Aberraciones corneales de bajo orden en pacientes con ametropías miópicas / Low-order Corneal Aberrations in Patients with Myopic Ametropias

Objetivo: Caracterizar las aberraciones corneales de bajo orden en pacientes con ametropías miópicas. Métodos: Se realizó un estudio descriptivo, observacional y transversal, con una muestra de 104 ojos de 104 pacientes adultos con ametropías miópicas y un grupo control de 104 ojos de 104 voluntarios emétropes, que asistieron a consulta de Cirugía Refractiva del Instituto Cubano de Oftalmología. Se definieron las variables demográficas, clínicas y para la cuantificación de las aberraciones corneales la elevación-depresión y el valor cuadrático medio, aportadas mediante el mapa aberrométrico del Pentacam HR. Resultados: Hubo un predominio del sexo femenino, el rango de edad estuvo comprendido entre 18 y 39 años en ambos grupos. La mediana del equivalente esférico de los pacientes de ametropías miópicas fue -3,25 dioptrías, con agudeza visual sin corrección de 0,10, esfera de -2,63 D y cilindro de -1,00 D, 91 ojos (87,50 por ciento) tenían astigmatismo miópico compuesto. Los valores de elevación-depresión y el valor cuadrático medio de bajo orden fueron mayores en los pacientes con ametropías miópicas que los emétropes (p< 0,001). El astigmatismo vertical, desenfoque y el astigmatismo horizontal no presentaron diferencia estadísticamente significativa entre ambos grupos. Conclusiones: La miopía con o sin astigmatismo se debe estudiar y tratar como una aberración de bajo orden. Los valores de elevación-depresión y cuadrático medio son superiores en los ojos con ametropías miópicas respecto a los emétropes(AU)

Objective: To characterize low-order corneal aberrations in patients with myopic ametropia. Methods: A descriptive, observational and cross-sectional study was carried out with a sample of 104 eyes of 104 adult patients with myopic ametropia and a control group of 104 eyes of 104 emmetropic volunteers, who attended the Refractive Surgery Clinic of the Cuban Institute of Ophthalmology. Demographic and clinical variables were defined, and for the quantification of corneal aberrations, elevation-depression and average square value, provided by means of the Pentacam HR aberrometric map. Results: There was a predominance of female sex, the age range was between 18 and 39 years in both groups. The median spherical equivalent of myopic ametropia patients was -3.25 diopters, with uncorrected visual acuity of 0.10, sphere of -2.63 D and cylinder of -1.00 D, 91 eyes (87.50 percent) had compound myopic astigmatism. Elevation-depression values and low-order root average square value were higher in patients with myopic ametropes than emmetropes (p< 0.001). Vertical astigmatism, defocus and horizontal astigmatism showed no statistically significant difference between the two groups. Conclusions: Myopia with or without astigmatism should be studied and treated as a low-order aberration. The elevation-depression and average square values are higher in eyes with myopic ametropia than in emmetropic eyes(AU)

Effects of different contact lens correction on Zernike aberrations of human eye / 中华实验眼科杂志

