• Journal of Korean Ophthalmic Optics Society
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• v.21 no.1
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• pp.35-45
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• 2016

Purpose: The present study was aimed to investigate the effect of corneal eccentricity on the axial rotation when wearing toric soft contact lenses were worn for certain time and changing the gaze directions. Methods: Toric soft contact lenses with double thin zone design applied on 85 of with-the-rule astigmatic eyes. Then, rotational direction and amount of contact lenses were measured after 15 minutes and 6 hours of lens wear. The difference was further compared and analyzed according to corneal eccentricity. Results: The rotation of toric lens showed a tendency to rotate to temporal direction in all gaze directions except temporal-upper direction in all groups of corneal eccentricity. The amount of lens rotation in the frontal gaze direction exhibited a negative correlation since the amount was decreased with increasing corneal eccentricity after both 15 minutes and 6 hours of lens wearing. In many cases, the cornea with small eccentricity also showed the lens rotation larger than $10^{\circ}$. The difference in rotational amount after 15 minutes of toric lens wear was small according to the corneal eccentricity however, the change of rotational amount of contact lens according to corneal eccentricity was shown after 6 hours of lens wear. Conclusions: The present study revealed that the amount of axial rotation was largely varied according to the wearer's corneal eccentricity when wearing toric lens and the rotational amount after certain time of lens was also affected by corneal eccentricity. Thus, it is suggested that the selection of toric soft contact lenses based on corneal eccentricity is necessary.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.5-11
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• 2003

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2006.05a
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• pp.53-55
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• 2006

본 논문은 청소 로봇 메카니즘을 위한 소프트 팁의 접촉력을 제어하기 위한 방법을 제안한다. 제안한 방법에 사용하면, 어떤 소프트 팁의 기하학적인 탄성 모델을 근거로, 청소작업이 수행되는 동안 소프트 팀에 작용되는 접촉력을 팁의 압축변위 정도에 따라 적절히 판단할 수 있다. 이것을 청소 로봇 메카니즘에 탑재된 매니퓰레이터의 위치제어 변위로 활용함으로써, 소프트 팁의 적절한 접촉상태를 유지하는 것이 가능해진다.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.2
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• pp.147-157
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• 2011

Purpose: The present study was conducted to investigate the actual condition of circle lens wear and the differences caused by the pigmentation in blinking rate, non-invasive tear break-up time (NIBUT), and lens surface between circle and soft contact lens wear during clinical application. Methods: Eighty subjects were surveyed to know the actual condition of wearing circle lens. Blink rate, NIBUT of 20 subjects in twenties were measured after separately wearing soft contact lens and circle lens for 5 days. Their lens surfaces were also observed by scanning electron microscope. Results: Fifty percent of circle lens wearers answered that major reason for changing circle lens was discomfort and 67% of answerers wore circle lens more than 6 hours a day. The tendency of increased blink rates in both wearers of circle and soft contact lens at 30 minutes later when tear film stabilized and 3 hour after lens wearing was shown on the 1st, 3rd and 5th day with expanding wearing time. Especially at 3 hours after lens wearing on the 3rd and 5th day, the difference of blink rates was statistically different in circle lens wear and soft contact lens wear. The NIBUTs of soft contact lens wearers and circle lens wearers were 6.0 and 3.7 secs, respectively, at 30 min later on 1st day and were significantly different. NIBUTs of soft contact lens wearers and circle lens wearers were also statistically different 3 hrs after lens wearing on the 1st day and the similar pattern of NIBUTs was shown on the 3rd and 5th day. The roughness of both surfaces in soft contact lens and front surface in circle lens was same. However, pigmented front surface of circle lens was rougher and uneven. Conclusions: As the results, the circle lens wearers might feel discomfort in clinical application since the difference in lens surface of circle lens would change lens wettability during wearing. The difference by tinting contact lens was shown from the result, which could help better wearing circle lens.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.05
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• pp.223-225
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• 1996

