• Journal of Korean Ophthalmic Optics Society
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• v.18 no.4
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• pp.457-463
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• 2013

To determine the impact of artificial tears which include carboxymethyl cellulose on a hydrogel contact lenses. Methods: A contact lenses made of the cross-linking agent, EGDMA (ethylene glycol dimethacrylate) and HEMA (2-hydroxyethyl methacrylate) and with added NVP (n-vinyl-2-pyrrolidone) and MMA (methyl methacrylate) was evaluated for water content, refractive index, spectral transmittance and contact angle of produced contact lens. Results: The physical properties of the sampled copolymerized polymers showed that water content, refractive index, visible ray transmittance and contact angle were in the range of 26.61%~48.58%, 1.422~1.455, 80.8%~91.4% and $33.93^{\circ}{\sim}65.70^{\circ}$, respectively. In addition, after soaking with artificial tears, the water content, refractive index and contact angle were in the range of 24.46%~48.25%, 1.422~1.457, 77.0%~91.0% and $37.25^{\circ}{\sim}77.33^{\circ}$, respectively. The changes of the physical property depending on hydration time and showed an increase of refractive index and contact angle, decrease of water content and visible ray transmittance. Conclusions: Artificial tears which include carboxymethyl cellulose sodium which is used as a wetting agent influenced water content, refractive index, contact angle and spectral transmittance of a hydrogel contact lenses.

• Journal of Korean Ophthalmic Optics Society
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• v.8 no.2
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• pp.135-151
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• 2003

This study compared the effect of Polaroid$^{(R)}$ lenses on binocular vision by assessing visual acuity, stereopsis, and visual evoked potential(VEP), through Polaroid$^{(R)}$, CR 39 and sunglass lenses. The spectral absorptions of Polaroid$^{(R)}$, CR 39 and sunglass lenses were measured using a spectrophotometer (Hitachi. U-3501). The VEP were recorded by the Nicolet system. Thirty normal adult(fifteen males, fifteen females, mean=21.9 years, range=20 to 25) subjects were recorded. The subjects were provided a history including : general health, family health, medication, genetics, allergy and disease. All had normal or corrected to normal acuity with no history of visual disorders. Corrected visual acuity, colour vision and stereopsis were recorded for each subject monocularly and binocularly. Each test was repealed through the sunglass, CR 39, and Polaroid$^{(R)}$ lenses. Subjects viewed the VEP stimulus both monocularly and binocularly through the test lenses while the VEPs were recorded. The results suggest that the binocular visual acuity and stereoacuity is better than with monocular vision. On other hand, the analysis of VEP suggests that the amplitude of wave is smaller when the monocular eye receives the VEP stimulus compared with that when the binocular eye is stimulated by the VEP target with the sunglass, CR 39, and Polaroid$^{(R)}$ lens. But, the latency period of each eye was similar to results between the dominant eye and the non-dominant eye by the CR 39, sunglass, and polaroid lens. In conclusion, this study indicates that the binocular vision appears to be better through the brown Polaroid$^{(R)}$ lens than through the other test lenses.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.2
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• pp.107-115
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• 2013

Purpose: This study was conducted to investigate the change of soft contact lens parameters after eyeliner deposition and compare the cleaning efficiency and the recovery rate of lens parameters by different cleaning methods. Methods: The eyeliner was deposited on three types of soft contact lenses made of different materials for 1 hour, 4 hours and 6 hours and those lenses were washed by the eyeglasses ultrasonic cleaning and by hands. The changes in visible light transmittance, diameter and surface of those lenses were compared before and after cleaning of the lens. Results: The visible light transmittance of soft contact lenses decreased along with the deposition time of eyeliner. The patterns of the eyeliner deposition on soft contact lens appeared differently depending on the physical properties of the lens material. Thus, the largest eyeliner deposition was found on narafilcon A lens. The diameters of hilafilcon B and etafilcon A lenses were decreased, however, the diameter of narafilcon A lens was increased. The cleaning efficiency of the eyeliner deposition was greater with the multipurpose solution by hands than with the eyeglasses ultrasonic cleaner. However, the recovery of lens parameters such as the lens diameter, visible light transmittance and lens surface due to the eyeliner deposition to its original state was limited. Conclusions: From these results, it is suggested to minimize eye makeup when wearing soft contact lens. Furthermore, the reduced wearing time and shorter cycle of lens replacement may be needed by considering a change of lens parameter when the repeat eye makeup is applied.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.3
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• pp.349-354
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• 2015

