• Journal of Korean Clinical Health Science
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• v.10 no.2
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• pp.1587-1593
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• 2022

Purpose. This study was to investigate the degree of refractive error that occurs depending on the measurement location of the subject when performing a refraction test using the automatic refractor. Methods. When performing the auto-refraction test, measurements were taken while increasing the distance between the forehead and the forehead rest, and the measurements were made by tilting the head clockwise and counterclockwise. Results. During the auto-refraction test, significant refractive error occurred when the forehead was not attached to the forehead support or the subject's head was turned clockwise or counterclockwise. Conclusions. When performing a refraction test using an automatic refractor, the examiner will have to pay attention to whether the subject's forehead is in close contact with the forehead rest, and whether the head is tilted.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.1
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• pp.67-71
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• 2010

Purpose: The effect of two different levels of illumination and the effect of three letter chart types on subjective refraction findings were investigated. Methods: This study involved thirty Malay university students aged between 19 to 23 years old (7 males, 23 females), with their spherical refractive error ranged between plano to -7.75D astigmatism ranged from plano to -1.75D, anisometropia less than 1D and with no history of ocular injury and pathology. Monocular subjective refraction was measured under two levels of illumination (with and without room light) and with three different letter charts (Snellen letter chart, wall mounted letter chart and projected letter chart). Subjective refraction finding was calculated in spherical equivalent in unit diopter (D). Results: There was no significant effect in the subjective refraction findings with Snellen letter chart (t-test=0.15, p-value=0.88), projected letter chart (t-test=-0.19, p-value=0.85) as well as wall mounted letter chart (t-test=0.12, p-value=0.94). One Way ANOVA also revealed when the subjective refractive measures were compared under two different level of room illumination (with and without room light), no significant effect of letter chart types on subjective refraction readings with room light ($F_{2.185}$=0.11, p-value=0.89) and without room light ($F_{2.185}$=0.02, p-value=0.98). Conclusions: Subjective refraction findings were not affected whether the room light was on or off. They were also not affected by the types of letter chart used.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1078-1084
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• 2010

The tracking performance of a big parabola tracking antenna system for tracking and receiving of the signal from the vehicle is impacted by many factors of the internal and the external of the system. In this paper, we analyze the tracking error due to the radio refraction in the application of the tracking and positioning of the vehicle by using radio frequency. The real measurement data are used for the analysis which had been acquired by using GPS and the tracking systems of C- and S-band frequencies in NARO Space centre. To verify the correlation between the tracking errors measured and the radio refraction, we review the error factors and the accuracies of the tracking systems, and the characteristics of the refractivity. The analysis shows that there are angular errors which are due to the radio refraction and not to be neglected, compared to the accuracies of the tracking systems, in case of low elevation angle less than 10 degrees. Also, the tracking errors depend on the target altitude as well as the elevation angle for the case of the target in the troposphere. It is recommended to correct the tracking angle considering the target altitude and elevation angle for the precise target positioning.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.2
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• pp.17-22
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• 1999

In this study, corneal power and eye refraction error were studied on myopic of unaccommodated koreans. The mean of refraction error power is -2.39D(male : -2.75D, female : -2.02D). The mean of corneal refraction error power is +43.90D(male : +44.07D, female : +43.71D). It is +0.90D higher than that of the model eye by Gullstrand(about + 43.00D).

• Korean Journal of Remote Sensing
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• v.12 no.1
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• pp.81-88
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• 1996

The effects of atmospheric refraction of rays on the geometry of high-resolution images such as the KOMPSAT-EOC images are described. An atmospheric refraction mechanism is modelled and the geometric errors caused by the refraction are calculated from the model simulation. This paper shows that a maximum geometric error of 1 pixel (7m) occurs from the standard atmospheric condition. Severer geometric distortions in images cause from an atmopheric abnormality.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.2
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• pp.173-178
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• 2013

Purpose: This study is to predict refractive errors according to uncorrected visual acuity using uncorrected visual acuity of the first glasses wearers. Methods: For 886 children who visited an ophthalmic clinic, subjective refraction was carried out with maintain refraction (MR) and cycloplegic refraction (CR), and objective refraction was carried out using auto-refractometer. Uncorrected visual acuity and corrected visual acuity were tested using on a trial lens and a Han's visual acuity chart. Results: In correlation between with the uncorrected visual acuity and refractive the myopia was the highest (r=0.774) and followed by hyperopia (r=0.670), simple astigmatism (r=0.623), simple with-the-rule astigmatism (r=0.604)and simple against-the-rule astigmatism (r=0.508). Conclusions: There were differences in the predictions between uncorrected visual acuity and refractive error according to the types of refractive error and astigmatism.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.3
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• pp.217-223
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• 2006

