Comparative Accuracy of Barrett Integrated Keratometry Toric Calculator With Predicted Versus Measured Posterior Corneal Astigmatism
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Purpose: To compare the prediction accuracy of the Barrett toric calculator using standard or integrated keratometry (IK) mode in combination with predicted or measured posterior corneal astigmatism (PCA) in a group of patients with cataract implanted with non-toric IOLs. Methods: In this retrospective clinical cohort study, the medical records of patients with age-related cataract who underwent phacoemulsification with the implantation of an aspheric monofocal IOL were reviewed. Four methods, including standard keratometry with predicted PCA (PPCA), IK combined with predicted PCA (IK-PPCA), and IK combined with measured PCA derived from IOLMaster 700 (Carl Zeiss Meditec AG) or CASIA2 (Tomey) (IK-MMPCA or IK-CMPCA), were applied to the Barrett toric calculator to calculate the predicted residual astigmatism. The mean absolute prediction error (MAPE), centroid of the prediction error, and proportion of eyes within the prediction error of ±0.50, ±0.75, and ±1.00 diopters (D) were all ciphered out from the four methods, respectively. Results: Data from 129 eyes of 129 patients were included in this study. The MAPE of the IK-PPCA method (0.57 ± 0.36 D) was significantly smaller than that of the PPCA (0.62 ± 0.38 D) and IK-CMPCA (0.63 ± 0.46 D) methods ( P = .048 and .014, respectively). There were no significant differences in the centroid vectors of prediction errors and predictability rates among the four methods (all P > .05). Conclusions: In the current version of the Barrett toric calculator, the predictive accuracy of the IK mode incorporating PPCA was slightly superior to using the standard keratometry mode or incorporating MPCA. [ J Refract Surg . 2024;40(7):e453–e459.]Keywords:
Astigmatism
Nomogram
We performed an analysis of surgically induced astigmatism in 229 cases of extracapsular cataract extraction and posterior chamber lens implantation. The average length of follow-up for patients in this study was 34.4 months (2.87 years). We found that surgically induced astigmatism continued to change for at least three years after surgery. The preoperative astigmatism was found to have only minimal effect on the postoperative astigmatism if the corneal curvature was controlled with keratometry at the time of surgery. The optimal amount of with-the-rule astigmatism at three to five weeks postoperatively was found to be 0.75 diopter to 1.25 diopters for one surgeon and surgical technique.
Astigmatism
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A prospective randomized clinical study was performed to see the effect of donor-recipient corneal size on the ultimate refractive error induced in keratoconus at our facility. The patients were randomly divided into two groups, A and B. In Group A, the difference in size between the donor and the recipient cornea was 0.25 mm (18 patients). In Group B, the difference in size between the donor and the recipient cornea was 0.50 mm (20 patients). Both groups underwent the surgical procedure with the same surgeon (M.A.J.) and the same technique. Two months after suture removal, keratometry readings and refractive errors induced were compared. The mean keratometry reading in Group A was 43.3 diopters; in Group B, the reading was 44.8 diopters. There was a mean difference of 1.5 diopters between the two groups (p=0.01). The mean refractive error in terms of spherical equivalent in Group A was – 1.55 diopters and in Group B was –3.33 diopters. There was a difference of –1.8 diopters between the two groups (p<0.05).
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To evaluate the alterations in refractive and keratometric outcomes following intrastromal corneal ring segment implantation as a treatment for keratoconus. 20 eyes of 18 patients with keratoconus who underwent intrastromal corneal ring segment implantation were assessed retrospectively. The data assessed included the pre- and post-operative parameters (Kmin, Kmax, Kmedian), and the spherical and cylindrical refraction values. Age and sex of patients were also considered. Corneal topography analysis revealed an average decrease in the minimum central keratometry of 2.1, whereas a 4.0 reduction was seen in the maximum central keratometry. Moreover, an average decrease of -1.2 diopters in spherical lenses was observed, in comparison to a -2.3 reduction in the cylindrical ones. All keratometric parameters (Kmin, Kmax, Kmean) exhibited a significant reduction in values following intrastromal corneal ring segment implantation (p<0,005). Similarly, a significant reduction in spherical and cylindrical diopters, succeeding chirurgical intervention, was also detected (p<0,05). Our results revealed that intrastromal corneal ring segment implantation leads to a significant reduction in the keratometric values and spherical and cylindrical refractions of patients, resulting in visual improvement.
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The problem of astigmatism, occurring both congenitally and in conjunction with cataract and refractive surgery, is a common and significant one. A review of patients in this study shows 18% greater than 2 diopters and 6% greater than 3 diopters of astigmatism measured by keratometry. Many methods for correcting this astigmatism have developed, including long peripheral incisions, both straight and curved, the many varieties of the Ruiz procedure, and short paired relaxing incisions. I have reviewed my results for short paired incisions following cataract surgery, congenital astigmatism, and radial keratotomy at 6 months following surgery. The average change in astigmatism was 2.69 +/- 0.78 (manifest)/2.35 +/- 1.09 (keratometry) for the 5-mm optic zone following cataract surgery. Paired relaxing incisions following radial keratotomy showed a change in astigmatism of 0.92 +/- 0.19 (manifest)/1.29 +/- 1.29 (keratometry) diopters for the 6-mm optic zone and 2.12 +/- 0.34 (manifest)/2.25 +/- 0.49 (keratometry) diopters for the 5.5-mm optic zone. No significant complications and no large overcorrections were encountered.
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A Humphrey Auto Keratometer was used to evaluate the changes in corneal astigmatism that occurred under hypnosis. The measurements were made at the visual axis and the corneal apex in eight subjects. These measurements were taken before, during and after hypnosis. The mean of the changes occurring at the visual axis was 0.40 diopters with some corneas changing as much as 0.62 diopters. The mean change at the corneal apex was 0.23 diopters with some corneas changing as much as 0.37 diopters. These corneal changes are attributed to the relaxation of lid tension after hypnosis.
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ABSTRACT: A series of patients who had undergone penetrating keratoplasty was examined to determine the effect the use of the disparate diameter graft technique had on final corneal keratometry. Average keratometry for a control population was found to be 43.50 diopters. Forty-eight phakic grafts were performed with a 0.2 mm donor to recipient disparity resulting in an average postop K of 42.50 diopters. Thirty-four aphakic grafts using a 0.5 mm disparity resulted in an average postop K of 43.0 diopters. While many factors contribute to final corneal curvature and astigmatism including accuracy of trephination, and choice of suture material and pattern, we feel these data show the importance of the choice of disparate diameters in obtaining average final keratometry readings.
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The problem of astigmatism, occurring both congenitally and in conjunction with cataract and refractive surgery, is a common and significant one. A review of patients in this study shows 18% > 2 diopters and 6% > 3 diopters of astigmatism measured by keratometry. Many methods for correcting this astigmatism have developed, including long peripheral incisions, both straight and curved, the many varieties of the Ruiz procedure, and short paired relaxing incisions. I have reviewed my results for short paired incisions following cataract surgery, congenital astigmatism, and radial keratotomy at 6 months following surgery. The average change in astigmatism was 2.69 ± 0.78 (manifest)/2.35 ± 1.09 (keratometry) for the 5-mm optic zone following cataract surgery. Paired relaxing incisions following radial keratotomy showed a change in astigmatism of 0.92 ± 0.19 (manifest)/1.29 ± 1.29 (keratometry) diopters for the 6-mm optic zone and 2.12 ± 0.34 (manifest)/2.25 ± 0.49 (keratometry) diopters for the 5.5-mm optic zone. No significant complications and no large overcorrections were encountered.
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A number of studies have documented the reasonable efficacy and safety of radial keratotomy, but most based upon results obtained in low or moderate myopia or short term follow up after surgery. We complied 5 year and longer follow up data on 91 consecutive radial keratotomy surgeries on high myopia (over -6.00 diopters) performed by one surgeon 5 year-follow up was obtained on 21 (23%) of these eyes. The mean spherical equivalent before surgery was -11.02 diopters (D), the average keratometry value was 44.40 D, and all of the eyes had an uncorrected visual acuity of 0.04 or less. The average change in spherical equivalent was 3.44 D for eyes examined at 1 year, compared with 3.05 D for eyes at 3 years and 2.87 D at 5 years after surgery. Average keratometry value were 42.30 D at 1 year, 41.60 D at 3 years, and 41.30 D at 5 years after surgery. In our study, the decrease in spherical equivalent of 0.57 D was statistically significant (P < 0.05), as was the reduction in average keratometry value of 1.00 D. The effect of the surgery on spherical equivalent continued to regress through all the 5 years of follow up. However, the keratometric measurement decreased up to 5 years which indicated progressive flattening of the cornea. Also we divided these eyes into 2 groups, lower-myopic group (-6.00 D-(-)9.75 D) and higher-myopic group (over -10.00 D). In each category, the changes in spherical equivalent were 3.60 D, 2.21 D at 5 years, compared with 3.65 D, 3.25 D at 1 year respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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Anisometropia
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Abstract We compared one-year outcomes of conventional (3 mW/cm 2 , 365-nm ultraviolet-A light, 30 minutes) and accelerated (18 mW/cm 2 , 365-nm ultraviolet-A light, 5 minutes) collagen crosslinking (CXL) in patients with progressive keratoconus. Main outcome measures were change in keratometry, uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA). Nineteen patients in each group completed 1-year follow-up. Preoperatively, there were no inter-group differences for age, keratometry, corneal thickness and spherical equivalent (p > 0.127). One year postoperatively, maximum and minimum keratometry were flattened by 1.6 diopters (p < 0.023) and 2 diopters (p < 0.047) respectively after conventional CXL, and, 0.47 diopters (p = 0.471) and 0.19 diopters (p = 0.120) respectively after accelerated CXL. Association analysis showed significant negative association between baseline maximum keratometry and change in maximum keratometry after accelerated CXL (p = 0.002) but not after conventional CXL (p = 0.110). Corneal thickness was reduced significantly in both groups (p = 0.017). An improvement in UCVA (p < 0.001) and BCVA (p < 0.022) was noted in both groups along with a reduction in spherical equivalent postoperatively (p < 0.026). There were no inter-group differences for any of the parameters postoperatively (p > 0.184). Although no statistically significant differences were observed between both treatment modalities, a more effective topographic flattening was observed with conventional CXL as compared to accelerated CXL in this study.
Corneal collagen cross-linking
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Objective To investigate the accuracy of hand-held auto photokeratometer in measuring corneal diopter and its clinical application.Methods The corneal diopter in 60 cases(118 eyes) were measured by hand-held auto photokeratometer (SW-100 Suoer,TianJin) and manual keratometer (OM-4 Topcon,Japan),the results were compared.Results There was no significant difference in the highest(k1) and smallest(k2) value of mean corneal diopter,mean corneal astigmatism obtained from two photokeratometer(P0.05),but there was significant difference in axes of astigmatism between two photokeratometer(P0.05).Conclusion The hand-held auto photokeratometer is similar to manual keratometer in clinical value,and can be used in measuring corneal diopter.
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