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A. L. Sheppard, L. N. Davies; In vivo Changes in Human Ciliary Muscle Biometry With Accommodation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2796.
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To develop a novel, non-invasive method enabling in vivo quantitative analysis of changes in human ciliary muscle biometry with accommodation.
High-resolution images of nasal human ciliary muscle in various accommodative states were acquired of the right eyes of 15 pre-presbyopic subjects aged 20-31 years (mean age 24.07±3.38 years), using the Zeiss Visante anterior segment optical coherence tomographer (AS-OCT; Carl Zeiss Meditec Inc., Dublin, CA, USA). Images were captured whilst subjects viewed external fixation targets (at an angle of 45°) of 0D, 4D and 8D stimulus vergences, presented in random order. Three images were obtained and averaged for every accommodative state. Objective responses to the accommodative stimuli were recorded using the Shin Nippon SRW-5000 autorefractor (Shin-Nippon Commerce Inc., Tokyo, Japan). Images were processed with the Visante software (version 22.214.171.1246) to obtain mean measures of ciliary muscle length (measured from the scleral spur to the posterior limit of visible ciliary muscle) and ciliary muscle thickness at 25%, 50% and 75% (CM25, CM50 and CM75, respectively) of the visible ciliary muscle length at each accommodative state for all subjects. Change in ciliary muscle dimensions per dioptre of accommodative response was then calculated. The repeatability of the technique was investigated by imaging the nasal ciliary muscle of a single subject 10 times at 0D stimulus vergence.
Ciliary muscle contraction with accommodation resulted in an observed shortening of the visible ciliary muscle and a thickening of CM25, with no significant change in CM50 or CM75. Mean visible ciliary muscle length reduced by 56.94±29.66µm/D of accommodation, whilst CM25 thickness increased by 28.69±59.36µm/D of accommodative response. The repeatability study showed a mean ciliary muscle length of 4.10±0.07mm and mean CM25 of 705±7.2µm.
AS-OCT represents a new, non-invasive method for quantifying in vivo accommodative changes in human ciliary muscle. The observed shortening of the ciliary muscle and thickening of CM25 represents the known forwards and inwards movement of human ciliary muscle mass with accommodative effort. This technique could be further utilised to analyse ciliary muscle biometric changes in presbyopic eyes and eyes implanted with accommodating intraocular lenses to inform further development of such implants.
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