• Journal of Korean Ophthalmic Optics Society
• /
• v.19 no.2
• /
• pp.189-198
• /
• 2014

Purpose: The present has analyzed the correlation between the direction of lens and the amount of rotation upon soft toric contact lens fitting after classifying the corneal astigmatism. Methods: Soft toric contact lens was fitted on 114 with-the-rule astigmatic eyes with total astigmatism of at least -0.75 D in their 20s and 30s according to the fitting guideline of the manufacturer and the correlation between the astigmatic degree and the rotational direction/amount of rotation was analyzed by when keeping the eyes on the front and by changing the direction of gaze. As for re-orientation movement. The speed of lens re-orientation and total amount of lens rotation was compared and analyzed by corneal astigmatism after mis-location of lens of $45^{\circ}$ to temporal and nasal direction, respectively. Results: The positive correlations were shown between corneal astigmatism and the direction of lens rotation and between corneal astigmatism and the amount of lens rotation. Meanwhile, the amount of lens rotation was different by the direction of gaze however, there was no correlation with corneal astigmatism. The speed of lens re-orientation was fastest in the group of high astigmatic degree when the lens was mis-located to both temporal and nasal directions. Conclusions: For optimal axis stabilization of toric soft lens, it is proposed that the adjustment of fitting guideline considering corneal astigmatism is necessary since the current fitting guideline is only based on total astigmatism.

• Journal of Korean Ophthalmic Optics Society
• /
• v.18 no.4
• /
• pp.441-447
• /
• 2013

Purpose: The present study was conducted to investigate the axial rotations of toric soft lens during the change of lens wearer's posture, and the relationship between its rotation and corneal astigmatism. Methods: The amount, direction, and speed of toric soft contact lens rotation were measured for 42 eyes (aged 20s) with the rule astigmatism in the straight and lying postures, and it compared between their changes according to corneal astigmatism. Results: There was no significant difference in the axial rotation of lens for the astigmatism prescription between the straight and lying postures. However, the rotation angle was significantly different according to the posture of lens wearer. Rotating directions in straight posture were nasal direction for 20 eyes and temporal direction for 22 eyes. In lying posture, lenses of most wearers were rotated to a direction of lying posture, and the initial rotating speed was very fast in initial wearing for -0.75 D toric lenses, but consistency for -1.25 D toric lenses. The rotation angle in lying posture showed significantly different according to the amount of corneal astigmatism, the lens speed was also significantly different according to the wearing time but not the amount of corneal astigmatism. Conclusions: The axial rotation of toric soft lens was different by the lens wearer's posture and its amount was the greater with the higher degree of corneal astigmatism. Thus, these factors should be considered for the development of toric lens design.

• Journal of Korean Ophthalmic Optics Society
• /
• v.20 no.2
• /
• pp.133-140
• /
• 2015

Purpose: It was investigated whether two different stabilization designs of toric contact lenses changed the rotational axis and degree of toric lenses according to body posture and gaze direction in the present study. Methods: Toric soft contact lenses with Lo-Torque$^{TM}$ design and ASD design (accelerated stabilized design) were fitted on 52 eyes aged in 20s-30s. Then, rotational degree was measured at the five gaze directions including front gaze and the lying position. Results: When gazing the front and vertical directions in the upright posture, lens was much rotated to nasal side for the Lo-Torque$^{TM}$ design and temporal side for the ASD design. When gazing horizontal direction, both design lenses were rotated against to the gaze direction. Rotation degree was the smallest at superior direction gaze and the largest at nasal gaze. In case of the rotation degree less than $5^{\circ}$, Lo-Torque$^{TM}$ design was more frequent when gazing front and vertical directions, and ASD design was more frequent when gazing horizontal direction. In addition, the lens with Lo-Torque$^{TM}$ design was lesser rotation degree than with ASD design immediately after lying. On the other hand, the lens with ASD design was lesser rotation degree than with Lo-Torque$^{TM}$ design 1 minute later after lying. Conclusions: This study confirmed that axis rotation of the lens induced by gaze direction and posture was different according to axis stabilization design during wearing toric soft contact lens.

