Objective The present study used a corneal topographic device to record aberrations on the anterior surface of the cornea at different time-points prior to wearing and following discontinued use of rigid gas permeable (RGP) contact lenses. The effect of wearing RGPCL on the anterior surface of the cornea was discussed to provide guidance for clinical refractive error correction. Methods The study objects were 60 eyes from 30 patients. All patients underwent identical examination procedures prior to lens use, as well as afterwards, including slit-lamp examination, non-contact tonometer measurement, computer optometry & corneal curvature measurement, subjective refraction test, and corneal topography analysis. The patients wore contact lenses every day for 1 month and then discontinued. Corneal topographies were recorded at certain time points of 30 min, 1 day, 3 days, 1 week, and 2 weeks following use. Results Total corneal aberration at each time point following discontinued use of RGP contact lenses was less than the time point prior to use. Detailed results are as follows; root mean square (RMS) (pre) = (1.438 ±0.328), RMS (30 min) = (1.076 ± 0.355), RMS (1 day) = (1.362 ± 0.402) , RMS (3 day) =(1.373 ± 0.398), RMS (7 day) = (1.387 ± 0.415), and RMS (14 day) = (1.448 ± 0.423) .Results showed that at 30 minutes after discontinued use of RGP contact lenses, almost all 2nd-and 3rd-order aberrations were altered. Quadrafoil Z10 and spherical Z12 of the 4th-order were also changed. Alterations to Z5, Z6, and Z12 at 1 day after discontinued use were significant compared with the time period prior to RGP use: Z5 and Z6 decreased, and Z12 increased slightly( F =2. 869 ～5. 549 ,P =0. 001 ～0. 042). Z5 and Z6remained decreased at 3 days after discontinued use, but Z9 and Z10 continued to increase and Z12 returned to levels prior to RGP use ( P ＞ 0. 05 ). At 2 weeks after discontinued use, all aberrations were not significantly different from the values prior to use ( P ＞ 0. 05). Conclusions The use RGP contact lenses greatly reduced total aberration of the anterior surface of the cornea. Changes to 2nd- and 3rd-order aberrations ( including Z3, Z4, Z5, Z6, Z7, and Z8 ) were more significant. Following discontinued use of RGP contact lenses, the majority of lower order aberrations returned to original levels in a short period of time. During this process, a transient higher order aberration appeared, but all changes disappeared within 2 weeks after discontinued use of RGP contact lenses.
Key words:
Aberration; Contact lenses; Cornea
To investigate the influence of offsets of the pupil center from the corneal vertex on wavefront aberrations in the anterior cornea and the whole eye. Both right and left eyes of 103 subjects were measured for the wavefront aberrations in the anterior cornea, along with the offset of the pupil center relative to the corneal vertex, using a Humphrey corneal topographer, and for the wavefront aberration in the whole eye using a WASCA wavefront sensor. Correlations of the pupil center offsets with the Zernike aberrations were tested. X-axis shift of the pupil center from the corneal vertex was significantly correlated to horizontal coma for both the right (r = 0.54, P<0.0001) and left eyes (r=0.48, P<0.0001) in the cornea, but was weakly correlated to the coma in the whole eye (r=0.17, P=0.04 for OD; and r=0.17, P=0.05 for OS). Significant but weak correlations with the x-axis pupil center shift were also found for several other Zernike aberrations, including the oblique astigmatism, vertical trefoil and secondary astigmatism. Very few Zernike aberrations were significantly correlated to y-axis pupil center shift. Most Zernike aberrations were significantly correlated between the right and left eyes to produce bilateral symmetry in the cornea and the whole eye. The results suggest that offset of the pupil center from the corneal vertex plays an important role in determining horizontal coma and few other Zernike aberrations. Factors controlling bilateral symmetry of the wavefront aberrations between the two eyes could make important contributions to wavefront aberrations in the human eye. Investigar el efecto que tiene el descentramiento de la pupila con respecto al vértice corneal sobre las aberraciones del frente onda asociadas tanto a la cara anterior de la córnea como a la totalidad del ojo. En los ojos derecho e izquierdo de 103 sujetos se midieron las aberraciones del frente de onda asociadas tanto a la cara anterior de la córnea (utilizando un topógrafo corneal Humphrey), como a la totalidad del ojo (utilizando un sensor de frente de onda WASCA). Asimismo, se midió el desplazamiento del centro de la pupila respecto a la posición del vértice corneal, utilizando el mismo topógrafo corneal Humphrey anteriormente mencionado. Se investigó la posible correlación entre el valor del desplazamiento del centro de la pupila y los distintos términos de aberraciones de Zernike. El desplazamiento según el eje x del centro de la pupila respecto al vértice corneal muestra una correlación significativa con el valor del coma horizontal en la córnea tanto para los ojos derechos (r=0,54; P<0,0001) como para los izquierdos (r=0,48; P<0,0001); sin embargo, existe una correlación muy débil entre el valor de este desplazamiento y el coma de toda la óptica ocular (r=0,17; P=0,04 para OD; y r=0,17; P=0,05 para OI). También se obtuvieron correlaciones débiles aunque significativas entre el desplazamiento del centro de la pupila en el eje x y otros coeficientes de aberración de Zernike, entre los que se incluye el astigmatismo oblicuo, el astigmatismo triangular (trefoil) y el astigmatismo secundario. Muy pocos tipos de aberración (términos de Zernike) presentaron una correlación significativa con el desplazamiento del centro de la pupila en el eje y. También se encontró una correlación significativa para la mayoría de los términos de aberraciones (coeficientes) de Zernike entre el ojo derecho y el izquierdo de un mismo individuo, de tal forma que daba lugar a simetría bilateral tanto en la córnea como en la totalidad del ojo. Los resultados sugieren que el descentramiento de la pupila con respecto al vértice corneal tiene una notable influencia sobre el valor del coma horizontal y de algunas otras aberraciones de Zernike. Los factores que controlan la simetría bilateral entre ambos ojos (en lo que respecta a la aberración del frente de onda) podrían suponer una contribución importante a las aberraciones del frente de onda del ojo humano.
To investigate the relationship between corneal astigmatism and second order wavefront aberration in myopic eyes.The corneal astigmatism and the whole eye wavefront aberrations of both eyes of 246 subjects were measured using the Humphrey corneal topography and the WASCA wavefront analyzer. According to axial of the corneal astigmatism, the subjects were divided into five groups (WR(0), WR(180), AR, OA(45) and OA(135)). The corneal astigmatism was decomposed into J(45) and J(0) with a Vector-based method, and correlated with the 2nd order Zernike aberrations (C(3) and C(5)).The mean corneal astigmatisms for the five groups were -1.34 D x 6.87 degrees, -1.03 D x 23.15 degrees, -0.48 D x 89.55 degrees, -0.91 D x 156.87 degrees and -1.02 D x 176.74 degrees respectively. Most of the corneal J(45) and J(0) components were correlated significantly with the C(3) and the C(5) aberrations in the whole eye. While the correlation coefficients (R(2)) between the J(45) and the C(3) were 0.138, 0.119, 0.090, 0.526 and 0.501, the R(2) between the J(0) and the C(5) were 0.711, 0.736, 0.864, 0.866 and 0.785 for the five groups respectively.The corneal astigmatism plays an important role in determining the 2nd order wavefront aberration in the whole eye, and the combination processes between the corneal and internal astigmatism (compensation and/or addition) change with the axial of the corneal astigmatism.
