Corneal Astigmatism Measurements Research Articles

Univariate and bivariate polar value analysis of corneal astigmatism measurements obtained with 6 instruments

To compare the corneal astigmatism measurements from 6 instruments in preoperative assessment for toric intraocular lens (IOL) implantation. Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea. Prospective comparative observational study. This study included patients with cataract and more than 1.00 diopter (D) of corneal astigmatism. For preoperative evaluation of toric IOL implantation, the net astigmatism was evaluated using manual keratometry, autokeratometry, partial coherence interferometry (PCI) (IOLMaster), corneal topography/ray-tracing aberrometry (iTrace), scanning-slit topography (Orbscan), and Scheimpflug imaging (Pentacam). All net astigmatisms were converted to polar values. Using the astigmatism measurements from manual keratometry as a standard, Bland-Altman analysis, linear mixed-model, and bivariate graphic analysis were performed. The study group comprised 257 eyes of 141 patients. Bland-Altman plots showed good agreement between manual keratometry and each instrument for polar values. There was no significant between-instrument difference in KP(90) and KP(135) in the linear mixed model analysis or in bivariate polar values in bivariate confidence ellipses. The corneal astigmatism measurements from autokeratometry, PCI, corneal topography/ray-tracing aberrometry, scanning-slit topography, and Scheimpflug imaging were comparable to those from manual keratometry and can be used interchangeably with manual keratometry to measure corneal astigmatism.

Comparison of corneal power, corneal astigmatism, and axis location in normal eyes obtained from an autokeratometer and a corneal topographer

To assess the repeatability and agreement of corneal power, corneal astigmatism, axis location, and astigmatic vector component measurements using an autokeratometer and a corneal topographer in healthy subjects. Department of Ophthalmology, Kitasato University, Kanagawa, Japan. Evaluation of diagnostic test or technology. Keratometric readings were obtained with an ARK-700A autokeratometer and an Atlas corneal topographer. Measurement repeatability and agreement in corneal power (flattest and steepest meridians), mean corneal power, corneal astigmatism, axis location, and astigmatic vector components (Jackson cross-cylinders J0, J45) between the devices were evaluated. The repeatability of both devices in the flattest and steepest meridians, mean corneal power, corneal astigmatism, axis location, J0, and J45 was high. The 95% limits of agreement between the 2 devices were from -0.51 to 0.48 diopters (D) for the flattest meridian, from -0.74 to 0.71 D for the steepest meridian, from -0.56 to 0.53 D for the mean corneal power, from -0.58 to 0.58 D for corneal astigmatism, from -15.3 to 17.5 degrees for axis location, from -0.32 to 0.30 D for J0, and from -0.22 to 0.20 D for J45. In eyes with a small amount of astigmatism, there was wider disagreement in axis location between the 2 devices. Both devices provided excellent repeatability and comparability of corneal powers and corneal astigmatism, suggesting they can be used interchangeably for measurement of these corneal variables in healthy eyes. However, disagreement in axis location between the 2 devices was not negligible in some eyes, especially in those with low astigmatism.

Accuracy and validity of IK4 handheld video keratometer measurements in children

The infant keratometer (IK4) is a custom handheld instrument that was designed specifically to allow measurement of corneal astigmatism in infants as young as 6 months of age. In this study, accuracy of IK4 measurements with the use of standard toric surfaces was within 0.25 D. Validity measurements obtained in 860 children aged 3-7 years demonstrated slightly greater astigmatism measurements in the IK4 than in the Retinomax K+. Measurement success was 98% when the IK4 was used. The IK4 may prove to be clinically useful for screening children as young as 3 years of age at high risk for corneal astigmatism.

