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PubMed1999

[Corneal astigmatism as a special complication after lid-loading in patients with lagophthalmos].

UNLABELLED: Lid-loading with precious metals, described by Illig in 1958, has become increasingly important. because of its good functional and cosmetic results this method is superior to tarsorrhaphy. Furthermore, lid-loading can be combined with additional surgical techniques to achieve more dynamic lid-closure. In a prospective study we examined the results after lid-loading and discuss postoperative changes of the cornea. PATIENTS AND METHODS: Between May 1994 and June 1998, 36 patients with peripheral facial paresis and lagophthalmos were treated with a pretarsally fixed upper-lid implant. We used 99.99% gold for the implants with a weight of 1.5 g on average. RESULTS: In all cases we obtained sufficient postoperative lid closure which resulted in a statistically significant reduction in lagophthalmos and improved keratopathy. Postoperative complications were: pseudoptosis, remaining lagophthalmos, bulge, extrusion, migration and corneal astigmatism. Depending on the implant pressure, an astigmatism of 1-2 D developed in the vertical meridian. In all cases the initial visual acuity was reached by an ordination of cylindrical glasses. CONCLUSIONS: So far, corneal astigmatism as a complication after lid-loading has not received much attention in the literature. In our opinion, the development of astigmatism is caused by implants that are too heavy, an incorrect implant radius and individual cofactors (consistency of lid and cornea). There has been no need for an explantation in any case.

Adult↗
PubMed2001

[Iris metastases in breast carcinoma].

BACKGROUND: Metastatic cancer of the iris is rare. We report a case of breast carcinoma which metastasized to the iris and a review of the literature. METHOD: A 60-year-old woman with a history of breast carcinoma presented with lesions of the iris 5 years after diagnosis and tumor excision. In addition to slit-lamp examination including gonioscopy, ultrasound biomicroscopy, positron-emission tomography and fluorescein angiography of the iris were used for diagnosis. Furthermore, the literature was searched using the medline database. RESULTS: The iris metastasis exhibited multiple whitish to pink nodules on the inferior half of the iris and infiltration of the chamber angle. The main tumor mass was prominent and highly vascularized. Best corrected visual acuity was 20/40 and the intraocular pressure was 7 mmHg. Ultrasound biomicroscopy showed lobular masses characterized by mid to low reflectivity and there was no distinct border to the surrounding tissue. Fluorescein angiography of the iris showed tumor vessels with dye leakage. The positron-emission tomography displayed metastatic lesions to the liver, lung, bones and lymph nodules in addition to the lesion of the iris. The review of the literature revealed that breast carcinoma leads to choroidal metastases in 5% of cases and iris metastases are even rarer. In twothirds of these cases the lesions form unilateral whitish to red clumps at the horizontal meridian and in the inferior quadrants of the iris. The preferred treatment is chemotherapy and/or radiation therapy. CONCLUSIONS: Breast carcinoma is rarely associated with iris metastasis. Positron-emission tomography is a sensitive diagnostic tool to identify metastatic lesions and is a useful method for planning therapeutic approaches. Radiation therapy, argon laser treatment and block excision are therapeutic options with an isolated metastasis of the iris.

Breast Neoplasms↗
PubMed2002

Efficiency of a video-autorefractometer used as a screening device for amblyogenic factors.