Background Even though the change in wavefront aberrations with correction modality is well documented in the literature,little is known about the underlying mechanism.Complete understanding of the causes responsible for the wavefront change in the combined lens-eye system is important since it provides basic knowledge for further improving the technique to correct refractive error by correcting lenses.Objective The aim of this study was to investigate the influence of refractive correction lens on optical property of the eye by analyzing Zernike aberrations in myopic eyes with contact lens correction.Methods This study was approved by the Ethic Committee of Wenzhou Medical College.Written informed consent was obtained from each subject before entering this study.Zernike aberrations of 52 myopic eyes of 26 subjects with the spherical equivalent-1.75 to-8.50 D were measured using a Hartmann-Shock wavefront sensor.The human eye aberrations were examined at the uncorrected condition,rigid-gas-permeable contact lens (RGP-CL) corrected condition and soft contact lens (Soft-CL) corrected condition.The differences of wavefront aberrations and Zernike coefficients were compared by repeated measurement of single factor variance analysis,and correlation of the aberration changes between uncorrected condition and RGP-CL corrected condition or Sofi-CL corrected condition,between the right eyes and left eyes in different conditions were analyzed by Pearson linear correlation.Results Mean total root-mean-square (tRMS) was (0.71 ± 0.30)μm,(0.54±0.19)μm and (0.74±0.32)μm in the uncorrected condition,RGP-CL corrected condition and Soft-CL corrected condition,with a significant difference (F =8.758,P＜0.001),and tRMS was significant declined under the RGP-CL corrected condition compared with uncorrected condition (t =2.746,P =0.008),and tRMS in RGP-CL corrected condition was significantly lower than that in Soft-CL corrected condition (t =3.428,P =0.001).The high RMS (hRMS) was (0.34±0.12) μm,(0.28 ±0.12) μm,(0.40±0.14) μm in the uncorrected condition,RGP-CL corrected condition and Soft-CL corrected condition,with a significant difference among them (F =10.681,P＜0.001).An insignificant decrease of hRMS was seen in the RGP-CL corrected condition compared with uncorrected condition (t =1.987,P=0.053),but hRMS value was significant higher in the Soft-CL corrected condition than that in the uncorrected condition (t=2.101,P=0.041) and RGP-CL corrected condition (t=4.266,P＜0.001).Compared with uncorrected condition,the axis astigmatism (C5) and spherical aberration (C12) in the RGP-CL corrected condition and spherical aberration (C12) in the Soft-CL corrected condition were significantly reduced (P＜0.05),and the absolute values of trefoil (C6),vertical coma (C7) and tetrafoil (C10) in the RGP-CL corrected condition were lower than those of the uncorrected condition,but vertical coma (C7) absolute value in the Soft-CL corrected condition was increased (P＜0.05).A significantly positive correlation was seen in the spherical aberration (C12) between the RGP-CL corrected condition and uncorrected condition (r =0.763,P＜0.001),and less significant correlation was in the secondary astigmatism (C11) between the Soft-CL corrected condition and uncorrected condition(r=0.469,P＜0.001).Conclusions Different contact lens corrected conditions exert their effects on ocular wavefront structure due to its unique interaction with the eye.RGP-CL wearing has strong modification on wavefront aberrations probably due to its molding effect on corneal surface,which reduces the bilateral symmetry.High order wavefront aberration can be modified by Soft-CL wearing.

Variaciones en el grado de aberraciones ópticas corneales de alto orden en pacientes diagnosticados con ectasias corneales implantados con anillos intraestromales / Variations on the degree of high order corneal optical aberrations in patients diagnosed with corneal ectasia with intrastromal rings implanted

Objetivo: identificar si existen variaciones significativas en el grado de aberraciones corneales de alto orden después del implante de los anillos intraestromales, en pacientes diagnosticados con ectasias corneales. Materiales y métodos: se realizó un estudio analítico y longitudinal de intervención en pacientes mayores de 18 años. Se valoró el estado refractivo; la agudeza visual medida con log mar; la queratometría topográfica; las aberraciones ópticas corneales coma, trifoid, esférica y el Root Mean Square High Order (rms Ho), mediante el topógrafo Keratron Scout, y la calidad visual por medio de la prueba de letras de Mars para la sensibilidad al contraste. Todo lo anterior en tres momentos antes de la intervención, primer y tercer mes postoperatorio. Resultados: en 39 ojos de 26 pacientes evaluados antes, al mes y al tercer mes después del implante se presentaron diferencias significativamente clínicas, aunque no estadísticas: a) se incrementó la agudeza visual sin corrección, b) hubo disminución del valor esférico y cilíndrico, c) aplanamiento en la K1 y K2, d) diferencias en cuanto al grado de aberraciones ópticas de alto orden corneales, después del procedimiento, e) una mejor calidad visual para estos pacientes y f) uso de lentes oftálmicos con mayor tolerancia. Conclusión: las aberraciones ópticas de la superficie anterior de la córnea no presentan una diferencia estadísticamente significativa antes y después del implante de segmentos intraestromales, aunque sí existen cambios a nivel clínico y en magnitud.

Objective: To identify whether there are significant variations in the degree of higher-order corneal aberrations after implantation of intrastromal rings in patients diagnosed with corneal ectasia. Materials and methods: An analytical and longitudinal study of intervention in patients over 18 years was carried out. The refractive state was evaluated, as well as the visual acuity measured by logmar; the topographic keratometry, the corneal optical aberrations coma, the trifoid, the spherical and the Root Mean Square High Order (rms Ho), by the Keratron Scout topograph, and the visual quality through Mars letters test for contrast sensitivity. All of this was done in three times before surgery, first and third post-op months. Results: In 39 eyes of 26 patients evaluated before, after one and three months after the implantation, clinical differences were significant, though not statistical: a) visual acuity was increased with no correction, b) there was a decrease in spherical and cylindrical values, c) flatten ng in K1 and K2, d) differences in the degree of high order optical aberrations of cornea after the procedure, e) a better visual quality for these patients and f) use of ophthalmic lenses with a greater tolerance. Conclusion: The optical aberrations of the anterior surface of the cornea do not have a statistically significant difference before or after the implantation of intrastromal segments, although there are changes at a clinical level and in magnitude.