Purpose: To investigate the changes of corrective values of astigmatism caused by the position of circle of least confusion on retina in refining astigmatic test using cross cylinder. Methods: 62 subjects (115 eyes) aged $22.24{\pm}2.48$ years participated for this study. After astigmatic test using a radial chart, refining test was performed using a cross cylinder in a condition of maximum plus to maximum visual acuity (MPMVA). Astigmatic refining test was repeatedly performed in each condition of which S+0.75 D, S+0.50 D, S+0.25 D, S-0.25 D, S-0.50 D, and S-0.75 D are added to spherical lenses of MPMVA. The measured values were compared with the values in MPMVA condition. Results: As compared with values in condition of MPMVA, change of astigmatic axis was increased with add the power of (+) spherical lenses and (-) spherical lenses. In same spherical condition, change of astigmatic axis was decreased with increment of astigmatic power (p<0.05). The corrective power of astigmatism was reduced with increment of (+) spherical lenses (p<0.05), and was raised with increment of (-) spherical lenses compared with the power in MPMVA condition. In case of adding (+) spherical lenses, difference of astigmatic power increased with increment of corrective astigmatism power in same test condition. Conclusions: In order to obtain a proper values for corrective astigmatism, position of circle of least confusion should be accurately adjusted before the performing an astigmatism's refining test.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.4
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• pp.373-380
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• 2012

Purpose: The present study was performed to investigate a relationship between the stable centrations of spherical RGP lens and aspherical RGP lens on cornea and corneal eccentricity. Methods: Two RGP lenses with different designs were fitted in alignment, steep or flat on total 84 eyes having corneal eccentricity of 0.28~0.78. The stable centration of lenses on cornea was analyzed by taking photographs with a high-speed digital camera. Results: The stable centrations of spherical and aspherical RGP lenses in horizontal direction were decentrated to temporal side. More centration to median side was shown when corneal eccentricity was larger. The difference between the stable centrations of spherical and aspheric RGP lenses according to corneal eccentricity was bigger when the fitting state was flatter. The difference in the stable centrations of aspherical RGP lens was smaller than that of spherical RGP lens regardless of fitting status. The stable centrations of spherical and aspherical RGP lenses in vertical direction were located below corneal apex regardless of fitting status however, there was no significant difference analyzed by the variation of corneal eccentricity. However, there were many cases that RGP lenses were in upper eyelid with increasing corneal eccentricity. Conclusions: The consideration of corneal eccentricity is required for RGP lens fitting and manufacturing aspherical RGP lens since the stable centration of spherical RGP lens as well as aspherical RPG lens' centration was changed depending on corneal eccentricity.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.4
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• pp.381-388
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• 2012

Purpose: In this study, the changes in the shape of silicone hydrogel lenses, dryness of lens and objective/ subjective symptoms that could be induced by repeating dryness of lens and objective/subjective symptoms were investigated. Methods: After drying and rehydrating of silicone hydrogel lenses with different lens material and thickness for 4 times, their overall diameters and base curves were compared. Subjective symptoms, non-invasive tear break-up time (NIBUTs) and blinking rate were evaluated after wearing dehydrated silicone hydrogel lens. Results: Overall diameter and base curve increased in all tested silicone hydrogel lenses by repeating dryness and rehydration. The degree of change in over all diameter and base curve were variable on the material. There were irregular change of lens parameters in thicker lens. When the subjects wore silicone hydrogel lenses after drying and rehydrating, their NIBUTs were decreased and blink rates were increased regardless of lens material or thickness. In addition, repetitive drying of silicone hydrogel lenses affected the lens fitting. Therefore, subjective symptoms such as itching, pain, irritation, foreign body sensation, dryness tended to be increased. Conclusions: The results obtained from the study may suggest to develop durable silicone hydrogel contact lenses against dry environment since the changes in parameters of silicone hydrogel lens and the subjective discomfort were observed after repetitive drying and rehydration.

