Optical Low-coherence Interferometry Research Articles

Functional changes in the myopic retina compromise emmetropization

During emmetropization, the retina analyses the focus of the image and generates appropriate biochemical signals to control choroidal thickness and scleral growth. Using commercially available optical low coherence interferometry (the Lenstar LS 900), changes in eye length in the micrometre range can be picked up already after 30 min when young human subjects watch movies that were digitally filtered. We found that the emmetropic retina can distinguish real optical positive defocus from simulated/calculated defocus. It triggered choroidal thickening in the first case, and thinning in the second. Strikingly, the myopic retina was not responsive, and the choroid became thinner in both cases. Longitudinal chromatic aberration (LCA) would be a perfect signal to tell the retina where the focal plane is. We simulated chromatic defocus in our movies. Either the red or the blue plane of the RGB format was spatially filtered to simulate chromatic defocus. When blue was ‘in focus’, eyes became longer, but when red was ‘in focus’ eyes became shorter. Again, myopic eyes did not respond, suggesting that the myopic retina no longer responded to LCA. Taken together, we found that the myopic retina had undergone functional changes such that no growth‐inhibiting signal was generated. As a consequence, eye growth would become open loop, explaining why myopia does not inhibit itself.

Mirau-based line-field confocal optical coherence tomography for three-dimensional high-resolution skin imaging.

SignificanceLine-field confocal optical coherence tomography (LC-OCT) is a recently introduced high-resolution imaging modality based on a combination of low-coherence optical interferometry and reflectance confocal optical microscopy with line illumination and line detection. Capable of producing three-dimensional (3D) images of the skin with cellular resolution, in vivo, LC-OCT has been mainly applied in dermatology and dermo-cosmetology. The LC-OCT devices capable of acquiring 3D images reported so far are based on a Linnik interferometer using two identical microscope objectives. In this configuration, LC-OCT cannot be designed to be a very compact and light device, and the image acquisition speed is limited.AimThe objective of this work was to develop a more compact and lighter LC-OCT device that is capable of acquiring images faster without significant degradation of the resolution and with optimized detection sensitivity.ApproachWe developed an LC-OCT device based on a Mirau interferometer using a single objective. Dynamic adjustment of the camera frequency during the depth scan is implemented, using a faster camera and a more powerful light source. The reflectivity of the beam-splitter in the Mirau interferometer was optimized to maximize the detection sensitivity. A galvanometer scanner was incorporated into the device for scanning the illumination line laterally. A stack of adjacent B-scans, constituting a 3D image, can thus be acquired.ResultsThe device is able to acquire and display B-scans at 17 fps. 3D images with a quasi-isotropic resolution of (1.3, 1.9, and in the , and directions, respectively) over a field of () can be obtained. 3D imaging of human skin at cellular resolution, in vivo, is reported.ConclusionsThe acquisition rate of the B-scans, at 17 fps, is unprecedented in LC-OCT. Compared with the conventional LC-OCT devices based on a Linnik interferometer, the reported Mirau-based LC-OCT device can acquire B-scans times faster. With potential advantages in terms of compactness and weight, a Mirau-based device could easily be integrated into a smaller and lighter handheld probe for use by dermatologists in their daily medical practice.

Comparative Analysis of Axial Length Measurements by Optical Biometers Based on Partial Coherence Interferometry Versus Optical Low-Coherence Interferometry: An Office Audit.

PurposeIn this study, we aimed to compare axial length (AL) measurements of the IOLMaster 500 (Carl Zeiss Meditec AG, Jena, Germany), based on partial coherence interferometry (PCI) versus the Aladdin (Topcon Healthcare, Oakland, NJ), based on optical low-coherence interferometry (OLCI), in a clinical setting.MethodsA retrospective analysis of the records of patients presenting for cataract surgery at an ophthalmology practice between October 2019 and March 2020 was performed. All patients had biometry measurements on the IOLMaster 500 and the Aladdin. Data collected included patient demographics, cataract morphology and type, and AL measurements. The IOLMaster 500 and Aladdin measurements were compared using the unpaired t-test and Chi-squared test.ResultsIn total, 393 eyes (197 patients) were included (91 males, 107 females) in the study. The IOLMaster 500 was unable to successfully obtain AL measurements in seven eyes (1.8%) and the Aladdin in 26 eyes (6.6%). The difference was statistically significant (p=0.0007). Advanced and central posterior subcapsular cataracts were common in eyes that had unsuccessful measurements. In the eyes successfully measured, the mean AL for the IOLMaster was 24.04 ±1.32 mm, while it was 24.04 ±1.34 mm for the Aladdin. However, this difference was not statistically significant (p=0.9165).ConclusionThe IOLMaster 500 performed better in terms of the number of eyes for which AL measurements were successfully obtained compared to the Aladdin. This may be partly related to high volumes of advanced cataracts treated at our practice. However, this being a retrospective study, a cause-and-effect relationship could not be established.

Comparison of optical low coherence interferometry and Scheimpflug imaging combined with partial coherence interferometry biometers in cataract eyes.

PURPOSE:The purpose of the study was to evaluate the agreement between measurements by optical low-coherence interferometry (OLCI, Aladdin) and those by Scheimpflug imaging combined with partial coherence interferometry (Scheimpflug-PCI, Pentacam AXL) in cataract patients.METHODS:This was a retrospective comparative study conducted in the United Arab Emirates. Axial length (AL), corneal power (keratometry, K), anterior chamber depth (ACD), and corneal astigmatism in patients with cataracts were measured with both devices. Difference and correlation were evaluated with paired t-test (p) and Pearson's correlation coefficient®, respectively.RESULTS:A total of 164 eyes of 95 patients were analyzed (164 eyes for K, 155 for ACD, and 112 for AL). The mean AL taken by OLCI was longer than that by Scheimpflug-PCI (23.25 mm vs. 23.23 mm, P ≤ 0.0001), showing an excellent correlation between the two (r = 0.9990). ACD measured by OLCI was 0.08 mm shallower than that by Scheimpflug-PCI (P = 0.0003, r = 0.7386). Corneal power measured by OLCI was lower than that by Scheimpflug-PCI (differences in mean K, flat K, and steep K were 0.05 diopters (D), 0.08 D, and 0.02 D, respectively), showing very strong correlations between the two devices (r = 0.9614, 0.9445, and 0.9535, respectively). Only flat K values measured with the two devices were significantly different (P = 0.0428). There were no statistically significant differences in the magnitude of astigmatism or J45 vector between the two devices (P = 0.1441 and P = 0.4147, respectively). However, J0 vector values were significantly different (P = 0.0087).CONCLUSION:Although OCLI and Scheimpflug-PCI showed strong correlations for measurements of AL, K, ACD, and corneal astigmatism in cataract patients, there were small but statistically significant differences in AL, ACD, flat K, and J0 vector. Thus, these two devices are not interchangeable for calculating intraocular lens power.

New Approaches and Technologies to Improve Accuracy of Acute Otitis Media Diagnosis.

Several studies have shown that in recent years incidence of acute otitis media (AOM) has declined worldwide. However, related medical, social, and economic problems for patients, their families, and society remain very high. Better knowledge of potential risk factors for AOM development and more effective preventive interventions, particularly in AOM-prone children, can further reduce disease incidence. However, a more accurate AOM diagnosis seems essential to achieve this goal. Diagnostic uncertainty is common, and to avoid risks related to a disease caused mainly by bacteria, several children without AOM are treated with antibiotics and followed as true AOM cases. The main objective of this manuscript is to discuss the most common difficulties that presently limit accurate AOM diagnosis and the new approaches and technologies that have been proposed to improve disease detection. We showed that misdiagnosis can be dangerous or lead to relevant therapeutic mistakes. The need to improve AOM diagnosis has allowed the identification of a long list of technologies to visualize and evaluate the tympanic membrane and to assess middle-ear effusion. Most of the new instruments, including light field otoscopy, optical coherence tomography, low-coherence interferometry, and Raman spectroscopy, are far from being introduced in clinical practice. Video-otoscopy can be effective, especially when it is used in association with telemedicine, parents’ cooperation, and artificial intelligence. Introduction of otologic telemedicine and use of artificial intelligence among pediatricians and ENT specialists must be strongly promoted in order to reduce mistakes in AOM diagnosis.

Detection of Ultralow Light Power Back-Reflected or Back-Scattered by Optical Components Using Balanced Low-Coherence Interferometry

We use balanced optical low-coherence interferometry to measure the ultralow light power back-reflected and/or back-scattered by optical interfaces. Indeed, backscattered light from optical surfaces can be a critical source of noise in interferometric gravitational-wave detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, or the Laser Interferometer Space Antenna (LISA), and therefore, it is required to characterize, with high sensitivity, the scattering properties of elementary components involved in their optical design. The use of a broadband light source makes an easy identification of the scattering interface possible, while the implementation of balanced interferometric detection allows very low light levels to be detected, thanks to the simultaneous use of coherent gain and source intensity noise suppression. Experimental results are reported, first on bare glass optical windows (N-BK7 and S-LAH66) and then on a silver-coated mirror, that demonstrate the ability of this setup to quantify specular- or diffuse-reflectance coefficients as low as ${10}^{\ensuremath{-}11}$.

Tree shrews do not maintain emmetropia in initially-focused narrow-band cyan light

We asked if emmetropia, achieved in broadband colony lighting, is maintained in narrow-band cyan light that is well focused in the emmetropic eye, but does not allow for guidance from longitudinal chromatic aberrations (LCA) and offers minimal perceptual color cues. In addition, we examined the response to a −5 D lens in this lighting. Seven tree shrews from different litters were initially housed in broad-spectrum colony lighting. At 24 ± 1 days after eye opening (Days of Visual Experience, DVE) they were housed for 11 days in ambient narrow-band cyan light (peak wavelength 505 ± 17 nm) selected because it is in focus in an emmetropic eye. Perceptually, monochromatic light at 505 nm cannot be distinguished from white by tree shrews. While in cyan light, each animal wore a monocular −5 D lens (Cyan −5 D eyes). The fellow eye was the Cyan no-lens eye. Daily awake non-cycloplegic measures were taken with an autorefractor (refractive state) and with optical low-coherence optical interferometry (axial component dimensions). These measures were compared with the values of animals raised in standard colony fluorescent lighting: an untreated group (n = 7), groups with monocular form deprivation (n = 7) or monocular −5 D lens treatment (n = 5), or that experienced 10 days in total darkness (n = 5). Refractive state at the onset of cyan light treatment was low hyperopia, (mean ± SEM) 1.4 ± 0.4 diopters. During treatment, the Cyan no-lens eyes became myopic (−2.9 ± 0.3 D) whereas colony lighting animals remained slightly hyperopic (1.0 ± 0.2 D). Initially, refractions of the Cyan −5 D eyes paralleled the Cyan no-lens eyes. After six days, they gradually became more myopic than the Cyan no-lens eyes; at the end of treatment, the refractions were −5.4 ± 0.3 D, a difference of −2.5 D from the Cyan no-lens eyes. When returned to colony lighting at 35 ± 1 DVE, the no-lens eye refractions rapidly recovered towards emmetropia but, as expected, the refraction of the −5 D eyes remained near −5 D. Vitreous chamber depth in both eyes was consistent with the refractive changes. In narrow-band cyan lighting the emmetropization mechanism did not maintain emmetropia even though the light initially was well focused. We suggest that, as the eyes diverged from emmetropia, there were insufficient LCA cues for the emmetropization mechanism to utilize the developing myopic refractive error in order to guide the eyes back to emmetropia. However, the increased myopia in the Cyan −5 D eyes in the narrow-band light indicates that the emmetropization mechanism nonetheless detected the presence of the lens-induced refractive error and responded with increased axial elongation that partly compensated for the negative-power lens. These data support the conclusion that the emmetropization mechanism cannot maintain emmetropia in narrow-band lighting. The additional myopia produced in eyes with the −5 D lens shows that the emmetropization mechanism responds to multiple defocus-related cues, even under conditions where it is unable to use them to maintain emmetropia.

Agreement of ocular biometry measurements between 2 biometers

To establish the agreement of routine measurements taken before cataract surgery between the Aladdin biometer, which is based on optical low-coherence interferometry (OLCI), and the Lenstar biometer, which is based on optical low-coherence reflectometry (OLCR). Virginia Eye Consultants, Norfolk, Virginia, USA. Prospective case series. Biometry parameters in the same eye were measured using the OLCI biometer and the OLCR biometer at separate preoperative visits. Measured parameters included axial length (AL), anterior chamber depth (ACD), keratometry (K) values (flat K, steep K, steep K axis), lens thickness, central corneal thickness (CCT), and the white-to-white (WTW) distance. Adverse events were monitored. Data were collected for 101 eyes (65 right eyes) of 101 patients (mean age 67.9years±7.2 [SD]). The mean values measured by the OLCI biometer and OLCR biometer, respectively, were as follows: AL, 23.88±1.23mm and 23.89±1.23mm; ACD, 3.24±0.36mm and 3.25±0.37mm; flat K, 43.63±1.65 diopters (D) and 43.61±1.67 D; steep K, 44.59±1.76 D and 44.61±1.77 D; lens thickness, 4.61±0.39mm and 4.45±0.45mm; CCT, 0.55±0.04mm and 0.55±0.04mm; and WTW distance, 11.63±0.41 and 12.03±0.49mm. There was a high correlation between all parameter measurements obtained by the 2 devices. No adverse events occurred. The measurements of the OLCI biometer were as reliable and reproducible as those of a leading biometer on the market, with the former having the advantage of an incorporated full corneal topographer.

Evaluation of biometry and corneal astigmatism in cataract surgery patients in Northern United Arab Emirates.

To analyze biometric parameters and patterns of corneal astigmatism in cataract surgery patients using optical low-coherence interferometry in Northern United Arab Emirates (UAE). Axial length (AL), anterior chamber depth (ACD), horizontal corneal diameter (white to white, WTW) and flat and steep keratometry (K1 and K2, respectively) were optically measured using optical low-coherence interferometry (Aladdin). Ocular datasets acquired between 2015 and 2018 were collected and analyzed. This study evaluated 238 eyes of 123 cataract patients with a mean age of 67.1 ± 9.4years. Mean AL, ACD, WTW, K1, and K2 were 23.22 ± 0.99mm, 3.05 ± 0.36mm, 11.19 ± 0.46mm, 43.72 ± 1.80 diopter (D), and 45.04 ± 1.71D, respectively. Mean corneal astigmatism was 1.32 ± 0.97D. Corneal astigmatism of 1.5D or greater was found in 32.4%. With the rule, against the rule, and oblique astigmatism were found in 29.8%, 57.1%, and 13.0% of eyes, respectively. Results of this study provide normative data for cataract surgery as an informative reference in Northern UAE, the Middle East. This study showed higher corneal astigmatism in Northern UAE than those in other countries.

Ocular measurements of a swept-source biometer: Repeatability data and comparison with an optical low-coherence interferometry biometer

To assess the repeatability of a swept-source biometer in phakic and pseudophakic patients, including astigmatism analysis, and to compare measurement data with those obtained by an optical low-coherence interferometry method. Borsod-Abaúj-Zemplén County Central Hospital and University Teaching Hospital, Miskolc, Hungary. Evaluation of diagnostic technologies. One eye of each patient was examined with the Argos and Aladdin devices. With the Argos, three repeated measurements were performed. Biometric parameters and cross-cylinder power vector components of astigmatism were assessed. Descriptive and repeatability data of the Argos were observed, and Bland-Altman plots were created. The study comprised 96 eyes (50 phakic and 46 pseudophakic) of 96 patients (mean age 69.22years and 71.14years, respectively). The two devices showed a significant difference regarding astigmatism and corneal diameter in the phakic group (measured larger by Argos, P<.05). In the pseudophakic group, only the corneal diameter data were significantly different (measured larger by Argos, P=.02). No other statistically significant differences were observed in either group. An excellent intraclass correlation coefficient (ICC) was reported on the Argos device in the case of all measured parameters except for the diopter values of astigmatism and the vector values of the astigmatism in the phakic group. In the pseudophakic group, the ICC was moderate in the case of anterior chamber depth (ACD) and good in the case of astigmatism and vectorial data. The repeatability data regarding the Argos biometer were excellent for all parameters except astigmatism data in both groups and ACD readings in the pseudophakic group. However, only a limited agreement was observed between these devices in both groups.

Large Axial Range Frequency-Domain Optical Low Coherence Interferometry

In this letter, we propose a new experimental setup to extend the measurement range of frequency-domain low coherence interferometry (FD-LCI) from 3 mm to 2 cm. The FD-LCI can be extended to the technique of frequency domain optical coherence tomography by performing additional lateral scanning. This new and simple arrangement just attaches an extra interferometer before the spectrometer in a typical FD-LCI setup. With this configuration, it is possible to overcome the limitation of the dynamic range of the conventional technique. This allows us to measure the optical path difference of the sample of interest, which is outside the detection range of the spectrometer, using an extra interferometer as a tuner system. In addition, this tuning allows significant minimization of the effects produced by the fall-off. The accuracy of the new system is obtained by adding the FD-LCI and the tuning micrometric translator accuracies. In our experimental setup, this value is 20 $\mu \text{m}$ .

Ultra-long (290 km) remote interrogation sensor network based on a random distributed feedback fiber laser.

In this work, an interferometric sensor has been interrogated 290 km away from the monitoring station, reaching the longest distance in fiber optic sensing up to date. This has been attained by employing a double-pumped random distributed feedback fiber laser as the light source for a fiber optic low-coherence interferometry scheme. Additionally, the capability of the system to achieve coherence multiplexing for ultra-long range measurements (up to 270 km) has been proved, without presenting crosstalk between the sensors. The use of coherence multiplexing together with a random distributed feedback fiber laser addresses two of the main limitations of long-range sensing setups: their limited multiplexing capability and the need to reach the maximum monitoring distance.

Analysis of corneal astigmatism with NIDEK axial length scan in caucasian cataract surgery candidates.

The aim of the study was to analyze and quantify the pattern of corneal astigmatism in Caucasian cataract surgery patients using a new optical biometer (axial length [AL] Scan, NIDEK Co., Gamagori, Japan). The datasets of cataract surgery patients acquired between March 1, 2014, and April 15, 2016, were collected and analyzed. The corneal power (flat keratometry, steep keratometry, and mean keratometry), negative cylinder power, and axis of astigmatism were recorded. Keratometry values were optically measured by optical low coherence interferometry (AL-Scan, NIDEK Co., Ltd.,) before cataract extraction. The study comprised 1233 eyes of 838 consecutive cataract candidates with a mean age of 66.8 ± 10.7 years (range 40-97 years). The mean keratometry value and corneal astigmatism were 43.69 ± 1.61 D and 0.84 ± 0.70 D, respectively. Corneal astigmatism of 1.00 D or greater was found in 344 eyes (27.9%), and 548 eyes (44.4%) had against-the-rule astigmatism. A trend toward decreasing J0 and J45 with age was found by linear regression models. The per-year increase in age was associated with a J0 and J45 decrease of 0.002 D and 0.001D, respectively. This study provides the distribution of astigmatism axis and power for cataract patients in age subsets from Turkey.