El frente de onda y su representación con polinomios de Zernike / The wavefront and its representation with Zernike Polynomials

Se presenta una revisión del concepto frente de onda a partir del principio de Fermat, primero de forma general y luego para la pupila de salida de un sistema óptico formador de imagen. En la pupila de salida se definen el frente de onda de referencia y el frente de onda real, y la diferencia entre estos dos define la aberración de frente de onda. Luego, se representan matemáticamente el frente de onda y la aberración de frente de onda. En principio se emplea el sistema de coordenadas cartesiano para describir el polinomio de aberración en su forma general y discutir el significado de los primeros términos (aberraciones primarias), después se pasa al sistema de coordenadas polar. En dicha representación los términos de aberración tienen una forma matemática más simple y resulta ideal para describir el frente de onda sobre una pupila circular. Finalmente, adicionando algunos términos de compensación a las expresiones matemáticas en la representación polar con el fin de minimizar el efecto de las aberraciones en la imagen final, se llega a los polinomios de Zernike. Se explica el uso de los coeficientes de Zernike y se presenta un ejemplo del frente de onda obtenido con un aberrómetro experimental tipo Hartmann-Shack cuando se emplea un modelo físico del ojo humano.

This paper is a review of the wavefront concept based on Fermat’s principle, first in general terms and then for the exit pupil of an optical system that creates images. The reference wavefront and the real wavefrontare defined in the exit pupil and the difference between them determines the wavefront aberrations. The wavefront and the wavefront aberration are then represented mathematically.The Cartesian coordinate system is used as at the beginning to describe the aberration polynomial in general terms and discuss the meaning of the first terms (primary aberrations), and then the polar coordinate system is used.The aberration terms in this representation have a simple mathematical form and it is ideal to describe the wavefront of a circular pupil. Finally, after adding a few compensation terms to the mathematical expressions in the polar representation in order to minimize the effect of the aberrations in the final image, we reach the Zernike polynomials. The use of Zernike coefficients is explained, and an example is presented of the wavefront obtained with an experimental Hartmann-Shack aberrometer when using a physical model of the human eye.

Changes of the Corneal Aberration Following Cataract Surgery

PURPOSE: To assess the changes of corneal aberration in the front and rear surface measured by Pentacam(R) following cataract surgery. METHODS: Thirty-two eyes of 30 consecutive patients that underwent phacoemulsification and IOL insertion via 3 mm superotemporal corneoscleral incision were examined. The corneal aberration was measured with Pentacam(R) (Oculus, Wetzlar, Germany) at 1 week and 1 month after the surgery, and these postoperative values were compared with values taken before the operation. The data were analyzed from 6 mm pupil size, using Zernike's polynomial expansion. RESULTS: In anterior corneal aberration, Z (4, -2); secondary astigmatism at 1 week postoperatively and Z (3, -3); the trefoil at 1 month postoperatively changed significantly (p<0.05). By contrast, in posterior corneal aberration, Z (2, -2), Z (2, 0), Z (2, 2), Z (3, 1), Z (4, -4), and Z (4, -2) changed significantly (p<0.05). However, there were no significant changes at 1 month postoperatively (Paired t-test). CONCLUSIONS: There were significant changes in posterior corneal aberration compared to anterior corneal aberration at 1 week postoperatively. However, the corneal aberration recovered to the preoperative level at one month after the operation. Presumably, these results might be due to the corneal edema of the incision site, caused by measuring the corneal thickness in the early phase of surgery.

Clinical Outcomes of Wavefront-guided LASIK using the Fourier Algorithm: 6-Month Follow-up

PURPOSE: We evaluate the clinical outcomes after wavefront-guided LASIK using the Fourier algorithm. METHODS: The uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest refraction measured with auto refractometer, spherical aberration, coma, trefoil, total high order aberrations and contrast sensitivity of daytime and nighttime in 23 eyes of 13 patients who had undergone wavefront-guided LASIK using the Fourier algorithm preoperatively and at 1 day, 1 week, 1 month, 2 months and 6 months postoperatively. RESULTS In the wavefront-guided LASIK using the Fourier algorithm, the preoperative UCVA was 0.13+/-0.10 and increased to 1.02+/-0.29 (p=0.000) at 6 months postoperative, the postoperative spherical equivalent was -6.48+/-1.68D and 1.02+/-0.29 (p=0.000) at 6 months postopertive. The total high order aberration was 0.324+/-0.107 preoperative and 0.338+/-0.167 (p=0.810) at 6 months postoperative in wavefront-guided LASIK using the Fourier algorithm. Preoperative daytime contrast sensitivity increased preoperative from 0.75+/-0.24 to 1.11+/-0.35 (p=0.026) at 12 cpd, and that at 6-month preoperative increased from 1.05+/-0.26 to 1.41+/-0.41 (p=0.003) at 7.5 cpd and from 1.45+/-0.34 to 1.69+/-0.42 (p=0.028) at 4.8 cpd. CONCLUSIONS: The clinical outcomes of wavefront-guided LASIK using the Fourier algorithm after 6 months were stable visual acuity, no increase in high order aberration and no increase in contrast sensitivity.