Poly (ethylene glycol) (PEG)macromers terminated with acrylate groups and interpenetrating polymer networks(IPN) composed of poly(hydroxyethyl methacrylate)(PHEMA) or poly(hydroxyethyl methacrylate-co-hydropropyl methacrylate-co-N-vinyl pyrrolidone) [P(HEMA-co-HPMA-co-NVP)] and PEG macromer were synthesized with the aim of obtaining protein adsorption resisatnt soft contact lens. Polymerization of PEG macromer resulted in the formation of cross-linked gels due to the multifunctionality of macromer. Crosslinked P(HEMA) or P(HEMA-co-HPMA-co-NVP) chains were interpenetrated into the cross-linked three-dimensional networks of PEG. It was found that albumin adsorption onto the contact lens prepared by P(HWMA)/PEG IPN decreases with a decrease of molecular weight of PEG whereas its adsorption onto the contact lens prepared by P(HEMA-co-HPMA-co-NVP)/PEG IPN decreases with an increase of molecular weight of PEG. Also, it was found that albumin adsorption onto the both contact lens decreases with an increase of concentration of PEG macromer in the IPN preparation. There are also more adequate in the bioinertness and bioadhesion for the contact lens by P(HEMA)/PEG IPN or P(HEMA-co-HPMA-co-NVP)/PEG IPN than that by P(HEMA) or P(HEMA-co-HPMA-co-NVP).

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.59-69
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• 2019

This paper focuses on the numerical simulation of ice abrasion induced by unbreakable ice floe. Under the assumption that unbreakable floes behave as rigid body, the Discrete Element Method (DEM) was applied to simulate the interaction between a fixed structure and ice floes. DEM is a numerical technique which is eligible for computing the motion and effect of a large number of particles. In DEM simulation, individual ice floe was treated as single rigid element which interacts with each other following the given interaction rules. Interactions between the ice floes and structure were defined by soft contact and viscous Coulomb friction laws. To derive the details of the interactions in terms of interaction parameters, the Finite Element Method (FEM) was employed. An abrasion process between a structure and an ice floe was simulated by FEM, and the parameters in DEM such as contact stiffness, contact damping coefficient, etc. were calibrated based on the FEM result. Resultantly, contact length and contact path length, which are the most important factors in ice abrasion prediction, were calculated from both DEM and FEM and compared with each other. The results showed good correspondence between the two results, providing superior numerical efficiency of DEM.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10a
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• pp.52-56
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• 1990

An algorithm is proposed to determine the optimal contact forces of robotic hands, where the soft finger contact as well as the frictional point contact are considered. Especially, the algorithm can be efficiently applied to the case of multi-point contact by inner-link as well as fingertip. To show the validities of the algorithm, several numerical exampies are presented by employing a robotics hand with three fingers each of which has four joints.

• Journal of Korean Clinical Health Science
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• v.4 no.4
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• pp.662-670
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• 2016

Purpose. Because of a recent increase in use of soft contact lens at younger ages, in the present study, the correlation between corneal eccentricity and radius of curvature and fitting types of contact lens was investigated. Methods. The study evaluated the fitting status of targets through lens centration, push-up test, dynamic lag test and static lag test of lenses usually worn by 49 men and women (98eyes) in their 20s to 30s who put on soft contact lenses. After evaluation, the subjects were classified into 3 categories by fitting status(steep, aligment and flat). The radius of corneal curvature in the naked eyes was measured by using keratometer. Moreover the corneal eccentricity in the nasal side, temporal side, superior side and inferior side was measured by using the device capable of measuring the corneal eccentricity. Results. The radius of corneal curvature and corneal eccentricity of soft lenses worn by subjects were higher in the order of steep fitting and flat fitting, and the higher average corneal curvature radius and corneal eccentricity is intend to be more steep fitting(p=0.051, p=0.052). The corneal eccentricity showed a tendency to nasal fitting type at the higher eccentricity and temporal fitting type at the smaller eccentricity, statistically significant difference was observed(p<0.05). The study showed there were low correlation that nasal and temporal side at steep fitting, superior side at normal fitting and 4side(nasal, temporal, superior, inferior) at flat fitting, therefore when the corneal eccentricity changed the radius of corneal curvature also changed. The corneal eccentricity and the radius of corneal curvature showed statistically significant difference at 4side and each fitting types(p<0.05). Conclusions. The results of this study, the fitting status, of wearer are based on radius of corneal curvature and corneal eccentricity, and if lens fitting would be done considering that, it seems to be useful in a soft contact lens prescription.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.4
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• pp.383-390
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• 2011