To test the hypothesis that human eyes have a central tendency to be free of higher-order aberrations by analyzing wavefront aberrations for two young populations of respectively emmetropic and myopic subjects. Both right and left eyes of 75 emmetropes and 196 myopes were measured for corneal wavefront aberration using a Humphrey corneal topographer and for the whole eye wavefront aberration using a WASCA wavefront sensor without pupil dilation. 35 Zernike aberration coefficients over a 6.0 mm pupil diameter were derived, and statistics of the higher-order terms (3rd to 5th orders) were tested. When signed Zernike aberrations of the right and left eyes were averaged together for the emmetropes, three higher-order modes (j=6, 12 and 13) were significantly different from zero in both the cornea and the whole eye (P<0.0005), and three additional terms (j=14, 15 and 17) were statistically non-zero for the whole eye. As the signs of y-axis asymmetrical terms in the left eye were flipped, three more terms in either the cornea (j=8, 18 and 19) or the whole eye (j=8, 10 and 20) became statistically non-zero. For the myopes, 8 corneal terms and 5 whole-eye terms were statistically non-zero when the two eyes were averaged together. As the signs flipped, the majority of the Zernike aberration terms were statistically different from zero. Human eyes have systematical higher order aberrations in population, and factors that cause bilateral symmetry of wavefront aberrations between the right and left eyes made important contribution to the systematical aberrations. Poner a prueba la hipótesis de que el ojo humano, en promedio, tiende a estar libre de aberraciones de alto orden. Para ello se analizó la aberración de onda en dos poblaciones distintas: una compuesta por jóvenes emétropes, la otra por jóvenes miopes. Se estudiaron los ojos izquierdo y derecho de 75 emétropes y de 196 miopes. En cada ojo, sin dilatar la pupila, se midieron las aberraciones corneales utilizando un topógrafo corneal Humprey y también se obtuvo la aberración de onda de toda la óptica ocular por medio de un sensor de frente de onda WASCA. A partir de estos datos se calcularon los 35 coeficientes de aberración de Zernike que caracterizan cada patrón de aberración para un diámetro de pupila de 6,00 mm, realizándose a continuación un análisis estadístico de los términos de alto orden (del 3° al 5° orden). Cuando para los emétropes se promedian los coeficientes de aberración de Zernike para los ojos izquierdo y derecho, manteniendo su signo, hay tres modos de alto orden (j=6, 12 y 13) que resultan ser significativamente distintos de cero, tanto para la córnea como para todo el ojo. Además, otros tres términos (j=14, 15 y 17) resultaron ser también estadísticamente distintos de cero cuando se analiza todo el ojo en su conjunto. Cuando se cambia para el ojo izquierdo el signo de los coeficientes correspondientes a los términos de aberración que son asimétricos respecto al eje y, hay tres términos más (en la córnea: j=8, 18 y 19, y para todo el ojo: j=8, 10 y 20) que pasan a ser estadísticamente distintos de cero. En lo que respecta a los miopes, hay 8 términos para la córnea y 5 términos para todo el ojo que resultan ser estadísticamente distintos de cero cuando se promedian los dos ojos de todos los integrantes del grupo. Cuando se cambian los signos, de forma análoga al grupo anterior, la mayoría de los coeficientes de aberración de Zernike resultan ser estadísticamente distintos de cero. El ojo humano presenta de forma sistemática aberraciones de alto orden. Los factores que provocan la simetría bilateral de la aberración de onda entre el ojo izquierdo y derecho de cada individuo contribuyen de manera importante a la presencia de dichas aberraciones sistemáticas.
Objective To compare aberrations in eyes wearing different designs of rigid gas permeable contact lenses (RGPCLs) using a wavefront analyzer.Methods Forty-eight eyes of 24 patients were included in this two-phase crossover design study.They were randomly divided into two groups with 24 eyes of 12 patients in each group.One group wore Meikang lenses (spherical design) first and then wore Menicon Z lenses (aspherical design) one month later.The order was reversed for the other group.An Allegretto wavefront analyzer was used for analyzing aberrations.data were analyzed with crossover design ANOVA.Results There were no significant differences for the root mean square (RMS) values with different lens designs:RMSMenicon [(0.439±0.183)μm] vs RMSMeikang [(0.427±0.190)μm].However,there were some differences for single aberrations:Z20 (F=56.175,P＜0.01) was larger with Menicon lenses than with Meikang lenses.On the contrary,Z22 (F=4.263,P=0.029) and Z44 (F=3.410,P=0.037) were larger with Meikang than with Menicon.Conclusion Different designs for RGPCLs had no significant effect on the RMS values.However, the negative tear-lens caused by aspheric lenses may lead to more positive defocus.At the same time, the aspheric lens design can control astigmatism and some higher-order aberrations better than the spherical lens.
Key words:
Aberration; Contact lenses,rigid gas permeable; Contact lenses,aspheric; Cornea
Objective
To investigate the effects and safety of wearing orthokeratology lenses for 2 years.
