Partial Coherence Interferometry Device Research Articles

Correlation Between Corneal Keratometry, Central Corneal Thickness and Anterior Chamber Depth as Measured by Wavelight OB 820 Biometer and Wavelight Oculyzer II in Preoperative Cataract Surgery Patients.

To compare and correlate corneal keratometry (K), central corneal thickness (CCT), and anterior chamber depth (ACD) using a partial coherence interferometry device and a Scheimpflug camera system device in patients planned for cataract surgery. Comparative cross-sectional study. Place and Duration of the Study: Armed Forces Institute of Ophthalmology, from December 2021 to June 2022. Patients planned for cataract surgery underwent measurement of central corneal thickness (CCT), anterior chamber depth (ACD), and keratometric values (K) by Wavelight OB 820 biometer and Allergo Oculyzer II, preoperatively. Correlation and inter-device agreement were assessed between two devices. There were 115 patients with a mean age of 64.23 ± 9.26 years. All anterior segment parameters showed excellent agreement and high degree of correlation between the two optical devices. Correlation coefficient (r) for central corneal thickness was r = 0.958 (p<0.001) while correlation coefficient for anterior chamber depth was r = 0.965 (p<0.001), r = 0.966 (p<0.001) for flat K, and r = .0969 (p<0.001) for steep keratometry, respectively. Ophthalmic parameters assessed by both devices were comparable and are recommended to be used in the clinical practice of keratorefractive and cataract surgeries interchangeably. ACD, CCT, Keratometry, Cataract, OB 820 biometer, Oculyzer II.

Swept-source OCT reduces the risk of axial length measurement errors in eyes with cataract and epiretinal membranes.

AimsTo compare the biometric data from partial coherence interferometry (PCI) and swept-source OCT (SS-OCT) in patients with age-related cataract and epiretinal membrane (ERM): ERM, ERM with foveoschisis and macular pseudohole.Methods49 eyes of 49 subjects including 36 ERM, 9 ERM foveoschisis and 4 macular pseudohole were analysed to evaluate the axial length (AL) measurements and the presence of AL measurement errors, defined basing on the shape of the biometric output graphs and on the concordance of AL values between instruments. Eyes with ERM were divided in four stages according to OCT features (i.e. presence/absence of the foveal pit, presence of ectopic inner foveal layers, disrupted retinal layers).ResultsThe devices provided similar mean AL measurements in all subgroups, with differences <0.1 mm in 41/49 cases (83.6%). AL measurement errors were observed in ERM stages 3 and 4, characterized by ectopic inner foveal layers, and were significantly more frequent with the PCI (8/17, 47%) as compared with the SS-OCT device (2/17, 12%), p = 0.02. The refractive prediction error in cases with AL measurement errors was significantly greater using the PCI compared to the SS-OCT device (p<0.05).ConclusionBoth devices provide reliable biometric data in the majority of patients and can be used in the preoperative assessment of patients with age-related cataract and ERM. In eyes with ectopic inner foveal layers, attention should be paid as AL measurement and refractive prediction errors may occur, more frequently with the PCI device.

The role of preoperative Pentacam in optimizing visual outcome after cataract surgery

Objective To evaluate the role of preoperative Pentacam in optimizing visual outcome after cataract surgery. Background It has been suggested that Pentacam gives comprehensive data about preoperative astigmatism, lens density, and refractive power helping in optimizing the visual outcome after cataract surgery. Patients and methods Preoperatively, the patients were subjected to careful history taking, thorough ocular examination including assessment of manifest refraction, measurement of logMAR uncorrected distance visual acuity, and corrected distance visual acuity, biometry and keratometry with the Intraocular lens (IOL) Master partial coherence interferometry device, corneal topography (Pentacam) and to exclude irregular astigmatism, mean lens density, and cataract grading score were evaluated. Slit lamp examination, dilated funduscopy under pharmacological, intraocular pressure, and Hoffer Q formula was used in eyes with an axial length shorter than 22 mm, and SRK/T formula was used for all other cases. Cataract surgery were performed according to the standard protocols. Postoperative manifest refraction (sphere and cylinder) and visual acuity (uncorrected and corrected) were obtained. Results There was significant improvement of astigmatism postoperatively. Also, there were significant improvements of UCVA and BCVA in postoperative assessment as compared with preoperative evaluation. Conclusion Preoperative Pentacam can help in the improvement of preoperative astigmatism. It also resulted in the improvement of Uncorrected visual acuity (UCVA) and Best corrected visual acuity (BCVA).

