Purpose:
To study the modulation transfer functions (MTFs) of the total visual perception, the optical, and the neurophysiologic systems using wavefront analysis.
Methods:
Ten eyes of five healthy individuals (average age, 29.6 ± 2.6 years) without cataract were tested. The contrast visual acuities using the Landolt ring charts of various sizes and contrasts were measured and the contrast sensitivity function of the total visual perception system was obtained. The wavefront aberrations were measured using a wavefront analyzer (KR-1W, Topcon), and the MTF of the ocular optical system was obtained. According to wavefront analysis, simulated images, in which the Landolt rings with contrast values of recognition-threshold levels were projected on the retina, were synthesized using optical simulation software (RetinageTM), and the contrast values at the break in the simulated Landolt ring image (i.e., neurophysiologic contrast sensitivity) were calculated. The MTFs of the total visual perception, the optical, and the neurophysiologic systems were compared.
Results:
The mean threshold contrast sensitivity values in the total visual perception/neurophysiologic systems were 74%/6.0% at logMAR (-0.1), 27%/4.1% at logMAR (0), 14%/2.5% at logMAR (0.1), 6.0%/1.4% at logMAR (0.2), 4.0%/0.8% at logMAR (0.3), and 3.0%/0.48% at logMAR (0.4), respectively. Decreased contrast images projected on the retina through the optical system seemed to be enhanced by neurophysiologic functions depending on the image size.
Conclusions:
These data provide a useful basic physiologic background on the vision tests using Landolt rings. Wavefront analysis combined with an accumulated clinical database of normal values of neurophysiologic contrast sensitivity may be useful in differential diagnosis between optical and neurophysiologic functions in cases with visual disturbances.
Keywords: visual acuity • optical properties