• Journal of Korean Ophthalmic Optics Society
• /
• v.17 no.1
• /
• pp.83-89
• /
• 2012

Purpose: This article was to study the optical and surface properties of soft contact lenses (SCL) exposed to eye make-ups. Methods: Rates of the light transmission of etafilcon A (HEMA based hydrogel lens) and lotrafilcon B (silicone based hydrogel lens) exposed to four different cosmetics over time were investigated. After cleansed with multi-purpose solution (MPS), rates of the light transmission and surface change of lens that were exposed to the cosmetics for 7 consecutive days were analyzed. Results: Visible light transmissions of all lenses exposed to cosmetics decreased to 93.35% (HEMA based hydrogel lens) and 90% (silicone based hydrogel lens) compared with those of the fresh SCLs, such as 97.8% and 96.4%, respectively. It was found that cosmetic residues from powder eye shadow and mascara attached to the lenses were not removed completely when cleansed with MPS. Especially with silicone based hydrogel lens, we found a decrease in visible light transmission of the lens and noticeable particles on lens surface imaged by SEM. Conclusions: Depending on types of eye make-ups and contact lens materials, make-ups were not completely eliminated with current cleansing methods and that caused a decrease in optical property and a change in surface property of the lenses.

• Journal of Korean Ophthalmic Optics Society
• /
• v.6 no.2
• /
• pp.85-97
• /
• 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
• /
• v.18 no.3
• /
• pp.279-289
• /
• 2013

Purpose: To evaluate the changes of refractive power when worn soft contact lenses were temporarily removed. Methods: 91 soft contact lens wearers (15 males and 76 females; total 182 eyes) from 17 to 39 years of age (average: $24{\pm}4.8$ years) were participated. Objective and subjective refraction, and corneal radius were measured at 0, 30, 60 and 90 min after lens removal. The changes in refractive power were evaluated between measurements over time. The other parameters such as types of lenses, fitting and wearing conditions were also assessed. Results: Objective refraction, subjective refraction and corneal radius were significantly changed according to measured time (p<0.0001). A moderate myopic shifts was observed at the beginning (30 min after lens removal) and a slight myopic shift at the late of measurement (60 min to 90 min after lens removal). There are no significant differences between lens types, fitting states, wearing time, wearing days and sleeping time in the previous day. However, there was significant interaction in changes for corneal radius between measuring time and lens type (p=0.017), fitting state (p=0.019), and sleeping time prior to the test (p=0.010). Conclusions: Time to reach refractive and corneal radius stability after contact lens removal revealed at least more than 60 min, regardless of types of lenses, fitting and wearing conditions. Therefore, refraction for correction should be performed after waiting for more than that time as possible.

• The Korean Journal of Vision Science
• /
• v.20 no.4
• /
• pp.431-442
• /
• 2018

Purpose : The purpose of this study was to investigate subjective symptoms according to the wearing, purchase and fitting status of soft contact lens wearers, and consumer perception of base curve. Methods : A survey was conducted for those who visited optical shops and lens shops in Seoul from June to August 2018. A total of 98 answer sheets they submitted were used for the analysis. The chi-square test and Fisher's exact test were used to compare subjective symptoms (dryness, glare, uncomfortable fitting, and decreased vision) according to whether fitting condition is screened (case history and push-up test, ect relevant to wearing sensation), and the odds ratio (OR) was obtained by the logistic regression analysis. Results : When the contact lenses were purchased, the rate of which the visual acuity test was performed was 86.6% at optical shop and 64.7% at lens shop. When purchasing contact lens and the contact lens was not tested for fitting, they more experienced dryness (OR 4.41, 95% CI 1.25-15.62) and uncomfortable fitting (OR 2.68, 95% CI 1.08-6.64) than testing for fitting. In addition, it was investigated that 87.8% of contact lens wearers did not know about the term base curve, 92.9% did not listen to an explanation related to the base curve when purchasing contact lenses, and 96.9% did not experience with base curve test. Conclusion : It would be thought that satisfaction of the contact lens fitting of existing consumers should be improved by changing a proper base curve by confirming the fitting condition when prescribing soft contact lens.