The purpose of this study is to provide improvements and standards of trial lens, in a situation that there is a lack of standards of trial lens set that have been used for self-conscious refraction test after helm refraction test at about 5,000 opticians, ophthalmologic clinics and hospitals, and contact-lens shops, that there is a lot of discrepancies between refraction specified and the actual power, and that there is no regulation of optical tolerance error. For the study, opticians who have used Trial lens set were asked to participate in a questionnaire survey through continuing education, and divided into those who have used domestic lens and those who have used imported lens, 5 opticians each for less than 5 years, 5 to 10 years, more than 10 years. The measurement of both refraction specified and the actual diopter was compared to Japan Industrial Standards(JIS T4402). As a result of comparative analysis, more than 80% of respondents have had reliability on the refraction of trial lens they had used, indicating that they have never measured the refraction specified and the actual diopter after buying them. Besides, Korean Industrial Standards(KS P4402) has been imperfect in diopter range since it was legislated in 1979. More than 95% of respondents have been unsatisfied with optometry. Also, it has indicated that refraction error is more frequent in long-term-used trial lens. The conclusion is that it is necessary to standardize trial lens set and that it is required to add lens to lens set provided under KS P4402. Moreover, it is necessary to have supervisory agency for a standardization of trial lens. I hope that both domestic lens and imported lens, as in German and Japan, will be tested to find whether they meet optical tolerance error and standard trial lens will be distributed. Good optic inspection is required for the improvement and management of eye health and optical function, and the same standard trial lens set should be used. whoever is tested. Also, I hope that trial lens set will be specified within standards and tolerance error.

• Journal of the Optical Society of Korea
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• v.17 no.4
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• pp.328-335
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• 2013

Due to the rapid advancement of auto-refractor technology, most optometry shops provide refraction services. Despite their speed and convenience, the measurement values provided by auto-refractors include a significant degree of error due to psychological and physical factors. Therefore, there is a need for repetitive testing to obtain a smaller mean error value. However, even repetitive testing itself might not be sufficient to ensure accurate measurements. Therefore, research on a method of measurement that can complement auto-refractor measurements and provide confirmation of refraction results needs to be conducted. The customized optometry model described herein can satisfy the above requirements. With existing technologies, using human eye measurement devices to obtain relevant individual optical feature parameters is no longer difficult, and these parameters allow us to construct an optometry model for individual eyeballs. They also allow us to compute visual images produced from the optometry model using the CODE V macro programming language before recognizing the diffraction effects visual images with the neural network algorithm to obtain the accurate refractive diopter. This study attempts to combine the optometry model with the back-propagation neural network and achieve a double check recognition effect by complementing the auto-refractor. Results show that the accuracy achieved was above 98% and that this application could significantly enhance the service quality of refraction.

• Journal of the Korea Convergence Society
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• v.9 no.12
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• pp.273-279
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• 2018

This study researched how the refraction error and illumination influence to contrast sensitivity when we wear the circle contact lenses. The study population comprised 16 students and adults(5 of Male, 11 of Female). The study population comprised 16 students and adults(5 of Male, 11 of Female), We measured the contrast sensitivity on uncorrected vision, according to color of circle contact and change the illumination of laboratory. The contrast sensitivity by illumination decreased than unaided vision when they wore the color contact lenses and more increased mesopic than photopic. Compared between black and brown lenses, brown was higher the contrast sensitivity than black. Also emmetropia had significantly differences when we compared the contrast sensitivity of subjects who had emmetropia, myopia and myopia astigmatism whether refractive error has or not. Therefore, it is important to provide sufficient understanding and recognition of color contact lenses.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.3
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• pp.413-420
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• 2010

An Estimation of VHF data link range for EW(Electronic Warfare) equipment in the sea environment was studied to predict the data link range between transmitting and receiving station. The theoretical estimation predicts within 3% error with actual measurement of VHF data link range at sea. Data link range factors including refraction and reflection are added in the basic wave propagation equation. The effect of refraction and reflection to the range is analysed with quantity level.