• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.85-97
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• 2001

A mathematical model was proposed to analyze the damped motion of contact lens which is initially displaced from the equilibrium position. The model incorporates the differential equations and their numerical solution program, based on the formulations of restoring force arising from the capillary action in the tear-film layer between the lens and cornea. The model predicts the capillary action induced surface tension, time dependence of displacement of lens when it is released from the equilibrium position. It seems that the motion of lens is similar to the typical over-damped oscillation caused by the large viscous friction in the liquid layer between the cornea and lens. The effect of variables such as base curves, lens diameters and thickness of tear film layer were illustrated by the computer simulation of the derived program. The time required for the lens to return to the original position increases as the liquid layer thickness increases and it decreases as the diameter of lens increases. With the certain value of base curve the time interval is found to be minimum. The free vibrations of lenses were also simulated varying the parameters such as base curve, diameter, layer thickness. The resonant frequencies are inversely proportional to the liquid layer thickness and it increases as the lens diameter increases. The resonant frequency of lens has a maximum when the diameter is of certain value. If the external impulse or force of the same frequency as the natural frequency of contact lens acted on the cornea in vivo it may cause an excessive movement and thus it might cause the distortion 10 the lens or be pulled off the eye.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.2
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• pp.215-222
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• 2012

Purpose: This study was performed to investigate the influence of indoor air qualities of an office environment on dry eye syndrome for wearing contact lens and non-wearing contact lens. Methods: To study the effects of indoor air qualities on dry eye syndrome for seventy-one subjects, $CO_2$, temperature, humidity, TSP, PM10, HCHO were measured. Each subject was tested by a McMonnie's dry eye syndrome questionnaire, a Schirmer Tear Test-I (S.T.T-I), a Schirmer Tear Test-II with anesthetics (S.T.T-II), and Tear film break-up time (T.B.U.T) in the their offices. Results: There was significant relation between the indoor air quality and dry eye syndrome for wearing contact lens and non-wearing when TSP was over $200{\mu}g/m^3$, PM10 was higher than $86.7{\mu}g/m^3$ and Formaldehyde was over $0.4{\sim}1.0{\mu}g/m^3$. However, there was no significant effect on dry eye syndrome with $CO_2$ (p=.0146), temperature (p=0.074) and humidity (p=0.053). Conclusions: It was indicated that $CO_2$, temperature and humidity were no effect on dry eye syndrome in the office environment. However TSP, PM10, formaldehyde, and wearing contact lens were effect on dry eye syndrome. Therefore, the entire management of wearing contact lens and the individual evaluation of the indoor air quality are required.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.1
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• pp.15-20
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• 2008

Purpose: To study on the confidence of dry eye diagnosis methods which need to prescribe contact lens. Methods: Non-invasive tear film break-up time (NIBUT) and tear film break-up time (TBUT) were measured in forty healthy subjects in their 20s, and then the subjects were classified into normal eye and dry eye. The results of McMonnies questionnaire, tear prism height measurement, Hardtack test, blink rate measurement and Schirmer test were compared with the results of NIBUT and TBUT. Results: The results of NIBUT and TBUT were as follows; 20 subjects had normal eyes, 10 subjects had dry eyes in both NIBUT and TBUT, and 10 subjects showed different results. In McMonnies questionnaire, the score of normal eye group averaged 8.2 and that of dry eye group averaged 18.5, which showed statistically significant difference. Furthermore, 100% of normal eye group classified by the results of NIBUT and TBUT corresponded with the result of McMonnies questionnaire and 90% of dry eye group showed the correspondence. Tear prism height of normal eye group averaged 0.32 mm and that of dry eye group averaged 0.23 mm, which were significantly different. Hardtack test, blink rate measurement and Schirmer test without local anesthesia showed no statistically significant difference between normal eye group and dry eye group. Conclusions: On dry eye diagnosis methods, the results of McMonnies questionnaire and tear prism height measurement had close correlation with the results of NIBUT and TBUT.

• 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.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.21-30
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• 2011

Purpose: The study was performed to compare the differences in lens rotation, lens movement by blinking and lens centration with alignment or steep fitting of soft contact lens in normal and dry eyes. Methods: Total 40 eyes (aged 20~30 years) were classified into the normal (n=20) or dry eye group (n=20) by the diagnosis methods for dry eyes and worn soft contact lens (polymacon material) with alignment fitting or steep fitting. Lens rotation, lens movement by blinking and lens centration were separately measured immediately after lens wearing and after stabilization of tear film and compared by fitting states of soft contact lenses. Results: With steep fitting of soft contact lens in dry eyes, averaged lens rotation immediately after lens wearing was not significantly different from that of the normal eye group with alignment fitting however, lens rotation after stabilization in dry eyes was significantly larger than that in normal eyes. Any significant difference in lens movement by blinking was not shown in normal eyes. However, lens movement by blinking in dry eyes was increased with steep fitting. The range of lens centration on cornea in normal eyes with alignment fitting was more vertically distributed. On the other hand, the range of lens centration on cornea in dry eyes with alignment fitting was more horizontally distributed. Lens centration was shown to be changed by stabilization of tear film. That is, lens centrations were somewhat vertically widespread immediately after lens wearing and restrictively distributed in horizontal direction, respectively, with steep fitting in dry eyes. Conclusions: These results suggested that lens movements and centration in dry eyes were different from those of normal eyes. Especially, those differences between normal and dry eyes were much bigger with steep fitting of soft contact lenses. Thus, those differences should be considered for the comfortable and safe fitting of soft contact lens in dry eyes.

• Journal of Convergence Society for SMB
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• v.6 no.4
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• pp.85-91
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• 2016

This study is to research the tear film stability for 48 eyes, agreed the purpose of study, didn't have no contact lens wearing and were tested all two times in a day. Their visual acuity was more than 0.8, corrective visual acuity more than 0.8, the fattest K-reading, apical corneal radius, was in 7.40~8.40mm, corneal astigment was less than 1.00D and orthophoria. The tests, tear scope test, tear film break up time test(TBUT) and schirmer test order, were performed their functions before and after their working at interval of 6 hours over. The tearscope test results was no difference, TBUT was no difference, although 1.2 seconds more in the afternoon, shcirmer test was decreased 2.0mm in the afternoon.

• Journal of Korean Ophthalmic Optics Society
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• v.21 no.3
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• pp.191-201
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• 2016

Purpose: In the present study, the effect of artificial tears with different ingredients on tear film stability and subjective symptoms of dry eyes in the early stage of soft contact lenses wear was investigated. Methods: The three kinds of artificial tears and saline solution were respectively applied onto 50 dry eyes which wore soft contact lenses made of etafilcon A. Then, non-invasive tear film break-up time (NIBUT) was measured at every five minutes for 30 minutes right after the instillation of artificial tears, and the changes in blink rate and subjective symptoms were estimated after 30 minutes from the instillations. Results: All three kinds of artificial tears increased NIBUT larger than saline. The effect of increasing NIBUT immediately after the instillation of artificial tears was the largest when the artificial tear containing viscosity enhancer was used. The duration time of the effect was the longest when the artificial tear having both surfactant and viscosity enhancer was applied. The blink rate was not significantly changed when both artificial tears and saline solution were instilled. Subjective symptoms were significantly improved by the instillation of both artificial tears and saline solution and dryness, irritation, tiredness, stiffness, dazzling were improved by the use of most solutions. However, the subjective symptoms were rebounded to the level before the instillation of artificial tears after 30 minute-instillation. Conclusions: It was revealed that both artificial tears and saline solution could improve the subjective symptoms of dry eye in the early stage of soft contac lenses however, the effect of these solutions on the tear film stability was different according to the components. From the results, it is suggested that the proper selection of artificial tears is necessary for the improvement of dry eye symptoms at the early stage of soft contact lenses wear in dry eye.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.2
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• pp.1-7
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• 2008

Purpose: This study was performed to evaluate the changes of lens morphology and tear stability during wearing soft contact lenses (SCLs) which were kept in drying condition like dry eye or became to be dried due to heedless care. Method: SCLs having different water content, thickness or material were rehydrated after being dehydrated artificially 2 or 4 times, and estimated their diameter and radius. Furthermore, the changes of tear film break-up time (TBUT) during SCL wearing were also measured. Result: Due to the dryness, the diameter of both 70% water content SCL and 59% water content SCL decreased, but the decrement was larger in 59% water content SCL. The more 59% water content SCL was dehydrated, the more its radius changed. However, the radius of 70% water content SCL did not change by 2 times dehydration and increased greatly by 4 times dehydration. The reduction of diameter of -1.00 D SCL was greater than that of -9.00 D SCL. Moreover, the radius of -1.00 D SCL increased depending on the frequency of dehydration but that of -9.00 D SCL did not changed. The diameter and radius changes of lotrafilcon B, silicone hydrogel lens, were less than those of hilafilcon B, copolymer of HEMA and N-vinyl pyrrolidone. TBUT during wearing SCLs decreased by wearing dehydrated SCLs. Conclusion: The diameter and radius of dehydrated SCLs as well as TBUT during wearing them were changed in spite of rehydration, which would be the important cause of uncomfortable feeling when people wore dehydrated SCL. The changes of SCL morphology and TBUT differed according to the water content, lens thickness and material.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.333-343
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• 2004

Impression cytology refers to application of cellulose acetate filter material to the ocular surface to remove the superficial layers of the conjunctival epithelium. The technique is non-invasive, is easy to perform, causes minimal discomfort to the patient, and can be used to follow changes in the conjunctival ocular surface over time. With this method, the morphology of the conjunctival ocular surface can be studied and the degree of squmaous metaplasia assessed. This study was performed to evaluate the conjunctival surface by impression cytology in dry eye patients. A total of 70 students with no contact lens wearing history were recruited. Subjects were required to fill in a McMonnies dry eye symptom questionnaire. The non-invasive tear thinning time(TIT) test of each subject was measured, followed by Schirmer tear test(STI), tear film break-up time(TBUT) tests and Rose-bengal staining were performed as a baseline. Conjunctival epithelial cells from the inferior bulbar conjunctiva were harvested by the impression cytology technique. The specimens collected were labelled and stained with PAS(Periodic Acid Schift)-haematoxylin. The goblet cells and conjunctival epithelial cells were observed under a light microscope of 400x magnification. The specimens were classified according to the Nelson Grading scale which was based on the degree of squamous metaplasia such as changes of goblet cells density, size/form, N:C(nucleus : cytoplasm) ratio. Dry eye patients were observed morphological changes of the epithelial cells, different nuclear alterations, decrease of the goblet cells density. The degree of cytological changes was related to severity of dry eye conditions. When the epithelial cell morphology was graded according to the system described by Nelson, specimens from the control group revealed 91.43% of the eyes to be grade 0 and 8.57% to be grade 1, whereas of the dry eye patients, 20% were grade 0, 42.86% grade 1, 34.29% grade 2 and 2,86% grade 3. Impression cytology represents a non- or minimally invasive biopsy of the ocular surface epithelium with no side effects or contraindications. It has demonstrated to be a useful diagnostic aid for a wide variety of processes involving the ocular surface. This technique is a safe, simple method and may help increase understanding of various ocular surface alterations in dry eye patients.