Age-related changes in human ciliary muscle and lens: a magnetic resonance imaging study.

PURPOSE: To use high-resolution magnetic resonance (MR) images of the eye to directly measure the relationship between ciliary muscle contraction and lens response with advancing age. METHODS: A General Electric, 1.5-Tesla MR imager and a custom-designed eye imaging coil were used to collect high-resolution MR images from 25 subjects, 22 through 83 years of age. A nonmagnetic binocular stimulus apparatus was used to induce both relaxed accommodation (0.1 diopter [D]) and strong accommodative effort (8.0 D). Measurements of the ciliary muscle ring diameter (based on the inner apex), lens equatorial diameter, and lens thickness were derived from the MR images. RESULTS: Muscle contraction is present in all subjects and reduces only slightly with advancing age. A decrease in the diameter of the unaccommodated ciliary muscle ring was highly correlated with advancing age. Lens equatorial diameter does not correlate with age for either accommodative state. Although unaccommodated lens thickness (i.e., lens minor axis length) increases with age, the thickness of the lens under accommodative effort is only modestly age-dependent. CONCLUSIONS: Ciliary muscle contractile activity remains active in all subjects. A decrease in the unaccommodated ciliary muscle diameter, along with the previously noted increase in lens thickness (the "lens paradox"), demonstrates the greatest correlation with advancing age. These results support the theory that presbyopia is actually the loss in ability to disaccommodate due to increases in lens thickness, the inward movement of the ciliary ring, or both.

Magnetic resonance imaging and morphometric quantitation of cartilage histology after chronic infusion of interleukin 1 in rabbit knees.

Cartilage pathology in rabbit knees was monitored by noninvasive magnetic resonance imaging (MRI) and evaluated using morphometric histologic measurements. Infusion of rabbit knees with the cytokine interleukin 1 induces cartilage degradation and inflammation. A miniosmotic pump was implanted subcutaneously to deliver interleukin 1 through a polyethylene catheter inserted into the rabbit knee. Rabbit knees were imaged using MRI and prepared for histologic examination at 5 and 12 days after chronic infusion of interleukin 1. MRI obtained 0.7-mm sections for three-dimensional reconstruction of cartilage image. Cartilage deterioration near the site of infusion was visible on MRI. MRI measurements indicated a reduction in cartilage thickness. Histology revealed a loss of staining of cartilage matrix proteoglycan, synovial hypertrophy, and perichondral bone resorption. Morphometric analysis of cartilage histology indicated a reduction in both cellularity (chondrocytes/m mu 2 area) and cell to matrix area ratio. These observations suggest that a loss of proteoglycan, an early event in cartilage degeneration, can be detected by MRI.