Centripetal Ciliary Body Accommodative Movements May Mitigate Age-Related Loss of Forward Ciliary Body and Centripetal Lens Movement

Abstract

Purpose:: Forward ciliary body movement positively correlates with accommodative lens centripetal movements and accommodative amplitude.[Croft et al 2006] Our goal was to further elucidate how lens and ciliary body accommodative function changes with age in rhesus monkeys.

Methods:: Twenty-six rhesus monkeys, aged 5.8-27 yrs were grouped as young, middle-aged and old. Edinger-Westphal (E-W) stimulated accommodation was measured by coincidence refractometry, centripetal ciliary body (CCB) and lens equator movements by computerized image analysis of goniovideographic images and forward ciliary body (FCB) movement, by ultrasound biomicroscopy (UBM; 50 MHz) [Croft et. al. IOVS 2006].

Results:: The best-fit model for the CCB versus accommodation regression was quadratic for all three age groups (p=0.0001) while the lens movement vs accommodative amplitude relationship was linear. Lens centripetal movement played a significant role in explaining accommodative amplitude for all three age groups and the CCB and CCB² parameters became more important with age in explaining accommodative amplitude. FCB movement declined by 51% (p=0.002), lens centripetal movement declined by 28% (p=0.0.07), CCB movement declined by 18% (p=0.029) and accommodative amplitude declined by ~43% (p=0.01) in the middle-aged eyes compared to the young eyes. The unit of accommodative CCB movement that occurred per unit of FCB movement progressively increased in middle-aged and older eyes compared to the young eyes (p<0.05). Despite the apparent compensation for the age-related loss in FCB movement by increased CCB movement per unit of lens movement, there was an upper limit (~0.28mm) to lens equatorial movement, thus, limiting accommodative amplitude.

Conclusions:: Age-related changes in lens function may be secondary to the loss in FCB movement, given that the age-related loss in FCB movement occurs sooner and in a more pronounced manner than the age-related loss in lens centripetal movement. Based on decreased accommodative amplitude and lens centripetal movement in middle-aged compared to young eyes, increased centripetal accommodative movements of the ciliary body per unit of lens movement partially compensate for the age related loss in FCB movement. There may be zonular attachments between the lens and ciliary body that are more dependent on FCB than CCB movement to achieve relaxation.

Keywords: presbyopia • ciliary body • aging