• Journal of Korean Ophthalmic Optics Society
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• v.8 no.1
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• pp.11-15
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• 2003

Purpose : The purpose of this study is to investigate the corneal topography changes as a result of near task in myopes and emmetropes. Methods : Thirty university students, aged from 18 to 24 years old, were randomly selected. They were divided into two refractive groups of fifteen each : myopia and emmetropia. The corneal topography of each subject was measured with the Eye-Sys Videokeratography system. Measurements were taken : before and after 30 minutes of near task (copy N10 text at 20 cm working distance). Both simulated keratometry and semi-meridian keratometric map program were used in the data analysis. Results : Our results reveal no significant changes in both simulated keratometry and semi-meridian presentation as a result of near task for both myopes and emmetropes, except a significant change (p<0.05) found at the flattest meridian of the central (3 mm) portion of the corneal topography after near task for emmetropes only. Conclusions : We conclude that the corneal topography, does not change significantly as a result of near task in both myopes and emmetropes.

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.2
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• pp.9-14
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• 2009

Purpose: The purpose of this study was to examine the relationship between the accommodative facility, blink rate and accommodative lag according to the change of angles of main viewpoint of near distance worker and study an appropriate viewing angle that mitigates asthenopia, such as headaches or eye fatigue accompanied when reading and staring at the computer or TV for a long time. Methods: Total of 27 people including 12 male university students and 15 female university students in the age of 20 to 36 with frequent near distance works, such as computers, were selected to study the accommodative facility, the blink rate and the accommodative lag in accordance with the change of viewing angles of the near distance workers. The refraction error was corrected completely and the phoropter was shifted to near distance mode to locate the near distance indication at 40 cm. The accommodative facility and the blink rate were measured for one minute at each viewing direction of $40^{\circ}$ downward, $20^{\circ}$ downward, horizontal, and $20^{\circ}$ upward directions based on the horizontal line and the accommodative lag was measured in dynamic retinoscopy using retinoscope. Results: As a result, when the main viewpoint was moved on upper direction from the $40^{\circ}$ below, the accommodative facility was reduced and the blink rate and the accommodative lag were increased so their eyes became dry and the accommodation response was reduced. Conclusions: In near distance works, the eye fatigue level can be minimized by locating a book or a computer screen $40^{\circ}$ below than the horizontal direction.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.118-124
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• 2008

Allowable level of blasting vibration for earth retaining wall was examined in this study. Blasting vibration was measured at near field blasting to evaluate the influence of the blasting work to earth retaining wall and rear ground. Although small scale blasting with $0.5{\sim}2.0kg$ explosives per round merely influenced to the structure and ground, but it was suggested to blast at the distance of twice the least burden considering the block movement.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.51-60
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• 2011

Purpose: This study was to investigate visual performance and subjective satisfaction with multifocal soft contact lenses at near works in university students. Methods: In a cross-over study design, 26 students (6 male, 20 female) who did not have any ocular disorder with at least 20/20(1.0) binocular vision were fitted with singlevision lenses (SofLens$^{TM}59$, Bausch + Lomb Co. USA) or multifocal lenses (SofLens Multifocal, Bausch + Lomb Co. USA). After 2 weeks, visual performance assessments included visual acuity, stereoacuity and contrast sensitivity function at distance and near. Near point of accommodation, accommodative facility, near point of convergence, vergence facility and near range of clear vision at near were examined. Students' satisfaction and preference were measured using survey questionaries. Results: Subjects maintained at least 20/20 binocular vision with multifocal and single-vision lenses at distance and near. There was no difference between multifocal and single-vision lenses in stereoacuity, contrast sensitivity function and vergence facility at far and near. The near point of accommodation, accommodative facility, near point of convergence and the near range of clear vision with multifocal lenses were better than single-vision lenses. On the survey questionaries, subjects reported that they preferred and satisfied with multifocal lenses with near works, and single-vision lenses with distance works. Conclusions: The majority of university students preferred multifocal to single vision lenses because multifocal lenses provided better visual performance at near works. This study suggests that multifocal lens is helpful for young adult in prolonged near works.

• Explosives and Blasting
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• v.25 no.2
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• pp.23-33
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• 2007

It is difficult to measure a blast noise in the vicinity of tunnel blasting works and the effect of lowering noise changes very highly with types of soundproof materials. So, the main interest of this study focuses on the materials of a soundproof facilities and the method of noise forecast in a near distance. 20 types of the soundproof facilities are established and blast noise is generated using firecracker in a Hume concrete pipe. To analyze the variations of magnitudes of noise and frequency with the soundproof materials and types, the noise and frequency is measured in a short distance next to blast area.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.17 no.3
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• pp.257-264
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• 1999

The lens distortions were corrected directly using the high-order polynomial which was offered in camera calibration data for the forward transformation and the root of Newton-Raphson's $2\times{2}$ nonlinear system for the backward transformation. The 0.04~0.08 pixels increase in accuracy was indicated through the use of direct correction of lens distortions instead of least square methods of commercial software. The least square adjustment method of high-order polynomial requires many control points which has a same weight. But this suggested method which is unnecessary to determine control points was developed and applied. The algorithm showed improved efficacy.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.117-124
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• 2015

