Full-field Testing Research Articles

ОБРАБОТКА ТОРЦОВ ЗАГОТОВОК ДЕТАЛЕЙ

The study objective is to increase turn process efficiency of corrosion-resistant stainless hard-to-machine steel 12X18H10T. The task is to reduce tool costs. Research methods are the following: full-field testing and simulation in deform software environment. The novelty of the work: a new approach is formed to increase the durability of a metal-cutting tool for turning the ends of workpieces. This made it possible to find out the most rational coatings for different operating conditions. Research results: recommendations are developed to choose a rational coating for hard alloy of VK8 grade.

Full-field dynamic response of low-velocity impact on an elastic plate using 3D digital image correlation

Measurement of the impact process is challenging due to its short duration and high frequency response. Due to the very small strain in low-velocity impacts, the requirements for the temporal and spatial resolution of test methods are extremely high. Traditionally, strain gauges or lasers are commonly used to measure the dynamic response of a single point, or quasi-static loading is used to achieve full-field response. To finely describe the transient full-field deformation process of low-velocity impacts, a high-speed imaging system combined with 3D digital image correlation (DIC) technique is set up to investigate the instantaneous responses of impact on a polyvinyl chloride (PVC) plate at the ms and με level. The full-field deformation of the contact surface and the whole process of elastic wave propagation are measured. The measurement by DIC closely matches the measurement by strain gauges and agrees well with the numerical simulation results. The measurement reveals that the “multi-micro-impacts” phenomenon may happen during a complete impact process due to the complex strain wave propagation. This work provides a benchmark case for low-velocity impact full-field testing, and the results show that 3D DIC can accurately evaluate dynamic behaviors of low-velocity impact between flexible bodies and can accurately describe the spatiotemporal propagation characteristics of strain waves.

Mobility test to assess functional vision in dark-adapted patients with Leber congenital amaurosis

BackgroundInherited retinal degenerations (IRDs) affect daylight and night vision to different degrees. In the current work, we devise a method to quantify mobility under dark-adapted conditions in patients with severe childhood blindness due to Leber congenital amaurosis (LCA). Mobility thresholds from two different LCA genotypes are compared to dark-adapted vision measurements using the full-field stimulus test (FST), a conventional desktop outcome measure of rod vision.MethodsA device consisting of vertical LED strips on a plane resembling a beaded curtain was programmed to produce a rectangular pattern target defining a ‘door’ of varying luminance that could appear at one of three positions. Mobility performance was evaluated by letting the subject walk from a fixed starting position ~ 4 m away from the device with instructions to touch the door. Success was defined as the subject touching within the ‘door’ area. Ten runs were performed and the process was repeated for different levels of luminance. Tests were performed monocularly in dark-adapted and dilated eyes. Results from LCA patients with the GUCY2D and CEP290 genotypes and normal subjects were analyzed using logistic regression to estimate the mobility threshold for successful navigation. The relation of thresholds for mobility, FST and visual acuity were quantified using linear regression.ResultsNormal subjects had mobility thresholds near limits of dark-adapted rod vision. GUCY2D-LCA patients had a wide range of mobility thresholds from within 1 log of normal to greater than 8 log abnormal. CEP290-LCA patients had abnormal mobility thresholds that were between 5 and 6 log from normal. Sensitivity loss estimates using FST related linearly to the mobility thresholds which were not correlated with visual acuity.ConclusionsThe mobility task we developed can quantify functional vision in severely disabled patients with LCA. Taken together with other outcome measures of rod and cone photoreceptor-mediated vision, dark-adapted functional vision should provide a more complete understanding of the natural history and effects of treatment in patients with LCA.

Qualitative and quantitative comparison of ERGs with contact lens and adhesive skin electrodes.

