title: [Qualitative analysis of the evaluation indicators and their related parameters of ametropic state].
abstract: OBJECTIVE
  To investigate the theoretical basis and practical limitations of the existing calculation formulas in the evaluation of ametropic state.
  
  
  METHODS
  The evaluation indicators and their calculation parameters of ametropia were analyzed by using the reduced schematic model eye, the paraxial imaging principle, and the dimension laws.
  
  
  RESULTS
  The existing formulas resulted from the reduced object vergence of object distance and image distance relation. Regarding the two measurement indicators of the existing formulas, diopter was misused for refractive power. "Ametropia degree" was a non-standard diction. Both of them were not suitable as the evaluation indicators. The outcomes of the existing formulas and their related plus or minus sign rules showed refractive corrections instead of refractive errors proper. For refractive errors, there was no suitable evaluation indicator.
  
  
  CONCLUSIONS
  In the evaluation of ametropic state, there are fundamental problems in the existing formulas resulting from the reduced object vergence. The measurement indicators and their dimensional units are confused and misused. The calculation results refer to the refractive corrections only. The evaluation indicators for ametropia need to be further discussed.
authors.affiliation: Department of Ophthalmology, the First Hospital of Peking University Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100044, China.
authors.forename: Zeqin
authors.initials: Z
authors.lastname: Ren
mesh_terms: D006801:Humans; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology