Intersession Reproducibility Research Articles

Corneal Deformation Measurement Using Scheimpflug Noncontact Tonometry

To determine the intraexaminer repeatability and intersession reproducibility of corneal deformation measurement using Scheimpflug noncontact tonometry (Corvis ST) on normal subjects. Thirty-seven adults aged 20 to 48 years were invited to have their corneal deformation and curvature measurements taken using Corvis ST and Pentacam, respectively. Three consecutive measurements were taken for each instrument between 9:00 and 11:00 AM for intraexaminer repeatability analysis. Participants returned between 3:00 and 5:00 PM the same day for intersession reproducibility analysis. The most repeatable corneal parameter measured by Corvis ST was central corneal thickness ([CCT] ICC, 0.96; precision, 10.85 μm; repeatability, 15.34 μm; CV, 1.01%), followed by deformation amplitude ([DA] ICC, 0.80; precision, 0.08 mm; repeatability, 0.13 mm; CV, 4.33%), first applanation time ([1st A-time] ICC, 0.77; precision, 0.22 milliseconds; repeatability, 0.31 milliseconds; CV, 1.42), and intraocular pressure ([IOP] ICC, 0.75; precision, 1.39 mm Hg; repeatability, 1.97 mm Hg; CV, 4.98). Other parameters showed poor repeatability. The DA and 1st A-time showed good intersession reproducibility. The 95% limits of agreement were +0.13 to -0.13 mm for DA and +0.27 to -0.33 milliseconds for 1st A-time. The DA was negatively correlated with central corneal thickness (r = -0.53, p < 0.001) but not with corneal curvatures (flattest curvature, r = 0.13, p = 0.46; steepest curvature, r = 0.05, p = 0.75). Corneal deformation parameters DA and 1st A-time were repeatable and reproducible. A thinner cornea was associated with a higher corneal deformation. Measurement of DA serves as an indicator of corneal biomechanical properties.

Precision of a new Scheimpflug and Placido-disk analyzer in measuring corneal thickness and agreement with ultrasound pachymetry

To assess the precision of corneal thickness measurements obtained by a new Scheimpflug camera combined with Placido-disk corneal topography (Sirius) and compare the measured values with those obtained by ultrasound (US) pachymetry. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative evaluation of a diagnostic test or technology. Eyes of healthy subjects were examined with the Scheimpflug-Placido topographer. Central (CCT) and thinnest (TCT) corneal thickness were recorded after 3 consecutive measurements. For US pachymetry, only CCT was measured. Measurements were repeated within 1 week. The within-subject standard deviation (S(w)), test-retest repeatability, coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were calculated to evaluate intrasession repeatability and intersession reproducibility. Interdevice comparison was analyzed with paired t tests and Bland-Altman plots. The intrasession repeatability of Scheimpflug-Placido measurements was high, with test-retest and CoV close to 9 μm and 0.6% for CCT and TCT, respectively. The intersession test-retest and CoV were close to 10 μm and 0.7%, respectively. The ICC was higher than 0.98 for repeatability and reproducibility. High agreement was found between Scheimpflug-Placido and US pachymetry measurements, with narrow 95% limits of agreement. The Scheimpflug-Placido instrument showed excellent intrasession repeatability and intersession reproducibility of CCT and TCT measurements in healthy eyes. High agreement and lack of statistically significant difference suggest that the instrument's TCT and the US pachymetry-CCT measurements can be used interchangeably in subjects with normal corneal thickness. No author has a financial or proprietary interest in any material or method mentioned.

Increasing acclimation period improves the reproducibility of short-heating local thermal hyperemia

ObjectivesThe axon reflex (AR) can be induced by the activation of afferent C-fibers during local skin heating. The previously used long-heating local thermal hyperemia (LTH) protocols tested AR flare by normalizing to endothelial-mediated maximal vasodilatation to adjust capillary heterogeneity when the recording sites were randomly selected. The AR flare induced by short local heating can be reproducible without using the data from subsequent longer heating for normalization when the recording sites were fixed with holders in the same session. The aim of this study was to investigate the effect of acclimation period on the intersession reproducibility of short-heating LTH when the recording sites were relocated after a longer interval of 1–3days. MethodsAfter 30 or 60min acclimation, LTH with 5min heating was assessed on bilateral human forearms using single-point laser Doppler flowmetry. The test was repeated at the same recording sites again at the same time 1–3days later. Baseline and heating blood flux were analyzed and the data were expressed as different forms. Reproducibility of two tests was assessed using coefficient of variation (CV) and intra-class correlation coefficient (ICC) statistics. ResultsThe intersession reproducibility of peak cutaneous vascular conductance (CVC) (CV=18.38%, ICC=0.82), peak CVC change (CV=20.38%, ICC=0.83) and 4min area-under-the-curve (AUC) (CV=18.66%, ICC=0.75) of the right forearm and time to peak (CV=16.84%, ICC=0.52) of the left forearm were acceptable after 30min acclimation. When the acclimation period was increased to 60min, all of these data except 4min AUC of both sides reached an acceptable level. ConclusionsThe AR flare induced by short local heating is reproducible when the recording sites are relocated by a predefined rule. The reproducibility of LTH on right forearm is different from that on left forearm, and increasing acclimation period improves the reproducibility.

Precision of higher-order aberration measurements with a new Placido-disk topographer and Hartmann-Shack wavefront sensor

To assess the intrasession and intersession precision of ocular, corneal, and internal higher-order aberrations (HOAs) measured using an integrated topographer and Hartmann-Shack wavefront sensor (Topcon KR-1W) in refractive surgery candidates. IOBA-Eye Institute, Valladolid, Spain. Evaluation of diagnostic technology. To analyze intrasession repeatability, 1 experienced examiner measured eyes 9 times successively. To study intersession reproducibility, the same clinician obtained measurements from another set of eyes in 2 consecutive sessions 1 week apart. Ocular, corneal, and internal HOAs were obtained. Coma and spherical aberrations, 3rd- and 4th-order aberrations, and total HOAs were calculated for a 6.0 mm pupil diameter. For intrasession repeatability (75 eyes), excellent intraclass correlation coefficients (ICCs) were obtained (ICC >0.87), except for internal primary coma (ICC = 0.75) and 3rd-order (ICC = 0.72) HOAs. Repeatability precision (1.96 × S(w)) values ranged from 0.03 μm (corneal primary spherical) to 0.08 μm (ocular primary coma). For intersession reproducibility (50 eyes), ICCs were good (>0.8) for ocular primary spherical, 3rd-order, and total higher-order aberrations; reproducibility precision values ranged from 0.06 μm (corneal primary spherical) to 0.21 μm (internal 3rd order), with internal HOAs having the lowest precision (≥0.12 μm). No systematic bias was found between examinations on different days. The intrasession repeatability was high; therefore, the device's ability to measure HOAs in a reliable way was excellent. Under intersession reproducibility conditions, dependable corneal primary spherical aberrations were provided. No author has a financial or proprietary interest in any material or method mentioned.

Precision of a Commercial Hartmann-Shack Aberrometer: Limits of Total Wavefront Laser Vision Correction

To assess the intrasession and intersession precision of higher-order aberrations (HOAs) measured using a commercial Hartmann-Shack wavefront sensor (Zywave; Bausch & Lomb) in refractive surgery candidates. Prospective, experimental study of a device. To analyze intrasession repeatability, 1 experienced examiner measured 30 healthy eyes 5 times successively. To study intersession reproducibility, the same clinician obtained measurements from another 30 eyes in 2 consecutive sessions at the same time of day 1 week apart. For intrasession repeatability, excellent intraclass correlation coefficients (ICCs) were obtained for total ocular aberrations, total HOAs, and second-order terms (ICC, > 0.94). The ICCs for third-order terms also were high (ICCs, > 0.87); however, fourth-order ICCs varied from 0.71 to 0.90 (Z(4)(0) = 0.90); and fifth-order ICCs were less than 0.85. For intersession reproducibility, only total ocular aberrations, total ocular HOAs, second-order terms, Z(4)(0), Z(3)(1), and Z(3-)(3) had ICCs of 0.90 or more. Bland-Altman analysis showed that the limits of agreement (were clinically too wide for most higher-order Zernike terms, especially for the third-order terms (> 0.21 μm). Total ocular aberrations, total HOAs, and second-order terms can be measured reliably by Zywave aberrometry without anatomic recognition. Third-order terms and Z(4)(0) are repeatable, but not as reproducible between visits. Fourth-order terms, except for Z(4)(0), and fifth-order terms are not sufficiently reliable for clinical decision making or treatment. Because the variability of Zywave can be a major limitation of a truly successful wavefront-guided excimer laser procedure, surgeons should consider treating HOA magnitudes that are more than the intrasession repeatability values (2.77 × S(w)) as those presented in this study.

An age-related change in the ipsilateral silent period of a small hand muscle

ObjectiveTo establish the presence or absence of an age effect on the ipsilateral silent period (iSP) for the abductor pollicis brevis (APB) muscle in healthy subjects. MethodsTwenty young adults (10 men, 10 women; age range: 20–40) and 20 older adults (10 men, 10 women; age range: 50–70) were matched by age (+30years), gender and height (±5cm). All were right-handed. We investigated the iSP for the APB by applying transcranial magnetic stimulation (TMS) and recording surface electromyograms. The contralateral motor-evoked potential (MEP) onset latency, the iSP onset and end latency (iSPOL and iSPEL) were measured and the iSP duration (iSPD) and transcallosal conduction time (TCT) were calculated. We evaluated the correlation between age and iSP, the latter’s intra- and intersession reproducibility and potential influencing factors. ResultsMean iSPOL, iSPEL and TCT values were significantly greater in older adults (both men and women) than in young adults. Intra- and intersession reproducibility was good. The mean left-side iSPEL and iSPD were longer than the right-side mean values in young adults but not in older adults. In both age groups, women displayed shorter latencies than men. ConclusionsThere is a strong effect of age on iSP parameters. SignificanceOur iSP results may evidence a decrease in transcallosal excitability with age, rather than slowing of the transcallosal interneuron conduction velocity.

Biomedical signal acquisition with streaming wireless communication for recording evoked potentials

Commercial electrophysiology systems for recording evoked potentials always connect patients to the acquisition unit via long wires. Wires guarantee timely transfer of signals for synchronization with the stimuli, but they are susceptible to electromagnetic and electrostatic interferences. Though wireless solutions are readily available (e.g. Bluetooth), they introduce high delay variability that will distort the evoked potential traces. We developed a complete wireless acquisition system with a fixed delay. The system supports up to 4 bipolar channels; each is amplified by 20,000× and digitized to 24 bits. The system incorporates the "driven-right-leg" circuit to lower the common noise. Data are continuously streamed using radio-frequency transmission operating at 915 MHz and then tagged with the stimulus SYNC signal at the receiver. The delay, noise level and transmission error rate were measured. Flash visual evoked potentials were recorded monocularly from both eyes of six adults with normal vision. The signals were acquired via wireless and wired transmissions simultaneously. The recording was repeated on some participants within 2 weeks. The delay was constant at 20 ms. The system noise was white and Gaussian (2 microvolts RMS). The transmission error rate was about one per million packets. The VEPs recorded with wireless transmission were consistent with those with wired transmission. The VEP amplitudes and shapes showed good intra-session and inter-session reproducibility and were consistent across eyes. The wireless acquisition system can reliably record visual evoked potentials. It has a constant delay of 20 ms and very low error rate.

Reproducibility of Macular, Retinal Nerve Fiber Layer, and ONH Measurements by OCT in Rhesus Monkeys: The Beijing Intracranial and Intraocular Pressure (iCOP) Study

We evaluated repeatability and reproducibility of measurements of the retinal nerve fiber layer thickness (RNFLT), optic nerve head (ONH), and macular inner retinal layer (MIRL) by RTVue spectral-domain optical coherence tomography (OCT) in normal Rhesus monkeys. The experimental study included 15 adult Rhesus macaque monkeys. RNFLT, ONH parameters (area of disc, cup, and rim; volume of cup and rim; and cup-to-disc ratios), and MIRL thickness were imaged at three separate examinations within one month. Each eye was imaged three times at the first examination, and once at each of the two following examinations. We determined the intra-session and inter-session (inter-visit) within-subject SD (Sw), precision (1.96 × Sw), coefficient of variation (CVw, 100 × Sw/overall mean), and intraclass correlation coefficient (ICC). For the intra-session repeatability, ICC values ranged between 0.97 and 1.00 for all ONH parameters, and between 0.80 and 0.98 for all regional RNFLT parameters, with a value of 0.97 for the average RNFLT. For the inter-session (inter-visit) reproducibility, ICC values ranged from 0.93-1.00 for the ONH measurements and from 0.63-0.97 for regional RNFLT parameters, with a value of 0.96 for the average RNFLT. Again, the ICC values were lowest in the temporal inferior and temporal superior regions. The ICC value for the average MIRL thickness was 0.95. Repeatability and reproducibility of spectral-domain OCT measurements of the RNFL, ONH, and MIRL were high in normal monkey eyes. Spectral-domain OCT may be suitable to assess changes in follow-up examinations of monkeys with experimental glaucoma.

Atlas-based analysis of resting-state functional connectivity: Evaluation for reproducibility and multi-modal anatomy–function correlation studies

Resting state functional connectivity MRI (rsfc-MRI) reveals a wealth of information about the functional organization of the brain, but poses unique challenges for quantitative image analysis, mostly related to the large number of voxels with low signal-to-noise ratios. In this study, we tested the idea of using a prior spatial parcellation of the entire brain into various structural units, to perform an analysis on a structure-by-structure, rather than voxel-by-voxel, basis. This analysis, based upon atlas parcels, potentially offers enhanced SNR and reproducibility, and can be used as a common anatomical framework for cross-modality and cross-subject quantitative analysis. We used Large Deformation Diffeomorphic Metric Mapping (LDDMM) and a deformable brain atlas to parcel each brain into 185 regions. To investigate the precision of the cross-subject analysis, we computed inter-parcel correlations in 20 participants, each of whom was scanned twice, as well as the consistency of the connectivity patterns inter- and intra-subject, and the intersession reproducibility. We report significant inter-parcel correlations consistent with previous findings, and high test-retest reliability, an important consideration when the goal is to compare clinical populations. As an example of the cross-modality analysis, correlation with anatomical connectivity is also examined.

Tract Specific Reproducibility of Tractography Based Morphology and Diffusion Metrics

IntroductionThe reproducibility of tractography is important to determine its sensitivity to pathological abnormalities. The reproducibility of tract morphology has not yet been systematically studied and the recently developed tractography contrast Tract Density Imaging (TDI) has not yet been assessed at the tract specific level.Materials and MethodsDiffusion tensor imaging (DTI) and probabilistic constrained spherical deconvolution (CSD) tractography are performed twice in 9 healthy subjects. Tractography is based on common space seed and target regions and performed for several major white matter tracts. Tractograms are converted to tract segmentations and inter-session reproducibility of tract morphology is assessed using Dice similarity coefficient (DSC). The coefficient of variation (COV) and intraclass correlation coefficient (ICC) are calculated of the following tract metrics: fractional anisotropy (FA), apparent diffusion coefficient (ADC), volume, and TDI. Analyses are performed both for proximal (deep white matter) and extended (including subcortical white matter) tract segmentations.ResultsProximal DSC values were 0.70–0.92. DSC values were 5–10% lower in extended compared to proximal segmentations. COV/ICC values of FA, ADC, volume and TDI were 1–4%/0.65–0.94, 2–4%/0.62–0.94, 3–22%/0.53–0.96 and 8–31%/0.48–0.70, respectively, with the lower COV and higher ICC values found in the proximal segmentations.ConclusionFor all investigated metrics, reproducibility depended on the segmented tract. FA and ADC had relatively low COV and relatively high ICC, indicating clinical potential. Volume had higher COV but its moderate to high ICC values in most tracts still suggest subject-differentiating power. Tract TDI had high COV and relatively low ICC, which reflects unfavorable reproducibility.

