Optical Low-coherence Reflectometry Research Articles

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.

Comparison of the ultrasonographic method with 2 partial coherence interferometry methods for intraocular lens power calculation

Background The accuracy of biometric measurements, particularly axial length, is critical for precise intraocular lens (IOL) power calculation and predictable refractive outcomes after cataract surgery. Partial coherence interferometry-based systems represent progress toward measurements that are more precise and reliable. The purpose of this study was to evaluate a new noncontact optical biometer (Lenstar; Haag-Streit AG, Koeniz, Switzerland) using optical low-coherence reflectometry and to compare the biometric measurements (including axial length, keratometry, anterior chamber depth, and IOL power) with those obtained from current clinical instrumentation. Methods Biometric measurements were obtained with Lenstar, IOL Master V.5 (Carl Zeiss Meditec AG, Jena, Germany), and A-scan applanation ultrasound scan combined with a Javal-type keratometer in 234 eyes of 234 subjects scheduled for cataract surgery. IOL power was calculated using Sanders, Retzlaff, Kraff II, Hoffer Q, and Holladay 1 formulas. Results The axial length readings were similar ( P = 0.997). The anterior chamber depth measurements obtained by IOL Master were slightly smaller than those obtained with other devices ( P = 0.092). The means of the average keratometry readings were 0.65 and 0.61 diopters lower when measured with Lenstar as compared with IOL Master and the Javal-type keratometer, respectively ( P = 0.002). All of the measurements were tightly correlated ( P < 0.001). For anterior chamber depth measurements, however, the correlation was slightly weaker. Using the above-mentioned formulas, the mean IOL power measurements were similar. These measurements were tightly correlated ( P < 0.001). The level of agreement was acceptable and comparable between devices. Conclusions The findings from this study show the validity and clinical utility of Lenstar compared with instrumentation currently used in clinical practice for assessing ocular biometry and IOL power calculation in cataractous eyes.

Quasi-distributed sensing network based on coherence multiplexing and spatial division multiplexing for coal mine security monitoring

A low-cost fiber Bragg grating (FBG) sensing system for coal-mine security monitoring is proposed in this paper. Based on the coherence multiplexing (CM) and spatial division multiplexing (SDM) techniques, this hybrid sensing network can support more than 40 sensors for quasi-distributed detection. It is demonstrated experimentally that the multiplexed sensing signal of each sensor can be clearly distinguished by an optical low-coherence reflectometry (OLCR). Methane concentration is detected with maximum sensitivities of an intensity variation of 10.92% and a concentration variation of 1%, using a well-designed sensor structure. Strain and temperature are also detected by this system, which also exhibits good results in the experiment.

Assessment of Central Corneal Thickness Using OCT, Ultrasound, Optical Low Coherence Reflectometry and Scheimpflug Pachymetry

Accurate measurement of central corneal thickness (CCT) is essential in refractive surgery and advanced glaucoma diagnostics. The gold standard for pachymetry is full-contact ultrasound-based pachymetry. As this method is associated with potential sources of error, noncontact methods have been introduced. The aim of this study was to compare CCT results measured using 4 different techniques. In this analysis of 20 patients (40 eyes) at the University Eye Hospital Heidelberg, Germany, we compared a slit-lamp-mounted optical coherence tomography (OCT) system (SL-OCT, Heidelberg Engineering, Heidelberg, Germany), conventional ultrasound pachymetry (IOPac, Heidelberg Engineering), optical low coherence reflectometry (OLCR, Haag-Streit, Germany), and scanning-slit pachymetry (Orbscan). Comparison among the 4 groups did not show significant differences, except the comparison of OLCR to Orbscan; the mean was significantly different (p=0.0247) and the Orbscan detected slightly thicker values than the other methods. Orbscan, SL-OCT, and OLCR provide non-touch technology, without the need for local anesthesia, and limiting the risk of infection or artifacts. Extreme care must be used interpreting the results obtained from Orbscan, as this technique may overestimate the CCT significantly.

