• Journal of Korean Ophthalmic Optics Society
• /
• v.17 no.1
• /
• pp.37-45
• /
• 2012

Purpose: The change of alignment between RGP lens and cornea according to the lens design was investigated by comparing the areas of fluorescein pattern in central and peripheral regions analyzed by astigmatic degree and corneal type when spherical and aspherical RGP lenses fitted in alignment. Methods: The fluorescein patterns of 90 eyes (19-30 years, $25.12{\pm}3.52$) having with-the-rule astigmatism were analyzed after spherical and aspherical RGP lenses fitted in alignment. Then, their fluorescent areas in central and peripheral regions were calculated and compared for the quantitative evaluation. Results: The case showing concordant base curve between spherical and aspherical RGP lenses in alignment fitting was 72% however, the possibility to have same base curves between spherical and aspherical RGP lenses in alignment fitting was to be less in the case of symmetric bowtietyped cornea and high astigmatism. The fluorescent area in peripheral region of aspherical RGP lens in alignment fitting was smaller than it of spherical RGP lens. Peripheral fluorescent areas in both RGP lenses decreased according to the increase of astigmatic degree and peripheral area in symmetric bowtie-typed corea was smaller than round-typed cornea's peripheral area. In the case of same astigmatic degree, peripheral fluorescent area of aspherical RGP lens was smaller in both corneal types. Conclusions: The results above suggest the changing degree in the alignment between RGP lens and cornea can be varied according to lens design, corneal astigmatism and corneal type. Thus, the results obtained from the quantitative analysis of the alignment between lens design and cornea may be used as the basic information about the establishment of guidelines for RGP lens fitting, the development of proper lens design, and different tear volume in partial regions.

• Journal of Korean Ophthalmic Optics Society
• /
• v.15 no.4
• /
• pp.329-337
• /
• 2010

Purpose: The surfaces and compositions of rigid gas permeable (RGP) contact lenses were analyzed with the consistent methods, and the basic informations for the composition design of lens materials were suggested. Methods: The bulk structures were analyzed by using Fourier infrared spectroscopy (FTIR), the compositions of surface components were observed by using x-ray photoelectron spectroscopy (XPS), the surface morphology and roughness were observed using atomic force microscopy (AFM), and the wettabilities were estimated by the surface wetting angles. The relations and trends of those results were analyzed. Results: The high oxygen permeability RGP lenses showed the trend that the fluorine decreases and the silicon increases. As the silicon and fluorine contents increased, the carbon and oxygen contents of RGP lens materials decreased at a constant ratio. The decreasing ratio of the carbon contents was three times larger than the decreasing ratio of oxygen contents. The composition of the surface treated lens was far from these tendency line. When the silicon contents increased, the rough surface was formed with the cohered particles. When the fluorine contents increased, the rough surface was formed with the deep flaws. The surface roughness increased and then wettabilities decreased as the silicon and fluorine contents increased. For the surface roughness changes, the increasing ratio of the silicon contents was two times larger than the increasing ratio of fluorine contents. The surface of RGP lens materials appeared the hydrophobic character of which the wettabilities decreased when the roughnesses increased. Conclusions: The surfaces and compositions of RGP contact lenses were measured by the same methods. Those results and relationships were compared and analysed. It is considered that these research results will be applied with the basic data for the composition design of lens materials.

• Journal of Korean Ophthalmic Optics Society
• /
• v.14 no.1
• /
• pp.31-38
• /
• 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
• /
• v.13 no.2
• /
• pp.9-16
• /
• 2008

