• Journal of Korean Ophthalmic Optics Society
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• v.16 no.2
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• pp.123-133
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• 2011

Purpose: The present study was conducted to analyze any difference in the movement of aspheric RGP lens by the amounts of keratometiric astigmatisms using keratometer and corneal topography. Methods: Corneal curvatures in thirty six eyes of males and females of with-the-rule keratometric astigmatisms in their twenties were measured by a keratometer and worn aspheric RGP lenses. Then, lens rotations, vertical and horizontal movements of lens by blinking were measured to compare with lens movements when aspheric RGP lenses were fitted by total keratometric astigmatisms using corneal topography. Results: The case having higher amount of central keratometric astigmatism was 61.1% of subjects, however, 36.1% of subjects showed higher total keratometric astigmatism indicating that central keratometric astigmatism was not always bigger than total keratometric astigmatism. Since over 0.25 diopter difference between total and central keratometric astigmatisms was shown in 19 eyes (52.8% of subjects), the prescription for lens fitting could be changed. Significant difference in horizontal movement was detected with increase of astigmatism when it compared based on the amount of keratometric astigmatism measured by a keratometer. However, there was no significant difference in lens rotation, horizontal and vertical movements by comparison with the amount of total keratometric astigmatism using a corneal topography. When central keratometric astigmatism measured by keratometer was bigger than total keratometric astigmatism estimated by corneal topography, bigger lens rotation was shown compared with opposite case. Also, the tendency of bigger lens rotation was measured with the increase of keratomatric astigmatism in the case of same prescription having same base curves with same amount of keratometric astigmatism but different curvatures. Conclusions: From the present study, we concluded that lens movements on cornea were not totally different when aspheric RGP lens fitted on with-the-rule astigmatism by keratometer and corneal topography. However, there was some difference in certain lens movements. Therefore, we concluded that further study on the relationship between the prescriptions for lens fitting should be conducted for improving the rate of successful lens fitting by keratometer or for the proper application of corneal topography for lens fitting.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.41-50
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• 2011

Purpose: The present study was conducted to compare the centration of RGP lens on cornea when lens was fitted based on keratometric astigmatisms measured by keratometer and the lens centration when fitted by corneal topography. Methods: Thirty eight eyes of 19 male and female in their twenties were applied RGP lens with 9.9 mm of diameter by the keratometric astigmatisms classified by the measurement with a keratometer. Then, lens centrations were estimated using high speed camera and compared with the lens centration when fitted by total keratometric astigmatism using corneal topography. The relationship of the steepest location of cornea and lens centration was further compared. Results: With the rule astigmatism, lens centration was not changed even with the difference in central and total keratometric astigmatisms. When the relationship of the steepest part of cornea measured by corneal topography and lens centration was analyzed, the lens centration in vertical direction was exactly correlated with the steepest part of cornea in 52.3% of subjects. In the case of non-correlation, the steepest part of cornea was mostly upper part of cornea, however, lens centration was located on lower part of cornea. The lens centration in horizontal direction was exactly correlated with the steepest region of cornea in 65.6% of subjects. In non-correlated case, the difference in cornea curvatures between the steepest and the flattest parts was smaller than 0.05 mm in 76.9% of subjects. Conclusions: From these results, we conclude that corneal topographic patterns may more contribute the centration of RGP lens on cornea than the difference in central and total keratometric astigmatisms.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.27-31
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• 2000

As the functional test of cornea. The clinical value of keratometric information was important for assessment the curvature of the cornea, the quality of the corneal surface, the stability of the corneal curvature, and the direction of the corneal astigmatism. This study was performed the comparative analysis of male and female of adult on the base curve, power and astigmatism of the Cornea. On the corneal base curve, the male right eye was 7.656 mm in vertical and 7.966 mm in horizontal. But, the male left cornea was 7.714 mm in vertical base curve and 8.026 mm in horizontal base curve. On the other hand, the female right eye cornea was 7.559 mm in vertical base curve and 7.695 mm in horizontal base curve. But, the female left eye cornea was 7.444 mm in vertical base curve and 7.742 mm in horizontal base curve. On the corneal diopter power, the male right eye was 44.063 diopter in vertical and 43.738 diopter in horizontal. But the male left eye was 44.046 diopter in vertical and 42.304 diopter in horizontal. On the other hand, the female right eye was 44.082 diopter in vertical and 43.77 diopter in horizontal. But, the female left eye was 44.347 diopter in vertical and 43.495 diopter in horizontal. According to the corneal astigmatism axis. The male right eye have 89.9% positive for with the - rule astigmatism, and 8.1 % positive for against - the - rule astigmatism. But, he male left eye have 91.89% positive for with - the - rule astigmatism, and 8.11 % positive for against - the - rule astigmatism. On the other hand, The female right eye have 76.92% positive for with - the - rule astigmatism, and 23.08 % positive for against - the - rule astigmatism. But, the female left have 80.76 % positive for with - the - rule astigmatism, and 17.31 % positive for against - the - rule as tigmatism. The diopter power of corneal astigmatism have 25.57% positive for behind 1 diopter, 44.89% positive for 1 diopter, 18.18% positive for 2 diopter, 5.11% positive for 3 diopter and 6.25% positive for over 4 diopter.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.3
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• pp.219-225
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• 2010

Purpose: Usefulness in predicting the power of spherical rigid gas-pearmeable (RGP) lenses prescription using dioptric power matrices and arithmetic calculations was evaluated in this study. Noncycloplegic refractive errors and over-refractions were performed on 110 eyes of 55 subjects (36 males and 19 females, aged $24.60{\pm}1.55$years) in twenties objectively with an auto-refractometer (with keratometer) and subjectively. Tear lenses were calculated from keratometric readings and base curves of RGP lenses, and the power of RGP lenses were computed by a dioptric power matrix and an arithmetic calculation from the manifest refraction and the tear lens, and were compared with those by over-refractions in terms of spherical (Sph), spherical quivalent (SE) and astigmatic power. Results: The mean difference (MD) and 95% limits of agreement (LOA=$MD{\pm}1.96SD$) were better for SE (0.26D, $0.26{\pm}0.70D$) than for Sph (0.61D, $0.61{\pm}0.86D$). The mean difference and agreement of the cylindrical power between matrix and arithmetic calculation (-0.13D, $-0.13{\pm}0.53D$) were better than between the others (-0.24D, $0.24{\pm}0.84D$ between matrix and over-refraction; -0.12D, $0.12{\pm}1.00D$ between arithmetic calculation and over-refraction). The fitness of spherical RGP lenses were 54.5% for matrix, 66.4% for arithmetic calculation and 91.8% for over-refraction. Arithmetic calculation was close to the over-refraction. Conclusions: In predicting indications and powers of spherical RGP lens fitting, although there are the differences of axis between total (spectacle) astigmatism and corneal astigmatism, Spherical equivalent using an arithmetic calculation provides a more useful application than using a dioptric power matrix.