Age–Related Loss of Accommodative Ciliary Body Forward Movement in the Rhesus Monkey

Abstract

Abstract: : Purpose: To further elucidate the ciliary body and lens function during accommodation and their change with age in rhesus monkeys.Methods: Accommodation was stimulated via the Edinger–Westphal (E–W) nucleus in 26 rhesus monkeys, aged 6–24 yr, and the refractive change measured by coincidence refractometry. Centripetal lens and ciliary process (CP) movements were measured by computerized image analysis of goniovideographic images. Ultrasound biomicroscopy (UBM) at 50 and 35 MHz was used to visualize accommodative movements of ciliary body and lens surfaces. Using these images the angle between the anterior aspect of the ciliary body and the inner aspect of the cornea (CB–Cornea angle) was measured in the unaccommodated (resting) eye and during supramaximal stimulation to induce accommodation. The extent that the CB–Cornea angle narrowed in the accommodated vs the unaccommodated state (defined as the accommodative CB–Cornea angle change) was examined in relation to age, accommodative amplitude and lens centripetal movement. Accommodative CB–Cornea angle change is a surrogate indicator of forward ciliary body movement. Results: CB–Cornea angle narrowing during accommodation declined significantly with increasing age (–2.71±0.39°/yr; p=0.01; n=21) and decreasing accommodative amplitude (3.34±0.54°/diopter; p=0.01; n=21). There was a significant positive relationship between the accommodative CB–Cornea angle change and the amplitude of the centripetal lens movement (0.0031±0.00085mm/°; n=19; p<0.002). The farther the ciliary body moved forward in the accommodated state (UBM), the greater the accommodative CB–Cornea angle change and the higher the maximum accommodative amplitude. The amplitude of centripetal CP movement did not decline significantly with age.^{[Croft ARVO 2003 & 2004]} Conclusions: Accommodative CB–Cornea angle change was significantly related to accommodative amplitude, declined significantly with age and was significantly related to lens equator movement. There appear to be differences in the age effect on forward vs centripetal ciliary body (CP) movement. A stiffening of the posterior attachments of the ciliary muscle with age may have more effect on forward than on centripetal ciliary body movement.

Keywords: ciliary body • aging • Bruch's membrane