• Journal of Korean Ophthalmic Optics Society
• /
• v.9 no.2
• /
• pp.233-239
• /
• 2004

This study investigated the status of soft contact lens wear in college students. The results were as follows: 1. The most prevalent age of initial contact lens wear was 19 years or 20 years, with an age distribution in females from as early as 10 years to 20 years. 2. For almost all subjects, the test clinic for the contact lens wear assessment and purchase of the contact lenses was an optical shop. 3. The main advantage for most male subjects was use for sports, whereas most female subjects used contact lenses for cosmetic reasons. 4. The most common side-effects experienced due to contact lens wear were red eye, foreign body sensation, and eye pain. 5. The most frequently reported eye disease caused by contact lens wear was conjunctivitis, with only few subjects experiencing keratitis. 6. Following treatment for the side effects of contact lens wear, most subjects hoped to re-use the previous contact lenses, some subjects wanted to change to new contact lenses, and others subjects refused further contact lens wear.

• Journal of Korean Ophthalmic Optics Society
• /
• v.19 no.2
• /
• pp.153-162
• /
• 2014

Purpose: This study was assessed to investigate the change of subjective and/or objective symptoms and the light transmittance of lens caused by the use longer than recommended wearing time of daily disposable circle contact lenses (circle lens) in dry eyes. Methods: Three daily disposable circle lenses made of etafilcon A, hilafilcon B, and nelfilcon A were applied on 30 dry eyes with smaller tear volume than normal eyes in their twenties free from any eye diseases by when subjects complained any kind of discomfort. On the first and the last days of lens wearing, subjective discomfort, blinking rate, lens centration on corneal surface and visible light transmittance of lens were recorded at every case and compared. Results: The circle lens wearers complained subjective discomfort and quit the lens wearing when they wore the circle lens longer than 10 hours even though there were some difference according to the lens materials of daily disposable circle lens. However, around 20% of dry eyes could wear the circle lens made of non-ionic materials longer than 40 hours. Dry eyes showed most sensitive feeling of subjective discomfort against the circle lens made of etafilcon A among three different lens materials. On the last day of lens wearing, the representative subjective discomforts were irritation, stiffness, dryness and tiredness. When the subjects wore circle lens more than the recommended time, blinking rate was significantly increased about 20~30% regardless of lens materials when it compared with the values right after lens wearing. On the last day of lens wearing, the vertical direction of lens centration was shifted to pupil center however, its distribution in horizontal direction was wide compared with the distribution right after lens wearing. Especially, the centration of etafilcon A lens was unstable. Furthermore, the visible light transmittance of 3 different circle lenses in dry eyes has significantly been reduced around 15% averaged. Conclusions: From these results, it was known that the increase of dryness and stiffness caused by overusage of daily disposable circle lens induced excess irritation and decreased visible light transmittance and caused significant more blinking, which provoked lens decentration. It was also revealed that dry eyes showed sensitive reaction subjectively and objectively against the overusage of circle lens made of high water content/ionic lens material even there were some difference of the degree depending on the individual and the lens material. Thus, this research can be suggested as the basic reference for the education about some unexpected problems and the side effect caused by the wearing of circle lens in dry eyes.

• Journal of Korean Ophthalmic Optics Society
• /
• v.16 no.3
• /
• pp.255-264
• /
• 2011

Purpose: To study the effect of hyaluronic acid(HA), which was widely used in artificial tears, multi-purpose solution(MPS), cosmetics, and drug acting on the musculo-skeletal system, in wettability and comfort of contact lens, we compared HA including lens(+HA) with HA excluding lens(-HA) by clinical evaluation. Methods: During four weeks, the selected 28 university student volunteers who did not have any eye disease wore +HA contact lens on their right eyes, and -HA contact lens on their left eyes, and then compared right eyes to left eyes as control. After prescribing by spherical equivalent calculation, over-refraction by auto-refractometer, and contact lens wearing for two weeks and four weeks, tear evaluation, the anterior of eyes examination, fitting convenience evaluation, surface wetting test, surveys were checked up. Results: Compared with the control group (-HA contact lens), +HA contact lens provided better wetting properties. The amount of released tear in -HA contact lens group became less in four weeks than before, but that in +HA contact lens group showed no significant difference from the initial one. In terms of the redness in eye, there was no significant difference between +HA and -HA contact lens groups. Fitting of +HA contact lens on eye was much easier than the control, -HA contact lens. From the results of survey, comfort, wettability, ease of cleaning, and dryness of eye in +HA contact lens group were generally better than those of -HA group, but redness and contact lens handling showed little difference. Conclusions: The addition of HA in soft contact lens(+HA) may enhance the wettability of lens during lens wearing, resulted in the better comfortable wearing of lens eventually.