Comparison of optical low-coherence reflectometry and applanation ultrasound biometry on intraocular lens power calculation

The aim of the study was to determine whether the innovative non-contact optical low-coherence reflectometry method utilized by the Lenstar LS 900® agrees sufficiently with applanation ultrasound A-scan technique in routine biometric measurement and intraocular lens power calculation to replace it. Twenty-two patients hospitalized at our eye clinic undergoing cataract surgery were assigned to have five consecutive measurements of axial length by two examiners in a single session using applanation ultrasound and the Lenstar. The applanation ultrasound intraocular lens power calculation was based on automated keratometry and applanation ultrasound axial length measurements. The Lenstar intraocular lens power calculation was based on its measurement of keratometry and axial length. Bland-Altman analysis was used to assess interobserver repeatability of applanation ultrasound and the Lenstar as well as agreement between the Lenstar and applanation ultrasound for axial length measurement and intraocular lens power calculation. Thirty-two eyes of 22 patients were analyzed. In 95% of the observations, predicted refractive error corresponded to -0.26 ± 0.62 D and 0.01 ± 0.20 D obtained with applanation ultrasound and the Lenstar, respectively. Based on excellent repeatability of the Lenstar and acceptable repeatability of applanation ultrasound, two techniques may be used interchangeably. The predicted refractive error of ± 0.20 D in 95% of the observations has never been achieved. Optical low-coherence reflectometry might become a new standard method for biometric measurement needed for intraocular lens-power calculation in patients with cataract.

Axial Length Changes During Accommodation in Myopes and Emmetropes

To investigate the influence of accommodation on axial length (AXL) and a comprehensive range of ocular biometric parameters) in populations of young adult myopic and emmetropic subjects. Forty young adult subjects had ocular biometry measured using a noncontact optical biometer (Lenstar LS 900) based on the principle of optical low coherence reflectometry under 3 different accommodation demands (0 D, 3 D, and 6 D). Subjects were classified as emmetropes (n = 19) or myopes (n = 21) based on their spherical equivalent refraction (mean emmetropic refraction -0.05 +/- 0.27 D and mean myopic refraction -1.82 +/- 0.84 D). AXL changed significantly with accommodation, with a mean increase of 11.9 +/- 12.3 mum and 24.1 +/- 22.7 mum for the 3 D and 6 D accommodation stimuli, respectively. A significant axial elongation associated with accommodation was still evident even after correction of the AXL data for potential error because of lens thickness change. The mean "corrected" increase in AXL was 5.2 +/- 11.2 mum and 7.4 +/- 18.9 mum for the 3 D and 6 D stimuli, respectively. There was no significant difference between the myopic and emmetropic populations in terms of the magnitude of change in AXL with accommodation, regardless of whether the data were corrected or not. A number of other ocular biometric parameters, such as anterior chamber depth, lens thickness, and vitreous chamber depth also exhibited significant change with accommodation. The myopic and emmetropic populations also exhibited no significant difference in the magnitude of change in these parameters with accommodation. The eye undergoes a significant axial elongation associated with a brief period of accommodation, and the magnitude of this change in eye length increases for larger accommodation demands, however, there is no significant difference in the magnitude of eye elongation in myopic and emmetropic subjects.

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.

Time-Frequency Analysis for an Efficient Detection and Localization of Side-Coupled Cavities in Real Photonic Crystals

We propose and demonstrate here the high efficiency of concurrent time and frequency analysis to detect and unambiguously identify the coupled cavities in real photonic crystals containing imperfections and/or process-induced disorder. This procedure when applied to reflectograms recorded using phase-sensitive optical low-coherence reflectometry allows a straightforward and complete assessment of cavities (spectral and spatial localization in addition to photon lifetime) over a wide spectral range. Considering such a reflectogram (recorded in ~ 2 s), we show that this procedure greatly eases the evaluation of cavities under guiding conditions in real photonic crystals by discriminating their signature from the in-plane scattering induced by disorder.

