Browsing by Author "Glasser, Adrian"
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Item Applicability of Infrared Photorefraction for Measurement of Accommodation in Awake-Behaving Normal and Strabismic Monkeys(Investigative Ophthalmology & Visual Science, 2/1/2009) Bossong, Heather; Swann, Michelle; Glasser, Adrian; Das, Vallabh E.Purpose: This study was designed to use infrared photorefraction to measure accommodation in awake-behaving normal and strabismic monkeys and describe properties of photorefraction calibrations in these monkeys. Methods: Ophthalmic trial lenses were used to calibrate the slope of pupil vertical pixel intensity profile measurements that were made with a custom-built infrared photorefractor. Day to day variability in photorefraction calibration curves, variability in calibration coefficients due to misalignment of the photorefractor Purkinje image and the center of the pupil, and variability in refractive error due to off-axis measurements were evaluated. Results: The linear range of calibration of the photorefractor was found for ophthalmic lenses ranging from ?1 D to +4 D. Calibration coefficients were different across monkeys tested (two strabismic, one normal) but were similar for each monkey over different experimental days. In both normal and strabismic monkeys, small misalignment of the photorefractor Purkinje image with the center of pupil resulted in only small changes in calibration coefficients, that were not statistically significant (P > 0.05). Off-axis measurement of refractive error was also small in the normal and strabismic monkeys (?1 D to 2 D) as long as the magnitude of misalignment was <10°. Conclusions: Remote infrared photorefraction is suitable for measuring accommodation in awake, behaving normal, and strabismic monkeys. Specific challenges posed by the strabismic monkeys, such as possible misalignment of the photorefractor Purkinje image and the center of the pupil during either calibration or measurement of accommodation, that may arise due to unsteady fixation or small eye movements including nystagmus, results in small changes in measured refractive error.Item Prediction of Accommodative Optical Response in Young and Pre-Presbiopic Human Eyes Using Ultrasound Biomicroscopy(2014-12) Ramasubramanian, Viswanathan; Glasser, Adrian; Stevenson, Scott B.; Porter, Jason; Anderson, Heather A.; Schwiegerling, JamesPurpose: Clinical accommodation testing involves measuring either the accommodative optical response (AOR) or the accommodative biometric changes in the ocular anterior segment. Currently, it is not possible to measure both with a single instrument. Measuring the AOR and the accommodative biometric changes are important for evaluating accommodation restoration concepts. The specific goals of this research are: 1) to perform automated, objective measurements of accommodative biometric changes from ultrasound biomicroscopy (UBM) images in young phakic eyes; 2) to measure the static AOR using a Grand Seiko (GS) autorefractor and infra-red photorefraction (PR) in young eyes and to predict the AOR from UBM measured biometric changes; 3) to measure the AOR using GS and PR and the biometric changes using UBM in pre-presbyopes to predict the AOR; 4) to calculate and correct the spatial and optical distortion in Visante optical coherence tomography corneal images; 5) to construct accommodative schematic eye models for individual eyes for each of the young and pre-presbyopic subjects and calculate refraction and AOR from the schematic eye models. Methods: Experiments were 1) Accommodative anterior segment biometric changes were measured in response to 0 D to 6 D accommodative stimuli in 1 D steps in 26 young human subjects using a 35 MHz UBM and an A-scan ultrasound. 2) Static AOR to the same stimulus demand were measured with GS and PR in the same group of young subjects. AOR was predicted from UBM measured biometry parameters using linear regression, 95% confidence intervals and 95% prediction intervals. 3) Static AOR to 0 D to maximal stimulus demand in at least 0.25 D steps was measured with GS and PR in 25 pre-presbyopic human subjects. Accommodative anterior segment biometric changes were measured using UBM and A-scan ultrasound. AOR was predicted from UBM measured biometry parameters as described in experiment 2. 4) Five contact lenses of known front and back surface radii of curvature and central thicknesses were imaged using the Visante to calculate spatial and optical distortion corrections which were then applied to corneal images captured from the young and pre-presbyopic subjects. 5) Ocular biometry parameters (Visante, A-scan and UBM) from Experiments 1, 3 and 4 in young and pre-presbyopic subjects were used to construct paraxial schematic eye models for each individual subject for each accommodative stimulus demand. Results: 1) Standard deviations of UBM measured parameters were smaller than A-scan measures. 2) Mean prediction errors of AOR using linear regression in young subjects for various biometry parameters ranged from 0.56 D to 0.91 D. 3) Mean prediction errors of AOR using linear regression in pre-presbyopic eyes ranged from 0.41 D to 0.62 D. 4) Root mean square (RMS) error of the power of the contact lens surfaces after distortion correction was 0.18 D for the front and 0.11 D for the back surfaces, respectively. 5) Mean ± SD of prediction errors of AOR from individual schematic eyes for the young and pre-presbyopic subjects were 0.50 ± 0.39 D and 0.50 ± 0.37 D, respectively. Conclusions: The results show: 1) the utility of automated image analysis to get accurate, rapid and objective measurements of anterior segment biometry from UBM images; 2) how spatial distortion in UBM images can be corrected to get accurate measurements and the ability of each UBM measured biometry parameter to predict the AOR; 3) how UBM, despite having low axial resolution, can predict AOR in pre-presbyopic eyes with low accommodative amplitudes; 4) how spatial and optical distortions in Visante images can be corrected to get accurate corneal biometry that can be used for schematic eye modeling; 5) how individual schematic eye predictions of the AOR are better than predictions using LR from individual UBM measured biometry parameters.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.