Pattern-reversal visual evoked potentials in patients with epiretinal membrane.

PURPOSE: To determine the extent of pattern-reversal visual evoked potential parameter alteration by epiretinal membranes and to investigate the use of pattern-reversal visual evoked potential in the estimation of macular function in eyes with epiretinal membrane and in the fellow eyes. METHODS: In both eyes of 162 patients with epiretinal membrane, 92 of primary and 70 of secondary origin, pattern-reversal visual evoked potentials were recorded. Check sizes of 17', 10', and 7' (minutes of arc) were used. Parameters investigated were N80 and P100 latencies and P100 amplitude. RESULTS: No significant difference was detected between eyes with epiretinal membrane of primary and secondary origin regarding visual acuity and the pattern-reversal visual evoked potential parameters for the different check sizes. Compared with the fellow eyes, the eyes with epiretinal membrane had a significantly reduced visual acuity, prolonged N80 and P100 latencies, and a reduced P100 amplitude for the different check sizes. Compared with a separate control group (N = 20) with patients 50 to 59 years old, eyes with epiretinal membrane (N = 9) showed the same features as in the total group, but only for the 17' and 10' check sizes. The fellow eyes (N = 9) showed a significant reduction of the P100 amplitude (P < .05) for the pattern sizes of 17' and 10', but no difference in visual acuity or pattern-reversal visual evoked potential latency was found. CONCLUSIONS: In eyes with epiretinal membrane, pattern-reversal visual evoked potential latencies are prolonged, and amplitude is reduced. Relationships between clinical parameters and pattern-reversal visual evoked potential parameters require further study.

The EOG in Best's disease and dominant cystoid macular dystrophy (DCMD).

The electro-oculogram (EOG) was studied in 156 normal patients, 103 patients with Best's disease, and 52 patients with dominant cystoid macular dystrophy (DCMD). Statistical analysis was performed by comparing the distribution of Lp/Dt ratios of the groups. Strength of association between Lp/Dt ratio and age was studied with correlation and regression analysis. In normal patients and in those with Best's disease, there was no significant correlation between age and Lp/Dt ratio. Obviously, the gene defect in Best's disease causes an altered light-sensitive slow oscillation that remains stable throughout life. In DCMD patients, there was a significant negative correlation between age and Lp/Dt ratio for the total sample and for the female subgroup. Likely, the gene defect in DCMD interferes with capillary permeability, that becomes susceptible to changes of the female hormones.

Treatment of hyperopia with contact Ho:YAG laser thermal keratoplasty.

PURPOSE: To evaluate the effectiveness, safety, and stability of contact Ho:YAG laser thermal keratoplasty for low to moderate hyperopia. METHODS: Fifty-five hyperopic eyes of 39 patients were treated with a Technomed contact Ho:YAG laser; 23 eyes were treated a second time. Treatment parameters were 1 octagonal ring of 8 spots with a treatment diameter of 6 mm, 7 mm, or 8 mm. Efficacy of the Ho:YAG laser treatment was evaluated after 6 months, comparing 3 treatment zone diameters. Stability and efficacy after 12 months was evaluated comparing 7-mm and 8-mm treatment zone diameters. RESULTS: Mean reduction of spherical equivalent refraction after 6 months was not statistically significantly different between the 6-mm or 7-mm diameter zones: 1.42 (+/- 1.30) D versus 2.22 (+/- 0.44) D. An 8-mm diameter treatment zone was significantly less effective, 1.12 (+/- 0.47) D. Longer follow-up did not show stability: mean reduction of spherical equivalent manifest refraction was 1.58 (+/- 0.45) D for the 7-mm diameter treatment zone and 0.82 (+/- 0.61) D for the 8-mm diameter treatment zone after approximately 12 months. Retreatment had a limited additive effect. No clinically significant loss of spectacle-corrected visual acuity was reported. No eyes lost more than 1 line of visual acuity. CONCLUSION: Contact Ho:YAG laser thermal keratoplasty corrected hyperopia up to 2.50 D, but predictability was poor and a regression of initial effect occurred. Instability of refraction persisted to 1 year after surgery.

Influence of histochemical preparation on acoustic parameters of liver tissue: a 5-MHz study.