Traditional ERGs recorded using corneal electrodes can be difficult for some patients to tolerate. In the last several years, adhesive skin electrodes have gained in acceptance. In this report we present a qualitative comparison of waveforms as well as a quantitative analysis of correlation of amplitudes and implicit times of simultaneous ERG recordings using contact lens and skin electrodes. 89 subjects were included; all were referred for full-field ERG testing for multiple indications. ERGs (obtained according to ISCEV standards) were recorded simultaneously from both eyes with ERG-jet corneal contact lens electrodes and LKC Technologies Sensor Strip adhesive skin electrodes using multi-channel instrumentation (Diagnosys LLC, Espion3). Waveforms, a-wave and b-wave amplitudes and implicit times were compared. Waveform morphologies were similar between electrode types. Regression coefficients (conversion factors) for a-wave and b-wave amplitudes under both photopic and scotopic conditions were tightly clustered. Regression coefficients for implicit times were nearly equal to 1.0. The regression coefficient for the entire amplitude dataset was 0.349, with an overall correlation of 0. 869 between amplitude recorded with skin and contact lens electrodes. The regression coefficient for the entire implicit time dataset was 0.967, with an overall correlation of 0.964 between skin and contact lens electrodes. Our best estimate for the conversion factor between ERG amplitudes recorded with adhesive skin electrodes and contact lens electrodes is 0.349-amplitudes with skin electrodes are about 1/3 the amplitudes recorded simultaneously from the same eyes with contact lens electrodes, with a high correlation. Implicit times are nearly identical for the two electrode types.

Experimental DVC validation of heterogeneous micro finite element models applied to subchondral trabecular bone of the humeral head.

Subchondral trabecular bone (STB) undergoes adaptive changes during osteoarthritic (OA) disease progression. These changes alter both the mineralization patterns and structure of bone and may contribute to variations in the mechanical properties. Similarly, when images are downsampled - as is often performed in micro finite element model (microFEM) generation - the morphological and mineralization patterns may further alter the mechanical properties due to partial volume effects. MicroFEMs accounting for material heterogeneity can account for these tissue variations, but no studies have validated these with robust full-field testing methods. As such, this study compared homogeneous and heterogeneous microFEMs to experimentally loaded trabecular bone cores from the humeral head combined with digital volume correlation (DVC). These microFEMs were used to compare apparent mechanical properties between normal and OA STB. Morphological and mineralization patterns between groups were also compared. There were no significant differences in tissue or bone mineral density between groups. The only significant differences in morphometric parameters were in trabecular thickness between groups. There were no significant differences in linear regression parameters between normal and OA STB apparent mechanical properties estimated using heterogeneous microFEMs with an element-wise bilinear elastic-plastic constitutive model. Clinical significance: Validated heterogeneous microFEMs applied to STB of the humeral head have the potential to significantly improve our understanding of mechanical variations in the bone that occur during OA progression.

Structural vibration mode identification from high-speed camera footages using an adaptive spatial filtering approach

As a non-contact and full-field testing method, high-speed camera-based modal analysis has become a feasible and acknowledged approach. However, extracting small displacements from noisy images has experienced high level of difficulty, especially in high frequency range. This paper proposes a novel adaptive spatial filtering (beamforming) algorithm to extract the displacement signals using high-speed camera. In the proposed algorithm, one pixel is considered as a sensor measuring displacement and a set of pixels are therefore taken as the elements of sensor array. Then, an adaptive spatial filtering acting on this sensor array is proposed. The proposed approach mainly includes three steps. Firstly, a set of pixels are selected to compose a sensor array according to signal to distortion and noise (SINAD). Secondly, a node/antinode searching scheme is proposed based on sinusoid-based piecewise functions, which works as an adaptive filter to match mode shape and enhance modal displacement. Finally, the output of spatial filtering is adopted as the system response for the identification of modal parameters. To validate the performance of the proposed method, simulation and experiment studies are conducted based on measuring the vibration model properties of a free-free beam, which includes a comparison with LK optical flow method and conventional accelerometer-based method. The results show that the SNR of estimated displacement and computational efficiency is significantly improved without using additional sensors. The proposed method paves a way for broadening the applications of using high-speed camera for full-field vibration measurements.

Automatic fringe pattern enhancement using truly adaptive period-guided bidimensional empirical mode decomposition.

Fringe patterns encode the information about the result of a measurement performed via widely used optical full-field testing methods, e.g., interferometry, digital holographic microscopy, moiré techniques, structured illumination etc. Affected by the optical setup, changing environment and the sample itself fringe patterns are often corrupted with substantial noise, strong and uneven background illumination and exhibit low contrast. Fringe pattern enhancement, i.e., noise minimization and background term removal, at the pre-processing stage prior to the phase map calculation (for the measurement result decoding) is therefore essential to minimize the jeopardizing effect the mentioned error sources have on the optical measurement outcome. In this contribution we propose an automatic, robust and highly effective fringe pattern enhancement method based on the novel period-guided bidimensional empirical mode decomposition algorithm (PG-BEMD). The spatial distribution of the fringe period is estimated using the novel windowed approach and then serves as an indicator for the truly adaptive decomposition with the filter size locally adjusted to the fringe pattern density. In this way the fringe term is successfully extracted in a single (first) decomposition component alleviating the cumbersome mode mixing phenomenon and greatly simplifying the automatic signal reconstruction. Hence, the fringe term is dissected without the need for modes selection nor summation. The noise removal robustness is ensured employing the block matching 3D filtering of the fringe pattern prior to its decomposition. Performance validation against previously reported modified empirical mode decomposition techniques is provided using numerical simulations and experimental data verifying the versatility and effectiveness of the proposed approach.

Local damage detection of a fan blade under ambient excitation by three-dimensional digital image correlation

Damage detection based on dynamic characteristics of a structure is one of important roles in structural damage identification. It is difficult to detect local structural damage using traditional dynamic experimental methods due to a limited number of sensors used in an experiment. In this work, a non-contact test stand of fan blades is established, and a full-field noncontact test method, combined with three-dimensional digital image correlation, Bayesian operational modal analysis, and damage indices, is used to detect local damage of a fan blade under ambient excitation without use of baseline information before structural damage. The methodology is applied to detect invisible local damage on the fan blade. Such a method has a seemingly high potential as an alternative to detect local damage of blades with complex high-precision surfaces under extreme working conditions because it is a noncontact test method and can be used under ambient excitation without human participation.

Experimental study on counterintuitive behavior of thin aluminium plates under free airblast loading

An experimental investigation of the counterintuitive behaviour in thin aluminium plates under fullfield test is presented in the paper. Special focus is placed on structural response and permanent deflection of the panels after the complex response. Thus, a series of tests with the plates varied in two kinds of thickness were conducted, where impulsive loading was generated by detonating the explosives at various standoff distances. As loaded impulsively, the vibration response was observed and the final configuration of each plate was measured and recreated. It is shown that all plates subjected to free air blast loading in such conditions exhibited plastic permanent deformation combined with distinct counterintuitive behaviour, as the plates deformed to the opposite direction of the incident wave. In addition, the characteristics of the permanent deflection can be divided into 2 typical deformation shapes, and the occurrences of which were correlated to the dimensionless parameter proposed in previous studies, confirmed to be an approximate indicator to describe the influence of loading conditions herein.

Full-Field Vibration Measurement Using Camera Through Shearlet System

Traditionally, vibration measurement is done using an accelerometer or Laser Doppler Vibrometer, which is an intrusive and single point measurement respectively. This paper demonstrated vibration signal extracted from a perceptually invisible vibrating object using only a camera non-intrusively at full-field capacity. the camera that is capable to capture 1000 frames-per-second video was used to capture the motion of the vibrating object. Each frame of the video was decomposed using complex shearlet transform and the extracted signal was compared to an accelerometer. Shearlet decomposed each frame of the video into complex coefficients which were later used to recover the motion between two consecutive frames. Phase information that were used to retrieve the vibration signal were weighted to decrease unwanted noise. Resonant frequencies of a simply supported beam at 104.0 Hz, 209.5 Hz and 396.0Hz were successfully recovered. Single frequency extraction from an excited loud-speaker at specific frequencies were also conducted and showed a clear peak-to-valley frequency spectrum recovery. the potential of using camera as a full-field displacement measurement where each pixel acting as a vibrometer was explored. Full-field test to recover the mode shape of a circular membrane showed promising result with eight mode shapes successfully retrieved. the experiments proved that each individual pixel was able to retrieve motion at subpixel level that is at 0.00001 pixel scale.

Methods for Prism Placement for Hemianopic Visual Field Loss in Adults with Low Vision

Several adult patients with low vision have come to the Advanced Low Vision Clinic at the Corporal Michael Crescenz Department of Veterans Affairs Medical Center (CMCVAMC), in Philadelphia, Pennsylvania, and to the Bucks County Association for the Blind and Visually Impaired, in Newton, Pennsylvania, with a diagnosis of hemianopic loss secondary to a stroke in the visual cortex; brain tumors; or traumatic brain injury. Prism placement for peripheral field loss allows patients to have enhanced peripheral awareness and an increased peripheral field depending on the type of prism used (Brillant, 1999). To determine prism placement, a low vision optometrist evaluates the patient. The evaluation consists of trials of different types of prism systems, including Fresnel, Gottlieb, Onufryk, and Eli Peli. When a preference for a particular prism system is shown, it is temporarily placed. The optometrist confers with the orientation and mobility (O&M) specialist to discuss patient goals and a plan of care. The O&M specialist performs an evaluation and provides visual scanning training as well as instruction in the functional use of prisms. This report describes the process used in these centers for assessing and placing the prism for these individuals. Prior to prism placement, a full visual field test is completed using a Zeiss, Octopus, or Goldman perimeter, which accurately define the visual field loss. The optometrist and O&M specialist review the results of this test to determine the plan of care for the patient. An Esterman visual field test is completed if the patient is interested in driving again. The Esterman test measures the visual field with both eyes open, as this is required by states that permit driving only if an individual has a visual field of 120 degrees across the horizontal meridian. Prism placement is first tested with a 20-40D Fresnel prism cut to the shape of the spectacle lens in the area of field loss with the prism's base facing in the direction of vision loss. The prism is placed by the optometrist to bisect the pupil so its edge can be seen without scanning into the prism. The edge is then trimmed with iridectomy scissors to the edge of the pupil. The patient then scans into the edge and is asked to count fingers within 10-15 degrees of the non-seeing field. The individual is then asked to ambulate and to detect objects in the non-seeing field. For example, if the non-seeing field is temporal, the scan would be to the left or right to view a painting on the wall, a doorway, or a person passing to the side. If the prism edge is causing diplopia, it is trimmed again to the edge of the dilated pupil. In another method of prism placement, an individual is asked to look straight ahead at his or her nose (if the nose can be seen). If they cannot see their nose, then they are asked to look towards the center of their face, then bring a Post-it note (a small self-adhesive piece of paper) along the plane of their glasses from the non-seeing area into the plane of where they can just see the edge of the Post-it note. They then move the Post-it note back 1 millimeter (mm) until they can no longer see it. When viewing straight ahead, they should not see the edge of the Post-it note. A permanent marker pen such as a Sharpie can then be used to mark the eyeglass lens for later placement of the Fresnel prism (Giorgi, Woods, & Peli, 2009). Choosing the strength of the prism depends on the size of the defect and the individual's tolerance. As a general rule of thumb, the number of degrees the image is moved is half the dioptric power of the prism. Therefore, a 30-diopter prism will move the image approximately 15 degrees. The base of the prism is always placed towards the area of the defect in order to move the image towards the seeing area. The base is marked on the Fresnel prism for orientation. The clinician places the prism to the edge of the defect as described above (Warren & Barstow, 2011). …

Estimating minimally important differences for two vision-specific quality of life measures.

