April 2011
Volume 52, Issue 14
ARVO Annual Meeting Abstract  |   April 2011
A Method of Detecting and Monitoring Central Fixation Using the Continuous Wavelet Transform
Author Affiliations & Notes
  • Boris I. Gramatikov
    Ophthalmology, Johns Hopkins Wilmer Eye Inst, Baltimore, Maryland
  • Footnotes
    Commercial Relationships  Boris I. Gramatikov, None
  • Footnotes
    Support  A 2009 Hartwell Individual Biomedical Research Award
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 6340. doi:
  • Views
  • Share
  • Tools
    • Alerts
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Boris I. Gramatikov; A Method of Detecting and Monitoring Central Fixation Using the Continuous Wavelet Transform. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6340.

      Download citation file:

      © ARVO (1962-2015); The Authors (2016-present)

  • Supplements

Techniques for amblyopia screening using the form birefringence properties of the Henle fibers surrounding the fovea have been reported earlier. A periodic signal s(t) is produced by circular scanning around the center of the fovea, generating a frequency of central fixation f2 =k2* fs, where fs is the scanning frequency. With no central fixation, f1=k1*fs is generated. The constants k1 and k2 depend on the optical design. All existing instruments analyze consecutive sub-epochs of s(t), with gaps in-between, during which the Fast Fourier Transform (FFT) is performed and signal analysis takes place. FFT power spectrum tells to what extent f1 and f2 are represented in the epoch analyzed, but it does not tell exactly where these frequencies appear. With pediatric patients, where subject cooperation is a problem, short lasting moments of central fixation (f2) may easily be lost. Moreover, in the gaps between the sub-epochs, valuable instants of central fixation may be missed.


To solve this problem, time-frequency distributions obtained by means of the Continuous Wavelet Transform (CWT) are proposed. CWT allows excellent localization in both time- and frequency domains and permits analysis of continuous signal epochs of any duration without any gaps.


Panel A of the figure shows the time domain scan signal s(t) (RE, 7 year old boy) of duration 400 ms (fs=96Hz; k1=1, k2=2). Panel C shows the FFT power of the same signal. One can see the two frequencies, but cannot tell where in time they appear. Panel B shows the CWT of the same signal. Here f1 and f2 episodes can easily be localized in time.


The Continuous Wavelet Transform is superior to the FFT in localizing fixation frequencies in both the time- and frequency domains. It is an excellent tool for precisely identifying central fixation in an uninterrupted manner, thus improving device reliability and shortening test time. Using modern digital signal processing hardware, the CWT can be performed in real time, and is expected to improve significantly detection sensitivity when testing uncooperative subjects.  

Keywords: amblyopia • strabismus: diagnosis and detection • eye movements 

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.