In this study the influence of various histological techniques on the acoustic parameters of liver tissue was investigated. Radiofrequency (RF) echographic data were obtained in vitro from 21 liver samples taken from 8 white New Zealander rabbits. The samples were measured in four different subsequent histological tissue processing conditions (freshly excised, 4% buffered formalin fixed, after it went through a paraffin cycle and after staining with hematoxylin and eosin). The acoustic parameters that were obtained from the rf data were velocity of sound, slope of the attenuation coefficient versus frequency between 1.9 and 6.9 MHz, attenuation coefficient at 4.4 MHz, slope of the backscattering spectrum between 1.9 and 6.9 MHz, and intercept of the backscattering spectrum. It was found that fixation by formalin preserves the acoustic properties of the tissue to a reasonable extent. Embedding in paraffin and deparaffinizing induces large changes in the acoustic properties of the tissue. As an alternative, freezing prior to cutting, rather than the paraffin cycle, was investigated also in 10 liver samples obtained from 4 New Zealander rabbits. This method produced no significant changes of the acoustic parameters and should therefore be preferred in acoustic microscopy.

Assessment of myocardial velocities in healthy children using tissue Doppler imaging.

The objective was to determine the normal range of tissue velocities in paediatric hearts as measured by tissue Doppler imaging. A prospective study was carried out involving 160 healthy children (mean age 10.8 y, range 4.0-17.9 y). Using tissue Doppler imaging (TDI) from parasternal long axis and apical views, peak velocities and peak myocardial velocity differences across the right ventricular anterior wall, interventricular septum and left ventricular posterior wall were assessed during systole, early and late diastole. The existence of transmyocardial velocity differences between the left and right side of the interventricular septum, as well as between the endocardium and epicardium of the left ventricular posterior wall was observed throughout the heart cycle. With range-gated TDI from apical four-chamber view, peak velocities were measured within the basal, mid and apical parts of the interventricular septum, and the left and right free ventricular walls. The highest peak systolic, early and late diastolic velocities were measured within the basal parts of all myocardial walls. The ranges of the calculated velocity ratios (early-to-late diastolic velocity and early diastolic-to-systolic velocity) for the various wall parts appeared to be overlapping. The correlations of peak myocardial tissue velocities and their ratios with age and weight were weak and practically irrelevant. These normal values of peak myocardial velocities, transmyocardial velocity differences and the ratios of peak wall velocities can be used as reference values in future investigations of ventricular dysfunction in this age group.

The inverse problem in electroretinography: a study based on skin potentials and a realistic geometry model.

The problem of obtaining the retinal source distribution that generates the electroretinogram (ERG) from measured skin potentials is addressed. A realistic three-dimensional (3-D) volume conductor model of the head is constructed from magnetic resonance image (MRI) data sets. The skin potential distribution generated in this model by a dipole layer source at the retina is computed by using the boundary element method (BEM). The influence of the various compartments of the complete model on the results was investigated, and a simplified model was defined. An inverse procedure for estimating the source distribution at the retina from ERG's obtained from skin electrodes was developed. The procedure was tested on simulated potentials. A fair correspondence between the original and estimated source distribution was found. Furthermore, the ERG's measured at seven skin electrodes were used to estimate the source distribution at the retina. The ERG potential waveform at an additional skin electrode was computed from this source distribution and compared to the measured potential at this electrode. Again a fair correspondence was obtained. It is concluded that the methods may become a useful tool for clinical applications, i.e., for the assessment of localized defects in retinal function.

Improving the ensemble average of visual evoked potentials. I. Theory of correction by spectral phase difference methods.

The considered causes of variability of visual evoked potentials (VEPs) are additive noise and time variability. The time variability can be modelled in three different ways: 1. time invariant VEP waveform and delay-time "jitter"; 2. time variant VEP waveform, due to 2a. jitter of individual components or 2b. constant VEP waveform and "wow", i.e. expansion or compression of the time scale. The wow model has not been considered so far in the literature. Correction of jitter and/or wow is based on a frequency domain method: the "spectral phase difference" method (SPD). When jitter is present the SPD method is applied in the frequency domain on the single responses, or on a subensemble of a small number of responses. For the wow a new method is proposed where the time scale is logarithmically compressed prior to the calculation of the spectrum. It is shown that the SPD method can also be applied then to estimate the compression factor yielding the wow. The single responses, or the averaged sub-ensembles, can subsequently be corrected by this factor and finally be averaged. Improvement of the precision and accuracy of estimates of both the peak latencies and the peak amplitudes, as well as a comparison between the results of the jitter and wow models, have been reported in a companion paper.

Improving the ensemble average of visual evoked potentials. II. Simulations and experiments.

