Comparison of corneal irregular astigmatism by the type of corneal regular astigmatism.

We investigated the relation between corneal regular and irregular astigmatism in normal human eyes. In 951 eyes of 951 patients, corneal irregular astigmatism, such as asymmetry and higher-order irregularity components, was calculated using the Fourier harmonic analysis of corneal topography data within the central 3-mm zone of the anterior corneal surface. The eyes were classified by the type of corneal regular astigmatism into four groups; minimum (< 0.75 diopters), with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The mean age was significantly different among the four groups (P < 0.001); patients with WTR astigmatism were the youngest, followed by those with minimum, oblique, and ATR astigmatism. Significant inter-group differences were found among the four groups in asymmetry (P = 0.005) and higher-order irregularity components (P < 0.001); the largest was in eyes with oblique astigmatism, followed by ATR, WTR, and minimum astigmatism. The stepwise multiple regression analysis revealed that corneal regular astigmatism pattern significantly influenced the amount of corneal irregular astigmatism after controlling for confounding factors (P < 0.001). Corneal irregular astigmatism, such as asymmetry and higher order irregularity components, was the largest in eyes with oblique astigmatism, followed by those with ATR, WTR, and minimum astigmatism, even after adjustment for age of subjects.

[Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes].

Objective: To study the compensation mechanism of aberrations between anterior and posterior corneal surface, and to investigate the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Methods: One hundred and sixty-one subjects (300 eyes) with myopia and myopic astigmatism were recruited randomly. Corneal aberrations (anterior, posterior and total) in three different optical zones (2 mm, 4 mm, and 6 mm) centered on the corneal vertex were assessed with a corneal topographer (Sirius). We also calculated compensation factors (CFs) as a measure of the relative efficiency of the aberration compensation mechanism. Astigmatism was divided into corneal astigmatism and non-corneal astigmatism. Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups. Spearman correlation was applied to analyze the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Results: As the order of the aberrations elevated from the second to the seventh, the RMS values decreased significantly. The larger the optical zone, the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms. At the same time, as the order of the aberrations increased, the predominance of the compensation mechanism was increasingly obvious. Slight compensation of spherical aberration (Z40) was observed in the peripheral. In the center of the analyzing zones (2 mm), compensation mechanism represented in coma (Z3±1), and it disappeared in the peripheral. We detected slight compensation of the corneal astigmatism (Z2±2) in the surrounding zone, although the compensation factors were closed to zero in diverse optical zones. Superposition was found in trefoil (Z3±3) straightly. Nevertheless, a tendency towards compensation was discovered with the enlargement of the optical zones. And the secondary spherical aberration (Z60) behaved compensation continuously. However, similar compensation was discovered between the right eye and left eye in different analyzing optical zones. There were significant correlations between the flattest K values and Z2±2, Z3±3and Z40 in the anterior, posterior and total cornea. It was similar with the steepest K values. When the optical zone expanded to 6 mm, Z3±1 and Z40 significantly decreased with intraocular pressure (rcoma=-0.188, P<0.05. rspherical=-0.147, P<0.05). No correlation was found between various aberrations and central corneal thickness (P>0.05). Conclusions: Compensation dominated in the corneal center, while the percentage decreased gradually as the optical zone extended. Slight compensation in astigmatism and spherical aberration between the anterior and posterior cornea may be benificial to the scotopic visual quality. Corneal aberrations were significantly related to K values and intraocular pressure. (Chin J Ophthalmol, 2016, 52: 840-849).

Topography-Guided Transepithelial Surface Ablation in the Treatment of Moderate to High Astigmatism.