Intraocular lens power calculation: Clinical comparison of 2 optical biometry devices

To evaluate intraocular lens (IOL) power calculation using a new optical low-coherence reflectometry (OLCR) biometer and compare the results with those obtained with a partial coherence interferometry (PCI) optical biometer. International Vision Correction Research Centre, Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany. Biometry measurements in eyes of cataract patients were performed by the same examiner with an OLCR biometer (Lenstar LS 900/Allegro Biograph) and a PCI optical biometer (IOLMaster). After determination of axial length (AL), corneal radii values by keratometry (R1 and R2), and anterior chamber depth (ACD), power calculation for an AcrySof MA60AC IOL was compared between the 2 devices using 4 formulas and the corresponding IOL constants. The target was emmetropia. One hundred eyes of 100 cataract patients (mean age 70.0 years +/- 10.6 [SD]) were measured. Of the biometry parameters, the only statistically significant differences between the 2 devices were in R2 (mean difference 0.02 +/- 0.05 mm), (R1 + R2)/2 (mean difference 0.01 +/- 0.04 mm), and ACD (mean difference 0.05 +/- 0.11 mm) (P<.01, Wilcoxon test). The mean differences in IOL power calculations using the 4 formulas were not statistically significant between the 2 devices (P>.01, Wilcoxon test). The OLCR biometry device provided precise and valid measurements and thus can be used for the preoperative examination of cataract patients.

Amadeus® II Microkeratome: Optimizing Microkeratome Settings for High Flap Accuracy Using Optical Low Coherence Reflectometry

To investigate the impact of various experimental microkeratome settings and blade reuse on the accuracy of the flap thickness created with the new Amadeus II microkeratome (SIS, Ziemer Ophthalmic, Port, Switzerland). In this prospective study, 120 porcine eyes were used to create corneal flaps with the Amadeus II using 2 different cutting heads (140 microm, 160 microm) with the Surepass blade. Using each blade twice, a head advance speed of 1.5 mm/s and 3.5 mm/s and oscillation rates of 8000 rpm, 10,000 rpm, and 13,000 rpm were used. Flap thickness was measured by optical low coherence reflectometry (OLCR). Descriptive statistical analysis was based on means, medians, and quartiles, with graphical representation on box plot. Pearson correlation test and Mann-Whitney U-test for unpaired samples were employed to identify the impact of different settings. Using the 140 microm cutting head, highest precision of the flap thickness was achieved with a head advance rate of 1.5 mm/s and an oscillation rate of 10,000 rpm (mean 132.1+/-10.0 microm; range 120.2-147.2 microm). Reusing the blade, highest accuracy (mean 130+/-6.9 microm; range 118.5-135 microm) was achieved with 8000 rpm. Using the 160 microm cutting head, an optimum flap thickness was reached with a head advance rate of 3.5 mm/s and an oscillation rate of 13,000 rpm (mean 162.4+/-7.7 microm; range 151.9-169.8 microm). Reusing the blade with the 160 microm cutting head, an adjustment to 3.5 mm/s and 10,000 rpm was necessary (mean 157.4+/-7.7 microm; range 153.7-161.8 microm). Optimized microkeratome settings lead to minimized deviation from the intended flap thickness and are mandatory to improve flap accuracy. OLCR is an ideal method to proof individualized settings.

Unravelling the endovascular microenvironment by optical coherence tomography

> “The more I see, the less I know for sure.” > > - John Lennon Undoubtedly, the field of interventional cardiology has evolved significantly over the past decades. A myriad of technologies, from mechanical devices that simply remove or displace obstructive atheroma to more complex energy-emitting or local drug delivery systems that interfere with critical molecular pathways, have been incorporated into our clinical armamentarium. This rapid pace of cardiovascular device development poses considerable challenges to contemporary clinician-investigators, who have at their disposal ageing X-ray coronary angiography and intravascular ultrasound (IVUS) imaging systems to take on the difficult task of judging these therapies ( Figure 1 ). We have relied on a presbyopic view of what happens in the vascular microenvironment after it receives high doses of potent drugs, once only given to patients with cancer or transplanted organs. Barlis et al. have reported the first multicentre experience on the use of optical coherence tomography (OCT) to evaluate the clinical outcomes of a new drug-eluting stent (DES).1 The term substudy in the title and the fact that OCT was not the primary endpoint of the main investigation should not distract the reader from realizing the historical value of this report as it indicates the early signs of a late catch-up phenomenon, not the one commonly associated with late lumen loss. It defines the somewhat late arrival of OCT, a derivative of optical low-coherence reflectometry introduced by James Fujimoto in the early 1990s,2 in cardiology clinical trials providing the corrective lens to allow a clear, close-up look at the vessel wall. In a simplified view, OCT is the optical cousin of IVUS: emitting and detecting backscattered signals. The use of light renders considerable advantages to OCT while creating some challenges—the most noticeable are the inability to see through blood or beyond 2 mm of tissue depth. The … *Corresponding author. Tel +1 216 844 5840, Fax: +1 216 844 8954, Email: marco.costa{at}uhhospitals.org