BACKGROUND: High ametropia is known as a risk factor in developing amblyopia. The aim of the study was to evaluate the efficiency of a commercially available infrared videorefractometer (PowerRefractor) in examining children, and to evaluate its effectiveness in detecting amblyogenic factors of the refraction. The influence of cycloplegia was of interest. METHODS: A total of 255 eyes (-28.25 D to +7.88 D spherical equivalent) of 128 patients (1-81 years) were examined by cycloplegic retinoscopy. All of them were measured with the PowerRefractor under cycloplegia. Fifty-four of these patients (108 eyes) were additionally measured without cycloplegia. The technique of the device is based on the eccentric photorefraction method. Both eyes can be measured simultaneously from a distance of 1 m. A video-analysis of each eye is computed in three meridians. The subject can be observed in real time on a screen, and the refraction is immediately available. RESULTS: Measurement of refraction was possible at all ages. More effort was required with young children who could not cooperate well with the procedure of conventional table-top autorefractometers. The mean sensitivity in detection of any amblyogenic ametropia was 80% with and without cycloplegia. The specificity was 61% with cycloplegia and 84% without. The rate of false-negative results in the detection of anisometropia, hyperopia and astigmatism ranged from 10% to 24%. In particular, high astigmatism and hyperopia remained undiscovered. CONCLUSIONS: The reliability of the photorefractor which was the subject of the evaluation in detecting amblyogenic ametropia was comparable to that of other devices described previously in the literature. The method is suitable for use in children, but anisometropia, high astigmatic and hyperopic ametropia remained undiscovered in several cases. Commercial interest: none.

Adolescent↗
PubMed2004

Distribution of scotoma pattern related to chiasmal lesions with special reference to anterior junction syndrome.

PURPOSE: To evaluate pathogenetic mechanisms and frequency distribution of visual field defects (VFDs) in patients with chiasmal lesions. Secondly, to reconsider the existence of "Wilbrand's knee" as far as referable to the anterior junction syndrome. METHODS: Consecutive visual field records related to chiasmal lesions were retrieved from the Tuebingen Perimetric Database. In all cases, at least one eye was examined with the Tuebingen Automated Perimeter using a standardized grid of 191 static targets within the central 30 degrees visual field, and a threshold-related, slightly supraliminal strategy. VFDs were classified according to standard neuro-ophthalmological categories. RESULTS: Results from 153 consecutive patients (65 male, 88 female) were evaluable. The majority (65%) of chiasmal lesions was due to pituitary adenoma, followed by craniopharyngioma (12%), astrocytoma (9%), and meningioma (8%). Vascular lesions in this region occurred rarely (2%). Three per cent of all patients had no final diagnosis. The majority (22%) of scotomas was attributable to involvement of the temporal hemifield in both eyes, with true bitemporal hemianopia being a very rare event (1%). Anterior junction syndrome, characterized by advanced visual field loss affecting the visual field centre in one eye and (possibly subtle) defects respecting the vertical midline in the fellow eye, was the second most frequent classifiable VFD (13%). Homonymous hemianopic VFDs occurred in 11% of all cases. Nine per cent of all patients exhibited monocular VFDs which did not respect the vertical midline, whereas in 3% of the subjects the monocular VFDs did not cross the vertical meridian. Binasal defects and posterior junction syndrome also occurred seldom (< 1%). Nineteen per cent of all visual field records of patients with chiasmal lesions had results, which could not be classified unequivocally, and an identical portion was rated normal. CONCLUSION: In patients with chiasmal lesions, incomplete involvement of the temporal hemifields in both eyes was the most frequent event (22%), followed by anterior junction syndrome (13%). The latter entity at least clinically indicates the proximity of the pre-chiasmal ipsilateral optic nerve and decussating fibres emanating from the inferior nasal hemiretina of the fellow eye. However, this cannot provide conclusive evidence for the existence of anterior Wilbrand's knee.

Adolescent↗
PubMed2004

Deficits of spatial localization in children with strabismic amblyopia.