Accuracy and feasibility of axial length measurements by a new optical low-coherence reflectometry-based device in eyes with posterior subcapsular cataract

To evaluate the feasibility and accuracy of measuring axial length (AL) by a new optical low-coherence reflectometry (OLCR)-based device in eyes with central posterior subcapsular cataract (PSC). Department of Ophthalmology, Assaf-Harofeh Medical Center, Zerifin, Israel. Retrospective case series. Consecutive cases of patients who had uneventful cataract surgery and whose preoperative AL measurements were not feasible with the partial coherence interferometry (PCI) device because of a central PSC were assessed. Preoperative AL was measured by the OLCR device and immersion ultrasound (US). Preoperative results were compared with the postoperative AL measurements obtained by the PCI. Twenty-seven patients (27 eyes) were enrolled in the study. The median difference between the OLCR and the PCI AL measurements (0.07mm) was lower than the median difference between the US and the PCI AL measurements (0.13mm)(P=.016). The ranges of the limits of agreement were 0.15mm between OLCR and PCI, and 0.88mm between US and PCI. The proportion of eyes with an AL difference of less than 0.1mm was significantly higher between the OLCR and the PCI devices (24 eyes [88.9%]) than between the US and the PCI devices (9 eyes [33.3%]) (P=.001). The OLCR-based device successfully measured the preoperative AL in all eyes with central PSC for which preoperative PCI scans were not feasible. These measurements had a high level of agreement with the postoperative AL measurements obtained by the PCI device.

Influence on intraocular lens power calculation of corneal radii measurement using an image-guided system

To analyze the influence on intraocular lens (IOL) power calculation of corneal radii measured by the Verion Image-Guided System in comparison with those measured by partial coherence interferometry (PCI) (IOLMaster) and optical low-coherence reflectometry (OLCR) (Lenstar) systems. International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany. Prospective case series. One eye of ophthalmologically healthy volunteers was examined with the image-guided, PCI, and OLCR systems. Corneal radii could be measured with all 3 devices; axial length (AL) and anterior chamber depth (ACD) could be measured with PCI and OLCR only. The IOL power calculations for the Acrysof SN60WF IOL using 4 formulas were compared between the image-guided system and both the PCI device and OLCR device. For IOL calculation with the image-guided system, the AL and ACD of the device used for comparison were applied. Of the 150 volunteers, 136 (mean age 39.60years±17.31 [SD]) had valid measurements with all 3 devices and were included in the analysis. Compared with PCI, the image-guided system measured statistically significant larger values for corneal radii and IOL power calculations for all 4formulas. There were no statistically significant differences between the image-guided system and the OLCR device. In both groups, the surgeon would have chosen the same IOL power in approximately 60% to 65% of cases and a ±0.5 diopter different IOL power in approximately 30% to 35% of cases when using the image-guided system. The IOL power calculation using the image-guided system showed statistically significant differences compared with the PCI device but not when compared with the OLCR device. The clinical relevance of this theoretical approach remains to be evaluated. Drs. Auffarth and Holzer received travel grants and lecture fees from Alcon Pharma GmbH and Carl Zeiss Meditec AG.

Comparison of a new image-guided system versus partial coherence interferometry, Scheimpflug imaging, and optical low-coherence reflectometry devices: Keratometry and repeatability

To determine the repeatability of keratometry of the Verion image-guided system and to compare the keratometry (K) values with those of established biometric devices. International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany. Prospective case series. One randomly chosen eye of volunteers was examined with partial coherence interferometry (PCI) (IOLMaster 500), optical low-coherence reflectometry (OLCR) (Lenstar LS 900), a Scheimpflug device (Pentacam HR), and the new image-guided system by the same examiner. None of the eyes had ocular pathology. Three consecutive measurements were performed with the image-guided system and 1 with the other devices. The flat, steep, and average corneal radii; steep axis; and white-to-white (WTW) distance were analyzed and compared. One hundred twenty-three eyes of 123 volunteers (mean age 37.9years±16.2 [SD]) had valid measurements for all examinations and were available for analysis. The image-guided system measured statistically significant smaller flat, steep, and average corneal radii than the Scheimpflug device, statistically significant larger flat and average corneal radii than the PCI device, and no statistically significant different values than the OLCR device. The measured steep axis did not differ significantly in any comparison. The WTW measurements were significantly higher than those of all other devices. The analysis of repeatability of the image-guided system showed high intraclass correlation coefficients (range 0.919 to 0.997). The new image-guided system had high repeatability for K, steep axis, and WTW measurements. The WTW measurements with the image-guided system were significantly higher than those using the other devices. None of the authors has a financial or proprietary interest in any material or method mentioned.

Prediction accuracy of preinstalled formulas on 2 optical biometers

To evaluate how well partial coherence interferometry (PCI) (IOLMaster) and optical low-coherence reflectometry (OLCR) (Lenstar LS 900) predict postoperative refractions using only the formulas that come preinstalled on the machines. Private practice, Saint Joseph, Michigan, USA. Retrospective consecutive case series. Eyes were measured with 2 biometers before cataract surgery. Six formulas were ranked by machine. Formulas were also ranked for extremely long and short eyes by averaging the ranks of 6 statistics (mean error, mean absolute error, standard deviation [SD], maximum error, and percentage of eyes within ±0.5 diopter [D] and ±1.0 D of prediction). Formulas were ranked by the SD of the prediction errors. The OLCR device outperformed the PCI device using the preinstalled formulas. The Olsen formula performed the best (0.378) but was preinstalled on the OLCR device only. Other formulas had the following SDs (OLCR device first, PCI device second): Haigis (0.393, 0.401), Holladay 1 (0.408, 0.414), Hoffer Q (0.428, 0.432), SRK/T (0.433, 0.440), and SRK II (0.623, 0.633). Rankings for long eye were (first to last) were Olsen, Haigis, SRK/T, Hoffer Q, and Holladay 1. Rankings for short eyes were Olsen, Haigis, Holladay 1, SRK/T, and Hoffer Q. The OLCR device outperformed the PCI device using the Olsen formula. The Olsen formula also ranked first for short eyes and long eyes. Other formulas performed about the same on both machines. The SRK II formula should be avoided.

Prevalence of corneal astigmatism before cataract surgery.

The purpose of this study was to describe and analyze the prevalence and pattern of corneal astigmatism in cataract surgery candidates. In a prospective cross-sectional study, preoperative demographics, and keratometric and refractive values of cataract surgery candidates were collected from January 2013 to December 2014. Axial length (AL) and flat and steep keratometry measurements were optically measured by a partial coherence interferometry device (IOLMaster). This study consisted of 2156 eyes of 1317 patients with a mean age of 64.92±11.48 (SD) (30-88years). The mean of AL was 23.33±1.37mm, and the mean of corneal astigmatism was 1.12±1.10 diopter (D) (range 0.0-7.00), in all patients. Furthermore, the mean of flat and steep keratometry were 43.70±1.70 and 44.83±1.79 D, respectively. Corneal astigmatism was 1.50 D or less in 1590 eyes (73.7%), more than 1.50 D in 566 eyes (26.2%), 3.00 D or more in 161 eyes (7.4%), WTR in 796 eyes (36.9%), ATR in 1010 eyes (46.8%), and oblique in 350 eyes (16.2%). ATR astigmatism axis significantly increased with the increase in age. Corneal astigmatism of most cataract surgery candidates fell between 0.50 and 1.50 D. The results of our study however is confined to our demographics might provide useful data for cataract patients, surgeons, and intraocular lens manufacturers for different purposes.

Measurement agreement between a new biometer based on partial coherence interferometry and a validated biometer based on optical low-coherence reflectometry

To evaluate the agreement of ocular measurements obtained with a new optical biometer (AL-Scan) and a previously validated optical biometer (Lenstar). Eye Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, China. Prospective observational cross-sectional study. For a comprehensive comparison between the partial coherence interferometry (PCI) device and the optical low-coherence reflectometry (OLCR) device, the axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth, mean keratometry (K), astigmatism, white-to-white (WTW), and pupil diameter were measured 3 times per device in eyes with cataract. The sequence of the device was in random order. The mean values were compared and 95% limits of agreement (LoA) were assessed. Ninety-two eyes of 92 cataract patients were included. Bland-Altman analysis showed excellent agreement between the PCI device and the OLCR device for AL, CCT, ACD and aqueous depth measurements with narrow 95% LoA (-0.05 to 0.06 mm, -13.39 to 15.61 μm, -0.11 to 0.10 mm, and -0.12 to 0.10 mm, respectively), and the P values were more than 0.05. The mean K, astigmatism, and WTW values provided by the PCI device were in good agreement with the OLCR device, although statistically significant differences were detected. A major difference was observed in the pupil diameter measurement, with a 95% LoA of -0.73 to 1.21 mm. The PCI device biometer provided ocular measurements similar to those provided by the OLCR device for most parameters, especially for AL, CCT, and ACD. The pupil diameter values obtained with the PCI device were in poor agreement with the OLCR device, and these measurements should be interpreted with necessary adjustment. None of the authors has a proprietary or financial interest in any material or method mentioned.

Comparison of 2 optical biometers and evaluation of the Camellin-Calossi intraocular lens formula for normal cataractous eyes

To compare the measurements and intraocular lens (IOL) power calculations obtained with an optical biometer (AL-Scan) and partial coherence interferometry (PCI) device (IOLMaster 500), and to evaluate the accuracy of the Camellin-Calossi IOL formula in virgin eyes. Saiseikai Kurihashi Hospital, Saitama, Japan. Prospective comparative study. Measurements were compared from 262 patients (450 eyes) scheduled for cataract surgery. Axial length (AL), keratometry (K), anterior chamber depth (ACD), and number of eyes that were successfully measured were compared. Comparisons were performed of the residual postoperative refractive error with the SRK/T, Haigis, and Camellin-Calossi IOL formulas with optical biometer data. The IOL constant was optimized for 81 eyes that had iSertMicro 251 IOL implantation. The mean difference in AL between biometers was -0.012 mm ± 0.031 (SD) (P < .0001). Correlation coefficients (r) for AL, keratometry, and ACD were 0.9997, 0.9836, and 0.9571, respectively. The calculated IOL constant for the Camellin-Calossi formula was 119.3. The optimized IOL constant for the SRK/T was 118.8, the same as that of the User Group for Laser Interference Biometry for the PCI device. For the Haigis formula, only a0 was optimized, and it was 1.390. After optimizing the A-constant for the Camellin-Calossi formula, the residual postoperative refractive error of the Camellin-Calossi formula was not statistically significantly different in comparison to those obtainied with the Haigis and SRK/T formulas. Ocular biometry measurements were equivalent for both devices, indicating that the AL-Scan can be used for routine preoperative cataract assessment. The predictive accuracy of the Camellin-Calossi formula included in the optical biometer was equivalent to common IOL formulas for virgin eyes. No author has a financial or proprietary interest in any material or method mentioned.

Comparability of anterior chamber depth measurements with partial coherence interferometry and optical low-coherence reflectometry in pseudophakic eyes

To assess whether anterior chamber depth (ACD) measurements in pseudophakic eyes obtained with partial coherence interferometry (PCI) and optical low-coherence reflectometry (OLCR) devices can be used interchangeably. Vienna Institute for Research in Ocular Surgery, A Karl Landsteiner Institute, Hanusch Hospital, Vienna, Austria. Prospective case series. The ACD measurements in 1 eye of each pseudophakic patient were performed with the PCI-based ACMaster device and the OLCR-based Lenstar LS900 device at least 1 day postoperatively. The study comprised 65 eyes of 65 patients with a mean age of 71.7 years ± 9.0 (SD) (range 39 to 91 years). In 15 eyes, no valid ACD readings could be obtained with the OLCR device. No obvious reason for these measurement failures was identified; however, tear-film alterations shortly after surgery were suspected. No significant difference in the mean ACD in the remaining 50 eyes was found between PCI measurements (5019 ± 660 μm; range 4008 to 6181 μm) and OLCR measurements (5015 ± 663 μm; range 4017 to 6163 μm) (P = .06). Three (6%) of 50 measurements were not within the 95% limits of agreement in the Bland-Altman analysis. Pseudophakic ACD measurements with the PCI and OLCR devices can be used interchangeably. The OLCR device proved to be more user-friendly and faster; however, in a substantial number of eyes, no usable values were obtainable. No author has a financial or proprietary interest in any material or method mentioned.

Agreement between a partial coherence interferometer and 2 manual keratometers

To establish repeatability and validity of a partial coherence interferometry (PCI) device in patients with astigmatism. Industry and university. Observational studies. A prospective study determined the agreement between the IOLMaster 500 PCI device and the Marco 1-position manual keratometer for measurement of mean corneal power, astigmatic power, and axis. Interinstrument and interoperator reproducibility was also assessed. A retrospective study determined the agreement between the PCI device and the Javal 2-position manual keratometer. Repeatability was also assessed. The 95% limits of agreement (LoA) were determined for all comparisons. Comparing the PCI device and the 1-position manual keratometer, the axis was within 5degrees in 72.1% of eyes; the cylinder power differed by 0.18 diopter (D) (95% LoA, ±0.45 D) and the mean power by 0.33 D (95% LoA, ±0.25 D). Comparing the PCI device and the 2-position manual keratometer, the axis was within 5 degrees in 77.1% of eyes. The mean difference in cylinder power between the 2 instruments was close to zero (95% LoA, ±0.37 D); however, the mean power differed by 0.34 D (95% LoA, ±0.25 D). The repeatability of the PCI device was better than that of both manual keratometers. Agreement between the PCI device and the 2-position manual keratometer for measures of corneal astigmatism and axis was excellent. The 1-position manual keratometer gave slightly lower estimates of corneal astigmatism, although the agreement for axis was excellent. Thus, the PCI device is an appropriate choice for the calculation of toric intraocular lenses. Dr. Bullimore is a consultant to Carl Zeiss Meditec AG and Alcon Surgical, Inc. Drs. Buehren and Bissmann are employees of Carl Zeiss Meditec AG.

Reproducibility of a Long-Range Swept-Source Optical Coherence Tomography Ocular Biometry System and Comparison with Clinical Biometers

To demonstrate a novel swept source optical coherence tomography (SS-OCT) imaging device using a vertical cavity surface-emitting laser (VCSEL) capable of imaging the full eye length and to introduce a method using this device for noncontact ocular biometry. To compare the measurements of intraocular distances using this SS-OCT instrument with commercially available optical and ultrasound biometers. To evaluate the intersession reproducibility of measurements of intraocular distances using SS-OCT. Evaluation of technology. Twenty eyes of 10 healthy subjects imaged at the New England Eye Center at Tufts Medical Center and Massachusetts Institute of Technology between May and September 2012. Averaged central depth profiles were extracted from volumetric SS-OCT datasets. The intraocular distances, such as central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), crystalline lens thickness (LT), vitreous depth (VD), and axial length (AL), were measured and compared with a partial coherence interferometry device (IOLMaster; Carl Zeiss Meditec, Inc., Dublin, CA) and an immersion ultrasound (IUS) A-scan biometer (Axis-II PR; Quantel Medical, Inc., Cournon d'Auvergne Cedex, France). Reproducibility of the measurements of intraocular distances, correlation coefficients, and intraclass correlation coefficients. The standard deviations of the repeated measurements of intraocular distances using SS-OCT were 6 μm (CCT), 16 μm (ACD), 14 μm (AD), 13 μm (LT), 14 μm (VD), and 16 μm (AL). Strong correlations among all 3 biometric instruments were found for AL (r > 0.98). The AL measurement using SS-OCT correlates better with the IOLMaster (r=0.998) than with IUS (r=0.984). The SS-OCT and IOLMaster measured higher AL values than ultrasound (175 and 139 μm, respectively). No statistically significant difference in ACD between the optical (SS-OCT or IOLMaster) and ultrasound methods was detected. High intersession reproducibility of SS-OCT measurements of all intraocular distances was observed with intraclass correlation coefficients >0.99. The SS-OCT using VCSEL technology enables full eye length imaging and high-precision, noncontact ocular biometry. The measurements with the prototype SS-OCT instrument correlate well with commercial biometers. The SS-OCT biometry has the potential to provide clinically useful comprehensive biometric parameters for pre- and postoperative eye evaluation.

White-to-white corneal diameter differences in moderately and highly myopic eyes: Partial coherence interferometry versus scanning-slit topography

To evaluate the differences between Orbscan scanning-slit topography and IOLMaster partial coherence interferometry (PCI) white-to-white (WTW) measurements in moderately and highly myopic eyes. IOBA-Eye Institute, University of Valladolid, Spain. Comparative case series. Myopic eyes were divided according to the degree of myopia as follows: Group 1 (<6.00 diopters [D]), Group 2 (between 6.00 D and 12.00 D), and Group 3 (>12.00 D). The WTW distance was measured with the scanning-slit topography and PCI devices. The study enrolled 328 eyes (64 subjects). The mean WTW in all eyes was 0.50 mm ± 0.26 (SD), lower with scanning-slit topography (11.69 ± 0.37 mm) than with PCI (12.19 ± 0.40 mm) (P<.01, paired t test). A low mean WTW was found in Group 2 (11.65 ± 0.34 and 12.15 ± 0.36 mm, scanning-slit topography and PCI, respectively) and Group 3 (11.51 ± 0.36 and 12.05 ± 0.46 mm, respectively) compared with Group 1 (11.79 ± 0.38 and 12.26 ± 0.40 mm, respectively) (P<.03, analysis of variance with Games-Howell correction). There was a low statistically significant relationship between WTW and spherical equivalent (SE) with both devices. Eyes with moderate and high degrees of myopia had lower WTW diameters than eyes with low spherical equivalent myopia measured with both devices. Scanning-slit topography provided less WTW distance than PCI in myopic eyes; thus, the devices are not clinically interchangeable.

Anterior chamber depth, intraocular lens position, and refractive outcomes after cataract surgery

To assess postoperative intraocular lens (IOL) position in relation to the cornea and iris, compare 2 devices for anterior chamber depth (ACD) measurement, and assess the impact of these factors on postoperative refraction in phacoemulsification. Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden. Evaluation of diagnostic test or technology. Biometry and measurement of the anterior segment were performed preoperatively and postoperatively with the partial coherence interferometry (PCI)-based IOLMaster and the Pentacam HR Scheimpflug device. Predicted refraction was calculated with ACD estimations according to the Haigis formula and was compared with the actual postoperative refraction. Changes in ACD and the distance between the cornea-iris and the iris-lens/IOL were assessed from Scheimpflug images. The theoretical refractive impact of differences in ACD was calculated. The mean preoperative ACD and refractive prediction error, respectively, was 3.22 mm ± 0.37 (SD) and 0.41 ± 0.43 diopters (D) for the PCI device and 3.21 ± 0.35 mm and 0.41 ± 0.41 D for the Scheimpflug device; the difference was not statistically significant. The mean ACD, cornea-iris distance, and iris-lens/IOL distance changes were 1.62 ± 0.38 mm, 0.78 ± 0.29 mm, and 0.85 ± 0.27 mm, respectively. The mean predicted refractive outcome from a 1.0 mm difference in ACD was 0.32 D. No difference was found between the measurement devices. Although the exact postoperative IOL position is difficult to predict, its impact on postoperative refraction was comparatively small compared with the impact of minor corneal curvature or axial length measurement errors.

Precision of biometry, keratometry, and refractive measurements with a partial coherence interferometry–keratometry device

To evaluate the precision of the axial length (AL), keratometry (K), anterior chamber depth (ACD), astigmatism, and minus astigmatic cylinder axis measurements by a partial coherence interferometry (PCI)-keratometry device. Private practice, Lynwood, California. This prospective comparative observational study analyzed measurements in the second eye to have cataract surgery. Before surgery in the first eye, AL, K, ACD, astigmatism, and cylinder axis in both eyes were measured with an IOLMaster PCI device. The measurements were repeated approximately 1 month later, before second eye-surgery. The 2 sets of measurements were compared. The study evaluated 121 eyes of 121 patients. The interclass correlation coefficient (ICC) for AL was 0.999 in all 3 signal-to-noise ratio (SNR) categories; the highest difference range was with an SNR below 100. Astigmatism, K, and cylinder axis had a high correlation in flat corneas (K reading <42.0 diopters [D]) (ICC = 0.994, 0.978, and 0.918, respectively) and a poorer correlation with K readings between 42.0 D and 44.0 D (ICC = 0.905, 0.774, and 0.456, respectively) and K readings above 44.0 D (ICC = 0.988, 0.729 and 0.446, respectively). The precision of the PCI measurements was extremely high for AL with low fluctuations (95% limits of agreement [LoA], 0.06 mm) and was relatively high for K readings with higher fluctuations (95% LoA, 0.55 D) and for ACD (95% LoA, 0.2 mm). The precision of astigmatism and cylinder axis was high in flat corneas and relatively low in steeper corneas.

Anterior chamber depth measurements in eyes with an accommodating intraocular lens: Agreement between partial coherence interferometry and optical coherence tomography

To determine agreement between partial coherence interferometry (PCI) and anterior segment optical coherence tomography (AS-OCT) measurements of anterior chamber depth (ACD) and axial intraocular lens (IOL) movement in eyes with an accommodating IOL. Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. In this prospective pilot study of cataract patients, the central ACD was measured by PCI (ACMaster) and AS-OCT (Visante) 6 months after unilateral OPAL-A accommodating IOL implantation. Measurements were performed with a distance target and 1.00 diopter (D) and 2.00 D accommodative targets and after administration of topical pilocarpine 4%. Agreement between PCI and AS-OCT ACD measurements and IOL movement was calculated. Measurements were obtained in 18 patients. There was a consistent and statistically significant bias toward shallower ACD measurements with AS-OCT than with PCI, with the bias most pronounced after pilocarpine (mean 4.117 mm +/- 0.291 [SD] versus 4.054 +/- 0.287 mm; bias 0.063 mm; P<.0001). Limited IOL movement to 1.00 D and 2.00 D accommodative stimuli was detected with both instruments. After pilocarpine, forward IOL movement measurements were statistically significantly greater by AS-OCT than by PCI (mean 0.306 +/- 0.161 mm versus 0.270 +/- 0.155 mm) (P = .017). The AS-OCT device showed a bias toward underestimation of ACD compared with the PCI device. The bias increased as ACD shallowed with pilocarpine, resulting in overestimation of forward IOL movement by AS-OCT. This may lead to overestimation of the accommodative performance of IOLs. The ACD measurements obtained by the 2 devices are not interchangeable.

Comparison of 2 laser instruments for measuring axial length

To compare axial length (AL), anterior chamber depth (ACD), and keratometric (K) measurements of 2 laser biometers. Private practices, Lynwood and Santa Monica, California, USA. In this prospective comparative observational study of eyes with cataract and eyes with a clear lens, AL, ACD, and K measurements were performed using an IOLMaster biometer, which uses partial coherence interferometry (PCI), and a Lenstar LS 900 biometer, which uses optical low-coherence reflectometry (OLCR). Intraocular lens (IOL) power calculation was performed using the Haigis formula. The IOL prediction error was calculated for each eye. The study evaluated 50 eyes with cataract and 50 eyes with a clear lens. There was a good correlation between AL, ACD, and K measurements in the cataractous eyes (r = 0.9993, 0.9667, and 0.9959, respectively) and in eyes with a clear lens (r = 0.9995, 0.8211, and 0.9959, respectively). The OLCR unit measured a slightly longer AL in the cataract group and clear lens group (mean difference 0.026 mm and 0.023 mm, respectively), a deeper ACD (0.128 mm and 0.146 mm, respectively), and a flatter K (-0.107 diopter [D] and -0.121 D, respectively). The differences were statistically significant (P<.0001). The mean absolute error in IOL power prediction was 0.455 D +/- 0.32 (SD) with the OLCR unit and 0.461 +/- 0.31 D with the PCI unit (P>.1). Measurements were comparable between the OLCR device and the PCI device. A slight decrease (0.050) in the a(0) constant is recommended if the Haigis formula is used.

Refractive Predictability of Partial Coherence Interferometry and Factors that can Affect It

PurposeTo evaluate the refractive predictability of a partial coherence interferometry (PCI) biometry device (IOL Master®) for cataract surgery and to investigate factors that may affect it.MethodsRetrospective review of 209 eyes from 151 patients that had undergone preoperative PCI biometry and an uneventful phacoemulsification cataract surgery with posterior chamber intraocular lens (IOL) implantation was conducted. Prediction error defined as the intended refraction minus the postoperative refraction in spherical equivalent (SE) and the absolute error were analyzed according to IOL calculation formulas, patient characteristics, preoperative visual acuity (VA) and refraction, posterior subcapsular cataract (PSC), signal-to-noise ratio (SNR), and axial length (AL).ResultsThe overall refractive predictability of the PCI device was good. Generally, the SRK/T formula performed better than the SRK-II formula. Refractive predictability was slightly worse in eyes with ≥+2.0 diopters (D) of preoperative SE (with both SRK-II and SRK/T) and in eyes with an AL≤23.0 mm (only with SRK-II. No other factors significantly affected the refractive predictability of the PCI, although poor VA, dense PSC, and poor SNR were closely interrelated.ConclusionsThe SRK/T formula performed significantly better than the SRK-II formula. Eyes with an AL≤23.0 mm were associated with significantly greater hyperopic shifts in postoperative refraction with the SRK-II formula, but not with the SRK/T formula. A preoperative SE≥+2.0D was related to a significantly greater hyperopic shift in postoperative refraction. With proper verification of measured data and a suitable IOL calculation formula, good refractive predictability is expected from PCI biometry regardless of patient characteristics, preoperative VA, SNR, PSC, and AL.