Formation by Near‐infrared Radiation in Rabbits

Abstract

Surveys and epidemiological studies have shown an increased prevalence of cataracts in workers in the glass and steel industries. These cataracts are associated with exposure to intense infrared radiation (IR) emitted from heated materials and industrial furnaces. Thermal model calculations predicted that near and far IR would cause cataract with different mechanisms. The present study investigated cataract formation by near IR. Eyes of pigmented rabbits were exposed to IR at a wavelength of 808 nm. Morphological changes in the anterior segment of the eye were assessed by slit‐lamp microscopy, and temperature distributions in the anterior chamber of the eye were observed during IR exposure using microencapsulated thermochromic liquid crystals. Cortical cataract appeared below the exposed area of the iris in eyes that had been exposed for 6 min to an irradiance of 1.27 W cm−2 or higher. The monitored temperature in the anterior chamber began to increase in the region adjacent to the exposed area of the iris with the onset of IR exposure. These results demonstrate that 808‐nm IR is absorbed and converted to heat within the iris, which is then conducted to the lens and produce a cataract, as Goldmann theory states.

Threshold Ocular Exposure to Near Infrared Radiation for Causing Acute Opacification in the Rabbit Lens

“…One possible explanation for this difference is that the IR-exposed area of the eye was small in his study compared with the present study (3 mm vs. 5 mm in diameter), allowing less radiant power (9/25 or 36%) to enter the eye for the same irradiance. However, in our present and previous studies, well-defined lens opacification of uniform density was observed under the part of the iris exposed to an IR beam with a top-hat intensity distribution (13), suggesting that the threshold irradiance is independent of the size of the exposed area. Thus, it is necessary to investigate if the threshold irradiance varies with the exposed-area size.…”

“…Thus, it may be necessary to lower the exposure limit for exposure durations shorter than 4 s. The finding that the threshold radiant exposure increases with increasing exposure duration (Fig. 3) adds to the evidence that 808 nm IR causes acute lens opacification by a thermal mechanism (13). In a thermal damage mechanism, as exposure duration increases, higher radiant exposure is required to achieve sufficiently high temperature to cause damage in the target tissue because heat is conducted away from it during the exposure (19).…”

“…The threshold irradiance was determined for 3-min, 1-min, 30-s, 10-s and 4-s exposures. The threshold irradiance for 6 min exposure was also determined from our previous data (13) as the midpoint between the lowest irradiance at which lens opacification was observed and the highest irradiance at which it was not. The threshold radiant exposure was calculated for each exposure duration as the product of the threshold irradiance and the exposure duration.…”

“…Previously, we exposed 19 rabbit eyes to 808 nm wavelength IR at different irradiances for 6 min and assessed morphological changes in the anterior segment of the eye by slit‐lamp microscopy (13). As a result, we observed acute opacification in the anterior lens cortex in eyes that were exposed to an irradiance of 1.3 W∙cm −2 or higher.…”

“…Surveys and epidemiological studies have reported an increased prevalence of cataracts in those who have worked for many years in the glass and steel industries (1)(2)(3)(4)(5)(6), and these industrial cataracts are associated with intense infrared radiation (IR) emitted from heated materials and the inside of industrial furnaces. Indeed, a number of animal studies have demonstrated that IR exposure can produce acute changes in the crystalline lens (7)(8)(9)(10)(11)(12)(13) that are likely to lead to cataract formation.…”