Ensemble averaging is generally used for the estimation of Evoked Potentials. This paper deals with the assessment of correction procedures for the time variability of the ensemble components, this time variability reduces the improvement of the signal-to-noise ratio (SNR) by averaging. Evoked potentials were estimated by ensemble averaging, synchronized to a periodic stimulus. It is assumed that VEP-instability is partly caused by time-variability of the evoked potentials. Two time-variate models were used, from which procedures were derived to correct the single VEP-responses prior to ensemble averaging. The models are: (1) variation in response delay (jitter), (2) variable compression/expansion of the time scale of the response (wow). The Spectral Phase Difference method was applied to estimate both the delay time jitter and the wow factor of single responses with respect to a template (conventional ensemble average). The effects of the devised correction on the average VEP waveform and on the SNR of the ensemble were investigated by using data from realistic simulations and from experiments (n = 23) with a number of healthy human volunteers (n = 17). Jitter- and wow-corrections were effective on simulations with time variability due to delay time jitter and time scale distortion (wow), respectively. Both wow- and jitter correction of the single responses improved the SNR of the VEP measurements significantly and to the same amount. A combined wow-jitter approach resulted in significantly better results than the exclusive application of jitter- or wow correction.

Retinal blood flow changes in diabetic retinopathy measured with the Heidelberg scanning laser Doppler flowmeter.

BACKGROUND: Investigation of retinal blood flow in patients with and without diabetic retinopathy (DR). Retinal blood flow is measured with the non-invasive Heidelberg Retinal Flowmeter (HRF). The clinical suitability of the HRF in patients with diabetes mellitus is investigated, and measured blood flow is compared with blood flow in a group of non-diabetic persons. METHODS: Cross-sectional study of retinal capillary perfusion in eighty diabetic patients and forty-nine control persons, non-invasively measured with the Heidelberg scanning laser Doppler flowmeter. RESULTS: In the control group, HRF measurements could be performed in all subjects. In the diabetes group some patients had media opacities or were not able to maintain stable fixation. Therefore HRF measurement was only possible in 79%, 75% and 60% of the subjects for the nasal, papillo-macular and foveal areas respectively. Retinal blood flow as measured in the perifoveal and nasal areas was associated with the level of diabetic retinopathy. In patients with proliferative DR (levels 4 and 5) the blood flow was reduced, in comparison with that of the patients with exudative or non-proliferative DR (levels 1 and 2) and preproliferative DR (level 3). Blood flow was not correlated with age, systemic blood pressure, intra-ocular pressure and perfusion pressure in either group. A significant negative correlation with the actual blood glucose level was found in the perifoveal area (R = -0.585, P = 0.0001). CONCLUSIONS: The HRF offers an interesting non-invasive method for measurement of retinal blood flow. In this cross-sectional study variations in retinal blood flow could be detected in various stages of DR in relation to clinically visible funduscopic changes.

Discriminative power of visual evoked potential characteristics in multiple sclerosis.

To investigate the discriminative power of pattern-reversal visual evoked potential characteristics (peak latencies and amplitude) and to test whether the addition of visual evoked potential amplitude can increase the power of the visual evoked potential in the diagnosis of multiple sclerosis, we retrospectively studied visual evoked potentials in 59 patients with definite multiple sclerosis and 126 control subjects. Two check sizes (17' and 10') were used. Females had significantly higher amplitudes and shorter latencies than males. N80 latency showed a gradual increase and P100 amplitude a decrease with age. P100 latency was stable between the ages of 20 and 55 years but was increased in childhood and the elderly. The significance of visual evoked potential peak latencies and amplitude in separating the two groups was investigated by means of a (multivariate) discriminant analysis. The visual evoked potential with a pattern of 10' could be measured in 58% of patients with multiple sclerosis. The exclusive use of the P100 amplitude in the discriminant analysis resulted in a percentage of correctly classified cases of 84%, whereas for P100 and N80 latency it was 85% and 90%, respectively. With the 17' pattern, the N80 latency yielded also a higher correct percentage than did the P100 latency. Although N80 latency is, to a greater extent than P100 latency, influenced by age, sex and size of stimulus pattern, when these influences are accounted for, the N80 latency is a more sensitive measure than P100 latency in the classification of multiple sclerosis. Combined use of latency and amplitude for discriminant analysis yielded no significant improvement of the percentage of correctly classified cases.

Echographic classification of intraocular tumours. A 15-year retrospective analysis.

