CILIARY MUSCLE AGING AND PRESBYOPIA

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To understand human presbyopia by studying the dynamics of accommodation and presbyopia in nonhuman primates. Nonhuman primates are the preferred model for human presbyopia, the age-related loss of the ability to focus. Focus depends on the ability of the lens to change shape (i.e. lens thickening and a concomitant decrease in lens equatorial diameter). Lens shape change depends upon forward and inward movement of the ciliary muscle. Previously, we found an age-related in loss in ciliary muscle movement that was more pronounced in the forward rather than the centripetal vector. Current findings show that accommodative lens thickening declined with age more markedly than accommodative lens diameter. This could be due to simple geometric / biophysical necessity and/or aging changes inherent in lens structure. Age-related changes in accommodative lens thickening may not be the same quantitatively or mechanistically as the age-related changes in accommodative diameter, regardless of the ciliary body state of contraction. The ciliary muscle's ability to maintain some centripetal movement while undergoing a dramatic loss in forward movement with increasing age may also have an impact on differential lens shape changes (i.e., accommodative thickening vs. equatorial movements). Whether the age-related differences in lens thickening vs. lens equator movements are due to the lens itself or to changes in ciliary body movements, these findings may provide insights into successful accommodating IOL design. The presence of the vitreous zonule was confirmed in the human eye. Disruption of the vitreous zonule restored forward muscle movement in the older rhesus monkey eye. This raises the possibility that the vitreous zonule could be a biological target, the disruption of which could be used to restore forward muscle movement. Further, there was an age-related decrease in width of the ciliary body in the vitreous zonule/pars plana region and this may have an effect on the vitreous zonule tension and may affect lens shape and thereby accommodation. Again, these findings may provide some insight into successful accommodating IOL design. This research used WNPRC Research Services. PUBLICATIONS: Croft MA, McDonald JP, Nadkarni NV, Lin TL, Kaufman PL: Age-related changes in centripetal ciliary body movement relative to centripetal lens movement in monkeys. Exp Eye Res 89:824-832, 2009 (Dec) PMCID278077 L¿tjen-Drecoll E, Kaufman PL, Wasielewski R, Lin TL, Croft MA: Morphology and accommodative function of the vitreous zonule in human and monkey eyes. Invest Ophthalmol Vis Sci, Epub ahead of print, Oct 8, 2009.