The use of progressive addition lenses (PAL) is a matter of increasing importance in this aging society. However the performance of PAL is not easy to explain to the public, because of the expertise requires. This article tries presents performance indexes which are easy to understand and shows them as lens maps.
Point spread function (PSF) and optical transfer function (OTF) are described. The PSF figure is affected by aberrations of the optics, diffraction effect of pupil and diffraction within the optics. When the aberration effect is smaller than the diffraction effect, the pupil function, together with the wavefront aberration, is transformed to PSF by Fourier transform. When the aberration effect is larger than the diffraction, effect, PSF is obtained directly via ray tracing of geometrical optics. OTF is obtained via Fourier transform of PSF, its absolute value being defined as modulation transfer function and its phase value as phase transfer function. Some physical meanings of these concepts are explained.
Purpose: To examine the effect of accommodation-inducing monitors on asthenopia during visual display terminal (VDT) work.
Methods: The objective refraction value and accommodative high frequency component (HFC) of accommodative microfluctuations were measured both before and after 2 hours of VDT work with an accommodation-inducing monitor and a laptop, respectively. Measurements were made on the right eye. The subjects comprised 6 normal healthy volunteers (5 males, 1 female; mean age±standard deviation: 29.5±7.6 years) with no ophthalmological diseases.
Results: VDT work with the laptop resulted in significantly increased myopia; HFC also showed a significant rise. There was no significant difference in objective refraction value and HFC when subjects used the accommodation-inducing monitor, although the results showed slightly increased hyperopia and decreased HFC.
Conclusions: The accommodation-inducing monitor inhibited persistent contractions of the ciliary muscle during VDT work. The results suggest that use of the accommodation-inducing monitor can therefore provide protective efficacy for asthenopia during VDT work.
Purpose: The purpose of this study was to examine whether aniseikonia is influenced by differences in distance measurement.
Method: Subjects comprised university students with the same refractive power in both eyes with voluntarily participated in this study. Artificial aniseikonia was produced using afocal size lenses of 0%, 2%, and 4%, added in random order before the left eye. The subjects were then asked to observe the new aniseikonia test (NAT) targets located at 50cm and 5m distance. Aniseikonia was measured by the complete up and down method.
Results: The main effect of difference in distance measurement was statistically significant (p < 0.01). Aniseikonia in the distance was perceived on average to be about 1.5 times larger than that in the near.
Conclusions: When treating the complaint of headache or asthenopia in the distance, such as in driving, we should not depend only on measurement of aniseikonia in the near.