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A.S. Vilupuru, A. Glasser; Refractive and Biometric Changes During Edinger-Westphal Stimulated Accommodation in Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2003;44(13):238.
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Purpose: To dynamically correlate accommodative changes in refraction with the biometric changes in the eye (lens thickness (LT), anterior chamber depth (ACD) and anterior segment length, i.e., LT+ACD (ASL)) during accommodation in vivo in rhesus monkeys. Accommodation occurs due to an increase in surface curvatures of the lens and an accompanying increase in LT and decrease in ACD. This study was conducted to understand how the accommodative refractive and biometric changes in the eye are related during accommodation in young rhesus monkeys. Methods: Three rhesus monkeys (aged 11.5 and two aged 4.75 years) which had undergone prior, bilateral, complete iridectomies were used. Increasing stimulus amplitudes were delivered to the Edinger-Westphal nucleus to elicit increasing accommodative responses in each eye of each monkey. Dynamic accommodative (refractive) responses were recorded with infrared photorefraction. At the same stimulus amplitudes, accommodative biometric changes were measured dynamically with continuous, high resolution A-scan ultrasound. The measured dynamic responses were fit with equations, the derivatives of which provided peak velocities of accommodation and disaccommodation for each response. In addition, dynamically measured refractive and biometric changes recorded for the same stimulus amplitudes were compared against each other. Results: Peak velocities of accommodation and disaccommodation of both refractive and biometric changes increased linearly with amplitude. Slopes of peak velocity vs accommodative amplitude ranged from 1.63 to 2.8 D/sec, whereas slopes of peak velocity vs disaccommodative amplitude ranged from 4.88 to 7.74 D/sec. Changes in LT were linearly correlated with refractive changes during accommodation in all eyes. Mean results from all eyes show that for 1 D of accommodation there is a 0.063±0.009 mm increase in LT, a 0.045±0.009 mm decrease in ACD and a 0.019±0.003 mm increase in ASL. An increase in ASL shows that the posterior lens surface moves backwards systematically with accommodation. Conclusions: Dynamic comparisons show that accommodation is accompanied by highly correlated systematic biometric and refractive changes. LT and ACD change linearly with accommodative refractive changes. High resolution A-scan measurements unequivocally demonstrate a posterior movement of the posterior lens surface during accommodation. Although the accommodative refractive changes in the eye are primarily due to changes in lens surface curvature, the refractive changes are also highly correlated with the non-optical, accommodative biometric changes.
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