BACKGROUND: Besides loss of visual acuity and binocularity, spatial localization deficits (comprising both increased spatial uncertainty and spatial distortions) are an important feature of strabismic amblyopia. Although they have been extensively investigated in adult amblyopes, there are still many open questions concerning their substrate and relationship to clinical parameters. Our aim was to develop a procedure for assessing vertical alignment, which enabled us to find out whether children with strabismic amblyopia had similar spatial localization deficits, and their relation to the children's clinical condition. METHODS: Vertical alignment was assessed in children by comparing the visual direction in space of three loci along the vertical meridian, separated by 5 deg of visual angle. We tested alignment in the amblyopic and dominant eyes of 32 strabismic and in both eyes of 35 control children from 4.5 to 10 years, together with a careful orthoptic examination. RESULTS: In the amblyopic eyes, increased uncertainty and systematic distortions outside the normal range occurred. Large angles of deviation and pathological fixation patterns were necessary, but not sufficient conditions for gross spatial deficits to occur. The fellow dominant eyes showed spatial localization similar to normal eyes. CONCLUSIONS: Children with strabismic amblyopia exhibited localization deficits and relationship to clinical data similar to those in adult amblyopes. These data are important for further investigations about the substrate, plasticity and the clinical relevance of perceptual distortions.

Amblyopia↗
PubMed2004

Lamellar keratotomy to correct astigmatism in cataract surgery.

BACKGROUND: For the correction of astigmatism in cataract surgery, several incisional procedures have been developed. In this study, a modification of lamellar keratotomy was evaluated to correct astigmatism in cataract surgery. METHODS: Prospectively 32 eyes of 25 patients with a preoperative astigmatism greater than 1.5 D were studied. All patients were treated with lamellar keratotomy with an incision width of 6 mm and a radial length of 1.5 mm placed at the limbus in the steep meridian. Phacoemulsification and IOL implantation were then performed through a 3.2-mm corneal tunnel incision. After 4 weeks, mean astigmatism, mean corneal power changes, and mean surgically-induced astigmatism derived from vector analysis in the central 3-mm optical zone were determined. RESULTS: The mean astigmatism decreased from 2.75 +/- 0.80 D preoperatively to 1.58 +/- 0.91 D after 4 weeks (P < 0.001). There were no significant changes (P=0.614) of the mean corneal power. The mean surgically-induced astigmatism was 2.59 +/- 1.50 D. The induced changes were more accentuated in superior incisions. In corneal topography, 78% of the treated eyes revealed a characteristic threefold pattern of the mid-peripheral cornea postoperatively, which impaired the corneal optical performance in ray-tracing analysis. CONCLUSIONS: Lamellar keratotomy effectively reduced high preoperative astigmatism in cataract surgery. This surgical approach was combined with a superior, temporal, or oblique corneal incision.

Adult↗
PubMed2006

Horizontal and vertical micropsia following macula-off rhegmatogenous retinal-detachment surgical repair.

BACKGROUND: Dysmetropsia or distorted image size perception (smaller: micropsia; larger: macropsia) is known to occur after successful surgical re-attachment for macula-off rhegmatogenous retinal detachment. However, the vertical and horizontal components of size distortion have not been previously quantified separately. The purpose of this article is to describe horizontal and vertical dysmetropsia occurring in patients following pars plana vitrectomy and gas treatment (octafluoropropane, C(3)F(8) or sulfur hexafluoride, SF(6)) for macula-off rhegmatogenous retinal detachment. MATERIAL AND METHODS: Four patients (mean+/-SD, 59+/-8 years; three women and one man) who had had pars plana vitrectomy and gas treatment for macula-off rhegmatogenous retinal detachment 6-7 months earlier underwent ocular examination, best corrected visual acuity test, threshold horizontal and vertical dysmetropsia measurement using a computerised version of the New Aniseikonia Test, slit-lamp examination and optical coherence tomography of the macula. RESULTS: All patients had binocular visual complaints including difficulty judging distances or reading, rivalry or asthenopia. The logMAR visual acuity (mean+/-SD) in the operated eye was 0.52+/-0.199 and 0.02+/-0.171 in the unaffected eye. All patients perceived the image as smaller (micropsia) with the affected eye, with differences ranging from -9 to 0%. Four patients showed 3% or more size difference between horizontal and vertical meridians. CONCLUSIONS: Dysmetropsia does occur in symptomatic patients following successful surgical repair of macula-off rhegmatogenous retinal detachment by pars plana vitrectomy and gas treatment. The effect on image size is heterogenous across the retinal area affected.

