"The etiology of presbyopia remains unclear. Presbyopia could occur consequent to loss of ciliary muscle function or loss of lens function. Recent literature suggests loss of lens compliance as the primary pathology. However, the extent to which ciliary muscle contraction during accommodation is preserved in the presbyopic eye has been debated. Lens instability during and after saccadic eye movement may reflect ciliary muscle function and zonular tension. The dual Purkinje image (dPi) eye tracker can be used to evaluate this instability through the "lens wobble artifact". The amplitude of the lens wobble may indirectly reflect the extent of ciliary muscle contraction. In this study, saccadic lens wobble was quantified in presbyopes with accommodative stimuli of 9 different amplitudes... A ray tracing eye model (Advanced Human Eye Model, AHEM, Breault Research Organiztion, Inc.) was used to model the fourth Purkinje image shifts for a certain range of lens translations and rotations."
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