PURPOSE: To analyze the outcomes of treatment of astigmatism of 2.00 diopters (D) or greater with topography-guided transepithelial surface ablation. METHODS: Retrospective analysis of a series of 206 eyes divided into two groups: myopic astigmatism (153 eyes) and mixed astigmatism (53 eyes). All cases were treated with topography-guided transepithelial surface ablation. Efficacy, safety, and predictability were evaluated, and vector analysis of cylindrical correction was performed. RESULTS: The median preoperative spherical equivalent was -2.63 and -0.63 D for the myopic and mixed astigmatism groups, respectively, with median cylinder of -2.50 D. Postoperative uncorrected distance visual acuity was 20/20 or better in 92% and 83% of eyes in the myopic and mixed astigmatism groups, respectively; the corresponding efficacy indices were 1.00 and 0.96 and residual astigmatism of 0.50 D or less was present in 82.4% and 56.7% of eyes in the myopic and mixed astigmatism groups, respectively. The arithmetic mean magnitude of the difference vector was 0.38 (myopic) and 0.65 (mixed) D. Difference vector magnitude was positively correlated with the magnitude of target induced astigmatism in both groups. The geometric mean coefficient of adjustment index was 1.04 and 1.19, representing undercorrection of 4% and 19% in the myopic and mixed astigmatism groups, respectively. CONCLUSIONS: Topography-guided transepithelial ablation is a safe, effective, and predictable treatment for moderate to high astigmatism. [J Refract Surg. 2016;32(6):418-425.].

Induced Higher-order aberrations after Laser In Situ Keratomileusis (LASIK) Performed with Wavefront-Guided IntraLase Femtosecond Laser in moderate to high Astigmatism.

BACKGROUND: Wavefront-guided Laser-assisted in situ keratomileusis (LASIK) is a widespread and effective surgical treatment for myopia and astigmatic correction but whether it induces higher-order aberrations remains controversial. The study was designed to evaluate the changes in higher-order aberrations after wavefront-guided ablation with IntraLase femtosecond laser in moderate to high astigmatism. METHODS: Twenty-three eyes of 15 patients with moderate to high astigmatism (mean cylinder, -3.22 ± 0.59 dioptres) aged between 19 and 35 years (mean age, 25.6 ± 4.9 years) were included in this prospective study. Subjects with cylinder ≥ 1.5 and ≤2.75 D were classified as moderate astigmatism while high astigmatism was ≥3.00 D. All patients underwent a femtosecond laser-enabled (150-kHz IntraLase iFS; Abbott Medical Optics Inc) wavefront-guided ablation. Uncorrected (UDVA), corrected (CDVA) distance visual acuity in logMAR, keratometry, central corneal thickness (CCT) and higher-order aberrations (HOAs) over a 6 mm pupil, were assessed before and 6 months, postoperatively. The relationship between postoperative change in HOA and preoperative mean spherical equivalent refraction, mean astigmatism, and postoperative CCT were tested. RESULTS: At the last follow-up, the mean UDVA was increased (P < 0.0001) but CDVA remained unchanged (P = 0.48) and no eyes lost ≥2 lines of CDVA. Mean spherical equivalent refraction was reduced (P < 0.0001) and was within ±0.50 D range in 61% of eyes. The average corneal curvature was flatter by 4 D and CCT was reduced by 83 µm (P < 0.0001, for all), postoperatively. Coma aberrations remained unchanged (P = 0.07) while the change in trefoil (P = 0.047) postoperatively, was not clinically significant. The 4th order HOAs (spherical aberration and secondary astigmatism) and the HOA root mean square (RMS) increased from -0.18 ± 0.07 µm, 0.04 ± 0.03 µm and 0.47 ± 0.11 µm, preoperatively, to 0.33 ± 0.19 µm (P = 0.004), 0.21 ± 0.09 µm (P < 0.0001) and 0.77 ± 0.27 µm (P < 0.0001), six months postoperatively. The change in spherical aberration after the procedure increased with an increase in the degree of preoperative myopia. CONCLUSIONS: Wavefront-guided IntraLASIK offers a safe and effective option for vision and visual function improvement in astigmatism. Although, reduction of HOA is possible in a few eyes, spherical-like aberrations are increased in majority of the treated eyes.