The data on echographic routine diagnosis of intraocular tumours (prominence equal to, or larger than 2 mm) during the years 1976-1990 in the authors' department, were analyzed by multivariate statistical methods, using the final diagnosis either from pathology after enucleation or from the confirmed clinical diagnosis. The material consisted of melanomas (n = 325), metastases (n = 44), haemangiomas (n = 19) and other intraocular tumours (n = 16). The best set of echographic parameters in descending order of significance was: reflectivity (A-mode), choroidal excavation (B-mode), shape (B-mode), and regularity (A/B mode). Echographic differentiation by computer analysis of data on the three main kinds of tumours (melanoma/metastasis/haemangioma) separate from all the remaining tumours was expressed by the correct fraction: melanoma 89%, metastasis 80% and haemangioma 97%. The clinical echographic classification for these cases was 89%, 93% and 99.5%, respectively. The simultaneous differentiation between the three classes was found to yield a correct fraction of 85% by computer statistics and 95% by routine echography. The results of the present study might be used for prospective classification through the use of the parameter 'knowledge base' contained in the statistical classification procedure.

Prognostic value of pattern reversal visual-evoked potentials in idiopathic epiretinal membrane.

BACKGROUND: Prognostically favorable factors for epiretinal membrane removal have been described in the literature by several authors. Little information, however, is available about the objective assessment of the preoperative macular function. This study reports the results of idiopathic epiretinal membrane removal and the prognostic value of preoperative, pattern reversal visual-evoked potentials (PRVEPS) in recovery of visual acuity (VA). METHODS: In 60 patients (60 eyes) with idiopathic epiretinal membrane we performed PRVEP examination preoperatively. All eyes were operated on by standard three-port vitrectomy with membrane removal. Two eyes were excluded because of postoperative complications. Follow-up VA was compared with preoperative VA for the 58 study eyes and correlated with preoperative PRVEP parameters. RESULTS: The mean preoperative VA was 0.2, the mean postoperative VA, 0.4. The PRVEP was recordable in 74%, 67% and 36% of cases for check sizes of 17, 10 and 7 arcmin respectively. Twenty patients (50%) had an increase in VA of two lines or more, in 25 patients (43%) VA remained within one line of the preoperative value, and in 4 patients (7%) VA decreased by two lines or more. The mean preoperative VA was not significantly different between the group with an improved VA and the group that did not benefit from membrane removal. Of the PRVEP parameters, only the N80 latency for the 17' check size was significantly associated with postoperative visual outcome. CONCLUSION: The PRVEP is applicable as a predictor for visual outcome in cases of epiretinal membrane removal. For the 17' pattern size we found a significant association of the combination of recordability and delayed N80 latency with visual outcome.

Performance testing of medical echo/Doppler equipment.

This paper describes the methods applied in a software package developed by the authors for use in a performance testing protocol for medical ultrasound equipment. The history of performance testing of medical ultrasound equipment is briefly reviewed. This paper is confined to the testing of performance of usage aspects, i.e. imaging performance and Doppler velocity estimation performance. Simple test objects are used which have a long life expectancy. The tests performed both in fundamental and in (tissue) harmonic modes when applicable are spatial resolution, contrast sensitivity, and clutter. The concept of a computational observer is used to define the lesion signal-to-noise ratio and the tissue-to-clutter ratio. Further imaging performance features are penetration depth, slice thickness and geometric conformity of display. Pulsed Doppler velocity measurement features tested are: sensitivity, depth and 3D size of the sample volume, velocity measurement, channel separation. The whole performance measurement protocol as well as the quantitative measurements in the digitized images are implemented in software, together with the graphs and data obtained from the measurements.

Ocular hypotony after laser suture lysis following trabeculectomy with mitomycin C.

BACKGROUND: To report our experience with laser suture lysis (LSL) following trabeculectomy with mitomycin C, its timing, effectiveness and related complications. METHODS: We retrospectively examined 38 consecutive eyes of 36 patients that underwent LSL following trabeculectomy with mitomycin C. RESULTS: The mean preLSL intraocular pressure (IOP) was 27.0 mm Hg (SD 6.3, range 16-39 mm Hg) and the postLSL IOP (IOP 1 h after the last session of LSL) was 16.0 mm Hg (SD 7.2, range 3-31 mm Hg). Following the LSL in 7 eyes (7 of 38) hypotony (IOP<6 mm Hg, lasting more than 24 h) developed. Two groups were defined. In group I no hypotony was found after LSL and group II went through a period of hypotony. The time interval between surgery and LSL was significantly shorter in group II (mean 5.7, SD 7.5, range 1-19 days), compared to group I ( mean 14.7, SD 13.0, range 1-44 days) (p=0.041). The mean final IOP (IOP measured at the last visit) was 13.3 mm Hg (SD 3.4, range 6-20 mm Hg) and mean follow-up was 6.1 months (SD 3.9, range 2.0-15.2 months). No hypotony was found at final examination. PostLSL IOP and final IOP were significantly lower in group II (p=0.002 and p=0.024 respectively). IOP reduction by LSL was significantly greater in group II (p=0.046). CONCLUSION: LSL is an effective and safe procedure to lower the IOP following trabeculectomy with mitomycin C. Early application of LSL results in lower final IOPs, but has a higher risk of hypotony.

