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L. He, S. B. Stevenson, A. Glasser, W. J. Donnelly, III; Saccadic Lens Instability Increases With Accommodative Stimulus in Presbyopes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2800.
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Ultrasound and MRI imaging of presbyopic eyes shows ciliary muscle function is preserved, a prerequisite for the success of accommodating IOL implants. Here we used an SRI dual Purkinje image (dPi) eye tracker to measure lens wobble following saccades with increasing accommodative effort to evaluate ciliary muscle function in presbyopes.
Ten presbyopic subjects executed a total of 32 4-degree saccades at one second intervals between targets arranged in a cross on illuminated cards at each of 9 viewing distances ranging from 0.5 to 8 D accommodative demands. Viewing was binocular; targets were aligned with the dilated (2.5% phenylephrine) left eye. Left eye position was monitored with the dPi eye tracker and both Purkinje (P) image P4 and P1 signals were recorded at 360 Hz. Post-saccadic lens wobble artifacts were extracted by subtraction of P1 from P4 signals. A ray tracing eye model (Advanced Human Eye Model, AHEM, Breault Research) was also employed to model P4 image shifts for a range of lens translations and rotations.
Considerable variability was noted between subjects. Combining all saccades from all subjects showed a significant positive relationship between artifact amplitude and accommodative demand [F(1, 649) = 146.49, P < 0.001]. Artifact amplitude depended on saccade direction as well as size, with abducting saccades showing larger artifacts than adducting ones [F(1, 131) = 20.21, P < 0.001]. Eye model simulations indicated that artifacts of the size measured could arise from either lens rotations (in the range of 2-4 degrees) or lens translations (in the range of 0.1 to 0.2 mm).
Lens wobble artifacts increase with accommodative effort in presbyopes, indicating preserved ciliary muscle function and greater decreases in zonular tension with accommodative effort. Variation across subjects may reflect differences in accommodative effort, ciliary muscle function for a given effort, and/or intraocular anatomy.
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