Zheng Yan-Zhen, Chen Yan-Peng, Qiu Yan, Zhai Guo-Guang, Li Yao-Yu
Department of Ophthalmology, General Hospital of Beijing Military Command of Chinese PLA, Beijing 100700, China.
Int J Ophthalmol. 2012;5(2):196-201. doi: 10.3980/j.issn.2222-3959.2012.02.16. Epub 2012 Apr 18.
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.
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.
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).
MTF can be used to describe the imaging quality of optical systems at anterior corneal surface objectively in detail.
描述角膜前表面调制传递函数（MTF）的特征，获取近视患者角膜前表面不同空间频率和光学区MTF的正常参考范围。
对200例患者的400只眼行SIRIUS角膜地形图系统检查。应用Phoenis分析软件模拟角膜3、4、5、6、7mm光学区垂直和水平子午线方向角膜前表面的MTF曲线。选取空间频率为5、10、15、20、25、30、35、40、45、50、55和60周/度（c/d）时的MTF值。
角膜各光学区角膜前表面MTF曲线在低频至中频（0 - 15cpd）迅速下降，高频（>15cpd）时数值缓慢下降。随着角膜光学区增大，MTF曲线逐渐下降。在角膜3mm - 6mm光学区内，各空间频率水平子午线方向测量的MTF值大于垂直子午线方向相应值，差异有统计学意义（P<0.05）。在角膜7mm光学区，10 - 60空间频率（cpd）水平子午线方向测量的MTF值小于垂直子午线方向相应值，在25、30、35、40、45、50cpd差异有统计学意义（P<0.05）。
MTF可客观、详细地描述角膜前表面光学系统的成像质量。