Aged↗
PubMed1998

Holmium:YAG thermokeratoplasty: treatment parameters for astigmatism induction based upon spherical enucleated human eyes.

BACKGROUND: The refractive outcome of thermokeratoplasty for astigmatism correction depends upon the optical zone diameter (OZD) and coagulation angle (CA; distance between two coagulation spots around the flat meridian). METHODS: Astigmatism was induced in 36 spherical human eye-bank eyes (Ho:YAG laser, 15 Hz, 20 mJ/pulse, 25 pulses per coagulation spot) with different OZDs and CAs. Thirty eyes received free-hand laser application (marked positions). Six eyes were treated using a suction mask, providing a constant OZD of 8.1 mm and an angle of 22.5 degrees between the laser spots. To compare the results, silicone replicas of the eyes were made pre- and postoperatively and analyzed by video-topometery. RESULTS: With an average decrease of 4 D/mm the refractive change is inversely linear to the OZD. Changes of the CA showed significant variations between 22.5 degrees and 45 degrees, only. Mask guidance leads to the same amount of average refractive change. The deviation is +/- 3.4 D for the freehand application but only +/- 0.8 D for mask guidance. CONCLUSION: The data obtained in this in vitro study are transferred to a treatment nomogram describing the immediate postoperative refractive change, not identical with the final refraction. The results of the study are limited by the fact that astigmatism was induced in spherical corneas, rather than correcting preexisting ones.

Astigmatism↗
PubMed1998

Corneal shape changes after pars plana vitrectomy.

BACKGROUND: The purpose of this prospective, controlled, clinical study was to investigate corneal shape changes due to pars plana vitrectomy (PPV) in patients with potential visual improvement postoperatively. METHODS: A total of 36 consecutive patients undergoing conventional PPV combined with or without macular surgery were studied. Sequential determinations of the corneal curvature by manual keratometry and corneal topography were performed preoperatively, during the first postoperative week, at 4 weeks and after 2-8 months (mean 4 months). RESULTS: The mean surgically induced keratometric astigmatism was 2.92 +/- 1.98 diopters (D) (P < 0.0001) during the first postoperative week. After 4 weeks and 4 months the values decreased to 1.01 +/- 0.97 D and 0.67 +/- 0.43 D, respectively. Videokeratographic analysis confirmed significant curvature changes, with corneal steepening (P < 0.008) which corresponded to the superonasal and temporal semimeridian, and flattening (P < 0.008) along the inferior and inferonasal semimeridians. Corneal changes persisted in some cases for several weeks, partly in an asymmetric and irregular configuration. Shifts in axis to against-the-rule and oblique meridians were noted postoperatively with redistribution within preoperative values in 53% of the cases at 4 weeks after surgery. Subgroup analysis revealed that suture diameter, as well as the use of gas endotamponade, influenced the induced astigmatism. CONCLUSION: A substantial increase of the corneal astigmatism and distinct shape changes can occur after PPV in the immediate postoperative period. Consecutive stabilization at preoperative values was observed after several weeks. The time course of the corneal curvature alterations should be considered in the postoperative management to detect refractive causes of inadequate visual acuity.

Adult↗
PubMed1999

Familial macular cone dystrophy: diagnostic value of multifocal ERG and two-color threshold perimetry.

BACKGROUND: It is difficult to detect receptor dysfunction in patients with marked bilateral visual loss but only mild morphological alterations of the fundus. METHODS: Two patients, father and son, with visual acuity loss to 20/100 were examined. Using the multifocal ERG, 61 local cone ERGs from each eye were derived from the central visual field. The dark-adapted two-color threshold perimetry using stimuli of 500 nm and 656 nm for rod and cone function was investigated along the horizontal meridian of the visual field. RESULTS: In the multifocal ERG of both patients a macular response was absent. From eccentricity at and anterior to 5 degrees, good multifocal cone activity was recorded. Cone thresholds were markedly diminished in the macula. The rod thresholds were borderline in the father and normal in the son. CONCLUSIONS: Multifocal ERG is a novel technique, very well suited to reveal the topography of cone function. Using two-color threshold perimetry affords an opportunity to differentiate between rod and cone functional defects. Both together helped to establish the diagnosis of macular cone dystrophy in the present family.

Adult↗
PubMed2000

Development of the standard reference plane for the Heidelberg retina tomograph.

BACKGROUND: Topometry of the optic disc is the quantitative assessment of the structure of the optic nerve head by means of three-dimensional parameters. The parameter values depend on definitions of intraocular reference planes. PURPOSE: To describe the development of intraocular reference planes in laser scanning tomography for the Heidelberg Retina Tomograph (HRT) using image intrinsic data with a fixed offset reference plane (320 microm) and to present a contour-line-based "flexible" standard reference plane ("SRP") for calculation of intrapapillary stereometric parameters taking the interindividual variability of optic disc topography into account. METHODS: Ten-degree triple images were obtained by laser scanning tomography from 99 glaucoma eyes and 180 normal eyes. The images were evaluated to assess the variability of height measurements of an optic disc border contour-line segment (6 degrees width) corresponding to the site of the papillo-macular bundle as indicated by the average optic disc surface inclination angle. RESULTS: The average optic disc surface inclination angle was -7 degrees +/- 3 degrees below the horizontal meridian (0 degrees). The 6 degrees wide contour-line segment for the SRP was chosen according to the average surface inclination angle (-10 degrees to -4 degrees). The reproducibility of the SRP-segment height measurements was 16.0+/-10.8 microm for normal eyes and 23.4+/-18.0 microm for glaucoma eyes. To ensure that the automatic reference level determination for intrapapillary parameters remained below the disc border height, we defined the SRP level at a 50 microm offset (>2 SD of average segment height reproducibility in glaucoma) added to the individual height position of the 6 degrees contour line segment. CONCLUSION: The flexible standard reference plane allows for automatic determination of intrapapillary variables once a disc border contour line is interactively defined. In contrast to a fixed offset reference plane (e.g. 320 microm below the mean retina height), the interindividual variability of optic disc topography (oblique insertion, glaucomatous surface flattening) is respected at the cost of the need for an accurate optic disc border outline.

Diagnostic Techniques, Ophthalmological↗
PubMed2003

A space-variant filter model of texture segregation: parameter adjustment guided by psychophysical data.

This article presents a space-variant version of a standard spatial filter model of texture segregation of the "back-pocket" type (i.e., two filter layers with an intermediate pointwise nonlinearity). The model was tested with psychophysical data from experiments with line textures in which target lines differed in orientation from background lines. The textures were presented briefly and then masked. Segregation performance was evaluated along the horizontal meridian up to retinal eccentricities of about 10 deg. Data are reported from two experiments with different line densities (Kehrer 1989) and two experiments with different orientation contrasts between target lines and background lines (Kehrer 1990). Segregation performance proved to depend strongly on these texture variations, and it peaked several degrees from fixation in all cases. The filter model provided satisfactory predictions of experimental data when model parameters were adjusted appropriately. It is concluded (1) that filter models defined in strictly spatial terms (i.e., without temporal properties) offer a sufficient framework to account for the psychophysical data and (2) that the particular course of the performance curve (i.e., the performance peak outside the central region) must be attributed to the characteristics of second-layer filters.

Humans↗
PubMed2005

The existence of a linear system consisting of sympathetic endings in rat skin.

