Corneal Topographic versus Manifest Refractive Astigmatism in Patients with Keratoconus: A Retrospective Cross-Sectional Study (original) (raw)
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Journal of ophthalmic & vision research, 2013
To determine the prevalence of keratoconus (KCN) and subclinical KCN among subjects with two or more diopters (D) of astigmatism, and to compare Pentacam parameters among these subjects. One hundred and twenty eight eyes of 64 subjects with astigmatism ≥2D were included in the study. All subjects underwent a complete ophthalmic examination which included refraction, visual acuity measurement, slit lamp biomicroscopy, retinoscopy, fundus examination, conventional corneal topography and elevation-based topography with Pentacam. The diagnosis of KCN and subclinical KCN was made by observing clinical findings and topographic features; and confirmed by corneal thickness and elevation maps of Pentacam. Several parameters acquired from Pentacam were analyzed employing the Mann-Whitney U Test. Mean age of the study population was 29.9±9.8 (range 15-45) years which included 39 (60.9%) female and 25 (39.1%) male subjects. Maximum corneal power, index of vertical asymmetry, keratoconus index a...
Characteristics of posterior corneal astigmatism in different stages of keratoconus
Journal of Ophthalmic and Vision Research
Purpose: To evaluate the magnitudes and axis orientation of anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA), the ratio of ACA to PCA, and the correlation between ACA and PCA in the different stages of keratoconus (KCN). Methods: This retrospective case series comprised 161 eyes of 161 patients with KCN (104 men, 57 women; mean age, 22.35 ± 6.10 years). The participants were divided into four subgroups according to the Amsler-Krumeich classification. A Scheimpflug imaging system was used to measure the magnitude and axis orientation of ACA and PCA. The posterior-anterior corneal astigmatism ratio was also calculated. The results were compared among different subgroups. Results: The average amounts of anterior, posterior, and total corneal astigmatism were 4.08 ± 2.21 diopters (D), 0.86 ± 0.46 D, and 3.50 ± 1.94 D, respectively. With-the-rule, against-the-rule, and oblique astigmatisms of the posterior surface of the cornea were found in 61 eyes (37.9%), 67 eyes (41.6%), and 33 eyes (20.5%), respectively; corresponding figures in the anterior corneal surface were 55 eyes (32.4%), 56 eyes (34.8%), and 50 eyes (31.1%), respectively. A strong correlation (P ≤ 0.001, r = 0.839) was found between ACA and PCA in the different stages of KCN; the correlation was weaker in eyes with grade 3 (P ≤ 0.001, r = 0.711) and grade 4 (P ≤ 0.001, r = 0.717) KCN. The maximum posterior-anterior corneal astigmatism ratio (PCA/ACA, 0.246) was found in patients with stage 1 KCN. Conclusion: Corneal astigmatism in anterior surface was more affected than posterior surface by increasing in the KCN severity, although PCA was more affected than ACA in an early stage of KCN.
International journal of ophthalmology, 2016
To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus. Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є(2)), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices. The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672...
Inter-eye asymmetry in manifest refraction, keratometry and pachymetry in eyes with keratoconus
2020
CORRESPONDING AUTHOR Magdalena Maleszka-Kurpiel MD, Optegra Eye Health Care Clinic in Poznan; Department of Optometry, Chair of Ophthalmology and Optometry, Poznan University of Medical Sciences, 5 D Rokietnicka St., 60-806 Poznan, Poland, e-mail: magdamaleszka@wp.pl INTRODUCTION Keratoconus (KC) is a progressive corneal, bilateral ectasia characterized by thinning and weakening of the cornea that results in corneal steepening, protrusion, irregular astigmatism, and gradual impairment of vision [1]. Worldwide, KC occurs in approximately 1 in 2000 individuals, as reported by Rabinowitz at the end of the 20th century [1]. However, reported epidemiological data differ between geographical zones and other factors such as age or gender. Ethnicity has been reported to play a role in keratoconus. Asians have 4.4 times higher risk for developing keratoconus than Caucasians, and Indians have steeper corneas than Chinese patients with keratoconus [2, 3]. Recently reported KC prevalence in the...
European journal of ophthalmology
To evaluate agreement in measurements of astigmatic axis power and location between keratometry and computer assisted videokeratography (corneal topography) on normal corneas with less than 1.50 D of idiopathic astigmatism. Keratometric readings with the 10 SL/O Zeiss ophthalmometer and corneal topographic maps with the TMS-1 were obtained by two independent examiners on 32 normal corneas. Measurement agreement between the two instruments was evaluated in regard to steep and flat meridian power and location, and in astigmatism magnitude (D). The limits of agreement (d-2 SD to d+2 SD) between the two instruments were found to be broad for clinical purposes in measuring the steep meridian power (-0.16 to -1.20 D), flat meridian power (0.43 to -1.25 D), and astigmatism (0.60 to -1.12 D). A constant bias of the TMS-1 towards the 10 SL/O Zeiss ophthalmometer was found, in measuring steeper both principal meridians and higher amount of astigmatism. Mean location difference was 19 degrees ...