Noncontact measurement of substrate temperature by optical low-coherence interferometry in high-power pulsed magnetron sputtering

Substrate temperature is one of the important parameters that affect the quality of deposited films. The monitoring of the substrate temperature is an important technique of controlling the deposition process precisely. In this study, the Si substrate temperature in high-power pulse magnetron sputtering (HPPMS) was measured by a noncontact method based on optical low-coherence interferometry (LCI). The measurement was simultaneously performed using an LCI system and a thermocouple (TC) as a contact measurement method. The difference in measured value between the LCI system and the TC was about 7.4 °C. The reproducibilities of measurement for the LCI system and TC were ±0.7 and ±2.0 °C, respectively. The heat influx from the plasma to the substrate was estimated using the temporal variation of substrate temperature and increased from 19.7 to 160.0 mW/cm2 with increasing target applied voltage. The major factor for the enhancement of the heat influx would be charged species such as ions and electrons owing to the high ionization degree of sputtered metal particles in HPPMS.

Accuracy of optical biometry combined with Placido disc corneal topography for intraocular lens power calculation.

PurposeTo investigate the accuracy of a new optical biometer for intraocular lens (IOL) power calculation in eyes undergoing cataract surgery.MethodsConsecutive eyes of patients undergoing cataract surgery with the same IOL model were enrolled in a prospective cohort study.Axial length (AL) and corneal power were measured with an optical biometer based on optical low-coherence interferometry and Placido-disc corneal topography. IOL power was calculated with the Hoffer Q, Holladay 1 and SRK/T formulas. For each formula the lens constant was optimized in retrospect in order to achieve a mean prediction error (PE) of zero (difference between the predicted and the postoperative refraction). Median absolute error (MedAE) and percentage of eyes with PE ±0.50 D were calculated.ResultsSeventy-four eyes of 74 cataract patients were enrolled. The MedAE was 0.25 D with all formulas. A PE within ±0.50 D was obtained in 89.04% of cases with the Hoffer Q and SRK/T formulas, and in 87.67% of cases with the Holladay 1 formula.ConclusionsThe optical biometer investigated in the present study provides accurate measurements for IOL power calculation.

Axial Length Measurement Failure Rates With Biometers Using Swept-Source Optical Coherence Tomography Compared to Partial-Coherence Interferometry and Optical Low-Coherence Interferometry

To compare a new swept-source optical coherence tomography (SSOCT)-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. Reliability study. A total of 377 eyes of 210 patients were scanned with the 3 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 3 biometers. 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. χ2 analyses indicated a significant difference in failure rate between all 3 devices (P < .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 vs IOLMaster-0.09 to 0.08mm; OA-2000 vs Aladdin-0.10 to 0.07mm; IOLMaster vs Aladdin-0.05 to 0.04mm). The OA-2000, a new SSOCT-based biometer, outperformed both the IOLMaster and Aladdin biometers in very advanced cataracts of various morphologies. The use of SSOCT 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.

Comparative analysis of optical biometers

To evaluate the level of agreement, repeatability, and correlation of 2 optical biometers, the IOLMaster (based on partial coherence interferometry [PCI]) and Aladdin (based on optical low-coherence interferometry [OLCI]) in terms of axial length (AL), mean keratometry (K), anterior chamber depth (ACD), and corneal diameter. Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom. Prospective comparative case series. Each participant had biometry with both biometers. The level of agreement between thebiometers was calculated using the Bland-Altman method. Double-angle polar plots were used to display the astigmatism vectors. Internal consistency was computed with the Cronbach α coefficient of reliability, whereas the dispersion of probability distribution was assessed with the coefficient of variation (CoV). The intraoperator repeatability was analyzed using the intraclass correlation coefficient (ICC); the AL was evaluated in all eyes and the mean K and the ACD in a subset of eyes. The study comprised 215 eyes; the ICC for the mean K and ACD was calculated in a subset of 54 eyes. There was a statistically significant difference between the 2 biometers in all measurements (P<.05). The level of agreement was high with both methods. The ICC and internal consistency were excellent with both biometers; the CoVs were low. The OLCI biometer provided good agreement and repeatability compared with the PCI biometer, the current gold standard in ocular biometry. Further comparative studies are necessary to clearly define the role of the OLCI biometer in predicting postoperative refractive outcomes. Dr. Findl is a scientific advisor to Carl Zeiss Meditec AG. None of the other authors has a financial or proprietary interest in any material or method mentioned.

Multicenter study of optical low-coherence interferometry and partial-coherence interferometry optical biometers with patients from the United States and China

To evaluate the agreement between the measurements provided by a new optical biometer, the Aladdin, based on optical low-coherence interferometry (OLCI), and those provided by the most commonly used optical biometer (IOLMaster 500), based on partial-coherence interferometry (PCI). Multicenter clinical trial. Prospective evaluation of diagnostic test. In this study, 2 samples of adult patients were enrolled, 1 in the United States and the other in China. The U.S. group included a sample of consecutive patients scheduled for cataract surgery. The China group included a sample of healthy subjects with no cataracts. In both cases, only 1 eye of each patient was analyzed. Axial length (AL), corneal power (in diopters [D]) (K), anterior chamber depth (ACD) (corneal epithelium to lens), and corneal astigmatism were measured. All values were analyzed using a paired t test, the Pearson product-moment correlation coefficient (r), and Bland-Altman plots. In the U.S. and China groups, the OLCI mean AL values did not show a statistically significant difference from PCI values and showed excellent agreement and correlation. On the contrary, OLCI measured a lower mean K (-0.14 D) and a deeper ACD measurements (U.S. +0.16 mm and China +0.05 mm). These differences were statistically significant (P < .0001). Vector analysis did not show a statistically significant difference in astigmatism measurements. Agreement between OLCI and PCI was good. However, the small but statistically significant differences in K and ACD measurements make constant optimization necessary when calculating the intraocular lens power using theoretical formulas. Dr. Hoffer licenses the registered trademark name Hoffer to Carl Zeiss-Meditec (PCI), Haag-Streit (Lenstar), Movu (Argos), Oculus (Pentacam, AXL), Nidek (AL-Scan), Tomey (OA-2000), Topcon EU Visia Imaging (Aladdin), Ziemer (Galilei G6), and all A-scan biometer manufacturers. Dr. Shammas licenses his formulas to Carl Zeiss-Meditec (PCI), Haag-Streit (Lenstar), Nidek (AL-Scan), and Topcon EU (Visia Imaging) (Aladdin). None of the other authors has a financial or proprietary interest in any material or method mentioned.

Wavelength dependence for silicon-wafer temperature measurement by autocorrelation-type frequency-domain low-coherence interferometry.

We investigate silicon wafer temperature measurement characteristics based on optical low-coherence interferometry by altering the light source wavelength. Variations in Si wafer optical thickness with temperature are expressed by thermal expansion and the refractive index. The optical characteristics determine the measurement precision and range. In this study, the measurement precision and the measurable temperature range were evaluated for three wavelengths: 1040, 1310, and 1550nm. The maximum measurable temperature at 1040nm was the lowest because of signal light absorption caused by fundamental interband absorption. The measurement precision at 1040nm was the highest at 0.020°C because optical thickness changes per degree C increase with decreasing wavelength.

Strain Sensing Comparison Between Single and Multimode Fibers using Optical Low Coherence Interferometry

Optical low coherence interferometry is one of the accurate optical sensing technologies and widely utilized in various physical sensing properties. The system principle is to characterize the relative interferogram movement distance caused by the various strain on a sensing arm. An interferometric strain sensor from two-stage Mach-Zehnder interferometer was demonstrated for double sensitivity improvement. The strain performance comparison between single and multimode fibers will be analyzed for fiber sensing applications. The stepper motor was set up with a movement distance of 20 nm in every step and the velocity could achieve 10000 step/s. The fiber strain was characterized as 22.22 μe on a 9-cm length. The experimental results demonstrated the multimode fiber sensitivity is higher than single mode fiber. Repeatability of both single and multimode are uncertain. The interferogram movement distance from the multimode fiber was higher than a single mode and demonstrates higher sensitivity