SUMMARY The effect on the human lens of prolonged hyperbaric oxygen therapy is reported. Eye examinations were given to 25 patients before, during, and after a series of 150 or more exposures to hyperbaric oxygen. All patients changed refraction in the direction of myopia during treatment. Fifteen of the patients had clear lens nuclei before treatment. Seven of these developed a nuclear cataract with reduced visual acuity during treatment. Reversible lens myopia has previously been noticed as a side effect of exposure to hyperbaric oxygen, but the cataractogenic effect in man has not been reported by other workers. This report strongly supports the theory of an oxidative damage to the lens proteins as a cause of nuclear cataract.

Two lenses with atopic cataract, one from a 33-year-old man and one from a 50-year-old man, were examined by light and electron microscopy. The younger man had an anterior polar cataract and the older a subcapsular opacification of the entire subcapsular cortex. In the younger lens the epithelial cells in front of the anterior opacity were extremely large and contained an increased number of mitochondria. In the older lens epithelial cells were missing centrally. These morphological changes probably reflect a malfunction of the lens epithelium.

Abstract. Nuclear cataract is a common type of senile cataract characterized by an increased turbidity and often a yellow to brown pigmentation of the nucleus. Twenty‐one human lenses with different degrees of nuclear turbidity were, after intracapsular cataract extraction, examined by a quantitative microradiographic technique. The dry mass concentration was determined along the lens axis, and revealed an overall distribution similar to the normal lens. The concentration increased from the poles towards the center of the lens, to reach a mean level of 0.47 g cm−3 (range 0.38‐0.55). Though the appearance of the nucleus as well as the dry mass were relatively uniform. In addition, different types of formations with reduced or increased dry mass were found in the nucleus. The location of these formations are described and their nature discussed.