To estimate minimally important differences (MIDs) for the Visual Activities Questionnaire (VAQ) and the National Eye Institute-Visual Function Questionnaire (NEI-VFQ). A total of 607 subjects with newly-diagnosed open-angle glaucoma (OAG) was enrolled in the Collaborative Initial Glaucoma Treatment Study (CIGTS) and randomized to initial treatment with medications or surgery. Subjects underwent an ophthalmic examination and telephone-administered quality of life (QOL) interview before randomization and every six months thereafter. The VAQ and NEI-VFQ were used to assess participants' perceptions of their visual function. Clinical measures included the mean deviation (MD) from Humphrey 24-2 full threshold visual field (VF) testing, and best-corrected visual acuity (VA) measured using the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol. Anchor-based (using MD and VA) and distribution-based methods were used to estimate MIDs. Anchor-based cross-sectional analyses at 66 months follow-up found a 10-letter increment in better eye VA corresponded to MIDs of 5.2 units for VAQ and 3.8 units for NEI-VFQ total scores. A 3-dB increment in the better eye MD yielded MIDs of 2.6 and 2.3 units for the same two questionnaires. In longitudinal analyses, MIDs for the VAQ were 3.2 units for a 10-letter change of VA and 3.4 units for a 3-dB change in the MD. Distribution-based MIDs were larger. A range of MIDs for the VAQ (2.6-6.5 units) and NEI-VFQ (2.3-3.8 units) was found. Although similar in magnitude, MIDs were sensitive to the MID estimation method, the anchor chosen, and differences between questionnaires. (ClinicalTrials.gov number, NCT00000149.).

Stimulated decomposition in peat for engineering applications

Peat deposits are highly compressible, undergoing significant long-term settlement, particularly for fibrous peat. Since decomposition of organic matter can have a significant effect on compression behaviour, the ability to artificially stimulate and pre-decompose a bearing peat stratum prior to the main construction works may mitigate against increased compression rates reported to occur over the design life. This paper presents a feasibility trial of a technique that accelerates the decomposition process in peat prior to entering into full laboratory and field testing. The main decomposition limiting factors of pH and carbon:nitrogen (C:N) ratio are adjusted by adding sufficient amounts of basic and nitrogenous materials. The proposed technique can be tailored for specific peat deposits and can also be achieved in a more sustainable manner. In the trial on moderately decomposed fibrous Sphagnum peat, different peat blends were prepared using additives of peat pulverised fuel ash (PPFA) and urea. Optimum C:N ratio and pH for decomposition were achieved by adding ∼21 kg PPFA and ∼1·5 kg urea per cubic metre of wet peat. The availability of natural decomposers in the peat was also confirmed pre- and post-treatment using a plate count technique, with measured microorganism populations of the order of 105colony-forming units (CFU)/g dry peat.

Effect of binasal occlusion (BNO) on the visual-evoked potential (VEP) in mild traumatic brain injury (mTBI)

Primary objective: The purpose of the experiment was to assess the effect of binasal occlusion (BNO) on the visually-evoked potential (VEP) in visually-normal (VN) individuals and in those with mild traumatic brain injury (mTBI) for whom BNO frequently reduces their primary symptoms related to abnormally-increased visual motion sensitivity (VMS).Design and methods: Subjects were comprised of asymptomatic VN adults (n = 10) and individuals with mTBI (n = 10) having the symptom of VMS. Conventional full-field VEP testing was employed under two conditions: without BNO and with opaque BNO which blocked regions on either side of the VEP test stimulus. Subjective impressions were also assessed.Results: In VN, the mean VEP amplitude decreased significantly with BNO in all subjects. In contrast, in mTBI, the mean VEP amplitude increased significantly with BNO in all subjects. Latency was normal and unaffected in all cases. Repeat VEP testing in three subjects from each group revealed similar test–re-test findings. Visuomotor activities improved, with reduced symptoms, with BNO in the mTBI group.Conclusions: It is speculated that individuals with mTBI habitually attempt to suppress visual information in the near retinal periphery to reduce their abnormal VMS, with addition of the BNO negating the suppressive influence and thus producing a widespread disinhibition effect and resultant increase in VEP amplitude.

Blind phase error suppression for color-encoded digital fringe projection profilometry

Color-encoded digital fringe projection profilometry (CDFPP) has the advantage of fast speed, non-contact and full-field testing. It is one of the most important dynamic three-dimensional (3D) profile measurement techniques. However, due to factors such as color cross-talk and gamma distortion of electro-optical devices, phase errors arise when conventional phase-shifting algorithms with fixed phase shift values are utilized to retrieve phases. In this paper, a simple and effective blind phase error suppression approach based on isotropic n-dimensional fringe pattern normalization (INFPN) and carrier squeezing interferometry (CSI) is proposed. It does not require pre-calibration for the gamma and color-coupling coefficients or the phase shift values. Simulation and experimental works show that our proposed approach is able to effectively suppress phase errors and achieve accurate measurement results in CDFPP.

Electrodiagnostic and two-wavelength fundus autofluorescence imaging investigations in acute idiopathic maculopathy

The aim is to characterise a case of acute idiopathic maculopathy (AIM) using detailed electrophysiology and 2-wavelength fundus autofluorescence (FAF) imaging. A 32-year-old woman presented with reduced visual acuity in her right eye. Imaging investigations performed included 1 & 2 wavelength FAF, fluorescein and ICG angiography and Fourier domain OCT imaging. International-standard pattern and full-field electroretinography (PERG; ERG), electro-oculography (EOG) and multifocal ERG testing were performed. Multifocal ERGs demonstrated evidence of localised macular dysfunction consistent with mild right pattern ERG P50 reduction. Full-field ERGs were within normal limits. The EOG was normal bilaterally. The use of 1 & 2 wavelength FAF imaging revealed a low density macular area, not explained by luteal pigment absorption, that was associated with macular dysfunction. Two-wavelength FAF imaging allows the accurate quantification of macular pigment and the imaging of the underlying relative distribution of lipofuscin. AIM was characterised by a discrete area of disrupted retinal pigment epithelium metabolism and atrophy associated with localised macular dysfunction. Complimentary use of dual-wavelength FAF imaging and electrophysiology may have application to disorders other than AIM.

Electronic speckle pattern interferometry applied for three-dimensional displacement measurement of a sandwich plate containing a fully potted insert

This study presents the construction and operation of a novel electronic speckle pattern interferometry (ESPI) technique, which was applied earliest to sandwich plates containing a single insert. The proposed ESPI is a full-field and non-destructive test that can measure tiny out-of-plane and in-plane displacements under an elastic loading condition. Experimental construction integrates out-of-plane and in-plane measurements into a single optical system to measure three-dimensional displacement of sandwich plates. The ESPI experimental result indicates that displacement of the sandwich plate decreased as the core thickness increased. This experimental result also suggests that displacement decreased as the insert diameter increased; however, estimated strength increased. For validation purposes, the analytical and finite element method (FEM) were utilized to compare the experimental result with ESPI measurements. Comparison between analytical results, ESPI results, and FEM results revealed that all results were in agreement.

Electronic Speckle Pattern Interferometry Applied to the Displacement Measurement of Sandwich Plates with Single ‘Fully Potted’ Insert

AbstractThe construction and operation of electronic speckle pattern interferometer (ESPI) applied to single-inserted sandwich plates have been earliest presented in this paper. Proposed ESPI has advantages of full-field and non-destructive testing, which can measures microscopic out-of-plane displacement in the elastic region without wasting specimen. For validation purpose, the finite element method (FEM) analysis was conducted. By comparing the results of ESPI and FEM displacement fields around the inserts that a convincing agreement is revealed. The effect of potting material diameter on the displacement of single-inserted sandwich plates was obtained by the ESPI and FEM.

