Reproducibility of VERION Digital Guidance System and its comparability with iTrace, Lenstar LS900 and manual keratometer in measuring keratometry and astigmatism / 眼科新进展

Objective To analyze the reproducibility of keratometry and astigmatism measured by the VERION Digital Guidance System and the comparability of VERION with iTrace,Lenstar LS900 and manual keratometer.Methods The keratometry of 62 cataract patients were measured using four different devices.The steep keratometry (Ks),flat keratometry (Kf),astigmatic magnitude,astigmatic axis,cylinder at 0-degree meridian (vector component,J0) and cylinder at 45-degree meridian (vector component,J45) from each machine were recorded and analyzed.The three repeated measurements and the results of VERION system with other three devices were compared to analyze the reproducibility and comparability of VERION system.Results Reproducibility:Intraclass correlation coefficients and Cronbach's alpha values were higher than 0.9 for Ks,Kf,astigmatic magnitude,astigmatic axis,J0 and J45 measured by the VERION system (all P ＜ 0.001).Comparability:The results of Ks and magnitude of astigmatism of VERION were larger than the iTrace (all P ＜ 0.05) in the paired-samples t test.There was no statistical difference for the rest of parameters (all P ＞ 0.05).The Bland-Altman graphs revealed the 95％ limits of agreement (LOA) of J0,J45 and the astigmatic axis between VERION and iTrace were (-0.31-0.35) D,(-0.25-0.31) D and-13.5 °-12.3 °,respectively;There was no statistical differences for all parameters except for J45 in the paired-samples t test between the VERION and Lenstar LS900 (all P ＞ 0.05).The Bland-Altman graphs revealed the 95％ LOA of J0,J45 and the astigmatic axis were (-0.25-0.31)D,(-0.27-0.36) D and-13.5°-11.0°,respectively;There were statistical differences for the results of Kf and magnitude of astigmatism between the VERION and manual keratometer (all P ＜ 0.05).The Bland-Altman graphs revealed the 95％ LOA of J0,J45 and the astigmatic axis between VERION and manual keratometer were (-0.38-0.35) D,(-0.41-0.42) D,-12.6°-16.4°,respectively.Conclusion The VERION system is a reliable system for the measurement of keratometry and astigmatism.The keratometry and astigmatic magnitude of the VERION system have a good agreement with the iTrace,Lenstar LS900 and manual keratometer.However,the astigmatic axis measurements are significantly different among the four devices.

Measurement of Corneal Power and Astigmatism Using Placido-based Videokeratography and Comparison with Other Keratometers

PURPOSE: In the present study, the repeatability and reproducibility of the corneal power and astigmatism measurements using placido-based video keratography were evaluated and the agreement with other keratometers were compared. METHODS: This prospective study included 45 patients (45 eyes) scheduled to undergo cataract surgery between November 2015 and January 2016. Three sets of corneal power and astigmatism were measured using placido-based video keratometer (Keratograph® 5M), automatic keratometer (KR-8900®), manual keratometer (B×L manual keratometer®), Placido-scanning-slit keratometer (ORBscan II®), Scheimpflug keratometer (Pentacam®), and low coherence interferometry (Lenstar LS900®). Reliability of each device was analyzed using the coefficient of variation, standard deviation and intraclass correlation coefficient. Repeated measures analysis of variance was used to analyze the interdevice comparison of mean absolute difference. The agreement between the devices was evaluated with 95% limits of agreement (LoA) and Bland-Altman plots. RESULTS: The mean corneal power, astigmatism and power vector analysis (J₀, J₄₅) were not significantly different among devices (p > 0.05). In the Bland-Altman plot analysis, the 95% LoA of corneal power, J₀, and J45 when comparing Keratograph® 5M with others ranged from -0.78 to 0.55 D, from -0.42 to 0.45 D, and from -0.39 to 0.47 D, respectively. CONCLUSIONS: Keratograph® 5M showed good repeatability and reproducibility of corneal power and astigmatism measurements and was interchangeable with other keratometers.

Preoperative corneal astigmatism among adult patients with cataract in Northern Nigeria.

The prevalence and nature of corneal astigmatism among patients with cataract has not been well‑documented in the resident African population. This retrospective study was undertaken to investigate preexisting corneal astigmatism in adult patients with cataract. We analyzed keratometric readings acquired by manual Javal‑Schiotz keratometry before surgery between January 1, 2011 and December 31, 2011. There were 3,169 patients (3286 eyes) aged between 16 and 110 years involved with a Male to female ratio of 1.4:1. Mean keratometry in diopters was K1 = 43.99 and K2 = 43.80. Mean corneal astigmatism was 1.16 diopter and a majority (45.92%) of eyes had astigmatism between 1.00 and 1.99 diopters. Two‑thirds of the eyes (66.9%) in this study had preoperative corneal astigmatism equal to or above 1.00 diopter. Findings will help local cataract surgeons to estimate the potential demand for toric intraocular lenses.

Which Keratometer is Most Reliable for Correcting Astigmatism with Toric Intraocular Lenses?

PURPOSE: To evaluate the accuracy of preoperative keratometers used in cataract surgery with toric intraocular lens (IOL). METHODS: Twenty-five eyes received an AcrySof toric IOL implantation. Four different keratometric methods, a manual keratometer, an IOL master, a Pentacam and an auto keratometer, were performed preoperatively in order to evaluate preexisting corneal astigmatism. Differences between the true residual astigmatism and the anticipated residual astigmatism (keratometric error) were compared at one and three months after surgery by using a separate vector analysis to identify the keratometric method that provided the highest accuracy for astigmatism control. RESULTS: The mean keratomeric error was 0.52 diopters (0.17-1.17) for the manual keratometer, 0.62 (0-1.31) for the IOL master, 0.69 (0.08-1.92) for the Pentacam, and 0.59 (0.08-0.94) for the auto keratometer. The manual keratometer was the most accurate, although there was no significant difference between the keratometers (p > 0.05). All of the keratometers achieved an average keratometric error of less than one diopter. CONCLUSIONS: Manual keratometry was the most accurate of the four methods evaluated, although the other techniques were equally satisfactory in determining corneal astigmatism.

Comparison of the biometric measuring outcomes between Lenstar and A-scan ultrasound biometry or keratometer in cataract patient / 中华实验眼科杂志

Background The accuracy of biometric measurement is critical for precise diagnoses and prognosis evaluation of ocular diseases.Objective The present study was to evaluate the differences of Lenstar with A-scan ultrasound biometry or keratometer in ocular bio-measurement.Methods Written informed consent was obtained from each subject before examination.Total 43 eyes of 40 age-related cataract patients were enrolled in this study.Axial length,corneal curvature (K1,K2,Km) and intraocular lens (IOL) power were measured with Lenstar,A-scan ultrasound biometry and keratometer,separately.The differences of measuring outcomes were compared between these two methods according to a paired samples t test,and the agreement analysis of measuring outcomes between Lenstar and A-scan ultrasound biometry or keratometer was performed by Blant-Altman plots.Results Thirty-five eyes finished the clinical bio-measurement.The axial length was (23.341 ± 1.208) mm and (23.268 ±1.157)mm based on Lenstar method and A-scan ultrasound biometry method,respectively,with a insignificant difference between them(t =0.260,P=0.796).No significant differences were found in the K1,K2 and Km values between Lenstar and keratometer methods (t =0.526,P =0.601 ; t =0.927,P =0.357 ; t =0.213,P =0.832).The IOL power was (20.371 ±2.827) D and (20.729 ± 2.672) D,respectively in Lenstar method and keratometer method,without statistically significant difference between them (t =0.543,P =0.589).Bland-Altamn agreement analysis showed that the dots of 11％ (4/35),0％ (0/100),9％(3/35),9％ (3/35),6％ (2/35) were out of 95％ confidence limit,and the absolute values of maximal difference value between Lenstar and A-scan ultrasound biometry or keratometer methods was 0.39 mm,1.31 D,1.30 D,0.77 D and 1.00 D in ocular axial length,K1,K2 and Km values and IOL power,respectively.Conclusions As a new bio-measuring method,Lenstar can offer multiple biometric parameters by single procedure.However,an inconsistent measuring outcome is seen between Lenstar and Ascan ultrasound biometry or keratometer.So whether Lenstar can replace A-scan ultrasound biometry or keratometer still need further large simple clinical trail.

Comparison of Keratometric Values Measured by the Handheld Autokeratometer, On-table Autokeratometer and Manual Keratometer

PURPOSE: To compare the keratometry measurements by the handheld Nikon Retinomax K-plus2, the on-table Canon RK-5 autokeratometer, and the manual Topcon OM-4 keratometer and to evaluate the degree of agreement among the three instruments. METHODS: Adults (n=30) and children (n=40) presenting toa tertiary eye hospital clinic were examined by an optometrist. Topcon OM-4 keratometer, Nikon Retinomax and the on-table Canon RK-5 autokeratometer analyses were performed in order. The horizontal and vertical keratometry data were measured. The vector components of astigmatism, mean bias and agreement among the three types of measurements were evaluated. RESULTS: There were no significant differences among the three keratometers in horizontal or vertical keratometry or in central corneal astigmatism in both the adult and child groups (p-value>0.05). The keratometers which were estimated with Retinomax K-plus2 were highly correlated with those by on-table RK-5 autokeratometer (min. 0.89, max. 0.97) and Topcon OM-4 keratometer (min. 0.67, max. 0.94) in the adult group, while in the child group, the three instruments showed slightly decreased correlation (min. 0.45, max. 0.97 on RK-5, min. 0.36, max. 0.92 on OM-4), especially in the left eyes. CONCLUSIONS: The handheld Retinomax K-plus2 provided comparable data to that of the conventional on-table Topcon and manual keratometers. This instrument will beuseful in the clinic to measure keratometry in children or immobilized patients who have difficulty sitting during the examination.

¿Índice 1.3375? / ¿1.3375 index?

Para convertir las mediciones obtenidas de la superficie corneal a un valor dióptrico, el keratómetro de Bausch & Lomb Optical Company utiliza la fórmula (n’ – n)/ R y asume un índice n’ de 1,3375 (diferente al índice real de la córnea de 1,376). Este valor ficticio incluye una compensación para contrarrestar el pequeño pero significativo poder negativo de la superficie posterior de la córnea. Esto permite hacer la lectura directamente tanto del radio de curvatura como del poder dióptrico de la córnea.

To convert the measurements obtained from the corneal surface into dioptric value, the B&L keratometer uses the general lens formula (n’-n/R) and assumes an n’ of 1,3375 (compared to the actual corneal refractive index of n’=1,376). This is afictional value, which includes an allowance for the small, yet significant, negative power of the posterior corneal surface.

Analysis of The Accouracy of The Keratometer and Computer Assisted Videokeratography in IOL Power Calculation

We used to measure keratometric readings for IOL calculation as obtained by keratometer (Javal ophthalmometer) and recently computer assisted videokerato graphy (C.V.K.). To compare with accuracy of two different instruments we analyzed 100 eyes using Javal ophthalmometer and 100 eyes using C.V.K. in phacoemulsification procedures. Postoperative two months later, we had conclusion which had no significant difference in predicted refraction between two groups and there are a little tendency in myopic pattern in C.V.K. group. Also we found less dioptric power difference between the two groups in younger age, male, irregular astigmatism and small wound.

Postoperative Astigmatism Control Effects Using the Zeiss Surgical Keratometer During Cataract Surgery

In order to evaluate the effects of the postoperative astigmatism control, we compared 20 eyes measuring astigmatism at the end of operation with the Zeiss surgical keratometer and then had received loosening or tightening of sutures(keratometer group), with 20 eyes that were operated without the keratometer(control group). The mean cylindrical power of the keratometer group was lower than the control group at early postoperative period(P<0.001), but there was no statistical difference between both group at one or two months after operation. However the amount of cylinder was smaller in the keratometer group than in the control group. 19 of 20 eyes(95%) had less than 2D of astigmatism in the keratometer group, but in the control group 15 of 20 eyes(75%) had less than 2D of astigmatism at postoperative 60 days. 4 cases of posterior capsule rupture as intraoperative complication occured in the keratometer group. The posterior capsule rupture was caused by the decrease of surgical field clarity due to farther working distance by 17.5cm through attaching the Zeiss surgical keratometer to the operating microscope. From this study, Zeiss surgical keratometer seems to useful to reduce the early postoperative astigmatism but the intraoperative difficulty because of occupying space and decreasing clarity of surgical field is observed. The posterior capsule rupture as intraoperative complication occurs more frequently due to the disadvantages of this instrument.

The Changes of Astigmatism Following Horizontal Strabismus Surgery

The visual acuity changes following strabismus surgery are generally short-lived and tend to disappear with time. However, some cases of persistent decreased vision is considered to be caused by changes of corneal curvature following strabismus surgery, resulting in increased corneal astigmatism. To investigate the amount and frequency of corneal astigmatiy changes following horizontal strabismus surgery, the authors periodically examined pre-and postoperative corneal curvature using keratometer in 56 eyes of 34 patients who had undergone horizontal strabismus surgery from March, 1987 to February, 1989 at Gyeongsang National University Hospital and Masan Koryo General Hospital. An average of 0.41D in horizontal curvature and an average of 0.05D in vertical curvature was decreased at 8 weeks after operation. The changes of +0.5D or more were present in 53.6% in horizontal curvature and 42.9% in vertical curvature. In comparison of one muscle operation with two muscle operation in one eye, both horizontal and vertical curvature showed no significant changes statistically(p>0.05).