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A wavelet-based model for foveal detection of spatial contrast with frequency dependent aperture effect

Hooshangnejad H., Gharibzadeh S., Towhidkhah F.

Advances in Science and Technology. Research Journal

2016

Vol. 10, nr 30

51--68

The main purpose of this study is to build a Computational model based on ModelFest dataset which is able to predict contrast sensitivity while it benefits from simplicity, efficiency and accuracy, which makes it suitable for hardware implementation, practical uses, online tests, real-time processes, an improved Standard Observer and retina prostheses. It encompasses several components, and in particular, frequency dependent aperture effect (FDAE) which is used for the first time on this dataset, which made the model more accurate and closer to reality. Shortcomings of previous models and the necessity of existence of FDAE for more accuracy led us to develop a new model based on Wavelet Transform that gives us the advantage of speed and the capability to process each frequency channels output. Considering our goal for building an efficient model, we introduce a new formula for modeling contrast sensitivity function, which generates fewer errors and better timing performance. Eventually, this new model leads to having as yet lowest RMS error and solving the problem of long execution time of prior models and reduces them by almost a factor of twenty.

Visual parameters of Polish special schools students

Buczkowska H., Miskowiak B

Optica Applicata

2014

Vol. 44, nr 2

227--236

The purpose of this study was to coduct a visual screening of students in special schools with a set of tests chosen by the faculty and staff of the Department of Optometry and Visual System Biology of Poznań University of Medical Sciences. Students mentally handicapped (N = 318) between the age of 7 and 22 (mean age 14.4 ± 2.84) were screened. Group 1 were children aged 7 to 12 (n = 65), group 2 were subjects aged 13 to 16 (n = 167) and group 3 included people aged between 17 and 22 (n = 86). The scope of the screening included: auto-refractometer (Shin-Nippon A type) without cycloplegia, visual acuity for distance, positive lens test +1.00 D (diopter), spatial vision (stereo) at near, color vision and near point of convergence. 72 children (22.6%) were prescribed correction, but only 30 children actually wore glasses on a permanent basis (9.4%). Of those not using correction (n = 288): in group 1 the adopted criteria for visual acuity for the right eye were not met by the 38% of the respondents or 35% for the left eye; group 2 – 36% of the respondents failed (right eye) and 31% (left eye); 50% of students in group 3 did not meet the visual acuity criterion. Stereo was failed in groups 1 and 3 by almost 60% while in group 2 the test was failed by 47% of the respondents. The results of the refraction revealed a small degree of myopia in each eye of 38% in the entire sample. Hyperopia was found in 42% (right eye) of the students whereas 44% (left eye) in the entire sample. Astigmatism ranging from 0.75 to 2.00 D was noted in the case of 32% of people. This study indicates the need for a systematic vision screening, more than just visual acuity at distance, among the students in special schools.