| Objective: To describe the characteristics of modulation transfer function (MTF) ofcorneal surface and analyse the correlation between aberrations and MTF.Materials and Methods: Retrospective case series ,the data was collected from 200patients who have been conducted excimer laser surgery in our hospital. Inclusioncriteria:①The age from 18 to 40.②cylindrical refractive less than -1.00 Dipper.③cornealtransparency was confirmed without eye disease, and there was no nebula, macula.④Contactlens wearers should stop wearing for more than two weeks before the examination.⑤Schirmer，stest and break up time(BUT) values were normal. in which 93 patients (186 eyes) were male,107 patients (214 eyes) were female. They aged 18 to 39 years old, mean 26.58±5.18 years,the range of spherical myopia is -0.25 ~ -10D, mean -4.94±0.13 D; astigmatism -1 ~ 0 D,mean -0.46 0.02 D. The best corrected visual acuity for all patients≥1.0 D.3D Sirius - Complete Anterior Segment Imaging System(Italy CSO, software version:phoenis 1.2) was used to measure the MTF curves at various optical zones of cornea. Allexaminations were conducteded by the same doctor. The examination was conductedimmediately after blink of the eyes under natural light in the room. The patients were told togaze the blue curser of the corneal topography to fully expose the the cornea. The reproducibleresults were selected and analyzed, the phoenis 1.2 sofware was used to simulate the MTFcurves at horizontal meridian and the vertical meridian at the 3mm, 4mm, 5mm , 6mm, 7mmoptical zones of cornea and obtain the MTF values at 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55and 60 cycles/degree (c/d) spatial frequencies. Different optical diameter such as 3.0mm,4.0mm,5.0mm,6.0mm,7.0mm we analyzed . We analyze the SR and the RMS of total aberration, comaaberration, spherical aberration and trefoil aberration. All data was analyzed in SPSS16.0statical sofware package. The comparison of MTF values at the same spatial frequencies atvertical and horizontal meridian were conducted using paired t-test or signed rank test, p <0.05represents the difference is statistically significant.The MTF and different aberrations analyzedwith preason corrlation analyze.Results: The MTF curve of anterior corneal surface and total cornea surface :①decreasedrapidly from low to intermediate frequency (5 ~ 15cpd) at various optical zones of cornea, thevalue decreased to 0 slowly at higher frequency (>15cpd).②With the increase of the opticalzones of cornea, MTF curve decreased gradually, and to low spatial frequency in (5~ 15cpd) toreduce the more obvious high frequency MTF curve with changes in corneal optical region③Inthe 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 spatialfrequency, the difference was statistically significant (p <0.05). Namely the resolution of thehuman cornea on the vertical space than horizontal space resolution;④The anterior cornealsurface is always like the difference in 3mm, 5mm, 7mm corneal optical zone and the MTF ofthe orientation of the vertical and horizontal meridian has a good correlation;⑤Higher orderaberrations: coma Z (3,±1)] and trefoil [Z (3±3)], the spherical aberration Z (4,0)], Clover [Z(4±4)], secondary astigmatism Z (4,±2)], [Z (3,±1)] and [Z (3,±3)] in the corneal opticalzone for the 3mm and 5mm and horizontal The radial orientation of the MTF of a statisticallysignificant correlation;⑥No clear correlation between the orientation of corneal coma andcorneal optical quality;⑦In different optical zone trefoil aberration was statistically related tohorizontal meridian MTF.Conclusion:①MTF of the anterior corneal surface can describe corneal optical qualitycomprehensively, objectively and accurately;②The anterior cornea can react most of theoptical quality of the whole cornea;③The higher order aberrations and horizontal meridianorientation MTF of the anterior corneal has great significance, it is main at wavefront guidedcorneal ablation. |
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