Browsing by Author "Kao, Chiu-Yen"
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Item Measuring Ciliary Muscle Thickness Changes with Accommodation in Young Adults(Optometry and Vision Science, 2012-05) Lossing, Laura Ashley; Sinnott, Loraine T.; Kao, Chiu-Yen; Richdale, Kathryn; Bailey, Melissa D.Purpose: To develop a measurement protocol for changes in the shape and size of the ciliary muscle with accommodation using the Zeiss Visante™ Anterior Segment Optical Coherence Tomographer (AS-OCT) and to determine the test-retest repeatability of these measurements. Methods: Subjects were 25 adults ages 23–28 years. The ciliary muscle was imaged at two visits with the Visante™ while accommodative response was monitored during imaging using the PowerRefractor. Ciliary muscle thickness was measured at 1 mm (CMT1), 2 mm (CMT2), and 3 mm (CMT3) posterior to the scleral spur and at the point of maximal thickness (CMTMAX). Thickness was measured at these locations while subjects viewed a target at distance and at a 4.00-D accommodative stimulus. Outcome measures were the change in thickness between distance and the 4.00-D stimulus and the change in thickness per diopter of accommodative response (PowerRefractor). Finally, the repeatability measurements between visit 1 and visit 2 were determined with a Bland-Altman analysis. Results: The statistically significant modeled changes in ciliary muscle thickness were as follows: CMTMAX = 69.2 μm (4.00-D stimulus) and 18.1 μm (per diopter of accommodation); CMT1 = 45.2 μm (4.00-D stimulus) and 12.3 μm (per diopter of accommodation); and CMT3 = μ45.9 μm (4.00-D stimulus) and μ12.0 μm (per diopter of accommodation); p < 0.0001 for all. Conclusions: The combination of the Visante™ and the PowerRefractor is a feasible tool for measuring thickening of ciliary muscle at more anterior locations and thinning at more posterior locations during accommodation. We noted a wide range of accommodative responses during the time of image capture in this study indicating that the most accurate estimates of the change in ciliary muscle dimensions with accommodation may be obtained by using accommodative response rather than stimulus values and by using measurements taken simultaneously with image capture.Item Quantification of Age-Related and per Diopter Accommodative Changes of the Lens and Ciliary Muscle in the Emmetropic Human Eye(Investigative Ophthalmology & Visual Science, 2013-02) Richdale, Kathryn; Sinnott, Loraine T.; Bullimore, Mark A.; Wassenaar, Peter A.; Schmalbrock, Petra; Kao, Chiu-Yen; Patz, Samuel; Mutti, Donald O.; Glasser, Adrian; Zadnik, KarlaPurpose: To calculate age-related and per diopter (D) accommodative changes in crystalline lens and ciliary muscle dimensions in vivo in a single cohort of emmetropic human adults ages 30 to 50 years. Methods: The right eyes of 26 emmetropic adults were examined using ultrasonography, phakometry, anterior segment optical coherence tomography, and high resolution magnetic resonance imaging. Accommodation was measured both subjectively and objectively. Results: In agreement with previous research, older age was linearly correlated with a thicker lens, steeper anterior lens curvature, shallower anterior chamber, and lower lens equivalent refractive index (all P < 0.01). Age was not related to ciliary muscle ring diameter (CMRD) or lens equatorial diameter (LED). With accommodation, lens thickness increased (+0.064 mm/D, P < 0.001), LED decreased (−0.075 mm/D, P < 0.001), CMRD decreased (−0.105 mm/D, P < 0.001), and the ciliary muscle thickened anteriorly (+0.013 to +0.026 mm/D, P < 0.001) and thinned posteriorly (−0.011 to −0.015, P < 0.01). The changes per diopter of accommodation in LED, CMRD, and ciliary muscle thickness were not related to subject age. Conclusions: The per diopter ciliary muscle contraction is age independent, even as total accommodative amplitude declines. Quantifying normal biometric dimensions of the accommodative structures and changes with age and accommodative effort will further the development of new IOLs designed to harness ciliary muscle forces.Item Semi-Automatic Extraction Algorithm for Images of the Ciliary Body(Optometry and Vision Science, 2011-02) Kao, Chiu-Yen; Richdale, Kathryn; Sinnott, Loraine T.; Ernst, Lauren E.; Bailey, Melissa D.Purpose: To development and evaluate a semi-automatic algorithm for segmentation and morphological assessment of the dimensions of the ciliary muscle in Visante™ Anterior Segment Optical Coherence Tomography images. Methods: Geometric distortions in Visante images analyzed as binary files were assessed by imaging an optical flat and human donor tissue. The appropriate pixel/mm conversion factor to use for air (n = 1) was estimated by imaging calibration spheres. A semi-automatic algorithm was developed to extract the dimensions of the ciliary muscle from Visante images. Measurements were also made manually using Visante software calipers. Interclass correlation coefficients (ICC) and Bland-Altman analyses were used to compare the methods. A multilevel model was fitted to estimate the variance of algorithm measurements that was due to differences within- and between-examiners in scleral spur selection versus biological variability. Results: The optical flat and the human donor tissue were imaged and appeared without geometric distortions in binary file format. Bland-Altman analyses revealed that caliper measurements tended to underestimate ciliary muscle thickness at 3 mm posterior to the scleral spur in subjects with the thickest ciliary muscles (t = 3.6, p < 0.001). The percent variance due to within- or between-examiner differences in scleral spur selection was found to be small (6%) when compared to the variance due to biological difference across subjects (80%). Using the mean of measurements from three images achieved an estimated ICC of 0.85. Conclusions: The semi-automatic algorithm successfully segmented the ciliary muscle for further measurement. Using the algorithm to follow the scleral curvature to locate more posterior measurements is critical to avoid underestimating thickness measurements. This semi-automatic algorithm will allow for repeatable, efficient, and masked ciliary muscle measurements in large datasets.Item The Effect of Phenylephrine on the Ciliary Muscle and Accommodation(Optometry and Vision Science, 2012-10) Richdale, Kathryn; Bailey, Melissa D.; Sinnott, Loraine T.; Kao, Chiu-Yen; Zadnik, Karla; Bullimore, Mark A.Purpose: To objectively measure changes in the human ciliary muscle dimensions in vivo following instillation of topical phenylephrine, a mydriatic and vasodilating agent. Methods: A cross-sectional study of 25 healthy young adults was conducted. Measurements of pupil size, accommodation, and ciliary muscle thickness were made both before and 30 minutes after instillation of 1% proparacaine and 2.5% phenylephrine. Accommodation was measured three ways: subjectively using a push-up technique and Royal Air Force (RAF) rule, and objectively using both the Grand Seiko autorefractor and PowerRefractor. Images of the temporal ciliary muscle were made using the Visante Anterior Segment Optical Coherence Tomographer (OCT). Ciliary muscle images were objectively analyzed using a computer-based segmentation technique. Results: Amplitude of accommodation with the push-up test was reduced by about 1D with phenylephrine (p < 0.001). Phenylephrine did not change the accommodative response to a 4-D Badal target as measured by either autorefraction or photorefraction (p > 0.30). There was statistically significant thickening of the anterior region and thinning of the posterior region of the ciliary muscle with accommodation (p < 0.001, all locations). Phenylephrine did not affect either baseline ciliary muscle thickness, or the accommodative contraction of the muscle (p > 0.09). Conclusions: Low-dose phenylephrine does not affect ciliary muscle dimensions, ciliary muscle contractility, or accommodative response to a 4 D near target.