title: Visual evaluation of different multifocal corneal models for the correction of presbyopia by laser ablation.
abstract: OBJECTIVE
  To evaluate the visual quality of two theoretical multifocal corneal models designed to correct presbyopia by corneal photoablation.
  
  
  METHODS
  Two theoretical multifocal corneal surfaces were analyzed by ray tracing: a central model (with a central zone for near vision and a peripheral zone for distance vision), and a peripheral model (with a central zone for distance vision and a peripheral zone for near vision). For both models, the effect of the size of the central zone and transition zone as well as the size of the pupil was evaluated.
  
  
  RESULTS
  Our results show that a smaller transition zone favors total visual quality in both models. The optimal size of the central zone depends both on the size of the transition zone used as well as the model. However, both models responded similarly with respect to the variations in pupil size, providing the same visual quality although in an opposite way.
  
  
  CONCLUSIONS
  This work shows that the optimal diameter of the central zone is smaller for the central model than for the peripheral model. Also, pupil size plays a fundamental role in achieving multifocality, showing that patient's pupil size should be thoroughly evaluated prior to multifocal refractive surgery.
authors: Laboratory of Vision Sciences and Applications, University of Granada, Spain. aixaalarcon.ugr.es
authors: Aixa
authors: A
authors: Alarcón
authors: Rosario G
authors: RG
authors: Anera
authors: Margarita
authors: M
authors: Soler
authors: Luis Jiménez
authors: LJ
authors: Del Barco
mesh_terms: D003315:Cornea / Q000503:physiopathology*; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008962:Models, Theoretical; D011305:Presbyopia / Q000503:physiopathology* / Q000601:surgery*; D011680:Pupil / Q000502:physiology; D012029:Refraction, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology*