To evaluate the precision (repeatability and reproducibility) of the Pentacam HR (high-resolution) tomographer (Oculus, Wetzlar, Germany) across a large range of measurement parameters.
A randomly ...selected healthy eye of 100 subjects was scanned twice with the Pentacam HR by one observer for each of the three measurement modes: 25-picture (1 second) scan, 50-picture (2 second) scan, and cornea fine scan (50 pictures in 1 second). The repeatability of each scan mode was assessed. One additional 25-picture scan was acquired by a second observer to test reproducibility.
Overall, the Pentacam HR had good precision, with the cornea fine scan returning the most precise results: The 25- and 50-picture scans showed similar precision. The repeatability limits, expressed as the within-subject SD × 1.96√2 of the anterior keratometry (K)1 and K2 readings with the standard 25-picture scan, were 0.25 and 0.36 D, respectively. Pachymetry maps, corneal maps, anterior chamber depth maps, corneal volume, topometric Q values and indices were also found to be precise. Poor precision was found for estimates of axis (astigmatic and progression index), pupil center pachymetry, single points on corneal maps, refractive power maps, and equivalent K readings.
Measurements taken with the Pentacam HR are repeatable and reproducible, especially those obtained with the cornea fine scan. Although the Pentacam HR is clearly a very useful clinical and research tool, the measurement of corneal axes, pupil center pachymetry, front meridional and axial maps, refractive power maps, and equivalent K readings should be interpreted with caution.
Citation information: McAlinden C, Khadka J & Pesudovs K. Statistical methods for conducting agreement (comparison of clinical tests) and precision (repeatability or reproducibility) studies in ...optometry and ophthalmology. Ophthalmic Physiol Opt 2011, 31, 330–338. doi: 10.1111/j.1475‐1313.2011.00851.x
The ever‐expanding choice of ocular metrology and imaging equipment has driven research into the validity of their measurements. Consequently, studies of the agreement between two instruments or clinical tests have proliferated in the ophthalmic literature. It is important that researchers apply the appropriate statistical tests in agreement studies. Correlation coefficients are hazardous and should be avoided. The ‘limits of agreement’ method originally proposed by Altman and Bland in 1983 is the statistical procedure of choice. Its step‐by‐step use and practical considerations in relation to optometry and ophthalmology are detailed in addition to sample size considerations and statistical approaches to precision (repeatability or reproducibility) estimates.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
To evaluate the repeatability of Corvis ST corneal biomechanical, tonometry and pachymetry measurements, and agreement of pachymetry measures with the Pentacam HR and RTVue OCT. Three consecutive ...measurements of the right eye of 238 myopic subjects were acquired with the Corvis ST, Pentacam HR, and RTVue OCT. Repeatability of Corvis ST was evaluated by within-subject standard deviation S
and repeatability limit r. The agreement of central corneal thickness (CCT) measurements were compared among the three instruments using the Bland-Altman limits of agreement. Comparisons were further stratified by CCT (Cornea
≤ 500 µm; Cornea
= 500-550 µm; Cornea
> 550 µm). S
was below 1 mmHg in Cornea
, Cornea
, and Cornea
groups for IOP and bIOP. S
for SP-A1 were 4.880, 6.128, 7.719 mmHg/mm respectively. S
for CBI were 0.228, 0.157, 0.076, and correspondingly S
for TBI and SSI were 0.094 and 0.056, 0.079 and 0.053, 0.070 and 0.053. The Bland-Altman plots for CCT implied poor agreement with mean differences of 29.49 µm between Corvis and OCT, 9.33 µm between Pentacam and OCT, and 20.16 µm between Corvis and Pentacam. The Corvis ST showed good repeatability with the exception of CBI in the various CCT groups. The CCT measured by Corvis ST was not interchangeable with Pentacam HR and RTVue OCT.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Aims/Background. To assess astigmatic outcomes with the use of toric intraocular lenses (IOLs) for patients with significant amounts of corneal astigmatism undergoing cataract surgery. Methods. This ...audit was conducted in a UK ophthalmology department and included 48 eyes of 42 patients. Surgery was performed during 2019 in patients with 2.50 diopters (D) or more corneal astigmatism. Anterior keratometry readings were used to determine the toric IOL power. Vector analysis using the Alpins method was used to assess changes in astigmatism pre to postoperatively. Results. There were 18 right and 26 left eyes included. In terms of gender, 61% of patients were female and 39% were male. The mean (±standard deviation (SD)) age was 70 (±11) years. The mean (±SD) axial length, K1, K2, and delta K was 23.55 (±1.4) mm, 42.71 (±1.39) D, 45.78 (±1.60) D, and 3.01 (±0.89) D, respectively. Postoperatively, the median spherical, cylinder, and spherical equivalent refraction was 0.00 D, −1.00 D, and 0.00 D, respectively. Postoperatively, 41% of the eyes had ≤0.50 D of spectacle astigmatism and 80% had ≤1.00 D. No patient required a secondary procedure to reposition the IOL from rotation. In vector analysis with the use of polar diagrams, there was a tendency for overcorrection of with-the-rule astigmatism and undercorrection of against-the-rule astigmatism. Conclusions. Significant reductions in astigmatism can be achieved with the use of toric IOLs in patients undergoing cataract surgery. Further improvements may be possible with surgeon-specific determination of their surgically induced astigmatism and flattening effect from the main corneal incision. Furthermore, the use of an optical biometer that directly measures the posterior corneal curvature and permits automatic toric IOL power determination with modern formulas avoiding the need for manual data entry may reduce the risk of human error and improve visual and refractive outcomes.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
A critical component that influences the measurement properties of a patient-reported outcome (PRO) instrument is the rating scale. Yet, there is a lack of general consensus regarding optimal rating ...scale format, including aspects of question structure, the number and the labels of response categories. This study aims to explore the characteristics of rating scales that function well and those that do not, and thereby develop guidelines for formulating rating scales.
Seventeen existing PROs designed to measure vision-related quality of life dimensions were mailed for self-administration, in sets of 10, to patients who were on a waiting list for cataract extraction. These PROs included questions with ratings of difficulty, frequency, severity, and global ratings. Using Rasch analysis, performance of rating scales were assessed by examining hierarchical ordering (indicating categories are distinct from each other and follow a logical transition from lower to higher value), evenness (indicating relative utilization of categories), and range (indicating coverage of the attribute by the rating scale).
The rating scales with complicated question format, a large number of response categories, or unlabelled categories, tended to be dysfunctional. Rating scales with five or fewer response categories tended to be functional. Most of the rating scales measuring difficulty performed well. The rating scales measuring frequency and severity demonstrated hierarchical ordering but the categories lacked even utilization.
Developers of PRO instruments should use a simple question format, fewer (four to five) and labelled response categories.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
To evaluate the visual and refractive outcomes and quality of life after implantation of a multifocal intraocular lens (IOL) with a surface-embedded near section.
Private practice, United Kingdom.
...Case series.
This study comprised patients who had implantation of a Lentis Mplus multifocal IOL after phacoemulsification. The main outcome measures were refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuities (logMAR), uncorrected (UNVA) and corrected (CNVA) near visual acuities (M notation), reading speed (Radner reading chart), contrast sensitivity (Pelli-Robson), and Quality of Life Impact of Refractive Correction (QIRC) questionnaire scores. A +3.00 diopter (D) reading addition (add) IOL was placed in the nondominant eye and a +1.50 D add IOL in the dominant eye.
The study enrolled 44 eyes of 22 patients (mean age 59.9 years). The mean values 3 months postoperatively were UDVA, 0.04 logMAR ± 0.25 (SD); contrast sensitivity, 1.57 ± 0.13 logCS; near vision, M0.75 ± 0.33 at 32 cm and M0.90 ± 0.27 at 66 cm; reading speed, 161.74 words/minute; sphere, 0.08 ± 0.58 D; astigmatism, -0.60 ± 0.50 D; CDVA, -0.08 ± 0.07 logMAR. With best correction, intermediate (66 cm) and near (32 cm) vision were M0.89 ± 0.26 and M0.74 ± 0.32, respectively. The mean binocular UNVA at the preferred viewing distance was M0.57 ± 0.18, improving to M0.54 ± 0.19 with distance correction. The mean QIRC score improved from 42.15 ± 4.66 to 51.14 ± 8.22.
Postoperative visual acuity was good with high-level contrast sensitivity, producing significant improvement in quality of life.
Abstract Purpose To compare a new swept source optical coherence tomography (SS-OCT) based biometer (OA-2000) with the IOLMaster v5.4 (partial coherence interferometry) and Aladdin (optical ...low-coherence interferometry) biometers in terms of axial length measurement and failure rate in eyes with cataract. Design Reliability study Methods A total of 377 eyes of 210 patients were scanned with the three biometers in a random order. For each biometer, the number of unobtainable axial length measurements was recorded and grouped as per the type and severity of cataract based on the Lens Opacities Classification System III by the same experienced ophthalmologist. The Bland-Altman limits of agreement (LoA) method was used to assess the agreement in axial length measurements between the three biometers. Results The failure rate was 0 eyes (0%) with the OA-2000, 136 eyes (36.07%) with the IOLMaster and 51 eyes (13.53%) with the Aladdin. Chi-squared analyses indicated a significant difference in failure rate between all three devices (P<0.001). Logistic regression analysis highlighted a statistically significant trend of higher failure rates with increasing severity of nuclear, cortical and posterior subcapsular cataracts. Bland-Altman statistics indicated small mean differences and narrow LoA (OA-2000 versus IOLMaster -0.09 to 0.08mm; OA-2000 versus Aladdin -0.10 to 0.07mm; IOLMaster versus Aladdin -0.05 to 0.04mm). Conclusions The OA-2000, a new SS-OCT based biometer, outperformed both the IOLMaster and Aladdin biometers in very advanced cataracts of various morphologies. The use of SS-OCT technology may be the reason for the improved performance of the OA-2000 and may lead to this technology becoming the gold standard for the measurement of axial length.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
To evaluate axial length (AL) measurement failure rate with the IOLMaster (Carl Zeiss AG, Germany) and Lenstar LS 900 (Haag-Streit AG, Switzerland) in eyes with cataract.
Two hundred and ninety-six ...eyes of 170 patients with cataract were enrolled. Cataract type and severity were graded using the Lens Opacities Classification System III (LOCS III) and AL measurements were attempted with IOLMaster (version 5.4) and Lenstar LS 900 (version 1.1). Chi-squared analysis was used to assess if the difference in AL measurement acquisition rate was statistically significant between the two devices. The association of the different cataract types and severity with the AL measurement acquisition rate was evaluated with logistic regression analysis.
AL measurements were obtained in 184 eyes (62.16%) using the IOLMaster and 191 eyes (64.53%) using the Lenstar, which corresponds to a failure rate of 37.84% and 35.47% respectively. Chi-square analysis indicated no significant difference between the Lenstar and IOLMaster for AL measurement failure rate (x2 = 0.356, P = 0.550). Logistic regression analysis indicated no association between acquisition rates and cortical or nuclear cataracts with either device. There was a statistically significant association between acquisition rates and increasing severity of posterior subcapsular cataracts with the IOLMaster (β = -1.491, P<0.001) and Lenstar LS 900 (β = -1.507, P<0.001).
The IOLMaster and Lenstar LS 900 have similar AL measurement failure rates (35-38%) for Chinese public hospital cataract patients. Increasing severity of posterior subcapsular cataracts was problematic for both devices.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Purpose. To compare the through-focus visual performance in a clinical population of pseudophakic patients implanted with two new trifocal intraocular lenses (IOLs) and one extended depth of focus ...IOL. Methods. Prospective, nonrandomized, examiner-masked case series. Twenty-three patients received the FineVision® and seven patients received the PanOptix™ trifocal IOLs. Fifteen patients received the Symfony extended depth of focus IOL. Mean age of patients was 63 ± 8 years. Through-focus visual acuity was measured from –3.00 to +1.00 D vergences. Contrast sensitivity was measured with and without a source of glare. Light disturbances were evaluated with the Light Distortion Analyzer. Results. Though-focus evaluation showed that trifocal IOLs performed significantly better at near distance (33 and 40 cm), and extended depth of focus performed significantly better at intermediate distance (1.0 m). Contrast sensitivity function with glare and dysphotopsia was similar between the three IOLs and subjective response to questionnaire showed a significantly higher score (worse performance) for the extended depth of focus IOL compared to both trifocal IOLs in the bothersome subscale (p<0.05). Conclusions. Trifocal IOLs grant better performance at near distance while extended depth of focus IOL performs better at intermediate distance. Objective dysphotopsia measured with the Light Distortion Analyzer is not reduced in extended depth of focus IOL compared to trifocal IOLs.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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