Central Corneal Thickness During Treatment With Travoprost 0.004% in Glaucoma Patients

Experimental studies demonstrated an alteration of corneal collagen structure by prostaglandin analogues. The possible effect of the prostaglandin F(2alpha) analogue travoprost 0.004% on the central corneal thickness (CCT) in newly diagnosed glaucoma patients was evaluated. Consecutive, interventional case series. Seventy-four patients/136 eyes with glaucoma were included in the statistical analysis. All patients received travoprost 0.004% (Travatan(R)) once daily in one or both eyes. CCT was measured by using noncontact optical low-coherence reflectometry prior to the treatment and after 6 and 12 months. Mean CCT of all treated eyes (n = 136) was 546.71 +/- 34.63 mum at baseline, 535.14 +/- 34.78 mum after 6 months, and 532.38 +/- 34.18 mum after 12 months (ANOVA, P < 0.001). Ninety-five percent of all treated eyes showed a decrease of CCT. CCT reduction mainly developed within the first 6 months of the treatment period. After 12 months, a CCT reduction >30 mum occurred in 5.1% of all treated eyes. There was a significant correlation between the magnitude of corneal thinning and the initial CCT but not between corneal thinning and IOP reductions. Topical therapy with the prostaglandin derivate travoprost is accompanied by a significant reduction of CCT within one year of treatment. Further clinical studies are needed to evaluate the possible long-term effects of prostaglandins on the CCT of glaucoma patients.

Comparison and Evaluation of Ocular Biometry Using a New Noncontact Optical Low-Coherence Reflectometer

To evaluate a new high-resolution noncontact biometer (Lenstar; Haag-Streit AG, Koeniz, Switzerland) using optical low-coherence reflectometry and to compare the clinical measurements with those obtained from the IOLMaster (Carl Zeiss, Jena, Germany) and the Pachmumeter (Haag-Streit AG). Exploratory evaluation of diagnostic technology and nonrandomized, prospective clinical trial. Eighty subjects (144 eyes) aged 20 to 90 years with cataractous, pseudophakic, aphakic, silicon oil-filled, or normal eyes. Measurements of axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), corneal radius (R1 [flattest radius of corneal curvature] and R2 [steep radius, 90 degrees apart from R1]), and axis of the flattest radius (Ax1) obtained with the Lenstar were compared with those obtained with the IOLMaster or Pachmumeter. The results were evaluated using Bland-Altman analyses. The differences between both methods were assessed using the paired t test, and its correlation was evaluated by Pearson coefficient. Axial length, CCT, ACD, R1, R2, and Ax1. The overall mean AL measured with the Lenstar and the IOLMaster was 24.1 mm (r = 0.999). Anterior chamber depth was 3.19 mm (Lenstar) and 3.17 mm (IOLMaster; r = 0.875). Excellent correlations also were found for the corneal radius and the axis of flattest radius (R1, r = 0.927; R2, r = 0.929; and Ax1, r = 0.938). Mean CCT was 0.557 mm (r = 0.978) for both Lenstar and Pachmumeter. Measurements with the new Lenstar correlated well with those with the IOLMaster and Pachmumeter in cataractous, pseudophakic, aphakic, silicon oil-filled, and normal eyes. It is an accurate, fast instrument that provides additional information of interest to any cataract or refractive surgeon.