Purpose: The present study was conducted to investigate whether refractive powers of soft contact lenses were induced by the deposition of tear proteins when wearing soft contact lenses. Methods: The soft contact lenses (material: etafilcon A, hilafilcon A and comfilcon A) with refractive powers of -1.00 D, -3.00 D, -5.00 D and -7.00 D were incubated in artificial tear for 1 day, 3 days, 5 days, 7 days and 14 days, respectively. After incubation, their refractive powers were measured by wet cell method with an auto-lens meter and their protein deposited on the lenses was determined by the method of Lowry. Results: Among three types of soft contact lenses, the most protein deposition was detected in ionic etafilcon A lens material and significant change of its refractive power was manifested. In other words, refractive powers of etafilcon A lenses firstly decreased after 1 day incubation in artificial tear and then gradually increased with increasing incubation period again. The observed change in refractive powers of all diopters of etafilcon A material was beyond the scope of standard error and bigger in the lens with lower optical power. On the other hand, non-ionic hilafilcon A showed less protein deposition as much as about 20% in etafilacon A and statistically significant increase of refractive powers with increasing incubation period in artificial tear. The change in refractive power of hilafilcon A was also beyond the scope of the standard of error when incubating in artificial tear and greater in the lens with lower diopter. The least protein deposit was shown in silicone hydrogel lens material, comfilcon A as approximately 10% of it in etafilcon A, indicating less change in refractive power within the standard range of error. Conclusions: The large change of refractive powers that was beyond the scope of standard error by the deposition of tear proteins on soft contact lenses was differently detected depending on lens materials in the current study. Thus, the deposition of tear proteins induced by longer period of lens wearing may be one of the causes that induces blurred vision, suggesting that soft contact lens wearers with the amount of tear proteins may need to choose proper lens material.

• Journal of Oral Medicine and Pain
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• v.23 no.4
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• pp.457-473
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• 1998

This study was performed to investigate the morophological and positional correlation between the upper cervical vertebra, the oral structures and the pharyngeal tissues, and the correlation of these anatomical structures with dental features, such as teeth wear area nad tooth contact status, etc. Seventy patients with temporamandibular disorders and sixty three dental students without any signs and symptoms in head and neck region were selected for this study. All they had natural dentition without any fixed and removable protheses. Teeth wear area and arch width wre measured from the upper dental cast, tooth contact status were observed by T-Scan system$^\textregistered$ and four cephaloradiograpohs were taken from four head postures, namely, natural(NHP), forward(FHP), upward(UHP), and downward head postiure(DHP). 22 cephalometric items were measured on the films and the data were processed with SAS statistical program. The result of this study were as follows : 1. In normal group, angle of cervical vertebra tangent and of between hard and soft palate were broader in female subjects than those in male subjacets, but distance from subocciput to axis, size of soft palate, and pharyngeal space width were larger in male subjects. 2. In normal group with natural head posture, the items correlated each others from the three anatomical regions were distance between first nad second vertebra in posterior part, distance from the lingual surface of lower anterior teeth to anterior surface of soft palate, and distance from the hyoid bone to third vertebra. 3. Three set of items showed significant correlation each other in the four head postures in normal group. First set was the angle between hard and soft palate and the idstance from subocciput to posterior arch of first vertebra, second set was the distance between first and second vertebra in posterior part and the teeth wear area, third set was number and force of tooth contact and length of soft palate and distance from anterior tip of hyoid bone to mandibular plane.