1. Ce Zheng 1, 2, 3, John Mark S de Leon 1, Carol Y Cheung 1, Arun K Narayanaswamy 1, Sim-Heng Ong 4, Clement W Tan 2, Paul T Chew 2, Shamira A Perera 1, Tien Y Wong 1,2, Tin Aung 1, 2 1 Singapore Eye Research Institute, Singapore & Singapore National Eye Centre, 2 Yong Loo Lin School of Medicine, National University of Singapore and National University Health System, Singapore, 3 Joint Shantou International Eye Center of Shantou University and Chinese University of Hong Kong, Shantou, China, 4 Dept. of Electrical & Computer Engineering, National University of Singapore Determinants of Pupil Diameter and Pupil Dynamics in an Adult Chinese Population Aim: To investigate the determinants of pupil diameter (PD), amplitude of PD change (APC) and speed of pupil constriction (SPC) using video anterior segment optical coherence tomography (AS-OCT) in a population-based sample of Chinese adults. Methods: Chinese adults 40-80 yrs. old with no glaucoma, were recruited from the population-based Singapore Chinese Eye Study. The SPC was measured by AS-OCT videography. Results: TABLE 2 Parametersassociated with SPCassociated with PD UnivariateMultivariateUnivariateMultivariate βpβpβpβp Age-0.21<0.001-0.010.06-0.32<0.001-0.010.2 Gender, female0.10.120.070.25 AL0.020.770.040.50 ACD0.080.210.130.040.34<0.001 Dark-room gonioscopy (Shaffer) 0.090.150.060.32 VCDR-0.010.890.020.81 VF MD, dB0.040.480.10.12 VF PSD, dB0.0030.96-0.050.44 ACW0.090.140.060.32 PD/SPC0.31<0.0010.120.0060.3<0.001 LV-0.110.07-0.140.02-0.090.5 TISA500-0.040.51-0.140.03-4.51<0.001 IA-0.22<0.001-0.100.52-0.57<0.001-2.8<0.001 IB-0.060.32-0.20.001-0.430.28 ITDMR0.060.360.43<0.0016.57<0.001 Hypertension0.110.070.130.040.020.73 Diabetes0.0040.940.110.08 TABLE 1 Population based characteristics Mean ± SD or number (%)Range Age (years)56 ± 8.340 - 80 Gender, female171 (64.3%) Anterior chamber depth (ACD) (mm)3.3 ± 0.42.3 - 4.2 Axial length (AL) mm24.4 ± 1.621.8 - 30.4 Dark-room gonioscopy (Shaffer grade)3.6 ± 0.61 - 4 Visual field (VF) mean deviation (MD), decibels (dB) -2.2 ± 2.1-11.0 - 1.7 VF pattern standard deviation (PSD), dB2.4 ± 1.60.9 - 10.3 Iris thickness 750 (IT) (mm)0.5 ± 0.10.3 – 0.6 Iris bowing (IB) (mm)0.2 ± 0.1-0.7 - 0.4 Angle Opening Distance (AOD) 500 (mm)0.2 ± 0.20 - 0.8 Trabecular Iris Space Area (TISA) 500 (mm 2 )0.1 ± 0.10 - 0.2 Lens vault (LV) (mm)0.3 ± 0.3-0.4 -1.3 Anterior chamber width (ACW) (mm)11.6 ± 0.410.5 - 12.6 PD (dark) (mm)4.3 ± 0.82.5 - 6.1 PD (light) (mm)2.5 ± 0.51.7 – 4.2 APC (mm)1.8 ± 0.50.7 – 2.9 Iris Thickness at dilator muscle region (ITDMR) (mm)0.5 ± 0.10.3-0.7 Iris Area (IA) (mm 2 )1.6 ± 0.21.1 - 2.1 Hypertension58 (21.8%) Diabetes22 (8.3%) Visante® OCT (Carl Zeiss Meditec, Dublin, California, USA) measured the speed of pupillary constriction in response to illumination using a technique previously described. 1 Univariate & multivariate analyses were performed to examine the effect of demographic and ocular biometric factors on SPC, PD and APC. 302 eyes 266 eyes Posterior synechiae (n=3) Poor video images (n=19) Excessive eye movement (n=14 ) excluded Discussion: This is the 1 st population-based study of pupil dynamics using AS-OCT. Greater baseline PD's showed faster SPC (concurring with older studies). Eyes with greater baseline PD’s & greater dark-light APC were observed to have deeper ACDs, smaller IA, and greater IT. SPC was not significantly correlated with biometric eye parameters known to be angle closure risk factors (e.g. AL, ACD, LV). In addition eyes with greater baseline PDs were associated with narrower angles (TISA 500). Our findings corroborate with Aptel et al 2 & Quigley et al 3 that upon dilation in darkness of normal eyes, there is greater IT with AC angle narrowing and loss of IA. Conclusion: Among normal adult Chinese eyes, SPC was associated with larger baseline PDs. Eyes with greater baseline PDs and greater APC were observed in deeper ACs with smaller IA and greater IT. These results may be relevant when further investigating the mechanical and physiologic dynamic alterations inherent in the irides. References: 1.Zheng C, Cheung CY, Narayanaswamy A, et al. Pupil dynamics in Chinese subjects with angle closure. Graefes Arch Clin Exp Ophthalmol 2012; Sep; 250(9):1353-9 2.Aptel F, Denis P. Optical coherence tomography quantitative analysis of iris volume changes after pharmacologic mydriasis.Ophthalmology. 2010 ;117:3-10. 3.Quigley HA, Silver DM, Friedman DS, et al. Iris cross-sectional area decreases with pupil dilation and its dynamic behavior is a risk factor in angle closure. J Glaucoma. 2009 ;18:173-9.