Caracterización clínica y epidemiológica del queratocono / Clinical and epidemiological characterization of keratoconus

OBJETIVO: describir las características clínicas y epidemiológicas del queratocono en el Instituto Cubano de Oftalmología "Ramón Pando Ferrer". MÉTODOS: se realizó un estudio descriptivo en 72 pacientes (128 ojos) con queratocono, atendidos entre enero y diciembre de 2012, para identificar las enfermedades generales y oculares, tiempo de uso de lentes de contacto, manifestaciones clínicas, tipo de astigmatismo, poder queratométrico, espesor de la córnea central, topografía y microscopia confocal. RESULTADOS: el 50 % de los pacientes presentó disminución lenta y progresiva de la visión, con significativa ausencia de enfermedades generales. Fueron significativos (p< 0,05) el uso prolongado de lentes de contacto (67 %), la mejoría de la agudeza visual con corrección y el astigmatismo miópico compuesto (85,2 %). Predominó la disminución del espesor de la córnea central (493,2 µm). Los intervalos de poder queratométrico de la córnea central fueron igualmente representados (p= 0,211). Por topografía predominó el astigmatismo irregular (99,2 %) y el cono central (87,5 %). La microscopia confocal reflejó alteraciones en casi todas las capas de la córnea. CONCLUSIONES: la queratoconjuntivitis alérgica es la enfermedad ocular más frecuentemente asociada al queratocono. Posee un patrón topográfico de astigmatismo irregular con cono central y agudeza visual con corrección, con lentes de contacto de 0,6. La microscopia confocal constituye una herramienta valiosa en el diagnóstico del queratocono.

OBJECTIVE: to describe the clinical and epidemiological characteristics of keratoconus treated at "Ramón Pando Ferrer" Cuban Institute of Ophthalmology. METHODS: a descriptive study was conducted in 72 patients (128 eyes) with keratoconus, from January to December 2012, to identify general and ocular diseases, length of time wearing the contact lenses, clinical features, type of astigmatism, keratometric power and central corneal thickness, topography and confocal microscopy. RESULTS: in the group, 50 % had slow gradual decrease of vision, with no significant medical illnesses. Wearing contact lenses for a long time (67 %), the improvement of visual acuity with correction and myopic compound astigmatism (85,2 %) were significant (p< 0,05). Thinning of the central cornea (493,2 microns) predominated. Keratometric power intervals of the central cornea were equally represented (p= 0,211). The irregular astigmatism (99,2 %) and the central cone (87,5 %) prevailed in terms of topography. Confocal microscopy changes in almost all the corneal layers. CONCLUSIONS: Allergic keratoconjunctivitis is the most associated eye disease. It has topographic pattern of irregular astigmatism with central cone and corrected visual acuity, with 0,6 contact lenses. Confocal microscopy is a valuable tool in the diagnosis of keratoconus.

Caracterización clínica y epidemiológica del queratocono / Clinical and epidemiological characterization of keratoconus

Objetivo: describir las características clínicas y epidemiológicas del queratocono en el Instituto Cubano de Oftalmología Ramón Pando Ferrer. Métodos: se realizó un estudio descriptivo en 72 pacientes (128 ojos) con queratocono, atendidos entre enero y diciembre de 2012, para identificar las enfermedades generales y oculares, tiempo de uso de lentes de contacto, manifestaciones clínicas, tipo de astigmatismo, poder queratométrico, espesor de la córnea central, topografía y microscopia confocal.Resultados: el 50 por ciento de los pacientes presentó disminución lenta y progresiva de la visión, con significativa ausencia de enfermedades generales. Fueron significativos (p< 0,05) el uso prolongado de lentes de contacto (67 por ciento), la mejoría de la agudeza visual con corrección y el astigmatismo miópico compuesto (85,2 por ciento). Predominó la disminución del espesor de la córnea central (493,2 µm). Los intervalos de poder queratométrico de la córnea central fueron igualmente representados (p= 0,211). Por topografía predominó el astigmatismo irregular (99,2 por ciento) y el cono central (87,5 por ciento). La microscopia confocal reflejó alteraciones en casi todas las capas de la córnea. Conclusiones: la queratoconjuntivitis alérgica es la enfermedad ocular más frecuentemente asociada al queratocono. Posee un patrón topográfico de astigmatismo irregular con cono central y agudeza visual con corrección, con lentes de contacto de 0,6. La microscopia confocal constituye una herramienta valiosa en el diagnóstico del queratocono(AU)