Pattern reversal visual evoked potentials in eyes with macular holes and their fellow eyes.

PURPOSE: To investigate whether the pattern reversal visual evoked potential can be useful in the diagnosis and management of macular hole patients. METHODS: The pattern reversal visual evoked potential was measured in 66 patients with a macular hole and in 43 healthy control subjects. Check sizes of 34', 17' and 10' were applied. RESULTS: Results showed that, for the check sizes of 34', 17' and 10', eyes with a macular hole had significantly prolonged N80 and P100 latencies and a significantly reduced P100 amplitude as compared to their fellow eyes. Furthermore, for the 10' check size, the fellow eyes appeared to have a significantly reduced P100 amplitude in comparison with the control eyes, whereas N80 and P100 latencies of the fellow eyes of the macular hole patients were not prolonged. CONCLUSION: Significant pattern reversal visual evoked potential alterations were shown in eyes with macular holes and fellow eyes for small check sizes.

Relationship between anticoagulant medication and massive intraocular hemorrhage in age-related macular degeneration.

BACKGROUND: A massive intraocular hemorrhage in the course of age-related macular degeneration (AMD) is a devastating event. We set out to determine the role of anticoagulant therapy prescribed for vascular or cardiac indications in the development of a massive hemorrhage. METHODS: A retrospective case-controlled study was conducted of 50 cases of age-related macular degeneration complicated by massive subretinal and vitreous hemorrhage. The control group consisted of 50 cases of AMD with small subretinal hemorrhage. RESULTS: There was a significant difference in the use of anticoagulant medication (warfarin sodium) between the groups. The difference in the use of antiplatelet medication (aspirin) between the groups was not significant. A patient with a massive intraocular hemorrhage and AMD is 11.6 times more likely to use anticoagulant medication. It appeared that more than 50% of the patients in the massive hemorrhage group were allowed to stop the anticoagulant medication. CONCLUSION: Anticoagulant medication poses a significant risk in the development of a massive intraocular hemorrhage in patients with exudative AMD. Antiplatelet medication poses a less significant risk. Physicians prescribing anticoagulant medication should be informed about the macular status of the patient. the In case of neovascular AMD, anticoagulant medication should be prescribed only for absolute systemic indications.

Predictive value of pattern VEP, pattern ERG and hole size in macular hole surgery.

OBJECTIVE: To describe pattern-reversal visual evoked response (PRVEP) and pattern electroretinogram (PERG) parameters in eyes with macular hole and their value for predicting postoperative visual outcome. METHODS: Prospectively we studied 27 eyes (27 patients) with a full-thickness macular hole. Preoperatively the hole and rim were measured and the PRVEP and PERG were recorded. The preoperative parameters were correlated with postoperative visual outcome. RESULTS: The macular hole was closed in 26 of 27 eyes. Sixteen eyes (59%) had an increase in visual acuity (VA) of two lines or more, 10 eyes (37%) remained within one line of preoperative VA and 1 eye (4%) had a decrease in VA of two lines. Duration of symptoms was negatively correlated with preoperative VA (R=-0.547, P=0.0038) and postoperative VA (R=-0.519, P=0.0065) and positively correlated with hole area (R=0.533, P=0.0061) and rim area R=0.633, P=0.0009). Only the PRVEP P100 latency of the 10' check size and the PERG N35 latency were significantly associated with visual outcome (P=0.022 and P=0.042 respectively). CONCLUSIONS: There was no association of either hole or rim size with postoperative visual outcome. Preoperative electrophysiology, however, is useful as a prognostic tool. Utilization is limited to the use of latency parameters of the response and is dependent on the check size of the stimulus.

Congenital heart defects and maternal derangement of homocysteine metabolism.

Methionine loading tests and folate, vitamin B(6), and vitamin B(12) analyses were performed in 27 mothers of children with congenital heart defects. Median fasting plasma homocysteine concentrations were significantly higher in the study group as compared with 56 control subjects (P =.0001). Maternal hyperhomocysteinemia may be a risk factor for congenital heart defects.