title: [A design of refractometer based on blur circle].
abstract: OBJECTIVE
  Design a convenient and stable eye refractometer based on the theory of blur circle.
  
  
  METHODS
  Analyze the retinal blur circle in both Emsly reduced eye model and Liou & Brennan 1997 eye model by ZEMAX. Design the coefficients including PD (pupil diameter) and NO' (length between node point and fovea) with the purpose of improving the accuracy. At last, compare the clinical optometry data from this refractor with the data obtained from optometry hospital in Wenzhou.
  
  
  RESULTS
  The blur circle diameters are nearly the same in both reduced eye model and the Liou & Brennan 1997 eye model. With the PD = 4 mm and NO' = 20 mm, the refractor shows a fine accuracy in optometry. The paired t test shows that the myopia group and the astigmatism axial direction group have no statistical difference between the data from the blur circle refractor and the hospital (P > 0.05), while the astigmatism degree group has the result of P = 0.41 which may be caused by the poor cooperation of pediatric patients. 80% of the astigmatism degree data differ from the data from the hospital in less than 0.75D.
  
  
  CONCLUSIONS
  The blur circle refractor, with the features of convenience and fine accuracy, is promised to be a new style of refractometer in the future.
authors.affiliation: Institute of Optometry& Ophthalmology, Wenzhou Medical College, Wenzhou 325027. zyksight@yahoo.com.cn
authors.forename: Yikui
authors.initials: Y
authors.lastname: Zhang
authors.forename: Shenghai
authors.initials: S
authors.lastname: Huang
authors.forename: Huifang
authors.initials: H
authors.lastname: Ye
authors.forename: Ruitao
authors.initials: R
authors.lastname: Zou
authors.forename: Gengmin
authors.initials: G
authors.lastname: Tong
authors.forename: Ran
authors.initials: R
authors.lastname: Zhuo
mesh_terms: D001251:Astigmatism; D004867:Equipment Design; D005584:Fovea Centralis; D006801:Humans; D015233:Models, Statistical; D009216:Myopia; D019721:Ophthalmoscopes; D009887:Ophthalmoscopy; D012029:Refraction, Ocular; D014792:Visual Acuity