Methods
This was a retrospective analysis. The left eyes of 58 subjects (11.1 ± 2.0 years old with a spherical equivalent of -3.68±1.36 D) were examined by measuring refraction, axial length, corneal endothelial cells, central corneal thickness, corneal horizontal curvature, corneal vertical curvature and corneal astigmatism. The same data were also collected four weeks after removal of the orthokeratology lenses that had been worn every night for two years. Patients were divided into group A (38 eyes) and B (20 eyes) based on the type of materials used for the orthokeratology lenses (Boston EqualensⅡ for group A and Boston XO for group B) and data were analyzed for the two groups. A value of-3.00 D was used to further divide the patients in a low myopia group (19 eyes) and a moderate myopia group (39 eyes). All the data were analyzed by an independent t test, rank sum test and correlation analysis.
Results
After 2 years of wearing orthokeratology lenses, four values were significantly different from baseline four weeks after removing the orthokeratology lenses: spherical equivalent (-0.35±0.64 D, t=4.132, P<0.01), axial length (0.33±0.33 mm, t=4.411, P<0.01), corneal flat curvature (-0.33 ± 0.25 D, t=10.001, P<0.01), and corneal astigmatism (-0.34 ± 0.38 D, t=6.873, P<0.01). Significant differences were found between the two groups when SE, AL and corneal astigmatism were compared. For the low myopia group, the variations in spherical equivalent (-0.70 ± 0.68 D), axial length (0.47 ± 0.36 mm) and corneal astigmatism (-0.54 ± 0.37 D) differed from the moderate myopia group, which were-0.17 ± 0.54 D, 0.26 ± 0.29 mm, and-0.25(-1.00, 0.25)D, respectively. The differences were significant (t=3.193,-2.384, Z=-2.598, P<0.05).
Conclusion
The results suggest that there is slightly greater myopia and a longer axial length after 2 years of wearing orthokeratology lenses. And the lens seems to control myopia better in moderate myopes than in low myopes.
Key words:
Orthokeratologic procedures; Myopia; Astigmatism; Treatment outcome; Safety
Objective To compare changes in wavefront aberrations on the cornea after femtosecond laser LASIK (FS-LASIK) and sub-Bowman's keratomileusis (SBK),especially for total higher order aberrations (HOA),corneal spherical aberrations (C40),corneal horizontal coma (C31),corneal vertical coma (C3-1),corneal horizontal trefoil (C33) and corneal oblique trefoil (C3-3).Methods A prospective study was designed for 2 groups based on the procedure used.The groups were composed of 68 eyes of 34 patients who had undergone FS-LASIK and 90 eyes of 45 patients who had been treated with SBK.A Pentacam was used under dark room conditions to measure corneal aberrations before surgery and 1 and 3 months after surgery.Data were analyzed using ANOVA,an independent samples t test and Pearson correlation.Results The preoperative and postoperative differences for the total corneal HOA,corneal C40,and corneal C31in the FS-LASIK group were significant (F=8.511,12.356,11.843,P＜0.01).The corresponding differences and in addition corneal C31 were also significant for the SBK group (F=46.601,38.627,10.874,11.727,P＜0.01).One month after surgery,HOAs were higher in the SBK group than in the FS group (t=-3.063,P＜0.05),and the same tendency was found 3 months after surgery (t=2.998,P＜0.05).The differences for C40 at 1 month were not significant between the two groups (t=-1.990,P＞0.05) but the differences were statistically significant at 3 months (t=-2.666,P＜0.05).One and 3 months after surgery,the trefoil aberrations (C33,C3-3) of the cornea in the two groups were higher than before surgery; only the difference for C3-3 was significant.However,the difference in the trefoil aberrations of the cornea between the two groups was not statistically significant.Conclusion Both FS-LASIK and SBK can increase corneal HOA,corneal spherical aberrations and vertical coma,but the degree of increase after FS-LASIK is smaller than that after SBK.FS-LASIK improves visual quality more than SBK.
Key words:
Wavefront aberration ; Keratomileusis,laser in situ ; Femtosecond laser ; Keratomileusis,sub-Bowman's; Microkeratome
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