In a previous pilot study we suggested the novel notion that the catecholaminergic sympathetic nerve endings are non-homogeneously distributed in the rat skin. In the present study we have utilized several independent methods to determine the in vivo distribution of catecholamine-containing fibers in rat skin. Using whole body macro-autoradiography with an iodine125-labeled tyrosine, we localized the distribution of iodine-125-catecholamine in rat skin. The images on the film showed various pairs of symmetrical linear arrays running from the head through the back and to the hind limbs of the animal that we arbitrarily termed sympathetic substance lines (SSLs). The distribution of catecholamine in rat skin was also visualized by light microscopy autoradiography with tritiated tyrosine. The majority of silver grains in the sections were located among hair follicles along a band or zone. Furthermore, a modified sucrose-phosphate-glyoxilic acid (SPG) method was adapted to observe sympathetic fibers in the skin sections. Dense clusters of fluorescent nerve fibers in correspondence of arrector pili muscles (AP muscles) were located along lengthwise lines of the body, in a pattern coinciding with the linear arrays identified by macro-autoradiography. We concluded that concentrated clusters of noradrenergic nerve fibers innervate AP muscles and form a longitudinal linear system in the whole skin. These results are discussed in terms of physiological functions associated with hair follicles, sensory signal pathways and Meridians in Chinese traditional medicine.

Animals↗
PubMed1998

Cardiopulmonary interaction during partial liquid ventilation in surfactant-treated preterm lambs.

UNLABELLED: Gas ventilation following instillation of perfluorochemical (PFC) liquid, partial liquid ventilation (PLV), improves gas exchange and pulmonary mechanics in neonatal animals and humans with severe respiratory distress. The effect of PLV on cardiac contractility, performance, pulmonary blood flow and ductal shunt has not been fully described. To this end, we evaluated these indices of cardiopulmonary function in eight conventionally gas ventilated, surfactant-treated premature lambs (125 days gestation) before and during PLV. Animals were instrumented with central venous and aortic lines. Serial evaluation of arterial blood chemistry/pressure, and pulmonary mechanics was performed; cardiac contractility, performance, pulmonary blood flow and ductal shunts were serially assessed by echocardiography. As compared to conventional gas ventilation, during PLV there was a significant decrease in left ventricular meridian (22.5+/-6.6 SE vs 8.1+/-1.4 SE g/cm2, P < 0.02) and circumferential wall stress (54.1+/-16.5 vs 24.4+/-3.8 SE g/cm2, P < 0.04) at end systole. The fall in wall stress at end systole was associated with a significant decrease in left ventricular internal diameter (1.2+/-0.05 SE vs 1.04+/-0.045 SE cm; P < 0.01). There were no significant changes in heart rate, systemic arterial and central venous pressures, systemic vascular resistance, left ventricular shortening and ejection fractions during PLV. The decrease in wall stress was associated with a significant decrease in mean airway pressures (15.9+/-1.1 SE vs 9.9+/-0.2 SE cmH2O; P < 0.05) and ostensibly a change in intrathoracic pressures during PLV. There were no significant differences in blood flows (pre vs during PLV; ml/min/kg): pulmonary (226+/-62 SE vs 293+/-65 SE), aortic (237+/-36 SE vs 204+/-21 SE), and left to right ductal (119+/-25 SE vs 105.5+/-26 SE) measured before and during PLV. CONCLUSION: Cardiac output and pulmonary blood flow do not change significantly during PLV and therefore do not appear to contribute to improved gas exchange. This stable cardiac performance occurs at lower wall stress and thereby more advantageous energetic conditions.

Analysis of Variance↗
PubMed2006

High-intensity laser for acupuncture-like stimulation.

The insertion of needles into specific parts of the body was shown to provide analgesic and therapeutic effects. In this study, we tested the analgesic effects of high-intensity infrared laser for acupuncture-like stimulation. Twelve adult Sprague-Dawley rats weighing 230 to 250 g were randomly assigned to laser, needle, or restraint groups. Stimulation was directed to the meridian point Taixi (KI 3) for 10 min. For laser stimulation, a pulsed Er:YAG system was used. The laser settings were adjusted to provide a focal raise in the skin temperature to about 45 degrees C. The anti-nociceptive effect was evaluated by the tail-flick test. Both needling and laser stimulation significantly increased the tail-flick latency. Peak needling effect was observed immediately after treatment, while laser stimulation was effective both immediately and 45 min after treatment. High-intensity laser stimulation may be used alternatively or in combination with conventional acupuncture needling for pain relief.