Association of magnetic resonance imaging of anterior optic pathway with glaucomatous visual field damage and optic disc cupping.

To investigate the association of magnetic resonance imaging (MRI) of anterior optic pathway with glaucomatous visual field damage and optic disc cupping. Twenty-three healthy volunteers (controls) and 31 glaucoma patients (14 with primary open angle glaucoma and 17 with normal tension glaucoma) were enrolled. All the participants showed no abnormal signs in their intracranial space and optic tract causing optic nerve atrophy and visual field defect, as confirmed by MRI. Multislice T1-weighted spin-echo imaging was performed in the sagittal plane followed by the coronal plane. MRI enabled the evaluation of the diameter of the optic nerve located in the retro-bulb space and the height of the optic chiasm in an observer-masked fashion. The MRI data were compared with the mean deviation (MD) score of the full threshold static visual field test and the optic cup-disc ratio (C/D ratio). The optic nerve diameter was significantly smaller in glaucoma patients (2.25 +/- 0.33 mm) than in controls (2.47 +/- 0.24 mm) and the height of the optic chiasm was significantly shorter in glaucoma patients (2.12 +/- 0.37 mm) than in controls (2.77 +/- 0.36 mm). The optic nerve diameter showed significant correlation with MD score (r = 0.547, P = 0.001) and C/D ratio (r = 0.407, P = 0.009). These correlations are similar to that between MD score and C/D ratio (r = 0.490, P = 0.001). The height of the optic chiasm showed significant correlation with MD score (r = 0.503, P = 0.01) and low correlation with C/D ratio (r = 0.339, P = 0.113). Glaucoma affects the anterior visual pathway anterogradely at least up to the optic chiasm, and these morphologic changes in the anterior visual pathway are correlated with glaucomatous optic nerve damage. MRI of the anterior visual pathway may be a good tool for evaluating glaucomatous damage objectively.

Temporal contrast sensitivity using full-field flicker test (Erlangen flicker test) in patients after penetrating keratoplasty.

The purpose of this study was to evaluate the feasibility of temporal contrast sensitivity testing using full-field flicker stimulation in patients after penetrating keratoplasty (PK) and to assess whether this method is influenced by postoperative corneal topographic changes. Forty-five patients (age 46.5+/-14.2, median 47 years) who had undergone PK and 194 age-matched controls were included in this study. The postoperative interval was 11.8+/-10.2 months (median 9 months). Patients with pre-existing glaucoma or any postoperative intraocular pressure elevation were excluded. The indications for PK were keratoconus in 54% of cases, Fuchs' dystrophy in 38% and stromal dystrophies in 8%. Temporal contrast sensitivity was determined with sinusoidal flickering light (37.1 Hz) of constant mean photopic luminance (10 cd/m(2)) presented in a full-field bowl with an increasing threshold strategy. Mean temporal contrast sensitivity did not differ between patients after PK (1.49+/-0.13, range 1.26-1.78, confidence interval 1.45-1.53) and controls (1.55+/-0.17, range 1.16-1.98, confidence interval 1.47-1.51). No significant correlation between temporal contrast sensitivity and visual acuity could be found in patients after PK or in normals ( r<0.2, P=0.3). In patients after PK, temporal contrast sensitivity was statistically independent of keratometric astigmatism ( r=0.3, P=0.7), topographic astigmatism ( r=0.3, P=0.4), spherical equivalent ( r=0.07, P=0.7), central corneal thickness ( r=-0.06, P=0.7) and time since operation ( r=-0.07, P=0.6). Temporal contrast sensitivity using full-field flicker stimulation seems to be feasible in patients after PK and does not depend on topographic changes of the cornea. The results indicate that the full-field flicker test may be helpful as a supplementary means of detecting early glaucoma caused by ocular hypertension in patients after PK.