Clinical Outcomes of Wavefront-guided LASIK using the Fourier Algorithm: 6-Month Follow-up

PURPOSE: We evaluate the clinical outcomes after wavefront-guided LASIK using the Fourier algorithm. METHODS: The uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest refraction measured with auto refractometer, spherical aberration, coma, trefoil, total high order aberrations and contrast sensitivity of daytime and nighttime in 23 eyes of 13 patients who had undergone wavefront-guided LASIK using the Fourier algorithm preoperatively and at 1 day, 1 week, 1 month, 2 months and 6 months postoperatively. RESULTS In the wavefront-guided LASIK using the Fourier algorithm, the preoperative UCVA was 0.13+/-0.10 and increased to 1.02+/-0.29 (p=0.000) at 6 months postoperative, the postoperative spherical equivalent was -6.48+/-1.68D and 1.02+/-0.29 (p=0.000) at 6 months postopertive. The total high order aberration was 0.324+/-0.107 preoperative and 0.338+/-0.167 (p=0.810) at 6 months postoperative in wavefront-guided LASIK using the Fourier algorithm. Preoperative daytime contrast sensitivity increased preoperative from 0.75+/-0.24 to 1.11+/-0.35 (p=0.026) at 12 cpd, and that at 6-month preoperative increased from 1.05+/-0.26 to 1.41+/-0.41 (p=0.003) at 7.5 cpd and from 1.45+/-0.34 to 1.69+/-0.42 (p=0.028) at 4.8 cpd. CONCLUSIONS: The clinical outcomes of wavefront-guided LASIK using the Fourier algorithm after 6 months were stable visual acuity, no increase in high order aberration and no increase in contrast sensitivity.

Aberration Change in Pseudophakia with Three Types of Acryl Intraocular Lens

PURPOSE: To compare the aberration change in the pseudophakia with three types of acrylic intraocular lenses (IOL) as well as with normal phakic eyes METHODS: This single-center prospective study comprised of 51 cataract patients who underwent cataract surgery and 12 phakic eyes. Fourteen eyes received an Acrysof(R) MA60BM, 18 eyes, a Sensar(R) AR40, and 19 eyes, an Corneal(R) ACR6D. One month after cataract surgery, the aberration of the eyes was measured using a Hartmann-Shack type aberrometer. The same test was performed for 12 normal phakic eyes. The individual Zernike polynomials, and the root mean square (RMS) values of the third and the fourth order aberration among the groups were compared. The total RMS value of each group was also compared. RESULTS: The RMS value of the third and the fourth order aberration was similar in each group. In addition, there was no significant difference in the total RMS value among the groups. An individual Zernike coefficient (Z3(3); triangular astigmatism with a base on the y axis) showed a significant difference in all the IOL implanted groups compared to the normal phakic eyes. CONCLUSIONS: An ocular higher-order aberration after these 3 acrylic IOL implantations in cataract surgery is similar to that of the normal phakic eyes, but can differ in the local aberration.

The Change of Ocular Aberration after LASIK Surgery

PURPOSE: To evaluate the change of ocular aberration after LASIK using Zernike's polynomial expansions. METHODS: Sixty eyes of thirty consecutive patients that underwent LASIK were examined prospectively. The ocular aberration was measured with Hartman-Shack aberrometer (WASCA Wavefront Analyzer, USA) at postoperative 30, 90, and 180 days. The postoperative values were compared with that of preoperation. RESULTS: The average age is 27.6 years old. The range of preoperative refractory error were from -3.00 Diopter (D) to -11.00 D. The increase of spherical and triangular coma aberrations (4.7- fold and 3.5- fold, respectively), with respect to preoperative values. There were statistically significant differences between preoperative and postoperative high order RMS at the postoperative 180 days (p<0.05). CONCLUSIONS: The postoperative increases of RMS in higher order aberration, coma aberration, triangular aberration was observed.