Objective: to describe the clinical and epidemiological characteristics of keratoconus treated at Ramón Pando Ferrer Cuban Institute of Ophthalmology. Methods: a descriptive study was conducted in 72 patients (128 eyes) with keratoconus, from January to December 2012, to identify general and ocular diseases, length of time wearing the contact lenses, clinical features, type of astigmatism, keratometric power and central corneal thickness, topography and confocal microscopy. Results: in the group, 50 percent had slow gradual decrease of vision, with no significant medical illnesses. Wearing contact lenses for a long time (67 percent), the improvement of visual acuity with correction and myopic compound astigmatism (85,2 percent) were significant (p< 0,05). Thinning of the central cornea (493,2 microns) predominated. Keratometric power intervals of the central cornea were equally represented (p= 0,211). The irregular astigmatism (99,2 percent) and the central cone (87,5 percent) prevailed in terms of topography. Confocal microscopy changes in almost all the corneal layers. Conclusions: Allergic keratoconjunctivitis is the most associated eye disease. It has topographic pattern of irregular astigmatism with central cone and corrected visual acuity, with 0,6 contact lenses. Confocal microscopy is a valuable tool in the diagnosis of keratoconus(AU)

El análisis estadístico de los datos de la refracción / Statistical analysis of refractive data

OBJETIVO: describir la técnica de la descomposición en coordenadas cartesianas para el análisis estadístico de datos de la refracción. Proponer y ejemplificar una metodología. MÉTODOS: se realizó una revisión de la técnica de la descomposición cartesiana para el análisis estadístico de los datos de la refracción. Se emplearon datos de ejemplo para describir el algoritmo. En el análisis estadístico se realizaron pruebas de hipótesis con el uso del estadígrafo t de Student y T2 de Hotelling, para los datos univariados y multivariados, respectivamente. RESULTADOS: se describe y ejemplifica un método que transformó la información de un esferocilindro a un punto en un espacio tridimensional, mediante la conversión a 3 componentes independientes, ortogonales de un sistema de coordenadas cartesianas. A diferencia de otros métodos matemáticamente equivalentes, este procedimiento produjo 3 componentes con significación óptica para describir la esfera y el cilindro: equivalente esférico y 2 cilindros cruzados. Se eliminó el carácter direccional de los datos. En este sistema de coordenadas cartesianas están definidas las operaciones propias de los números reales: adición, multiplicación por escalares, entre otros que permiten con la ayuda de matrices de 3 x 1, la realización de análisis estadísticos y el cálculo de medidas de uso clínico como variación de astigmatismo, astigmatismo inducido, sorpresa refractiva o error del procedimiento refractivo, astigmatismo medio, comparaciones de medias de poblaciones, correlaciones, entre otras. CONCLUSIONES: la representación cartesiana de la refracción es una notación no polar que permite la representación gráfica y el análisis estadístico de los datos de individuos y de la población.

OBJECTIVE: to describe the decomposition technique into Cartesian coordinates for the statistical analysis of refractive data and the proposal and exemplification of a methodology. METHOD: the Cartesian decomposition technique for the statistical analysis of refractive data was reviewed. Sample data were used to exemplify the algorithm. In the statistical analysis, summary measures and hypothesis tests were applied by using Student's t statistic and Hotelling's T2 for univariate and multivariate data, respectively. RESULTS: a method that allows transforming data from one spherocylinder into a point in the three-dimensional space was described and exemplified, by means of the conversion of refraction into three independent orthogonal components of a Cartesian coordinate system. Unlike other mathematically equivalent methods, this technique brought about three components with optical significance to describe the sphere and the cylinder (the spherical equivalent and two Jackson crossed cylinders), thus eliminating the directional characteristics of data. In this system of Cartesian coordinates, the operations in real numbers are defined (addition, multiplication by scalars, among others), allowing mathematical and statistical analysis based on 3 x 1 matrices. The most common clinical measures that can be estimated with such a method are astigmatism variation, induced astigmatism, refractive surprise or error of the refractive procedure, mean astigmatism, comparison of population means, correlations, etc. CONCLUSIONS: the Cartesian representation of refraction is a non-polar notation that facilitates the graphical representation and statistical analysis of individual and population data.