Normalization of Visual Evoked Potentials Using Underlying Electroencephalogram Levels Improves Amplitude Reproducibility in Rats

The visual evoked potential (VEP) is a frequently used noninvasive measurement of visual function. However, high-amplitude variability has limited its potential for evaluating axonal damage in both laboratory and clinical research. This study was conducted to improve the reliability of VEP amplitude measurement in rats by using electroencephalogram (EEG)-based signal correction. VEPs of Sprague-Dawley rats were recorded on three separate days within 2 weeks. The original VEP traces were normalized by EEG power spectrum, which was evaluated by Fourier transform. A comparison of intersession reproducibility and intersubject variability was made between the original and corrected signals. Corrected VEPs showed lower amplitude intersession within-subject SD (Sw), coefficient of variation (CoV), and repeatability (R(95)) than the original signals (P < 0.001). The intraclass correlation coefficient (ICC) of the corrected traces (0.90) was also better than the original potentials (0.82). For intersubject variability, the EEG-based normalization improved the CoV from 44.64% to 30.26%. A linear correlation was observed between the EEG level and the VEP amplitude (r = 0.71, P < 0.0001). Underlying EEG signals should be considered in measuring the VEP amplitude. In this study, a useful technique was developed for VEP data processing that could also be used for other cortical evoked potential recordings and for clinical VEP interpretation in humans.

Effects of Covert and Overt Paradigms in Clinical Language fMRI

The aim of this study was to assess the intrasubject and intersubject reproducibility of functional magnetic resonance imaging (fMRI) language paradigms on language localization and lateralization. Fourteen healthy volunteers were enrolled prospectively and underwent language fMRI using visually triggered covert and overt sentence generation (SG) and word generation (WG) paradigms. Semiautomated analysis of all functional data was performed using Brain Voyager on an individual basis. Regions of interest for Broca's area, Wernicke's area, and their contralateral homologues were drawn. The Euclidean coordinates of the center of gravidity (x, y, and z) of the respective blood oxygenation level-dependent (BOLD) activation cluster, and the correlation of the measured hemodynamic response to the applied reference function (r), relative BOLD signal change as BOLD signal characteristics were measured in each region of interest. Regional lateralization indexes were calculated for Broca's area, Wernicke's area, and their contralateral homologues separately. Wilcoxon's signed-rank test was applied for statistical comparisons (P values < .05 were considered significant). Ten of the 14 volunteers had three repeated measurements to test intrasession reproducibility and intersession reproducibility. Overall activation rates for the four paradigms were 89% for covert SG, 82% for overt SG, 89% for covert WG, and 100% for overt WG. When comparing covert and overt paradigms, language localization was significantly different in 17% (Euclidean coordinates) and 19% (BOLD signal characteristics), respectively. Language lateralization was significantly different in 75%. Intrasubject and intersubject reproducibility was excellent, with 3.3% significant differences among all five parameters for language localization and 0% significant differences for language lateralization using covert paradigms. Covert language paradigms (SG and WG) provided highly robust and reproducible localization and lateralization of essential language centers for scans performed on the same and different days. Their overt counterparts achieved confirmatory localization but lower lateralization capabilities. Reference data for presurgical application are provided.

Reproducibility and Repeatability of Cirrus™ HD-OCT Peripapillary Retinal Nerve Fibre Layer Thickness Measurements in Young Normal Subjects

Purpose: To assess the reproducibility and repeatability of peripapillary retinal nerve fibre layer (RNFL) thickness measurements using a spectral-domain optical coherence tomography (SD-OCT) device in healthy subjects. Methods: In this observational study, 68 young Caucasian healthy volunteers (68 eyes) were subjected to Cirrus™ high-definition (HD) OCT (Zeiss) peripapillary RNFL thickness measurements by two experienced examiners in two different sessions. Average, 4-quadrant and 12-clock-hour sector RNFL thicknesses were analysed. For each option, intra-observer, intrasession repeatability and interobserver, intersession reproducibility were tested. To assess the repeatability of measurements, the Bland and Altman plots were used and the coefficient of repeatability was calculated. Interobserver and intersession reproducibilities were analysed by means of concordance correlation coefficients (CCCs). Results: The sample age ranged from 21 to 39 years (mean 29.09, standard deviation ±5.21). The average RNFL thickness ranged from 90.97 to 91.46 and from 91.34 to 91.78 µm, for the first and the second operator, respectively. The highest repeatability and reproducibility were obtained for average RNFL thickness with coefficients of repeatability of 5.30 and 6.05 µm for the first and the second operator, interoperator CCCs of 0.95 and 0.96 for the first and the second session, and intersession CCCs of 0.96 and 0.97 for the first and the second operator, respectively. Conclusions: Cirrus OCT peripapillary average RNFL thickness measurement in young healthy subjects showed high interoperator and intersession reproducibility. Intrasession repeatability as tested by coefficient of repeatability was next to the device resolution, with very similar results between the two operators. When analysing quadrant and clock hour sector RNFL thickness measurements, both repeatability and reproducibility tend to decrease.

Reliability of RTVue, Visante, and Slit-Lamp Adapted Ultrasonic Pachymetry for Central Corneal Thickness Measurement

PurposeTo evaluate reliability of Fourier-domain optical coherence tomography (OCT) (RTVue), time-domain OCT (Visante), and slit-lamp adapted ultrasonic pachymetry (SL-US) in the measurement of central corneal thickness (CCT).Materials and MethodsThirty healthy volunteers visited our clinic 3 times and fifty eyes were measured by one physician. RTVue and Visante were randomly performed, and then SL-US, in which the ultrasound probe was inserted into the Goldmann tonometry mount, was done. During the second visit, each measurement was repeated 3 times. Measurements on the second visit were averaged, and agreement among the instruments was investigated with Bland-Altman plots.ResultsRTVue showed smaller repeatability coefficient than Visante and SL-US (4.7, 8.3, and 7.7 µm, respectively). Intersession reproducibility of RTVue and Visante was worse than their repeatability. CCT of RTVue was estimated to be maximally different by 11.8 µm from CCT of Visante and 8.8 µm from CCT of SL-US. The repeatability coefficient of SL-US was 7.7 µm and its reproducibility was similar to the repeatability.ConclusionCCT measured by RTVue showed good reliability and generally agreed with Visante and SL-US. SL-US was as reliable as triple touching conventional US even with a single touch on the cornea.

Reproducibility of retinal thickness measurements in eyes with uveitic macular oedema using Spectralis optical coherence tomography