Purpose: The purpose of this study was to compare the accommodative function of young adult in their 20s wearing monovision, modified monovision, and aspheric multifocal contact lenses at near task. Methods: Thirty young adults ($23.53{\pm}2.37years$) were fitted with monovision, modified monovision (the application of single vision contact lenses and center-near low addition aspheric multifocal contact lenses), and aspheric center-near multifocal contact lenses. After wearing these modalities during a week for adaption, and after watching visual display at computer for inducing accommodative pressure for 1 hour. The following assessments of accommodative function were made: contrast visual acuity (VA) at distance and near; accommodative response; near accommodative facility; and negative relative accommodation (NRA)/positive relative accommodation (PRA). All measurements were carried out binocularly. Results: In binocular distance VA with contrast of 10%, monovision was the worst among the four modalities (p=0.005). In accommodative response at 1 m (1.00 D), monovision was the lowest (p<0.05) and accommodative response at 40 cm (2.50 D) with monovision was lower than that of modified monovision and multifocal contact lens (p<0.05). We also found that there were no significant differences in accommodative facility and NRA/PRA among the four modalities. Conclusions: In young adult (20s), monovision with low add reduced the accommodative response at near task, however, modified monovision and multifocal lens with center-near type did not affect accommodative relaxation.

• Journal of Preventive Medicine and Public Health
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• v.30 no.3 s.58
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• pp.599-608
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• 1997

We studied on change of lens accommodation and pupil light reflex caused by VDT work in six women and compared them with those of other office works. The results were as follows. 1. In VDT work the accommodation contraction velocity decreased during the first 2-hr VDT task, then recovered markedly by the end of the one-hour lunch break, and decreased again by the end of the 2nd 2-hr VDT task. Changes of relaxation velocity showed similar pattern although it was less typical than that of contraction velocity 2. There was no marked change in accommodation contraction velocity and amplitude of accommodation in general office work and near-distance office work, and in the near-distance office work accommodation relaxation velocity decreased according to work load without recovery after lunch break. 3. Initial pupil diameter, initial pupil area of light reflex decreased significantly during VDT task only in VDT work and didn't recover after lunch break. These results suggest possibility that changes of accommodation contraction velocity, accommodation relaxation velocity, near point distance, and pupil diameter and area are useful in evaluating characteristics of VDT work. For this, more research adjusted individual differences, circadian rhythm, emotional stress needs.

• Proceedings of the KSEE Conference
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• 2006.10a
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• pp.153-166
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• 2006

종래의 발파진동의 분석은 주로 대상 지장물에 대한 피해한계를 정립시키고자 하는 관점에서 발파공에서 비교적 원거리의 진동특성을 이해하기 위해 수행되어져 왔으나, 최근의 추이는 발파공 주변 암반의 손상의 정도를 평가하고자 하는 관점에서 그 분석영역의 범위가 근거리 진동특성 연구분야로 확대되고 있는 실정이다. 특히, 터널 발파작업시 여굴의 발생, 암반사면의 안정성 검토 등의 목적으로 암반의 손상영역을 평가하는데 있어서, 기초자료로 활용하고자 많은 연구가 이루어지고 있다. 암반손상의 평가를 위한 손상권 예측방법에는 여러 가지가 있으나, 그 중에서 대부분이 발파진동속도에 근거하고 있으며, 평가를 위한 진동의 예측은 기존에는 원거리 진동특성을 이용하여 근거리 진동을 예측하는 방법으로 그 손상의 정도를 평가하였으나, 최근의 추세는 계측기의 발달로 수m 이내의 진동특성의 계측이 가능하게 되었다. 이와 관련하여 국외에서는 수차례의 실험결과가 여러 문헌에서 보고되고 있으나, 실험장비의 선택 및 측정방법의 어려움 등의 연유로 국내에서는 아직까지 실시되지 못하고 있는 상황이다. 따라서, 본 연구에서는 실제 발파공 근접진동(near field vibration) 계측을 실시하고 그 결과를 분석하여 추후 지속적인 근거리 진동측정 방법 및 평가방법에 대한 기초자료를 제공하고자 하였으며, 무엇보다도 어떻게 계측할 것인가 하는 계측방법 및 그 계측결과의 분석방법에 대해 문제점 파악 및 향후 보완점에 대해 비중을 두어 수행하였다.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.219-228
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• 2015

Purpose: The current study was performed to compare the difference in binocular visual function depending on variable background colors at near work. Method: Fifty four adults (18 males, 34 females) who consented to the present study and had no ocular disease, ocular surgery history, strabismus and amblyopia with normal binocular vision were participated into this study. The subjects were asked to read the novels with black letter printed on white, red, green and blue background for 15 min. Then, their heterophoria, AC/A ratio, near point of convergence, accommodation facility, relative accommodation and vergence were measured before and after reading. The difference of measurements were compared. Result: Overall heterophoria was tended to decrease with regardless of background color. AC/A ratio showed a tendency of increase after reading the novels with all backgrounds except white background. Near point of convergence was significantly increased compared to before reading at all background color. Accommodative facility of dominant and non-dominant eyes were also significantly increased after reading however, binocular accommodative facility showed a tendency of decrease. Negative relative accommodation also decreased at all background colors however, the change of positive relative accommodation was not significantly different. In case of vergence, there was significant difference in break point of far BO and recovery point of far BI by the wavelength of background color. Conclusions: From the results, it was known there is convergence change depending on the wavelength of light even though same amount of accommodation and convergence is required when doing near work for certain period. Thus, it can be suggested that the adjustment of the near working environment which perception of various color was required, should be conducted according to the main wavelength.