El análisis estadístico de los datos de la refracción / Statistical analysis of refractive data

Objetivo: describir la técnica de la descomposición en coordenadas cartesianas para el análisis estadístico de datos de la refracción. Proponer y ejemplificar una metodología. Métodos: se realizó una revisión de la técnica de la descomposición cartesiana para el análisis estadístico de los datos de la refracción. Se emplearon datos de ejemplo para describir el algoritmo. En el análisis estadístico se realizaron pruebas de hipótesis con el uso del estadígrafo t de Student y T² de Hotelling, para los datos univariados y multivariados, respectivamente. Resultados: se describe y ejemplifica un método que transformó la información de un esferocilindro a un punto en un espacio tridimensional, mediante la conversión a 3 componentes independientes, ortogonales de un sistema de coordenadas cartesianas. A diferencia de otros métodos matemáticamente equivalentes, este procedimiento produjo 3 componentes con significación óptica para describir la esfera y el cilindro: equivalente esférico y 2 cilindros cruzados. Se eliminó el carácter direccional de los datos. En este sistema de coordenadas cartesianas están definidas las operaciones propias de los números reales: adición, multiplicación por escalares, entre otros que permiten con la ayuda de matrices de 3 x 1, la realización de análisis estadísticos y el cálculo de medidas de uso clínico como variación de astigmatismo, astigmatismo inducido, sorpresa refractiva o error del procedimiento refractivo, astigmatismo medio, comparaciones de medias de poblaciones, correlaciones, entre otras. Conclusiones: la representación cartesiana de la refracción es una notación no polar que permite la representación gráfica y el análisis estadístico de los datos de individuos y de la población(AU)

Objective: to describe the decomposition technique into Cartesian coordinates for the statistical analysis of refractive data and the proposal and exemplification of a methodology. Method: the Cartesian decomposition technique for the statistical analysis of refractive data was reviewed. Sample data were used to exemplify the algorithm. In the statistical analysis, summary measures and hypothesis tests were applied by using Student's t statistic and Hotelling's T² for univariate and multivariate data, respectively. Results: a method that allows transforming data from one spherocylinder into a point in the three-dimensional space was described and exemplified, by means of the conversion of refraction into three independent orthogonal components of a Cartesian coordinate system. Unlike other mathematically equivalent methods, this technique brought about three components with optical significance to describe the sphere and the cylinder (the spherical equivalent and two Jackson crossed cylinders), thus eliminating the directional characteristics of data. In this system of Cartesian coordinates, the operations in real numbers are defined (addition, multiplication by scalars, among others), allowing mathematical and statistical analysis based on 3 x 1 matrices. The most common clinical measures that can be estimated with such a method are astigmatism variation, induced astigmatism, refractive surprise or error of the refractive procedure, mean astigmatism, comparison of population means, correlations, etc. Conclusions: the Cartesian representation of refraction is a non-polar notation that facilitates the graphical representation and statistical analysis of individual and population data(AU)

Prevalence of high astigmatism in children aged 3 to 6 years in Guangxi, China.

PURPOSE: To investigate the prevalence and type of high astigmatism among children aged 3 to 6 years in Guangxi, a relatively undeveloped province in western China, and to examine the correlation between astigmatism and visual acuity. METHODS: Children aged 3 to 6 years in Nanning, the capital of Guangxi Province, participated in a population-based survey using a cluster random sampling technique. Eye examinations included autorefraction, visual acuity measurements, and assessments of the external eye, anterior segment, media, and fundus. Data for the right eyes were analyzed. RESULTS: Among the 2304 children examined, the overall prevalence of high astigmatism (≥1.25 diopters by noncycloplegic SureSight autorefraction) was 12.7% (95% confidence interval, 11.3 to 14.0%). The age-specific prevalences of high astigmatism in 3-, 4-, 5-, and 6-year-old children were 13.8, 13.2, 12.9, and 8.1%, respectively. The prevalence of high astigmatism did not vary with age or gender (p > 0.05). The majority of cases of high astigmatism were with-the-rule astigmatism (82.9%), followed by against-the-rule (12.6%) and oblique (4.5%) astigmatism. A linear correlation was found between astigmatism magnitude and visual acuity (logMAR acuity = 0.068 + 0.055 × astigmatism) in all participants. Multiple linear regression analysis further showed that the correlation of astigmatism with visual acuity was magnitude dependent (ß = 0.240). When with-the-rule astigmatism was used as a reference group, against-the-rule astigmatism (ß = 0.137) and oblique astigmatism (ß = 0.154) were closely correlated with visual acuity. CONCLUSIONS: High astigmatism was moderately prevalent among children aged 3 to 6 years in Guangxi Province. With-the-rule astigmatism was the dominant form of astigmatism. Magnitude- and orientation-dependent correlations of astigmatism with visual acuity were confirmed.

