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Yoko Hirohara, Toshifumi Mihashi, Hiroyuki Kanda, Tomomitsu Miyoshi, Takeshi Morimoto, James Wolffsohn, Takashi Fujikado; Functional imaging of retina in response to defocused grating light stimuli in cats. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4889.
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© ARVO (1962-2015); The Authors (2016-present)
We have reported that the reflectance changes (RCs), determined by functional imaging of the retina and elicited by a grating light stimuli, depended on the spatial frequency of the gratings (Hirohara ARVO2011). To investigate the influence of defocus on the retina, we recorded the RCs in response to defocused gratings of different spatial frequencies (SFs).
The retinas of the left eyes of five cats were examined by a functional imaging fundus camera (TRC-50LX, Topcon) under general anesthesia (Okawa IOVS 2007). The wavelength of the observation light was 730-780 nm. The retinal images were photographed at a frame rate of 40 Hz for 2 seconds before, 4 seconds during, and 20 sec after the white light stimulation. Vertical gratings of SFs of 0.22, 0.43, and 0.86 cycles/deg (cpd) were flickered at 4 Hz. The degree of defocus was either 8 D or 18.5 D in the near direction or 12 D and 20 D in the far direction. Ten repeated images were analyzed to obtain the peak value (PV) of the two dimensional fast Fourier transfer (FFT). The PV obtained just after the cessation of grating stimuli was defined as the contrast value (CV). The MTF was also determined from the data obtained by a Shack-Hartmann Wavefront Sensor.
The CV at 0 D (in focus) was the highest compared to all other defocused conditions at all SF (P<0.001, one way ANOVA). For defocuses in the far direction, the CV with a 12 D defocus was higher than that with 20 D at 0.22 and 0.43 cpd. For defocus in the near direction, the average CV with 8 D was higher than that at 18.5 D for all SFs. A decrease of the MTF was observed at ≥ 0.43 cpd and the decrease was dependent on the amount of defocus. However, the CV decreased steeply at SF of 0.43 cpd and did not change much after 0.83 cpd for all defocused conditions.
Our results showed that the effect of defocus on the RCs can be examined by retinal functional imaging. Because the SF characteristics were different between CV and MTF, we suggest that the CV is affected by not only the optical status of the retinal image but also on the metabolism of the retina which was influenced by defocus.
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