Editor, In eyes with uveitic macular oedema, the reproducibility of retinal thickness measurements is an essential parameter to monitor the progression of the disease and/or the therapeutic results. To date, there are no reports concerning reproducibility of optical coherence tomography (OCT) in this type of oedema. The aim of the present study is to value the intraobserver reproducibility of macular thickness measurements performed with Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) in inflammatory macular oedema. Thirty-three eyes of 33 consecutive patients, 15 men and 18 women, mean age 35.09 ± 16.64 years (range: 7–77) with uveitis and concurrent macular oedema were included in the study. All patients underwent three consecutive OCT examinations with Spectralis OCT performed by the same operator within one session. For retinal thickness measurements, 20 × 15 degree raster scans were taken consisting of 37 high-resolution line scans. The foveolar centre-point retinal thickness (CPT) and the Early Treatment of Diabetic Retinopathy Study (ETDRS) 9 region map were used for quantitative evaluation. The coefficient of repeatability (CR) was calculated according to Bland & Altman (1996). Also, coefficient of variation (COV) was obtained (Menke et al. 2009a,b). For the statistical analysis, Student’s t-test and Kendall’s τ correlation coefficient were used. p-value <0.05 was considered statistically significant. The results are summarized in Table 1. No significant correlation between thickness and CR and between thickness and COV was found (Kendall’s τ correlation coefficients = 0.022, −0.244; p = 0.29, 0.32). Our highest CR and COV were in the foveolar CPT. One reason we can suggest for this result is that the retinal thickening and the presence of most cysts in central area may affect the device measurement process and can slightly degrade the precision of the reproducibility. Also, we think that highest CR and COV in central area may be caused by a reduced fixation ability of patient owing to macular oedema. Nevertheless for the clinical practice, our findings show in any case an excellent index of reproducibility. This evidence is supported by the data reporting no significant difference between the measurements of CPT. The reproducibility can vary according to different OCT models. In eyes with diabetic macular oedema, Polito et al. (2005) reported a COV ranged from 4.84% to 8.33% using stratus OCT 3 (Carl Zeiss Meditec Inc., Dublin, CA, USA). Recently, some studies have reported high reproducibility of the new OCT generation in healthy eyes and in eyes with age-related macular degeneration (Menke et al. 2009a,b). There are not too many studies that compared reproducibility between different OCT types to make a firm statement about the “most reproducible” instrument. Wolf-Schnurrbusch et al. (2009) compared the intersession reproducibility of different commercially available OCT instruments concluding that Spectralis OCT showed the lowest COV (0.46%). The excellent reproducibility with Spectralis OCT is attributable to some technical features such as image speed, greater resolution and retinal segmentation algorithms, which increase the examination performance. However, the most important factor determining the high reproducibility is the eye-tracking mechanism that permits to scan the same scanning location on following visits. In inflammatory macular oedema, an excellent reproducibility permits to consider even any minimal thickness change as a real effect of the therapy and not as a consequence of a measurement error. As far as we know, this is the first study on the reproducibility of retinal thickness measurements in uveitic macular oedema using Spectralis OCT. As we did not study the reproducibility of the OCT performed by different operators, further studies will be needed to test the interobserver reproducibility in such a disease.

Improving reproducibility of VEP recording in rats: electrodes, stimulus source and peak analysis

The aims of this study were to evaluate and improve the reproducibility of visual evoked potential (VEP) measurement in rats and to develop a mini-Ganzfeld stimulator for rat VEP recording. VEPs of Sprague-Dawley rats were recorded on one randomly selected eye on three separate days within a week, and the recordings were repeated three times on the first day to evaluate the intrasession repeatability and intersession reproducibility. The VEPs were recorded with subdermal needle and implanted skull screw electrodes, respectively, to evaluate the effect of electrode configuration on VEP reproducibility. We also designed a mini-Ganzfeld stimulator for rats, which provided better eye isolation than the conventional visual stimuli such as flash strobes and large Ganzfeld systems. The VEP responses from mini-Ganzfeld were compared with PS33-PLUS photic strobe and single light-emitting diode (LED). The latencies of P1, N1, P2, N2, and P3 and the amplitude of each component were measured and analysed. Intrasession and intersession within-subject standard deviations (Sw), coefficient of variation, repeatability (R95) and intraclass correlation coefficient (ICC) were calculated. The VEPs recorded using the implanted skull electrodes showed significantly larger amplitude and higher reproducibility compared to the needle electrodes (P<0.05). The mini-Ganzfeld stimulator showed superior repeatability and reproducibility in VEP recording. The intra/intersession ICCs of latency were 0.85/0.70 for mini-Ganzfeld, 0.72/0.62 for PS33-PLUS and only 0.59/0.42 for single LED. The latencies of the early peaks (N1 and P2) demonstrated better reproducibility than the later waves. The mean intrasession and intersession ICCs were 0.96 and 0.86 for the early peaks. Using a combination of skull screw electrodes, mini-Ganzfeld stimulator and early peak analysis, we achieved a high reproducibility in the rat VEP measurement. The latencies of the early peaks of rat VEPs were more consistent, which may be due to their generation in the primary visual cortex via the retino-geniculate fibres.