Clinical evaluation of application of quantitative micro-keratoscope

目的 通过多家眼科单位对显微定量角膜检查镜(简称角膜镜)的临床试用检验角膜镜检查角膜散光度的准确性和稳定性.方法 前瞻性多中心临床试验研究.4家眼科单位分别用角膜镜和角膜曲率计对被检者156例156眼(均取右眼)进行角膜散光测量,其中角膜镜每眼测3次,角膜曲率计每眼测1次,将角膜镜测量均值与角膜曲率计测量值进行比较,采用组内相关系数分析角膜镜3次测量间的稳定性,采用Bland-Altman散点图评价角膜镜与角膜曲率计测量散光度的准确性和一致性.结果 角膜镜与角膜曲率计测量角膜散光度均值分别为(-1.96±1.16)D和(-1.84±1.17)D,二者呈高度线性相关(r=0.929,P=0.000),配对t检验示二者差异有统计学意义(t=-3.020,P=0.003).角膜镜与角膜曲率计测量角膜散光度差值为(-0.12±0.44)D.角膜镜与角膜曲率计测量角膜散光轴向的中位数均为0°,配对Wilcoxon符号秩检验示差异无统计学意义(Z=-1.775,P=0.076).单因素方差分析显示角膜镜散光度3次测量间差异无统计学意义(F=0.153,P=0.859).角膜镜对角膜散光度测量的组内相关系数(ICC)为0.975,对角膜散光轴向测量的ICC为0.988.角膜镜和角膜曲率计测量角膜散光度的一致性范围(差值均数±1.96SD)为(-1.00,0.76)D;将测量范围0～-8D分为0～、-1D～、-2D～、-4～-8D组段,结果显示角膜镜和角膜曲率计对各组段散光度测量的一致性范围均小于或接近于1.0D.结论 角膜镜测量角膜散光度具有良好的准确性和稳定性。

L’autogreffe limbo-conjonctivale dans la prise en charge chirurgicale des ptérygions

The aim of this study was to estimate the efficacy of limbal-conjunctival autograft in the treatment of pterygium. We conducted a retrospective study including 15 patients (16 eyes) operated on for pterygium by limbal-conjunctival autograft. The examination included the search for risk factors and visual acuity, as well as corneal astigmatism and pterygium measurement. The follow-up included an examination at day 8, 1 month, and 3 months and assessed the integration of the transplant on the eye's surface, the aesthetic aspect, and recurrence. We describe the patients' characteristics, visual acuity, and astigmatism before and after surgery. The mean age of the patients was 56 years (range, 31-81 years). Before surgery, irritative signs and astigmatism, were found in 37% and impaired visual acuity in 81%. The mean duration of the follow-up after surgery was 19 months. Visual acuity and astigmatism improved in 56% of our patients. All transplants and harvest sites had a satisfactory macroscopic aspect. However, one patient suffered from a corneal invasion by fibrovascular tissue, 7 months postoperatively, which remained stable at the end of follow-up. In our study, the limbal-conjunctival autograft was a safe and effective surgical treatment with a very low recurrence rate at long-term follow-up.

Intraobserver and interobserver repeatability of curvature and aberrometric measurements of the posterior corneal surface in normal eyes using Scheimpflug photography

To assess the intraobserver and interobserver repeatability of curvature and aberrometric measurements of the posterior corneal surface provided by a Scheimpflug photography system in normal eyes. Vissum-Instituto de Oftalmológico de Alicante, Alicante, Spain. All eyes received a comprehensive ophthalmologic examination including corneal topographic analysis with a Scheimpflug photography system (Pentacam). Three repeated consecutive measurements were taken by 2 independent experienced examiners to assess intraobserver and interobserver repeatability for posterior corneal surface measurements. Keratometry, astigmatism, best-fit sphere (BFS), asphericity (Q), and aberrometry (6.0 mm pupil diameter) were analyzed. Precision, repeatability, and intraclass correlation coefficients were calculated for evaluating intraobserver repeatability. Bland-Altman analysis was used for assessing interobserver repeatability. Twenty eyes (20 patients) were included. Patients ranged in age from 21 to 50 years. The best intraobserver precision values were for BFS and Q in the central 8.0 mm (0.037 mm and 0.05, respectively). For both observers, intraobserver precision and repeatability achieved an acceptable level for keratometric readings (precision <0.09 diopter). The most limited intraobserver precision was for Q in the central 6.0 mm (0.117 observer 1; 0.099 observer 2). Interobserver ranges of agreement were not clinically relevant for any parameter except Q in the central 6.0 mm (0.116). Regarding aberrometry, intraobserver repeatability and interobserver repeatability were acceptable only for primary and secondary spherical aberration. The Pentacam system provided reliable measurements of corneal posterior keratometry, astigmatism, and asphericity for large diameters of analysis. However, poor repeatability was observed for aberrometric measurements.

Reproducibility of corneal astigmatism measurements with a hand held keratometer in preschool children.

