Presbyopia and the water content of the human crystalline lens.

1. The water content of the human crystallaline lens nucleus is 63.4% S.D. +/- 2.9%, and cortex 68.6% S.D. +/- 4.3%.2. Neither the total water content of the cortex, nor that of the nucleus show any significant changes with age, so ;sclerosis' of the lens due to loss of water is not a cause of presbyopia.3. The initial loss of water from the nucleus of the lens substance obtained by drying in vacuo at 20 degrees C for 2 hr is related to age (P = 0.05) and deformability (0.02 > P > 0.01).4. The lens fibres of the ageing nucleus have an increased resistance to deformation associated with a decrease in initial water loss. These characteristics can be explained by a common physical property of the fibres, namely increased adhesion to each other as the lens nucleus ages. The newly formed cortical fibres do not appear to show these changes.