How to convert the obliquely crossed to non-crossed astigmatism? A simple method using vector analysis.

The authors discussed about the problem of special form in astigmatism classification. This special type of astigmatism is the form of obliquely crossed astigmatism. In which the meridians, major and minor, are not right angles. In this astigmatism is not possible to prescribing for cylindrical (toric) spectacle lens. Authors describe the Thompson formula for oblique crossed cylinder and observe that this formula is to complicate for calculation new cylinder power. In this reason, the authors create the new formula and simple procedure for this calculation. This simple formula based on vector analysis and read: DM3 = DM2 x cos2 beta.

[Relationships between refractive parameters: sphere, cylinder and axis]. / Relations entre les paramètres de la réfraction : sphère, cylindre et axe.

PURPOSE: To analyze the relationships between refractive parameters as well as the relationship between fellow eyes in a normal population. METHODS: Both subjective refraction and auto-refractometry data of 500 patients were prospectively recorded. Refraction data were analyzed on three rectangular coordinates in a dioptric space. WTR/ATR ratio of axis was quantified by the Cos2axis function. Enantiomorphism (mirror-image symmetry) between fellow eye axes was quantified by the absolute value of the difference between 180° and the sum of both axes. RESULTS: Mean refraction and mean cylinder were -1.74D (+0.28D × 91.5°) and 0.81 ± 0.89D respectively. The spherical component had no significant influence on refractive astigmatism (r(s)≤ 0.07, P ≥ 0.07) except for high spherical ametropia. Eyes with spherical equivalent greater than 4D (in absolute value) demonstrated higher cylinder (1.15D vs 0.84D, P<0.001). Cylinder influenced the WTR/ATR ratio (r(s)=-0.25, P<0.001) and the enantiomorphism (r(s)=0.36, P<0.001). Age also influenced the WTR/ATR ratio (r(s)=0.27, P<0.001) and the enantiomorphism (r(s)=0.14, P<0.001). Axes were more likely WTR and enantiomorphic when the cylinder was high and the subject young. Oblique axes were less enantiomorphic (35.5° vs 20.6°, P<0.001) and were associated with lower cylinder (0.56D vs 0.98D, P<0.001). Correlation between fellow eyes was significant for cylinder (r(s)=0.66, P<0.001) and for spherical equivalent (r(s)=0.96, P<0.001). Gender had no significant influence on refraction (P>0.12) except for spherical equivalent (relative hyperopia of +0.17D, P=0.04 in females). CONCLUSION: The spherical component of the refraction appears to be independent of the refractive astigmatism except for high spherical ametropia. Cylinder influences somewhat the WTR/ATR ratio of axis and the enantiomorphism. Relationships between refractive parameters are weak in comparison to the fellow eye relationships.

[Correction of irregular astigmatism with intracorneal ring segments]. / Correction des astigmatismes irréguliers par anneaux intra cornéens.

Management of irregular astigmatism with intracorneal rings segments is an intrastromal additive technique developed initially for myopia but eventually popularized for keratoconus and post LASIK ectasia. ICR's are indicated for rigid contact lens intolerance, as an alternative to corneal transplantation. The mechanism of action is complex and involves biomechanical changes leading to a centering and a flattening of the ectasia. The surgical procedure has become much easier thanks to the use of femtosecond lasers. Individualized implantation strategies, based on each patient's topographic and tomographic pattern, are constantly evolving. Patients' refraction and vision are usually improved in more than 70% of cases. Complications remain very rare. Intracorneal ring segments can often be combined with other types of keratoplasty, usually in a sequential fashion, so as to optimize functional results.