To evaluate the overall accuracy and reproducibility of the Alcon portable autokeratometer (PAK) measurements in infants and young children. The accuracy of the Alcon PAK in measuring toric reference surfaces (1, 3, 5, and 7 D) under various suboptimal measurement conditions was assessed, and the reproducibility of PAK measurements of corneal astigmatism in newborn infants (n = 5), children (n = 19, age 3-5 years), and adults (n = 14) was evaluated. Measurements of toric reference surfaces indicated (a) no significant effect of distance (17-30 mm) on accuracy of measurements, (b) no systematic relation between amount of toricity and accuracy of measurements, (c) no systematic relation between angle of measurement and accuracy, (d) no difference in accuracy of measurements when the PAK is hand held in comparison with when it is mounted, (e) no difference in accuracy of measurements when axis of toricity is oriented obliquely than when it is oriented horizontally, with respect to the PAK, and (f) a small positive bias (+0.16 D) in measurement of spherical equivalent. The PAK did not prove useful for screening newborns. However, measurements were successfully obtained from 18/19 children and 14/14 adults. There was no significant difference in median measurement deviation (deviation of a subject's five measurements from his/her mean) between children (0.21 D) and adults (0.13 D). The PAK produces accurate measurements of surface curvature under a variety of suboptimal conditions. Variability of PAK measurements in preschool children is small enough to suggest that it would be useful for screening for corneal astigmatism in young children.

Accuracy of Javal??s Rule in the Determination of Spectacle Astigmatism

Javal's rule and Grosvenor's simplification of it are commonly used formulas for predicting spectacle astigmatism from keratometric measurements. We assessed the accuracy of these two rules. Spectacle astigmatism was estimated using both rules from measurements of corneal astigmatism on 100 eyes of 100 subjects. These estimates were then compared to the subjectively determined spectacle astigmatism. Grosvenor's simplification of Javal's rule gave slightly more accurate assessments than the original rule. However, only 66% of results gave estimates within 0.50 D, and 7% differed by more than 1.00 D. This can be compared to previous reports on the accuracy of autorefractors, where approximately 95% of cylinder results were within 0.50 D of the spectacle astigmatism. These results indicate that using Javal's rule or Grosvenor's simplification of it to determine spectacle astigmatism from corneal cylinder readings is of limited clinical value.

Avantages et inconvénients à court et long terme des sutures au monofilament de Prolène dans les kératoplasties perforantes

The authors have studied the short and long-term advantages and inconveniences of Prolene monofilament sutures employed in perforating keratoplastic surgery. Contrary to Nylon, Prolene has the advantage of no structural or tensional modifications, postoperative measurements of corneal astigmatism thus remaining more stable with the time. Accordingly, where very little or no astigmatism is noted, the slight or no change in corneal refraction with time is an obvious advantage ot the patient. However, the use of Prolene in the beginning can cause some problems with continuous suture tension, either excessive or insufficient, which can result in serious complications. With training, these difficulties can be overcome and excellent results obtained.

Refractive errors associated with hemangiomas of the eyelids and orbit in infancy

Asymmetrical refractive errors, both astigmatic and myopic, were associated with infantile hemangiomas of the eyelids and orbit in 46% of 37 patients who had large lesions and upper eyelid involvement predisposing to the ammetropia. The axis of the astigmatic error related to the location of the eyelid hemangioma and correlated closely with keratometric measurements of corneal astigmatism. The refractive errors tended to be stable despite eventual resolution of the hemangiomas. Efforts to combat strabismic and refractive amblyopia were rewarding in many patients. A history of complete eyelid occlusion during part of the first year of life was associated with dense amblyopia and eccentric fixation in some patients, but in other patients this history was compatible with the eventual development of useful vision. Absence of an asymmetrical refractive error in patients with eyelid and orbital hemangiomas rendered the prognosis for vision good in involved eyes.

Refractive Errors Associated With Hemangiomas of the Eyelids and Orbit in Infancy

Asymmetrical refractive errors, both astigmatic and myopic, were associated with infantile hemangiomas of the eyelids and orbit in 46% of 37 patients who had large lesions and upper eyelid involvement predisposing to the ammetropia. The axis of the astigmatic error related to the location of the eyelid hemangioma and correlated closely with keratometric measurements of corneal astigmatism. The refractive errors tended to be stable despite eventual resolution of the hemangiomas. Efforts to combat strabismic and refractive amblyopia were rewarding in many patients. A history of complete eyelid occlusion during part of the first year of life was associated with dense amblyopia and eccentric fixation in some patients, but in other patients this history was compatible with the eventual development of useful vision. Absence of an asymmetrical refractive error in patients with eyelid and orbital hemangiomas rendered the prognosis for vision good in involved eyes.

I. On a portable ophthalmometer

The object of the instrument about to be described is to measure the curvature of the central area of the cornea, the polar or optical zone; or of any spherical reflecting surface of from 6 to 10 mm. of radius. In its present form the instrument can only be applied to the measurement of the corneal surface in the visual line. As this is the area of the cornea utilised for distinct vision, this instrument furnishes all the data practically requisite for the diagnosis and measurement of corneal astigmatism.