Optical Low Coherence Reflectometer Research Articles

Evaluating the prediction accuracy of the Hill-RBF 3.0 formula using a heteroscedastic statistical method.

To evaluate the accuracy of the Hill-RBF 3 formula, with and without direct measurements of total corneal power, using a heteroscedastic statistical method for analysis. Department of Ophthalmology, Shaare Zedek Medical Center, Jerusalem, Israel. Retrospective, consecutive case series. Records of consecutive patients who underwent routine cataract surgery between February 2018 and June 2020 were retrospectively reviewed. The prediction accuracy of the Hill-RBF 3.0 formula was compared with that of the Barrett Universal II, Emmetropia Verifying Optical 2.0, Haigis, Hill-RBF 2.0, Hoffer Q, Holladay 1, Holladay 2, Kane, Olsen, and SRK/T formulas, based on biometry measurements by swept-source optical coherence tomography (SS-OCT) with standard keratometry (K), SS-OCT with total keratometry (TK), and an optical low-coherence reflectometer (OLCR). Statistical analysis was applied according to a heteroscedastic statistical method with SD of prediction errors as the main parameter for formula performance. The study included 153 eyes of 153 patients. The SD values that were obtained by Hill-RBF 3.0 (0.266 to 0.285 diopters [D]) were significantly lower compared with those by Hill-RBF 2.0 (0.290 to 0.309 D), Hoffer Q (0.387 to 0.407 D), Holladay 1 (0.367 to 0.385 D), Holladay 2 (0.386 to 0.401 D), and SRK/T (0.377 to 0.399 D) formulas (P < .036). The prediction accuracy of the Hill-RBF 3.0 was similar across the SS-OCT (K), SS-OCT (TK), and OLCR methods of measurement (P > .51). The Hill-RBF 3.0 was more accurate than the Hill-RBF 2.0 and older generation formulas and had similar prediction accuracy compared with new generation formulas. The use of TK did not provide significant improvement to its prediction accuracy.

Validating e-norms methodology in ophthalmic biometry

ObjectiveTo validate the extrapolated norms or e-norms methodology in establishing a reference range for the biometric data used for intraocular lens power calculation.Methods and AnalysisAll measurements were performed with an...

Repeatability and reproducibility of optical biometry implemented in a new optical coherence tomographer and comparison with a optical low-coherence reflectometer

To examine the repeatability and reproducibility of biometry provided by a new anterior-posterior segment spectral-domain optical coherence tomography (SD-OCT) device (Revo NX) and compare it with that provided by a validated optical low-coherence reflectometry (OLCR) biometer (Lenstar LS 900). Hygeia Clinic, Gdańsk, Poland. Prospective evaluation of diagnostic test. The axial length (AL), lens thickness (LT), central corneal thickness (CCT), and anterior chamber depth (ACD) (corneal epithelium to lens) were measured in eyes of volunteers. Two skilled operators obtained 3 measurements in random order with the SD-OCT device. Repeatability was calculated for each observer, while reproducibility was assessed by a change in observer. To compare agreement between the SD-OCT device and OLCR device, the first observer took 3 measurements with both devices. The study evaluated 63 eyes of 63 volunteers. The mean AL measurement (+0.11mm±0.02 [SD]) and mean ACD measurement (0.05±0.04mm) were significantly higher with the SD-OCT device than with the OLCR device; the CCT measurements did not differ between the devices. A very strong correlation was found for all parameters, while Bland-Altman analysis showed narrow 95% limits of agreement for AL (0.06 to 0.15mm), ACD (-0.02 to 0.12mm), LT (-0.23 to 0.17mm), and CCT (-7.83 to 6.17μm). The new SD-OCT device provided repeatable and reproducible AL, ACD, LT, and CCT measurements. The results with the SD-OCT device showed strong correlations with those obtained with the OLCR device. However, the AL and ACD measurements of the 2 devices cannot be considered interchangeable.

Matching the LenStar optical biometer to A-Scan ultrasonography for use in small animal eyes with application to tree shrews

We describe an analysis strategy to obtain ultrasonography-matched axial dimensions of small animal eyes using the LenStar biometer. The LenStar optical low-coherence reflectometer is an attractive device for animal research due to its high precision, non-invasiveness, and the ability to measure the axial dimensions of cornea, anterior chamber, lens, vitreous chamber, and axial length. However, this optical biometer was designed for clinical applications in human eyes and its internal analysis provides inaccurate values when used on small eyes due to species-dependent differences in refractive indices and relative axial dimensions. The LenStar uses a near infrared light source to measure optical path lengths (OPLs) that are converted by the LenStar's EyeSuite software into geometrical lengths (GLs) based on the refractive indices and axial dimensions of the human eye. We present a strategy that extracts the OPLs, determines refractive indices specific for the small animal eye of interest and then calculates corrected GLs. The refractive indices are obtained by matching the LenStar values to ultrasonography values in the same eyes. As compared to ultrasounography, we found that the internal calculations of the LenStar underestimate the axial dimensions of all ocular compartments of the tree shrew eye: anterior segment depth by 6.17±4.50%, lens thickness by 1.37±3.06%, vitreous chamber depth by 29.23±2.35%, and axial length by 10.62±1.75%. Using tree shrew-specific refractive indices, the axial dimensions closely matched those measured by ultrasonography for each compartment. Our analysis strategy can be easily translated to other species by obtaining a similar paired data set using ultrasonography and LenStar, and applying our step by step procedures.

Ultra‐high spatial resolution Brillouin grating measurement using OLCR

A Brillouin grating-based optical low coherence reflectometer (OLCR) using a broadband light source is constructed. The reflection distributions of Brillouin gratings generated at mated fibre connectors are measured. The measured reflectograms agreed with theoretical curves calculated from the coherence function of the OLCR, showing that the OLCR technique made it possible to measure Brillouin gratings with a spatial resolution of the order of 100 μm.

New mode for measuring axial length with an optical low-coherence reflectometer in eyes with dense cataract

To evaluate a new algorithm for measuring eyes with dense cataract using a biometer based on optical low-coherence reflectometry (OLCR). Shammas Eye Medical Center, Lynwood, California, USA, and Augenarztpraxis EYEC, Bern, Switzerland. Cross-sectional retrospective study. Data were collected from 2 sites where the new Dense Cataract Measurement mode for the OLCR optical biometer (Lenstar LS 900) had been implemented. Related ultrasound (US) data for patients whose eyes could not be measured with optical biometry were also collected where available. The percentage of eyes that were measurable in the new mode that were not measurable in the standard mode was calculated. The quality of the measurements by the new mode was evaluated using postoperative axial length measurements and/or concurrent US measurements, where available. Data for 4791 eyes were available for analysis. Axial length measurement was possible using the standard algorithm in 94.4% of cases. The use of the new mode allowed for measurement of an additional 4.0% of cases, a statistically significant increase (P < .001). Comparisons of AL measurements with concurrent US or postoperative optical biometry showed high correlations, with the 95% limits of agreement of -0.47 to +0.29 mm, similar to results for standard measurements. The new measurement mode of the OLCR system provided a significant increase in the number of eyes that could be measured with optical biometry. Axial length measurements using the new mode appeared as reliable as those made using the standard measurement mode. No author has a financial or proprietary interest in any material or method mentioned.

Comparison of corneal power and astigmatism in normal eyes using 4 different devices

AbstractPurpose To compare corneal power and astigmatism in normal subjects obtained from dual Scheimpflug analyzer (Galilei), single Scheimpflug analyzer (Pentacam), optical low coherence reflectometer (Lenstar) and autokeratometer (AR)Methods Forty‐eight eyes of 27 subjects were evaluated with 4 different devices. Steep, flat and mean keratometry (K) values and astigmatism magnitude were measured. Corneal power vectors, J0 and J45, were calculated using Jackson cross cylinder. Repeated‐measured ANOVA with Bonferroni post hoc analysis was performed to compare the measurements, and correlation was accessed by Pearson correlation test. Agreement was assessed by Bland‐Altman analysis and 95 % limit of agreement (LoA) was calculated.Results Mean K values measured by Galilei, Pentacam, Lenstar, and AR were 44.34 ± 1.03 diopters (D), 44.52 ± 1.03 (D), 44.30 ± 0.98 (D), and 44.44 ± 0.92 (D), respectively. Steep K, J0, and J45 did not show significant differences (all p &gt; 0.05), however, mean K, flat K, and astigmatism were significantly different (p= 0.002, 0.002, 0.005, respectively). All measured parameters were significantly correlated with each other (Pearson correlation test, all p &lt; 0.05). For corneal power and astigmatism, 95% LoA varied from 1 to 2 (D).Conclusion Even though the measurements of corneal power and astigmatism were correlated with each other, some values showed significant differences and the agreements were not good. Therefore, the measurements of each device couldn’t be used interchangeably in clinical practice.

The Ocular Biometric Differences of Diabetic Patients

To investigate the differences in ocular biometric and keratometric characteristics in comparison with biometric measurements using the noncontact optical low coherence reflectometer (OLCR) (Lenstar LS 900, Haag-Streit) on diabetic patients. The eyes of 170 patients were included in this study, including 81 diabetic and 89 nondiabetic subjects. Optical biometric measurements of diabetic and nondiabetic patients (between the ages of 25 and 85 years) who applied to the ophthalmology clinic were noted from March to June 2013. Detailed ophthalmologic examinations were done for every subject. Biometric measurements were done using the noncontact OLCR device. Patient age ranged from 29 to 83 years. Subgroup analyses were done in diabetic patients according to their Hba1C levels. The minimum Hba1C value was 5.3, maximum was 12.4, and mean was 7.56 ± 1.48. The median duration of diabetes was 5 years (25th-75th percentile 3.00-11.75). Diabetic patients were found to have thicker lens and shallower anterior chamber in both eyes compared to nondiabetic control subjects. There were no statistical differences between the groups according to central corneal thickness, axial length, or keratometric values in both eyes. However, lens thicknesses were found to be thicker and anterior chamber depth values were found to be shallower in the diabetic group in both eyes. It may useful to determine eyeglasses prescription, refractive surgery calculation, lens selection, and previous cataract surgery according to biometric measurements after the regulation of blood glucose.

Repeatability and Reproducibility of Biometry and Keratometry Measurements Using a Noncontact Optical Low-Coherence Reflectometer and Keratometer

To evaluate the repeatability, reproducibility, or both of the biometry and keratometry measurements obtained by a new optical low-coherence reflectometer and keratometer (Lenstar LS 900, version 1.10; Haag-Streit). Prospective, comparative, observational study. Private practice, Lynwood, California, and Santa Monica, California. The measurements of the second eye to be operated on of 37 patients between October 2010 and January 2011 were analyzed. The axial length, central corneal thickness, aqueous depth, anterior chamber depth, crystalline lens thickness, white-to-white corneal diameter, as well as the keratometric readings at the flattest meridian, the steepest meridian, the average K, the amount of astigmatism, and the minus astigmatic cylinder axis were measured before surgery on the patient's first eye and were repeated 1 month later before the second eye surgery. main outcome measures: The repeatability and reproducibility of the biometry and keratometry measurements. Intrasession repeatability and intersession reproducibility were excellent with a very low coefficient of variation and high interclass correlation coefficients for all measured parameters. Bland-Altman plots show good correlation for axial length measurements (95% limits of agreement ranging from -0.056 to +0.04 mm), anterior chamber depth (-0.22 to +0.18 mm), crystalline lens thickness (-0.21 to +0.27 mm), corneal diameter (-0.28 to +0.24 mm), average keratometric readings (-0.56 to +0.47 diopters), and amount of astigmatism (-0.58 to +0.40 diopters). The precision of the measurements obtained by the new optical reflectometer and keratometer is extremely high.

In vivo measurement of central corneal thickness in normal chicks (Gallus gallus domesticus) with the optical low-coherence reflectometer

To determine the practicability and accuracy of central corneal thickness (CCT) measurements in living chicks utilizing a noncontact, high-speed optical low-coherence reflectometer (OLCR) mounted on a slit lamp. Twelve male chicks (Gallus gallus domesticus). Procedures Measurements of CCT were obtained in triplicate in 24 eyes of twelve 1-day-old anaesthetized chicks using OLCR. Every single measurement taken by OLCR consisted of the average result of 20 scans obtained within seconds. Additionally, corneal thickness was determined histologically after immersion fixation in Karnovsky's solution alone (20 eyes) or with a previous injection of the fixative into the anterior chamber before enucleation (4 eyes). Central corneal thickness measurements using OLCR in 1-day-old living chicks provide a rapid and feasible examination technique. Mean CCT measured with OLCR (189.7 ± 3.34 μm) was significantly lower than histological measurements (242.1 ± 47.27 μm) in eyes with fixation in Karnovsky's solution (P = 0.0005). In eyes with additional injection of Karnovsky's fixative into the anterior chamber, mean histologically determined CCT was 195.2 ± 8.25 μm vs. 191.9 ± 8.90 μm with OLCR. A trend for a lower variance was found compared to the eyes that had only been immersion fixed. Optical low-coherence reflectometry is an accurate examination technique to measure in vivo CCT in the eye of newborn chicks. The knowledge of the thickness of the chick cornea and the ability to obtain noninvasive, noncontact measurements of CCT in the living animal may be of interest for research and development of eye diseases in chick models.

Intraobserver and interobserver repeatability of ocular components measurement in cataract eyes using a new optical low coherence reflectometer

The purpose of the study was to assess intraobserver and interobserver repeatability of eight ocular components measurement in cataract eyes using the optical low-coherence reflectometer Lenstar LS 900®. Five consecutive measurements of ocular components were taken by two examiners using the Lenstar. Components analyzed were: central corneal thickness, lens thickness, anterior chamber depth, axial length, retinal thickness, keratometry, white-to-white distance, and pupillometry. Within-subject standard deviation and the coefficient of variation were calculated for evaluation of intraobserver repeatability. Bland-Altman analysis was used for assessment of interobserver repeatability. Thirty-two eyes of 22 patients were included. For both observers, the smallest intraobserver coefficient of variation was obtained for axial length, while the largest was found for corneal steepest meridian position. Interobserver repeatability demonstrated less repeatable results for white-to-white distance and corneal steepest meridian position. Considering axial length and anterior chamber depth values, predicted refractive error was 0 ± 0.05 D and 0.02 ± 0.19 D respectively in 95% of observations. The Lenstar LS 900® evidenced excellent repeatability and observers´ independent results of all components analyzed except white-to-white distance and corneal steepest meridian position measurements. To the best of our knowledge, this is the first study on interobserver repeatability of optical low-coherence reflectometry in cataract eyes.

Reproducibility of Ocular Biometry with a New Noncontact Optical Low-Coherence Reflectometer in Children

To evaluate the reproducibility of Lenstar in the pediatric population. Three consecutive measurements per eye by 2 ophthalmologists with a total of 6 measurements per eye were performed using Lenstar. Axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), and corneal curvatures (K1 and K2) were measured for right and left eyes in 154 school-age children. Right and left eyes were analyzed separately. Each optical parameter obtained by 2 examiners was compared by paired samples t test. Intraobserver and interobserver correlation coefficients (r) were calculated for each variable. Significance was attributed when p<0.05. Measurements could be performed in 152 of the children included. The mean measurements were not different statistically except for left AL (23.22±0.81 vs 23.21±0.82 mm; p=0.014), left CCT (548.5±32.3 vs 548.0±32.7 µm; p=0.013), and right ACD (3.19±0.25 vs 3.19±0.25 mm; p=0.033). Intraobserver r values were all above 0.957 except for left LT (r=0.786) for examiner 2. Interobserver r values were all above 0.979. Although statistical significance was obtained in some variables, they were clinically negligible. The intraobserver and interobserver relation coefficients were very high for all optical parameters including the r value for left LT for examiner 2 (r=0.786). Lenstar is a highly reproducible, user independent, and tolerable instrument for ocular biometry in the pediatric population, with no anesthesia or discomfort.

Analog-Based Detection Method in Optical Low-Coherence Reflectometer for Measurement of Retardation and Fast-Axis Angle

This study presents a novel detection method in optical low-coherence reflectometer for the simultaneous measurement of the reflectivity and birefringence characteristics of a sample. By implementing analog electronics in a standard two-channel time domain low-coherence reflectometer, the ratio of the envelope amplitude between two orthogonal interferometric signals, which is used for calculating the retardation angle, can then be analog-decoded using a differential detection scheme based on the quotient rule of a logarithmic function. The proposed method for direct retardation measurement benefits from common-mode noise suppression advantages that support efforts to improve the accuracy of phase retardation measurement. Furthermore, a full interferometric signal to extract the phase information is not needed for calculating fast-axis angle. Reductions in data acquisition rates and processing time are expected. The results from a calibrated test plate were correspondingly presented.

Uncertainties on distance and chromatic dispersion measurement using optical low-coherence reflectometry

The optical low-coherence reflectometer (OLCR) is a very powerful tool to characterize optical fibres and integrated optical components. However, this is a very complex set-up and in addition to that it performs Fourier transforms. Evaluating uncertainty in these conditions becomes very complicated. To overcome this difficulty, we chose to use an alternative statistical method as partly described in the ISO5725 standard. The most significant quantities which can be extracted from the OLCR measurements are length and chromatic dispersion (CD) of the optical component. An uncertainty of 0.036 mm (k = 2) for the length and of 0.12 ps nm−1 km−1 (k = 2) for the CD can be achieved for a 1 m long G652 type fibre.

Integrated-optic variable delay line and its application to a low-coherence reflectometer

We propose a large-scale variable delay line based on planar light-wave circuit technology and its application as a reference arm in an optical low-coherence reflectometer. This variable delay line is composed of 16 asymmetrical delay arm pairs sandwiched between 2 optical switches, which select the path for a needed delay. This configuration enables us to eliminate the need for a moving part in the reflectometer. We can scan the reference arm over a length of 262.1 mm with a step of less than 1.0 microm in air and achieve reflectometer sensitivity of about -47 dB.

Central corneal thickness measurement with the Pentacam Scheimpflug system, optical low-coherence reflectometry pachymeter, and ultrasound pachymetry

To assess the intraoperator repeatability and interoperator reproducibility of central corneal thickness measurements by the Pentacam Scheimpflug imaging system (Oculus) and the optical low-coherence reflectometer (OLCR) pachymeter (Haag-Streit) and to compare them with those of ultrasound (US) pachymetry. Assaf Harofe Medical Center Ophthalmology Outpatient Clinic, Zerifin, Israel. Repeatability was determined from 10 successive measurements in each of 4 healthy patients. Reproducibility for the Pentacam Scheimpflug system was determined from measurements by 2 operators in each of 24 patients; in these 24 patients, central corneal thickness measurements were compared between the Pentacam and US pachymetry. For the OLCR pachymeter, reproducibility was determined from measurements by 2 operators in each of 16 patients, in whom central corneal thickness was also measured with the Pentacam. Mean coefficient of repeatability was 0.84% for the Pentacam Scheimpflug system and 0.33% for the OLCR pachymeter. For the Pentacam, the coefficient of interoperator reproducibility was 1.10% and the 95% limits of agreement were -10.2 microm to +11.9 microm. Mean difference between Pentacam and US was 6.09 microm. For the OLCR pachymeter, the coefficient of interoperator reproducibility was 0.59% and the 95% limits of agreement were -5.4 microm to +7.0 microm. Mean difference between central corneal thickness values obtained with the OLCR pachymeter and Pentacam Scheimpflug system was 1.7 microm. Objective, noncontact measurement of central corneal thickness with the Pentacam Scheimpflug system and OLCR pachymeter was convenient and yielded excellent intraoperator repeatability and interoperator reproducibility. Central corneal thickness values obtained with the Pentacam were similar to those obtained with both the OLCR pachymeter and an US pachymeter. Further research is needed to corroborate whether central corneal thickness measurements by the Pentacam and OLCR devices can be used interchangeably and are more clinically useful than US pachymetry.

Dual reference arm low-coherence interferometer-based reflectometer for optical coherence tomography (OCT) application

The paper reports initial experimentation with an optical low-coherence reflectometer with two linked reference arms for optical coherence tomography (OCT) application. The reflectometer supports: (1) inherent doubling of achievable axial scanning range and, (2) quasi-simultaneous or simultaneous multiple specimen delay scanning. Extended axial scanning range was achieved simply by arranging the two reference arms, linked by a single variable optical delay line (ODL) for adjusting paths lengths, in opposite orientation to each other. This feature is particularly useful with ODLs of limited axial scanning range. The opposing reference arms scan different axial locations in the specimen remotely and quasi-simultaneous or simultaneous OCT imaging through multiple specimen delay scanning is possible. In this initial study the functionality of the dual channel reflectometer is illustrated by acquiring OCT images pairs at two axial positions quasi-simultaneously. The potential of the configuration in shortening A-scan time by factor 0.5 through simultaneous specimen multiple delay scanning is also explored in the paper.

Detection of neural activity using phase-sensitive optical low-coherence reflectometry

We demonstrate non-contact sub-nanometer optical measurement of neural surface displacement associated with action potential propagation. Experimental results are recorded from nerve bundles dissected from crayfish walking leg using a phase-sensitive optical low coherence reflectometer. No exogenous chemicals or reflection coatings are applied. Transient neural surface displacement is less than 1 nm in amplitude, 1 ms in duration and is coincident with action potential arrival to the optical measurement site. Because the technique uses back-reflected light, noninvasive detection of various neuropathies may be possible.

Analysis of optical-injected distributed feedback lasers using complex optical low-coherence reflectometry

A theoretical and experimental investigation of reflectograms obtained for a distributed feedback (DFB) semiconductor laser using a phase-controlled high-resolution optical low-coherence reflectometer was carried out, yielding the effective group refractive index and its variation above threshold, the cavity internal loss, as well as the grating coupling factor of a multiquantum-well DFB laser. In addition, direct measurements of the injection-induced complex-modal index changes are presented for the first time.

Analysis of polarization dependence of optical low coherence reflectometry using an active faraday rotator

This paper analyzes the polarization dependence of the reflection signal from an optical low coherence reflectometer (OLCR) with an active Faraday rotator. I derive output signals from the OLCR at Faraday rotations of 0 and 90/spl deg/, respectively, using unitary matrix representations of the states of polarization of the return and local oscillator lights. I investigate the polarization dependence of the reflection signal, defined as the sum of the two outputs, for different polarizer positions and show that polarization fading in the signal can be eliminated by placing the polarizer just before or after the Faraday rotator.