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.

The effect of increased overjet on the magnitude and reproducibility of smiling in adult females

The objective of this study was to determine if increased overjet (greater than 6 mm) influences the magnitude and reproducibility of natural smile and maximal smile in Caucasian adult females. Twenty adult females with an increased overjet (6-10 mm) and 20 control adult females (overjet 2-4 mm) with no history of orthodontic treatment volunteered to participate. The mean age in the control group was 30.1 ± 6.4 years and the mean age in the test group was 31.9 ± 10.8 years. Three-dimensional stereophotogrammetric images were captured of each subject for three expressions: at rest, natural smile, and maximal smile. The images were recorded twice on two separate occasions, 6 weeks apart. Images were landmarked and a partial ordinary Procrustes superimposition was used to adjust for the differences in head posture between the same expressions. The magnitude of movement relative to the rest position, averaged over all the landmarks, was calculated and compared between the groups using analysis of variance (linear mixed-effects model); the intra- and inter-session reproducibility of both expressions was assessed. There was greater mean movement, averaged over all the landmarks, in the control group than in the increased overjet group for both natural smile and maximal smile (P = 0.0068). For these expressions, there were no statistically significant differences in reproducibility within sessions (P = 0.5403) or between sessions (P = 0.3665). Increased overjet had a statistically significant effect on the magnitude of smiling but did not influence the reproducibility of natural or maximal smile relative to controls.

P8.5 An age-related change in the ipsilateral silent period of a small hand muscle

Abstract Objective To establish the presence or absence of an age effect on the ipsilateral silent period (iSP) for the abductor pollicis brevis (APB) muscle in healthy subjects. Methods Twenty young adults (10 men, 10 women; age range: 20–40) and 20 older adults (10 men, 10 women; age range: 50–70) were matched by age (+30 years), gender and height (±5 cm). All were right-handed. We investigated the iSP for the APB by applying transcranial magnetic stimulation (TMS) and recording surface electromyograms. The contralateral motor-evoked potential (MEP) onset latency, the iSP onset and end latency (iSPOL and iSPEL) were measured and the iSP duration (iSPD) and transcallosal conduction time (TCT) were calculated. We evaluated the correlation between age and iSP, the latter’s intra- and intersession reproducibility and potential influencing factors. Results Mean iSPOL, iSPEL and TCT values were significantly greater in older adults (both men and women) than in young adults. Intra- and intersession reproducibility was good. The mean left-side iSPEL and iSPD were longer than the right-side mean values in young adults but not in older adults. In both age groups, women displayed shorter latencies than men. Conclusions There is a strong effect of age on iSP parameters. Significance Our iSP results may evidence a decrease in transcallosal excitability with age, rather than slowing of the transcallosal interneuron conduction velocity.

Reproducibility of peripapillary retinal nerve fibre layer thickness measurements with spectral domain optical coherence tomography in normal and glaucomatous eyes

AimTo determine reproducibility of peripapillary retinal nerve fibre layer thickness (RNFLT) measurements by spectral optical coherence tomography scanning laser ophthalmoscope (Spectral OCT/SLO) in normal and glaucomatous eyes.Methods61 normal subjects and...