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.1
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• pp.31-38
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• 2009

Purpose: This study was to evaluate corneal topography, contrast sensitivity and ocular response of a RGP, back surface aspherical contact lens compared with a spherical contact lens. Methods: A total 37 subjects were fitted with a spherical lens in right eye and an aspherical in the left eye and were evaluated for changes in corneal topography and contrast sensitivity over a 2-month period. Results: Thirty-four of 37 subjects completed the 2-month study. The corneal topography did not show differences between spherical and aspherical RGP lenses. The eyes fitted with the aspherical lenses demonstrated a greater reduction in contrast sensitivity compared with their spherical counterparts under photopic condition. Subjects preferred comfort and ocular responses provided by the spherical lens. Conclusions: Corneal topography when comparing spherical and back surface aspherical RGP lenses did not show any significant difference in the subjects. Spherical RGP lens yields better contrast sensitivity and preference than aspherical RGP lens at photopic condition. Further investigation of aberrations induced by contact lens design is warranted to explain the observed differences in visual performance.

• Journal of Korean Ophthalmic Optics Society
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• v.21 no.1
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• pp.11-21
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• 2016

Purpose: The aim of this study was to analyze the difference in tear film stability according to the wearing time when wearing clear and circle soft contact lens(circle lens) made of same material. Methods: The clear and circle contact lenses of hilafilcon B and nelfilcon A materials were respectively applied on the subjects classified as normal and dry eyes depending on their tear volume, and their tear film stability was investigated by measuring the non-invasive tear film break-up times, lens centration and the first appearing area of tear breakup after 30 mins and 6 hrs of lens wearing. Results: Non-invasive tear film breakup time significantly reduced with increase of the wearing time for normal and dry eyes when wearing clear and circle contact lenses. The starting ratio of tear film break-up was higher at the peripheral area of clear and circle lenses in all two different materials, and higher at the peripheral area of dry eyes than normal eyes. Starting ratio of tear film break-up was higher at the peripheral area of nelfilcon A lenses compared with hilafilcon B lenses, however, its change with the increase of wearing time showed a different aspect. The number of tear film break-up per unit area when wearing circle lenses of nelfilcon A increased at the central area with the wearing time while its number was higher at the peripheral area when wearing circle lenses of hilafilcon B. The centration of clear lenses made of two materials was closer to pupil compared to circle lenses with the increase of wearing time, however, a larger decentration was shown in dry eyes compared with normal eyes. Conclusions: The research revealed that an effect on tear film stability may be changed by clear lenses as well as circle lenses with coloring process according to the increase of wearing time, and the factors affecting on tear film stability may also vary depending on lens materials. Thus, the appropriate lenses should be selected by the consideration of lens material as well as coloring method/dyes according to the wearers' habit such as daily wearing time and wearing period when trying to wear clear and circle lenses.

• Journal of Korean Ophthalmic Optics Society
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• v.10 no.3
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• pp.173-184
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• 2005

A capillary action-induced tension develops in the tear layer between the contact lens and cornea, which leads to the restoring force due to difference in the layer thickness between either upper and lower or left and right side of the lens when it is displaced off the equilibrium position as a result of blinking. Suppose the lens was displaced a certain distance from the equilibrium position, lens starts to oscillate toward the equilibrium position with the decreasing amplitude due to the restoring force as well as the velocity dependent viscous damping force in the tear layer. A mathematical model which consists of the differential equations and their numerical solution was proposed to analyze the damped oscillations of lenses. The model predicts the time dependence of lenses after the blink varying the various parameters such as Be, diameters, masses and positions displaced from equilibrium. As the Be and mass of lens increases the rate of amplitude reduction decreases, which requires a more time for the lens to return to the equilibrium position. It seems that varying the lens' displacement and diameters affect the lens' motion very little.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.2
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• pp.119-126
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• 2012

Purpose: To study changes in coating and lens materials after chemically etched different polymer based glass lenses in short-term and ambient condition using hydrofluoric acid. Methods: Vinyl ester polymer (Lens A) and thiourethane polymer (Lens B), both dyed in gray 70%, were etched in hydrofluoric acid solution for 5, 10, or 15 min. The mechanical properties, degrees of damages in hard coating, anti-reflection coating, and other coatings, rates of refractive index and light transmission of both polymer types were evaluated. Results: Rates of refractive index of both lens types were not changed significantly after chemical etching. However, anti-reflection coatings and hard coatings were removed and lens surfaces were damaged. As a results, UV light transmission of lenses increased and mechanical properties decreased. Chemical etching notably changed various properties of thiourethane polymer materials. Conclusions: Depending on types of polymer materials, chemical reactions by hydrofluoric acid were dissimilar. Thus, various properties of les materials were altered differently.