Vector Analysis of Evolutive Corneal Astigmatic Changes in Keratoconus
Investigative Opthalmology & Visual Science, 2011
PURPOSE. To evaluate by vector analysis the corneal astigmatic changes occurring in keratoconic corneas during a 3-year follow-up and to determine the relationship between these changes and other clinical changes. METHODS. Keratoconic eyes (n ϭ 114) of 75 patients ranging in age from 14 to 70 years were retrospectively reviewed in four different centers. In all cases, a 3-year follow-up was completed after the diagnosis of keratoconus. Visual, refractive, keratometric, aberrometric, internal astigmatism (IA), and pachymetric changes were evaluated during the follow-up. In addition, corneal astigmatic changes were evaluated by examining the following parameters, using a modification of the Alpins vectorial method: evolutive astigmatism (EA) and angle of error (AE). RESULTS. An increase in the magnitude of refractive (P ϭ 0.02) and corneal astigmatism (P ϭ 0.05) was found. The mean magnitude of EA was 1.21 Ϯ 0.97 D at 3 years, with no significant changes at each annual visit (P Ն 0.52). Mean absolute AE increased significantly by the end of the follow-up (P Ͻ 0.01). Absolute AE and the increase in corneal astigmatism were found to correlate at 2 years (r ϭ 0.675, P Ͻ 0.01). This correlation became poorer at 3 years (r ϭ 0.352, P ϭ 0.02). The magnitude of the EA was also found to be significantly correlated with central corneal thinning (r ϭ Ϫ0.441, P ϭ 0.02). Multiple regression analysis revealed that the magnitude of EA at 3 years correlated significantly with the baseline sphere and IA (R 2 ϭ 0.86, P Ͻ 0.01). CONCLUSIONS. Corneal vector astigmatic changes are related to some signs of keratoconus progression and are therefore predictive.
Journal of Cataract & Refractive Surgery, 2012
To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry. Siriraj Hospital, Mahidol University, Bangkok, Thailand. Prospective comparative study. Eyes with previous ocular surgery or abnormalities were excluded. All patients were examined with the ARK 730A autokeratometer and the Galilei analyzer. The steepest and flattest corneal power along with the steepest axis of the TCP, automated keratometry, and simulated keratometry were recorded. Vector analysis (J0 and J45) was calculated. Analysis of variance with Bonferroni correction was performed for multiple comparisons. Outcome measures were the magnitude and axis location of astigmatism. One hundred eyes of 100 cataract patients were randomly selected. There was no statistically significant difference in the mean steepest axis between TCP (93.31 ± 68.75 [SD]), automated keratometry (94.24 ± 64.78), and simulated keratometry (92.42 ± 64.30). However, the mean magnitude of astigmatism measured by TCP (1.23 ± 0.75) was significantly higher than that measured by automated keratometry (0.93 ± 0.68) (P=.01) but not than that measured by simulated keratometry (1.08 ± 0.68) (P=.43); there was no statistically significant difference in J0 or J45. Twenty two (40%) of 54 eyes with more than 1.00 diopter of TCP astigmatism had more than 10 degrees of axis difference from automated keratometry. The magnitude of TCP astigmatism was higher than that of automated keratometry. The axis location was similar. However, there was more than 10 degrees of axis difference between automated keratometry and TCP in patients with high astigmatism. No author has a financial or proprietary interest in any material or method mentioned.
Corneal topographic and pachymetric screening of keratorefractive patients
Journal of refractive surgery (Thorofare, N.J. : 1995)
To review the incidence of corneal abnormalities detected in the preoperative examination, using videokeratography and pachymetry that excluded patients from laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). We conducted a chart review of consecutive patients who had a preoperative examination and were excluded from refractive surgery. Eighteen patients from 1,392 refractive candidates (1.3%) were designated as poor candidates for LASIK or PRK based on corneal topography and/or pachymetry. Thirteen patients (0.9%) were identified as having keratoconus suspect, keratoconus, or pellucid marginal degeneration. Five patients (0.4%) were excluded due to thin corneas (<490 microm) despite normal corneal topography. Corneal topography and pachymetry are indispensable tools in the preoperative screening of refractive surgery candidates.
Journal of Cataract and Refractive Surgery, 2014
Prospective case series. METHODS: Corneal astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric astigmatism, anterior corneal astigmatism, posterior corneal astigmatism, and total corneal astigmatism were evaluated. Vector analysis was performed according to the Naeser method. RESULTS: One hundred fifty-seven eyes were enrolled. Keratometric astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal astigmatism, keratometric astigmatism overestimated WTR astigmatism by a mean of 0.22 D G 0.32 (SD), underestimated ATR astigmatism by 0.21
Clinical Ophthalmology, 2013
To survey the standard keratoconus grading scale (Pentacam ® -derived Amsler-Krumeich stages) compared to corneal irregularity indices and best spectacle-corrected distance visual acuity (CDVA). Patients and methods: Two-hundred and twelve keratoconus cases were evaluated for keratoconus grading, anterior surface irregularity indices (measured by Pentacam imaging), and subjective refraction (measured by CDVA). The correlations between CDVA, keratometry, and the Scheimpflug keratoconus grading and the seven anterior surface Pentacam-derived topometric indices -index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, index of height decentration, and index of minimum radius of curvature -were analyzed using paired two-tailed t-tests, coefficient of determination (r 2 ), and trendline linearity. Results: The average ± standard deviation CDVA (expressed decimally) was 0.626 ± 0.244 for all eyes (range 0.10-1.00). The average flat meridian keratometry was (K1) 46.7 ± 5.89 D; the average steep keratometry (K2) was 51.05 ± 6.59 D. The index of surface variance and the index of height decentration had the strongest correlation with topographic keratoconus grading (P , 0.001). CDVA and keratometry correlated poorly with keratoconus severity. Conclusion: It is reported here for the first time that the index of surface variance and the index of height decentration may be the most sensitive and specific criteria in the diagnosis, progression, and surgical follow-up of keratoconus. The classification proposed herein may present a novel benchmark in clinical work and future studies.