Increase in lens stiffness with age may cause presbyopia, study suggests

An increase in the stiffness of the human lens with age may diminish the ability of the lens to accommodate, contributing to the onset of presbyopia, Australian researchers suggest.

Karl Robert Heys and colleagues at the Australian Cataract Research Foundation used a custom-made probe to measure stiffness at 1 mm increments across equatorial sections of human lenses from individuals ranging in age from 14 to 78 years. A “pronounced” increase in lens stiffness was noted over this age range, the researchers said.

Within the nucleus, the stiffness values varied almost 1,000-fold over the age range, with the largest changes observed in lenses between the ages of 20 and 60. On average, nuclear stiffness values increased by a factor of 450. In the cortex, the average increase in stiffness was approximately 20-fold over the same time period, the researchers said.

All lenses older than 30 years had nuclear stiffness values higher than those of the cortex; the crossover age when the cortical and nuclear stiffness values were similar was in the 30s.

The researchers noted that the physical changes in the lens are part of a host of age-related ocular alterations, all of which may contribute to presbyopia. The increases in stiffness could also be the result of other factors “that over time may affect lens biochemical processes,” the researchers said.

“A quite unexpected finding was that the nuclei of young lenses (prior to age 30), were less stiff than those of the cortices. Given the requirement for substantial nuclear deformation during accommodation, one is tempted to suggest that such a difference may be present to facilitate the process of lenticular shape change,” the researchers speculated in Molecular Vision.