To assess the preference and efficacy of empirical fitting methods with spheric and aspheric RGP lenses. Methods: Healthy 37 subjects were fitted with spheric design (diameter 9.3 mm) on right eye and aspheric design (dia 9.6 mm) on the left eye. Base curves which were fitted empirically (using on-K, Kavg-0.50D (or 1.00D) and manufacturer's recommended fitting guide) were compared with another base curve which obtained the best diagnostic fit with spheric and aspheric RGP lenses. The preference and fitting type (lid attachment or interpalpebral) for two design lenses were investigated 2 weeks after fitting RGP lenses. Results: Of 33 successful RGP lens-wearing subjects, 76% preferred spheric design compared with 24% of aspheric RGP lens wearers. Sixty seven percent were fitted with lid-attachment in spheric lenses, whereas 64% were fitted with lid-attachment in aspheric lenses. The acceptable fit success rates within ${\pm}$0.50D of base curves were 97% for the on-K fit, 100% for the Kavg-0.50D fit and 100% of the manufacturer's guide fit compared with the diagnostic fit in spheric design, whereas 91%, 79% and 94% reported on-K, Kavg-1.00D and manufacturer's guide, respectively, in aspheric design. Conclusions: Although aspheric RGP lenses are more popular in the Korean market, it is still preferable to fit subjects with spheric RGP lenses. Empirical fitting may be best accomplished with the spheric lenses using Kavg-0.50D fit and the manufacturer's fitting guide, whereas aspheric RGP lens designs are unacceptable lens fit based on empirical fitting.

• Journal of Korean Ophthalmic Optics Society
• /
• v.20 no.2
• /
• pp.141-150
• /
• 2015

Purpose: In the present study, a difference in tear volume between the cornea and the rigid gas permeable (RGP) lens relative to corneal shape and corneal astigmatism was investigated by the alignment fitting status of spherical and aspherical RGP lenses. Methods: Spherical and aspherical RGP lenses were fitted with alignment in 77 subjects (135 eyes) who were in their 20~30s. Tear volume stained with fluorescein was qualitatively analyzed by dividing cornea into center, mid-peripheral and peripheral parts. Results: For the spherical RGP lens fitting, tear volume differences were found in each part in all corneal types. For the aspherical RGP lens fitting, tear volume differences were in each corneal part in symmetric bow tie- and asymmetric bow tie-type corneas. However, the tear was equally distributed from the center to the peripheral part in round- and oval-type corneas. In the group with corneal astigmatism lower than 1.25 D, tear volume between center and peripheral parts, and mid-peripheral and peripheral parts, was different when a spherical RGP lens was fitted. However, tear volume in each part was not different in the group with corneal astigmatism over 1.50 D. Moreover, the tear volumes of the central and mid-peripheral parts were proportionally increased with increasing corneal astigmatism in both spherical and aspherical RGP lenses. Furthermore, aspherical RGP lenses showed greater increments than spherical RGP lenses. Conclusions: The results revealed that the difference in tear volume between aspherical RGP lens and cornea was less than spherical RGP lens, and the difference in tear volume varied according to corneal shape and astigmatism. In addition, the method of measuring relative tear volume between RGP lens and cornea that was established in the present study can be used to evaluate tear volume between contact lens and cornea.

• Journal of Korean Ophthalmic Optics Society
• /
• v.17 no.3
• /
• pp.255-264
• /
• 2012

Purpose: In this study, the effect of lens fitting status on the contact area between spherical/aspherical RGP lens and the cornea having different astigmatic degree and corneal type was investigated for guiding the proper selection of RGP lens. Methods: Spherical and aspherical RGP lenses were applied on ninety eyes $(25.12{\pm}3.52years)$ having with-the-rule astigmatism by different fitting status. Then, their central, mid-peripheral and peripheral areas of fluorescein pattern were calculated and compared for the quantitative evaluation of the contact area between spherical/aspherical RGP lens. Results: The central and peripheral areas with the alignment fitting was significant different based on lens design. However, the central area didn't show any significant difference by lens design and corneal type when fitted in steep or flat. When analyzed by the corneal shape, both lenses with alignment and flat fitting had significant difference in central and peripheral areas. However, the central, mid-peripheral and peripheral areas with steep fitting didn't show the difference by corneal types. When analyzed by the astigmatic degree, the central and peripheral areas with alignment fitting changed proportionally to the increase of corneal astigmatism regardless of corneal shape. With steep and flat fitting, however, the central, mid-peripheral and/or peripheral areas in round- and symmetric bowtie-typed corneas showed the conflicting result when compared to those of alignment fitting when analyzed by the astigmatic degree. Conclusions: In this study, it was confirmed that the contact areas of cornea and RGP lens fitted steep and flat status were largely affected by the corneal type and corneal astigmatism rather than RGP lens fitted in alignment status. Also, this result commonly occurred in both spherical and aspherical RGP lenses.