Versatile Characterization of Specialty Fibers Using the Phase-Sensitive Optical Low-Coherence Reflectometry Technique

Emergence of new fibers families induces considerable requirements in terms of characterization and metrology (group delay, chromatic dispersion, birefringence, bending losses, etc.). The optical low-coherence reflectometry (OLCR) technique is demonstrated as a versatile method for the characterization of most types of optical fiber. A synthesis of multiple analysis concerning different families of specialty fibers including rare-earth-doped fibers, few-mode fibers, and microstructured fibers will be presented. OLCR allows measuring precisely the group velocity dispersion value for both polarization modes and birefringence. It is also possible to measure small refractive-index variations in a pumped Erbium-doped fiber. Unique dispersive properties of higher order modes fiber offer novel solutions for dispersion compensation or nonlinear effects management. OLCR can allow each LP mode characterization without the requirement for mode converters. A new method, called ldquotime-wavelength reflection mapping,rdquo based on the OLCR interferogram processing is applied to the determination of chromatic dispersion of each guided LP mode whatever their group index. Finally, different characterization results concerning photonics crystal fibers with guiding based on the conventional total internal reflection principle (high-index guiding) or photonic bandgap effect (low-index guiding) will be presented.

Correlation between estimated and measured corneal ablation and refractive outcomes in laser in situ keratomileusis for myopia

To evaluate the difference between the measured and the intended postoperative central corneal thickness (CCT) by optical low-coherence reflectometry (OLCR) for 3 months after myopic laser in situ keratomileusis (LASIK) and correlate it with refractive outcomes. Center for Refractive Therapy, Department of Ophthalmology, Ludwig-Maximilians-University Munich, Germany. The CCT was measured by OLCR before and 6 weeks and 3 months after myopic LASIK. The correlation between the difference in pachymetry and the difference in the measured and planned postoperative refraction was proven by linear regression and Pearson product moment correlation analysis (P<.05). In a subset of eyes with a 7.0 mm optical zone, the effect of the calculated ablation depth on the difference in pachymetry was evaluated. Based on the laser algorithm data, the intended ablation was 100 microm or less in Subgroup 1 and 100 microm or more in Subgroup 2. Forty-three eyes of 25 patients were evaluated, with 25 eyes in the subset. The difference between the measured and intended postoperative CCT was 11.1 microm +/- 8.1 (SD) at 6 weeks and 13.8 +/- 7.5 microm at 3 months. The correlation between this difference and the difference in refraction was poor (r(2) = 0.005 microm and r(2) = 0.009, respectively). With greater ablation depth (Subgroup 2), the difference in pachymetry decreased by 3 months postoperatively. The lack of correlation between differences in the measured and intended CCT and the final refraction shows the complexity of intraoperative variables in LASIK and the effect of individual wound healing.

Optical low-coherence reflectometry for deflection measurement with a fiber Bragg grating cantilever sensor

Optical low-coherence reflectometry (OLCR) for deflection measurement with a fiber Bragg grating (FBG) cantilever sensor is proposed and experimentally demonstrated to reveal the internal structure of the sensing fiber in correlation with its optical properties, which is the first report on a spatial-resolved technique to realize dynamic deflection measurement. The change in the fiber length during a convex or concave deflection of the cantilever sensor detected by OLCR achieves simultaneous determination of the magnitude and direction of the deflection by the use of a standard single-mode telecommunication fiber inscribed with single grating. The FBG plays a key role in selecting pre-strain set point and compensating the environmental temperature fluctuations. The experimental results are in good agreement with the theoretical analysis.

Comparison of two partial coherence interferometers for corneal pachymetry in high myopia and after LASIK

We aimed to compare the Haag-Streit optical low-coherence reflectometry (OLCR) pachymeter and the Zeiss Anterior Chamber Master (ACMaster) for measuring central corneal thickness (CCT) in high myopes and after laser in situ keratomileusis (LASIK) for myopia. Central corneal thickness was measured in 55 eyes of 30 myopic subjects (spherical equivalent refraction of - 5.25 D to - 10.75 D, maximal astigmatism of - 2 D), and in 37 eyes of 21 patients 3 months after LASIK for myopia (preoperative spherical equivalent refraction of - 6.0 D to - 10.75 D, maximal astigmatism of - 2 D). All measurements were performed with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster, using group refractive indices of 1.376 and 1.3851, respectively. Thickness measurements were compared using paired t-tests, Pearson's correlation, linear regression and Bland-Altman plots. In myopic subjects, CCT measured 531 +/- 28 microm and 533 +/- 27 microm with the OLCR pachymeter and the ACMaster, respectively (p < 0.01); all measurements correlated closely (r = 0.99, p < 0.01). In LASIK-treated eyes, CCT measured 472 +/- 24 microm using the OLCR pachymeter and 475 +/- 23 microm using the ACMaster (p < 0.01), again with close correlation between the two instruments (r = 0.99, p < 0.01). Measurements of CCT in high myopes and after myopic LASIK were very similar with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster. Using the current group refractive indices, the observed difference between the two instruments of < 3 microm is of little clinical importance. Thus, it would seem safe to use the OLCR pachymeter and the ACMaster interchangeably for CCT measurements in myopia as well as after myopic LASIK.

