The Howland's photoretinoscopy for static eye accommodation measurement was modified for dynamic measurement. In the Howland method, the pupil diameter and the width of the light fraction in the pupil, which determined the refraction of the eye, were manually measured on the photograph. However, an attempt to measure them by real-time image processing was difficult because the edge of the pupil image and the boundary of the light and dark fractions in the pupil were unclear. In the modified method, the paired images were captured while the shielded half of the video camera lens aperture was changed in the opposite direction with the eccentric infrared LED. The obtained two images were differentiated. In the difference image, the parameter replacing the width of the light fraction in the Howland method was proposed. The experimental results showed that the light fractions of Howland's and ours have a linear relationship in the narrow range of the eye refraction. To widen the range, several LEDs were used. The combination of this method and the pupil detection method that we had already developed was predicted to make real-time measurement of the accommodation possible in the near future.