[Astigmatism correction with Excimer laser]. / Correction de l'astigmatisme au laser Excimer.

Excimer laser is the best and the more used technique for Astigmatism correction. Lasik is generally preferred to PRK and must be the choice for hyperopic and mix astigmatisms. Myopic astigmatisms are the easier cases to treat: the length of the photoablation is placed on the flat meridian. Hyperopic and mix astigmatisms are more difficult to correct because they are more technically demanding and because the optical zone of the photoablation must be large. Flying spots lasers are the best for these cases. The most important point is to trace the photoablation very precisely on the astigmatism axis. The use of eye trackers with iris recognition or a preoperative marking of the reference axis avoid cyclotorsion or a wrong position of the head. Irregular astigmatism are better corrected with topoguided or wavefront guided photoablations.

[Astigmatism correction by femtosecond laser]. / Intérêt du laser femtoseconde pour le traitement de l'astigmatisme.

Through the creation of astigmatic keratotomies, femtosecond laser can correct congenital or post-surgical astigmatism. We have been using an optimized treatment nomogram, which offers superior and more predictable results than manual incisional techniques. Femtosecond arcuate incisions allow a reduction of over 50% of the preoperative astigmatism. Nonetheless, the efficacy can likely be improved further by refining these nomograms specific to the femtosecond laser.

Postoperative astigmatic outcomes based on the haptic axis of intraocular lenses inserted in cataract surgery.

PURPOSE: This study was conducted to compare post-operative astigmatic outcomes of two groups, with-the-rule (WTR) and against-the-rule (ATR) astigmatism patients, according to the haptic axis of intraocular lenses (IOLs) inserted in cataract surgery. METHODS: Seventy-two eyes with WTR astigmatism and 79 eyes with ATR astigmatism had cataract surgery through a clear corneal temporal incision. These two groups of eyes were then each divided into 2 groups based on whether the haptic axis of the inserted IOL was at 180° or 90°. For ATR patients, the outcomes were analyzed according to the three types of IOLs. RESULTS: There was no difference in corneal astigmatism, but WTR patients with a 180° haptic axis of the inserted IOL and ATR patients with a 90° hepatic axis of the inserted IOL had a significant decrease in postoperative refractive astigmatism (p < 0.05). The changes in ATR astigmatism according to the IOL type were more effective in single-piece acrylic IOLs than in the three-piece polymethylmethacrylate haptic IOL group. CONCLUSIONS: Insertion of the IOL at the 180° haptic axis in WTR patients and at 90° in ATR patients during cataract surgery may have an effect in reducing pre-existing astigmatism. This observed effect was not consistent among the different types of IOLs.

Prevalence of astigmatism in 6- to 72-month-old African American and Hispanic children: the Multi-ethnic Pediatric Eye Disease Study.

PURPOSE: To determine the age-, gender-, and ethnicity-specific prevalence of astigmatism in African American and Hispanic children aged 6 to 72 months. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: The Multi-Ethnic Pediatric Eye Disease Study is a population-based evaluation of the prevalence of vision disorders in children ages 6 to 72 months in Los Angeles County, California. Seventy-seven percent of eligible children completed a comprehensive eye examination. This report provides the results from 2994 African American and 3030 Hispanic children. METHODS: Eligible children in 44 census tracts were identified during an in-home interview and scheduled for a comprehensive eye examination and in-clinic interview. Cycloplegic autorefraction was used to determine refractive error. MAIN OUTCOME MEASURES: The proportion of children with astigmatism defined as cylindrical refractive error ≥ 1.50 diopters (D) in the worse eye. The astigmatism type was defined as with-the-rule (WTR) (+ cylinder axis 90 ± 15 degrees) and against-the-rule (ATR) (+ cylinder axis 180 ± 15 degrees); all other orientations were considered oblique (OBL). The prevalence of astigmatism and its types were also determined for worse eye cylindrical refractive error ≥ 3.00 D. RESULTS: Prevalence of astigmatism ≥ 1.50 D was higher in Hispanic children compared with African American children (16.8% vs. 12.7%, respectively; P<0.0001). Hispanic children also showed a higher prevalence of astigmatism ≥ 3.00 D than African American children (2.9% vs. 1.0% respectively; P<0.0001). The prevalence of astigmatism ≥ 1.50 D showed a significant decreasing trend with age (P<0.0001). The prevalence of WTR, ATR, and OBL astigmatism ≥ 1.50 D was 13.9%, 0.6%, and 2.2%, respectively, in Hispanic children, and 7.8%, 2.2%, and 2.7%, respectively, in African American children. CONCLUSIONS: We observed ethnicity-related differences in astigmatism prevalence in preschool children. The age-related decrease in astigmatism prevalence in preschool children likely reflects emmetropization.