The Relationship between Diurnal Variations in Intraocular Pressure Measurements and Central Corneal Thickness and Corneal Hysteresis

To examine the relationship between office-hour changes in IOP, measured with the Goldmann applanation tonometer (GAT) and dynamic contour tonometer (DCT), and the corneal characteristics central corneal thickness (CCT) and corneal hysteresis (CH). Sixty-two eyes of 62 untreated normal subjects and patients with untreated glaucoma had IOP measurements performed with the GAT (mm Hg) and DCT (mm Hg) over an 8-hour period at 2-hour intervals beginning at 9 AM. CCT (micrometers) was measured using a noncontact optical low-coherence reflectometry (OLCR) pachymeter, and CH (mm Hg) was measured with an ocular response analyzer (ORA). The associations between IOP measurements and corneal characteristics for each patient over the measurement period were assessed by using multilevel modeling. GAT and DCT IOP and CCT changed significantly during office hours (ANOVA; GAT: F = 19.9, P < 0.001; DCT: F = 4.6, P = 0.001; CCT: F = 16.4; P < 0.001). No significant changes were observed in CH (ANOVA; F = 1.8, P = 0.13). Multilevel modeling analysis of the interrelationships between CCT, CH, and age on IOP measurements revealed that both CCT and CH changes were significantly associated with GAT IOP changes (GAT IOP/CCT slope, 0.04 mm Hg/microm; 95% confidence intervals [CIs], 0.02-0.06; GAT IOP/CH slope, 0.20 mm Hg/mm Hg; 95% CI, 0.01-0.39). CCT, but not CH, changes were significantly associated with DCT IOP changes (DCT IOP/CCT slope, 0.03 mm Hg/microm; 95% CI, 0.00-0.05). However, although the association between CCT and GAT IOP was relatively uniform between subjects, association between CCT and DCT IOP showed greater intersubject variability. Age had no effect on the diurnal variation of IOP measured with either device. Measured IOP and corneal characteristics covary during office hours. Changes in CCT and CH are associated with changes in GAT IOP and, less consistently, with DCT IOP. The data suggest that variations in corneal characteristics explain a small proportion of the change in IOP measurements made with the GAT during office hours.

A new optical low coherence reflectometry device for ocular biometry in cataract patients

Background:A new commercially available optical low coherence reflectometry device (Lenstar, Haag-Streit or Allegro Biograph, Wavelight) provides high-resolution non-contact measurements of ocular biometry. The study evaluates the validity and repeatability of...

Correlation of histology and linear and nonlinear microscopy of the living human cornea

The morphology and the function of cellular and non-cellular structures in the living human cornea can be determined with modern correlative linear and nonlinear optical microscopic techniques and histology. Correlative microscopy is based on the use of different optical techniques to study the same specimen, ideally at the same location within the specimen, in order to increase the functional and/or morphological understanding of the specimen. A case study to assess the effect of overnight lid-closure on in vivo human corneal morphology is presented to illustrate correlative linear microscopy and optical low-coherence reflectometry. Nonlinear multiphoton excitation microscopy provides functional information on cellular metabolism based on the intrinsic fluorescence from the reduced pyridine nucleotides and the oxidized flavoproteins. Second-harmonic generation microscopy, a scattering process that does not deposit net energy into the tissue, provides structural information on corneal collagen organization. Molecular third-harmonic generation microscopy generates a signal in all materials and it an emerging technique. Coherent anti-Stokes Raman scattering microscopy provides chemical imaging for biology and medicine. The comparison and limitations of these microscopic modalities, linear and nonlinear microscopy applied to the cornea, and a review of some key findings is analyzed. A correlative integration and correlation of linear and nonlinear microscopies to study corneal function and structure is proposed to validate the clinical interpretation of microscopic images of the cornea.