Comparison of Time Domain and Fourier Domain by izd13617

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									  Comparison of Time Domain and Fourier
 Domain Optical Coherence Tomography in
    Determination of Corneal Thickness

 Jin Pyo Hong,MD1, Jae Lim Chung,MD1, Jung Won Park,MD2, Tae-im
  Kim,MD,PhD1, Kyoung Yul Seo,MD,PhD1, Eung Kweon Kim,MD,PhD1


1Department   of Ophthalmology, Yonsei University, College of Medicine, Seoul, Korea

                      2Daegu   Yonsei Eye Clinic, Daegu, Korea



                    I have no financial interest
                                  Purpose

   The accurate measurement of central corneal thickness(CCT) as a key factor
      Refractive surgery preop evaluation
      Monitoring corneal disease
      Measuring IOP
      Calculating risk of progression to glaucoma in patient with ocular hypertension

   Measuring methods for CCT
      Ultrasound pachymeter
      Confocal microscopy
      Specular microscopy
      Scanning slit methods(ORB scan)
      Optical coherence tomography(OCT)

   Optical coherence tomography(OCT)
      Non contact imaging modality
      Based on principles of low coherence interferometry
      Non invasive, high resolution imaging device
      Time domain OCT
      Fourier domain OCT
                               Purpose

 Time domain OCT (TD-OCT) vs Fourier domain OCT (FD-
  OCT)
                                 Time domain                     Fourier domain

    A scan generation    Sequentially one pixel at a time      Entire A scan at once

     Reference mirror             Moving type                     Stationary type

    Number of A scan             400 scans/sec                  26,000 scans/sec

     Depth resolution                10 μm                             5 μm

         B scan              512 A scan in 1.28sec            1024 A scan in 0.04sec

     Motion of speed       Slower than eye movements        Faster than eye movements


 In this study
    To measure corneal thickness in a group of normal healthy volunteers using
     ultrasound pachymetry, FD-OCT, TD-OCT
    To evaulate their corneal thickness measurement repeatability and
     reproducibility
                                 Methods

   Subjects
      40 eyes of 20 healthy normal volunteers
      No history of contact lens wearing nor any corneal disease
      No systemic disease , visual acuity over 20/25
      IOP less than 21mm Hg
      Endothelial cell count over 2000/mm2

   Devices
      Time domain OCT
        • Visante(Carl Zeiss Meditec, Dublin, CA)
      Fourier domain OCT
        • RTVue(Optovue Inc, Fremont, CA)
      Ultrasound pachymeter
        • UP-1000(NIDEK Co Ltd, Gamagori, Japan)
                                    Methods

        Protocol
           Measured by Visante OCT, RTVue, ultrasound pachymeter, in order
           Total 3 visits every 3-4 days
           4 times measurements per 1 visit
           Total 12 times measurements per one eye
           Measured by built in automatic pachymetry map protocol




       Pachymetry map of Visante OCT                    Pachymetry map of RTVue
                       Methods


 Statistical analysis

     Intrasession repeatability
     Intersession reproducibility
     Intrasession or intersession within subject SD(Sw)
     Precision (1.96xSw)
     Intraclass correlation coefficient(ICC)
                                Results


 Mean CCT of first visit


                                   Overall mean        95% CI

          Visante                   521.7±26.2      512.8 – 529.6
           RTVue                    526.7±26.5      518.9 – 536.0
   Ultrasonic pachymeter            525.4±26.1      516.8 – 533.6

   Pairwise comparison            Mean difference   p (Re-ANOVA)

       RTVue-Visante                    6.3           <0.0001
RTVue-ultrasonic pachymeter             2.3            0.001
Ultrasonic pachymeter-Visante           4.0           <0.0001
                              Results

 Intrasession Repeatability (visit 3)
               Mean ±SD(μm)      Sw      1.96xSw       ICC(95% CI)

   Visante       521.9±26.4      3.5       6.8      0.989(0.982~0.994)

   RTVue         526.2±26.5      1.8       3.6      0.997(0.995~0.998)
 Ultrasound
                 525.3±26.3      2.6       5.1      0.993(0.989~0.996)
 pachymeter




 Intersession Reproducibility

               Mean ±SD(μm)        Sw     1.96xSw      ICC(95% CI)

  Visante        521.7±26.1        4.3      8.4     0.995(0.992~0.997)

   RTVue         526.7±26.5        2.2      4.3     0.998(0.997~0.999)
 Ultrasound
                 525.4±26.1        3.1      6.1     0.996(0.993~0.998)
 pachymeter
                          Results


   Bland Altman plots




Visante – ultra pachy   RTVue – ultra pachy   Visante OCT – RTVue
                    Conclusion

 RTVue, Visante OCT
   Demonstraed high degree of repeatability and
    reproducibility
   Rapid and eazy methods to obtain CCT
   Good agreement with ultrasound pachymeter

 RTVue
   More repeatable and reproducible than Visante OCT
   Might be due to very fast acquisition time (0.04 sec/B
    scan)

								
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