• Journal of Korean Ophthalmic Optics Society
• /
• v.21 no.2
• /
• pp.99-108
• /
• 2016

Purpose: The present study was aimed to compare the tear volume and distribution by corneal eccentricity when fitted with spherical and aspherical RGP lenses. Methods: Spherical and aspherical RGP lenses were fitted in best alignment on a total of 77 subjects (136 eyes) in their twenties and thirties without any ocular disease or ocular surgery experience. The tear volume was analyzed by estimating the concentration of tear stained with fluorescein in the center of RGP lens as well as at the mid-peripheral and peripheral areas, and the difference of tear distributions was analyzed according to corneal eccentricity. Results: Tear distribution from the center to the peripheral area was not significantly different when spherical RGP lenses were fitted on the corneal eccentricities of e < 0.38 and $0.68{\leq}e$, indicating the relatively even tear distribution compared with other corneal eccentricity. In the case of aspherical RGP lenses, the difference of tear distribution between the central and peripheral areas was smaller than spherical RGP lenses. The significant difference of tear distribution according to RGP lens design was observed in the corneal eccentricity of 0.48 < e < 0.68. In other words, more even tear distribution was shown when aspherical RGP lenses were fitted on the cornea with eccentricity of $0.48{\leq}e<0.68$ and spherical RGP lenses were fitted on the cornea with eccentricity $0.68{\leq}e$. Furthermore, tear volume in the mid-peripheral area increased with higher corneal eccentricity. Conclusions: The results suggest that the appropriate selection of RGP lens design according to corneal eccentricity is necessary since tear volume and distribution by the regions of spherical and aspherical lenses are affected by corneal eccentricity.

• Journal of Korean Ophthalmic Optics Society
• /
• v.16 no.3
• /
• pp.273-281
• /
• 2011

Purpose: In order to provide the fundamental information for the design development of RGP lenses and its clinical prescription, the corneal types of Korean twenties were analyzed according to corneal shapes, astigmatic degree, and the certain distance from the corneal apex. Methods: Corneal types of total 252 eyes in 20s were firstly classified, then their corneal radii from the certain distance from the corneal apex were measured by corneal topography and further analyzed based on the astigmatic degree. Results: Korean 20s' corneal types were classified as 14.3%(36 eyes) of round, 31.3%(79 eyes) of oval, 28.6%(72 eyes) of symmetric bow tie, 17.5%(44 eyes) of asymmetric bow tie, 8.3%(21 eyes) of irregular shapes. The round and oval typed corneas had mild astigmatic degree whereas the higher astigmatic degree in symmetric and asymmetric bow tie typed corneas were shown. The relative corneal radii of round and oval typed corneas at each distance from corneal apex were shown to consistently increase regardless of astigmatic degrees when they measured at certain distances from the corneal apex. However, the relative corneal radii of symmetric and asymmetric bow tie typed corneas within 1.0-1.5mm from the corneal apex were decreased, which showed steeper slope than it within 1.0 mm and somewhat different based on astigmatic degrees. Bigger change of corneal radii outer 3.5 mm from the corneal apex in symmetric bow tie typed corneas with astigmatism of 1.50-2.00 D and 2.25-2.75 D appeared. Conclusions: The consideration of radial change from the central cornea to peripheral cornea is necessary for manufacturing RGP lens and its prescription since they showed different change in corneal radii by corneal patterns and astigmatic degrees.