title: Analysis of the optical quality by determining the modulation transfer function for anterior corneal surface in myopes.
abstract: OBJECTIVE
  To describe the characteristics of modulation transfer function (MTF) of anterior corneal surface, and obtain the the normal reference range of MTF at different spatial frequencies and optical zones of the anterior corneal surface in myopes.
  
  
  METHODS
  Four hundred eyes from 200 patients were examined under SIRIUS corneal topography system. Phoenis analysis software was applied to simulate the MTF curves of anterior corneal surface at vertical and horizontal meridians at the 3, 4, 5, 6, 7mm optical zones of cornea. The MTF values at spatial frequencies of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 cycles/degree (c/d) were selected.
  
  
  RESULTS
  The MTF curve of anterior corneal surface decreased rapidly from low to intermediate frequency (0-15cpd) at various optical zones of cornea, the value decreased to 0 slowly at higher frequency (>15cpd). With the increase of the optical zones of cornea, MTF curve decreased gradually. 3) In the range of 3 mm- 6 mm optical zones of the cornea, the MTF values measured at horizontal meridian were greater than the corresponding values at horizontal meridian of each spatial frequency, the difference was statistically significant (P<0.05). At 7 mm optical zones of cornea, the MTF values measured at horizontal meridian were less than the corresponding values at vertical meridian at 10-60 spatial frequencies(cpd), and the difference was statistically significant in 25, 30, 35, 40, 45, 50 cpd (P<0.05).
  
  
  CONCLUSIONS
  MTF can be used to describe the imaging quality of optical systems at anterior corneal surface objectively in detail.
authors: Department of Ophthalmology, General Hospital of Beijing Military Command of Chinese PLA, Beijing 100700, China.
authors: Yan-Zhen
authors: YZ
authors: Zheng
authors: Yan-Peng
authors: YP
authors: Chen
authors: Yan
authors: Y
authors: Qiu
authors: Guo-Guang
authors: GG
authors: Zhai
authors: Yao-Yu
authors: YY
authors: Li