Stimulus Phoria versus Response Phoria in a Prepresbyopic Population at COSI (Center of Science and Industry) THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Dix Hale Pettey Graduate Program in Vision Science The Ohio State University 2015 Master's Examination Committee: Melissa D. Bailey, OD, PhD, Advisor Donald O. Mutti, OD, PhD G. Lynn Mitchell, MAS Copyright by Dix Hale Pettey 2015 Abstract Background: Phoria measurement is a useful clinical tool in the diagnosis of binocular vision disorders and several methods of phoria measurement have been described. A common weakness of many of these methods is the exact amount of accommodation at the time of measurement must be assumed, which may lead to erroneous results in those who accommodate inaccurately. Purpose: This study evaluated if the Purkinje image technique using a Grand Seiko Autorefractor with an attached video camera could be used as an effective and accurate method for heterophoria measurement. The level of agreement between 4-D stimulus phoria (SP) and 4-D response phoria (RP) measurements obtained from the modified autorefractor was compared to those obtained from the Modified Thorington (MT) test. Methods: Subjects included 20 emmetropic children and adults with a mean age of 12.2 ± 4.5 years who were recruited from the population visiting the Center of Science and Industry (COSI) in Columbus, Ohio. Horizontal near phoria was first measured using the MT method. Accommodative response and refractive error were measured using a modified Grand Seiko autorefractor, with accommodation being stimulated by letter targets at distance (0.00 D stimulus), 4-D stimulus (25 cm) and 4-D response (≤ 25 cm) levels. Convergence was measured simultaneously by monitoring the relative movement of Purkinje images I and IV. Bland Altman methods were used to determine agreement between measurements. ii Results: When measured with MT at 40 cm, the mean ± SD horizontal phoria was −1.24Δ ± 3.28 (exophoria). When measured with the autorefractor, the mean phoria was more esophoric than MT for all three stimulus levels: 1.26Δ ± 5.75 (esophoria) at distance, 3.09Δ ± 6.86 (esophoria) for SP at 25 cm, and 5.80Δ ± 5.94 (esophoria) for RP at ≤25 cm. The mean of the differences was significantly different between SP and MT [4.60Δ ± 9.09 (esophoria), p = 0.04], RP and MT [7.30Δ ± 7.91 (esophoria), p = 0.001], and between RP and SP [2.71 ± 3.83Δ (esophoria), p = 0.005]. The difference between phoria measurements for both SP vs MT and RP vs MT was found to be dependent upon the mean. The mean ± SD gradient AC/A ratio for the entire sample was 4.59 ± 7.20 Δ/D. A significant correlation was found between the difference in RP and SP versus the RP – SP Response AC/A ratio (R2 = 0.98, p = <0.0001), suggesting subjects become more esophoric when forced to accommodate fully to a 4-D target. Conclusion: Video and still frames taken with the autorefractor and secondary CCD camera produced phoria measurements that were more esophoric than those obtained with Modified Thorington or reported in previous studies, but it is beneficial that the amount of accommodation at the time of measurement was known. Further investigation is necessary to determine if efficiency in this methodology could be improved and to explore the level of repeatability. These methods have potential to be useful both in the clinic and as a screening tool in diagnosing and monitoring binocular vision disorders. iii Dedication This document is dedicated to my beautiful wife Lacey and our children Shailey, Cambria, and Dax, who constantly make me laugh and whose support and encouragement have been priceless. iv Acknowledgments The work presented here would not have been possible without the tremendous contributions of: 1. Melissa Bailey for her encouragement, guidance, and expertise as my advisor 2. Don Mutti for his wise counsel and for serving on my thesis committee 3. Lynn Mitchell for her statistical expertise and for serving on my thesis committee 4. Danielle Orr, Morgan Garczyk, Landon Perry, Bradley Daugherty, and Nidhi Satiani for their assistance in recruitment and data collection at COSI. 5. Joe Lehman for the hours of assistance analyzing videos, pictures, and numbers All of your help and support are deeply appreciated. Thank you! v Vita 2010................................................................B.S. (Hons) Exercise & Sports Science, University of Utah 2011 to present ..............................................Optometry Doctoral Student, College of Optometry, The Ohio State University Publications Pettey D. Palmitate evokes ceramide-dependent reactive oxygen species (ROS) generation from sources other than NADPH oxidase in bovine aortic endothelial cells (BAECS). Thesis (Honors)- -Dept. of Exercise and Sport Science, University of Utah, 2010. Zhang QJ, Holland WL, Wilson L, Tanner JM, Kearns D, Cahoon JM, Pettey D, Losee J, Abel ED, Symons JD (2012). Ceramide mediates vascular dysfunction in diet-induced obesity by PP2A-mediated dephosphorylation of the eNOS-Akt complex. Diabetes, 61(7), 1848-59. Pettey JH, Mifflin MD, Kamae K, McEntire MW, Pettey DH, Callegan MC, Brown H, Olson RJ (2013). The impact of short-term topical gatifloxacin and moxifloxacin on bacterial injection after hypodermic needle passage through human conjunctiva. J Ocul Pharmacol Ther, 29(5), 450-5. vi Fields of Study Major Field: Vision Science vii Table of Contents Abstract ............................................................................................................................... ii Dedication .......................................................................................................................... iv Acknowledgments............................................................................................................... v Vita ..................................................................................................................................... vi List of Tables ...................................................................................................................... x List of Figures .................................................................................................................... xi Chapter 1: Introduction ....................................................................................................... 1 1. Horizontal Movement of the Eyes ........................................................................ 2 1.1 Vergence Eye Movements ................................................................................. 2 1.2 Disorders of the Vergence System .................................................................... 3 1.3 Anatomy and Innervation of Extraocular Muscles ........................................... 5 2. The Heterophoria ................................................................................................... 8 3. Heterophoria Measurement ................................................................................ 11 4. Accommodative Convergence / Accommodation (AC/A) Ratio ...................... 16 Chapter 2: Methods ........................................................................................................... 20 Chapter 3: Results ............................................................................................................. 29 viii Chapter 4: Discussion ....................................................................................................... 32 References ......................................................................................................................... 55 ix List of Tables Table 1. Innervation and actions of the extraocular muscles from the primary position. Adapted from Adler’s Physiology of the Eye.34 ................................................................ 39 Table 2. Demographic description of the 20 subjects in study sample. ........................... 40 Table 3. Mean, standard deviation, and distance to target of four different phoria measurements across 20 subjects. ..................................................................................... 41 Table 4. Agreement between three different near phoria measurements across 20 subjects. ............................................................................................................................. 42 x List of Figures Figure 1. Muscle Imbalance Measure Card used for measurement of heterophoria. ..... 43 Figure 2. Example photo of Grand Seiko Autorefractor measurement of right eye. ...... 44 Figure 3. View from above the apparatus used to measure accommodation and vergence.. .......................................................................................................................... 45 Figure 4. Example photo of Purkinje images I and IV produced by infrared light source. ........................................................................................................................................... 46 Figure 5. Difference versus mean plot for the agreement in phoria between 4D Stimulus Phoria (SP) and Modified Thorington (MT). .................................................................... 47 Figure 6. Difference versus mean plot for the agreement in phoria between 4D Response Phoria (RP) and Modified Thorington (MT). ................................................................... 48 Figure 7. Difference versus mean plot for the agreement