Corneal Astigmatism Measurements Research Articles

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.