In Vivo Imaging Studies of Age Related Changes of Accommodation in the Rhesus Monkey

Abstract

Abstract: : Purpose: To determine functional interaction of accommodative structures in young and old monkeys. Methods: Twenty-six anesthetized rhesus monkeys aged 6-24 yr that had undergone prior total iridectomy and implantation of a stimulating electrode in the E-W nucleus were studied. Centrally stimulated accommodative amplitude was measured with a coincidence refractometer. Scheimpflug photography, goniovideography and ultrasound biomicroscopy (UBM) were performed before and after intra- and extra-capsular lens extraction (ICLE, ECLE) and α-chymotrypsin regional zonulolysis of the posterior zonule (PRZ). Extent and dynamics of lens/capsule and ciliary process (CP) movements were measured by computerized image analysis. Results:The unaccommodated circumlental space decreased with age in the temporal quadrant but not the nasal quadrant (n=28 eyes). The slope on age in the temporal quadrant is -0.013±0.005 mm/yr (p=0.012). The slope on age in the nasal quadrant is -0.007±0.005 mm/yr (p=0.19). The slopes were significantly different from each other (p=0.01). Controlling for age, temporal circumlental space did not account for loss of accommodation (ACC). Loss of forward muscle movement with age is more pronounced than loss of inward movement. In the young eyes (n=4) with 15.9±1.1 diopters (D) of ACC, the CP and lens move ~0.38 and 0.30 mm respectively and in close association with each other. In old eyes (n=16) with 3.3±0.4 D of ACC, the CPs and lens move 0.36 and 0.15 mm respectively and they did not move in close association. There is a nasalward shift in lens position in 8/16 old eyes during ACC once the temporal CPs came in contact with the lens. One of these eyes underwent ECLE, resulting in elimination of asymmetry of lens capsule movement. Following ICLE in a young eye there was nasal vs temporal asymmetry of CP movement. Following ICLE in an old eye, nasal vs temporal asymmetry of CP movement was only slight. Following PRZ+localized severing of the choroid (age 24 yr), the amplitude of inward lens movement increased and was in closer association with the CPs. Conclusions: Nasal and temporal accommodative asymmetries exist and represent an underinvestigated aspect of accommodative aging. These findings suggest both a lenticular and extralenticular component to presbyopia.

Keywords: accommodation • aging • anatomy