Postoperative Astigmatic Outcomes Based on the Haptic Axis of Intraocular Lenses Inserted in Cataract Surgery

PURPOSE: This study was conducted to compare post-operative astigmatic outcomes of two groups, with-the-rule (WTR) and against-the-rule (ATR) astigmatism patients, according to the haptic axis of intraocular lenses (IOLs) inserted in cataract surgery. METHODS: Seventy-two eyes with WTR astigmatism and 79 eyes with ATR astigmatism had cataract surgery through a clear corneal temporal incision. These two groups of eyes were then each divided into 2 groups based on whether the haptic axis of the inserted IOL was at 180degrees or 90degrees. For ATR patients, the outcomes were analyzed according to the three types of IOLs. RESULTS: There was no difference in corneal astigmatism, but WTR patients with a 180degrees haptic axis of the inserted IOL and ATR patients with a 90degrees hepatic axis of the inserted IOL had a significant decrease in postoperative refractive astigmatism (p < 0.05). The changes in ATR astigmatism according to the IOL type were more effective in single-piece acrylic IOLs than in the three-piece polymethylmethacrylate haptic IOL group. CONCLUSIONS: Insertion of the IOL at the 180degrees haptic axis in WTR patients and at 90degrees in ATR patients during cataract surgery may have an effect in reducing pre-existing astigmatism. This observed effect was not consistent among the different types of IOLs.

[Methods of calculating surgically induced astigmatism]. / Metody obliczania niezbornosci indukowanej chirurgicznie.

Evaluation of surgically induced astigmatism is important, as it allows to thoroughly assess the influence of surgical incision on corneal refraction. This influence can be established by calculating surgically induced astigmatism according to an appropriate mathematical method. The purpose of the study was to describe various mathematical methods used in the current literature to calculate surgically induced astigmatism. When comparing results of calculation of surgically induced astigmatism among different studies, it is necessary to take into account values obtained with the use of the same method of calculation, as various methods evaluate astigmatism differently.

[Agreement measurement of ocular wavefront aberrations with three different aberrometers].

OBJECTIVE: To assess the repeatability and difference of ocular wavefront aberrations measured with ray-tracing, dynamic skiascopy, and Hartmann-Shack aberrometers. METHODS: It was an agreement study. Ocular aberrations data obtained by using iTrace (Tracey Technologies), OPD SCAN (Nidek) and WASCA (Zeiss) wavefront aberrometers were analyzed. Eighty six eyes of 45 patients were measured three times. The difference between the measurement and the mean of three consecutive measurements were analyzed to verify the reproducibility. The difference in sphere, cylinder, spherical equivalent (SEQ) and high order aberration (HOA) errors obtained from different aberrometers were evaluated. RESULTS: Repeatability errors of these three wavefront analyzer were found to be low. Comparisons on the same eye showed that there was a significant difference (P < 0.01) in sphere and cylinder between ray-tracing aberrometer and the others in high SEQ group (>or= -6.00 diopter). For HOA, all aberrometers obtained similar results in low SEQ group (< -6.00 diopter). In the high SEQ group, the ray-tracing aberrometer showed statistically higher data in HOA and coma (P < 0.01), and there was no significant difference between the skiascopy and the Hartmann-Shack aberrometer. The iTrace-OPD and iTrace-WASCA HOA difference correlated with spherical equivalent in the high SEQ group (r = -0.418, -0.399, P < 0.01). CONCLUSION: All devices produced similar results of reproducibility, but showed varying results in the ocular total wavefront reading.