title: Higher order aberrations in a normal adult population.
abstract: OBJECTIVE
  To determine the distribution of Zernike coefficients and higher order aberrations in a normal population and its relationship with age, gender, biometric components, and spherical equivalent.
  
  
  METHODS
  During the first phase of the Shahroud cohort study, 6311 people of the 40-64-year-old population of Shahroud city were selected through random cluster sampling. A subsample of participants was examined with Zywave aberrometer (The Bausch & Lomb, Rochester, NY) to measure aberrations. Measurements of aberrations were done before cycloplegic refraction, and values generated from a minimum pupil diameter of 5 mm were reported in this analysis.
  
  
  RESULTS
  After applying exclusion criteria, 904 eyes of 577 people were analyzed in this study and mean age in this study was 49.5 ± 5.7 years and 62.9% were female. Mean root-mean-square (RMS) of the third-, fourth-, and fifth-order aberrations was 0.194 μm (95%CI: 0.183 to 0.204), 0.115 μm (95%CI: 0.109 to 0.121), and 0.041 μm (95%CI: 0.039 to 0.043), respectively. Total RMS coma (Z3 (-1,) Z3 (1), Z5 (-1), Z5 (1)), Total RMS trefoil (Z3 (-3,) Z3 (3), Z5 (-3), Z5 (3)), and spherical aberration (Z4 (0)) in the studied population was 0.137 μm (95% CI:0.129-0.145), 0.132 μm (95% CI: 0.123-0.140), and -0.161 μm (95%CI:-0.174 to -0.147), respectively. Mean higher-order Zernike RMS in this study was 0.306 (95% CI: 0.295-0.318) micrometer, and in the multiple model, it significantly correlated with older age and short axial length. The highest amounts of higher-order RMS were observed in hyperopes, and the smallest in emmetropes. Increased nuclear opacity was associated with a significant increase in HO RMS (p < 0.001). Analysis of Zernike coefficients demonstrated that spherical aberration (Z4 (0)) significantly correlated with nuclear cataract only (age-adjusted Coef = 0.37 and p = 0.012).
  
  
  CONCLUSIONS
  This report is the first to describe the distribution of higher-order aberrations in an Iranian population. Higher-order aberrations in this study were on average higher that those reported in previous studies.
authors.affiliation: Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.affiliation: Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Khabazkhoob
authors.affiliation: Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Tehran, Iran; Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Jafarzadehpur
authors.affiliation: Department of Optometry, School of Paramedical Sciences, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Abbasali
authors.initials: A
authors.lastname: Yekta
authors.affiliation: Center for Health Related Social and Behavioral Sciences Research, Shahroud University of Medical Sciences, Shahroud, Iran.
authors.forename: Mohammad Hassan
authors.initials: MH
authors.lastname: Emamian
authors.affiliation: Department of Community Medicine, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shariati
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
keywords: Adult; Higher order aberrations; Population based study; Zernike coefficients