Quantitative and morphometric studies of age-related changes in human ciliary muscle.

The age-related changes in ciliary muscles were studied morphologically in 20 human eyes ranging from 3 months to 90 years of age. The meridionally cross-sectioned area and the volume of ciliary muscles increased with age until 70 years, but then decreased. The circular fiber in the ciliary muscle was undeveloped in the infantile eye. However, it continued to develop until about 70 years of age, and then decreased. The connective tissue in the ciliary muscle showed a proportional age-related increase. Over 71 years of age the proportion of connective tissue became larger than that of the muscle fiber. The number of nuclei in the ciliary muscle was maximum in eyes between 21 to 40 years of age, and subsequently there was a continuous and distinct decrease in the circular fiber with age. The age-related increase of connective tissue and decrease of nuclei in the ciliary muscle together with the decreasing circular fiber suggested a possibility of atrophy in the ciliary muscle with age-related deterioration of accommodation.