Acupuncture Points↗
PubMed2001

Differential effect of near-threshold stimulus intensities on sound localization performance in azimuth and elevation in normal human subjects.

The ability of humans to localize sounds remains relatively constant across a range of intensities well above detection threshold, and increasing the spectral content of the stimulus results in an improvement in localization ability. For broadband stimuli, intensities near detection threshold result in fewer and weaker binaural cues used in azimuth localization because the stimulus energy at the high- and low-frequency ends of the audible spectrum fall below detection threshold. Thus, the ability to localize broadband sounds in azimuth is predicted to be degraded at audible but near threshold stimulus intensities. The spectral cues for elevation localization (spectral peaks and notches generated by the head-related transfer function) span a narrower frequency range than those for azimuth. As the stimulus intensity decreases, the ability to detect the stimulus frequencies corresponding to the spectral notches will be more strongly affected than the ability to detect frequencies outside the range where these spectral cues are useful. Consequently, decreasing the stimulus intensity should degrade localization in both azimuth and elevation and create a greater deficit in elevation localization due to the narrower band of audible frequencies containing elevation cues compared to azimuth cues. The present study measured the ability of 11 normal human subjects to localize broadband noise stimuli along the midsagittal plane and horizontal meridian at stimulus intensities of 14, 22, and 30 dB above the subject's detection threshold using a go/no-go behavioral paradigm. Localization ability decreased in both azimuth and elevation with decreasing stimulus intensity, and this effect was greater on localization in elevation than on localization in azimuth. The differential effects of stimulus intensity on sound localization in azimuth and elevation found in the present study may provide a valuable tool in investigating the neural correlates of sound location perception.

Adult↗
PubMed2004

The effect of fixation instability on the multifocal VEP.

In multifocal visually evoked potentials (mfVEP), we find reversals in waveform near the horizontal meridian due to convolutions in the cortex. This renders the mfVEP very sensitive to small changes in gaze position. In this study we tested the effects of very small amounts of fixation instability on the mfVEP topography under controlled conditions using four normal subjects. In order to simulate unstable fixation, subjects were instructed to move their fixation point systematically in a clockwise direction between the endpoints of a fixation cross every few seconds (two degree diameter cross = one degree fixation error). Results were compared against a control condition with stable, central fixation. The effects of 0.5 degrees fixation error are small, but 1.0 degrees fixation error can produce a large decrease in root mean square signal amplitude (e.g., 60%) in the central foveal region (i.e., within 1.4 degrees eccentricity). The size of the effect drops off rapidly with eccentricity and varies greatly between areas within a subject, and between the four subjects. Beyond 3.0 degrees eccentricity the effects are minimal. Unstable fixation with relatively small fixation errors caused a dramatic decrease in mfVEP amplitude within three degrees of eccentricity, which can be misinterpreted as loss of macular function. Fixation monitoring is essential to obtain accurate results in the macular area when recording mfVEPs.

Electroretinography↗
PubMed2005

Using the flow cytometry to quantify the Giardia cysts and Cryptosporidium oocysts in water samples.

The flow cytometry (FC) has been used to detect Giardia cysts and Cryptosporidium oocysts quantitatively and instantaneously in this study. The experimental results showed that FC is potential to become a more precise method for the detection of Giardia and Cryptosporidium in water. This study also evaluated the staining efficiencies for three commercial antibodies. After staining Cryptosporidium oocysts with direct immunofluorescent antibodies in water samples, two populations were detected in the scatter-plots (FL1 versus SSC) of the FC. The Cryptosporidium oocysts and Giardia cysts are significantly separated from other particles while stained with direct immunofluorescent antibodies produced by Meridian Diagnostics and Waterborne Inc.

Animals↗