Clinical value of dacryoscintigraphy using a simplified analysis.

PURPOSE: To study the discriminatory ability of dacryoscintigraphy in differentiating between patients with epiphora and volunteers using a simple method. METHODS: Twenty eyes in ten volunteers and 66 eyes in 55 patients with severe epiphora were studied. Dacryoscintigraphy (15 frames of 1 min) was performed after administration of 4 MBq (99m)Tc-pertechnetate (10 mul) in both eyes. By mapping a single region of interest (ROI) over the conjunctival sac we determined T1 (%dose in first minute) and linear clearance rate (LCR, defined as [see text] from the tracer disappearance curve. Reproducibility was determined in volunteers. Conjunctival resorption was determined from completely obstructed systems. Sensitivity and specificity were calculated and receiver operating characteristics (ROC) analysis was conducted. RESULTS: In volunteers mean T1 was 52.8+/-11.9% (95% CI 47.1-58.4%), and LCR was 74.2+/-11.1% (95% CI 69.0-79.4%). Reproducibility was good (mean difference 4.1+/-13.3% for T1 and 0.7+/-17% for LCR). Epiphora patients had clearly higher T1 (82.1+/-15.2%, P<0.0001) and lower LCR (38.9+/-22.5%, P<0.0001) values. Tracer resorption was 24%. Based on ROC analysis 70% for T1 and 50% for LCR were considered optimal cut-off levels to separate patients from volunteers. Sensitivity/specificity were 77/95% for T1 and 71/100% for LCR. T1 and LCR values did not correlate with symptom scores or Anel test results. CONCLUSION: Dacryoscintigraphy, using LCR and T1 as parameters, is a reliable and objective method to detect tear-flow abnormalities.

Long-term patient satisfaction of external dacryocystorhinostomy.

PURPOSE: To evaluate patient's opinion on the long-term success of external dacryocystorhinostomy using the same quantitative parameter pre- and postoperatively. METHODS: A postal questionnaire was sent to 139 patients who had undergone external dacryocystorhinostomy. The only parameter for success of the treatment was the improvement of patient's subjective pre- and postoperative symptoms score. The duration of this follow-up ranged from 1 year up to 5 years postoperatively. Statistical analyses were performed using the Wilcoxon Signed-Ranks test and the chi2 test. RESULTS: According to the patient's own evaluation, external dacryocystorhinostomy is a successful operation. After 1 year the success percentage was 89%, after 2-3 years it was 79% and after 4-5 years it was 71%. CONCLUSION: External dacryocystorhinostomy is appreciated by the patients and considered a successful operation. The subjective evaluation of this operation should yield more creditability than objective methods.

Inhibition, response mode, and stimulus probability: a comparative event-related potential study.

OBJECTIVES: In the present study, effects of response mode (finger movement or counting) and stimulus probability on inhibitory processes were studied. METHODS: Electroencephalographic activity was registered in a visual go/nogo paradigm. Subjects either responded manually to go stimuli or counted silently the occurrence of each go stimulus in different conditions. In both response mode conditions, response probability was varied. RESULTS: For finger movement and counting, similar N2 and P3 go/nogo effects were found. The amplitude of the nogo N2 and nogo P3 varied as a negative function of nogo stimulus probability. The go P3 varied as a negative function of go stimulus probability. In the manual condition, however, the descending flank of the go N2 at anterior electrode sites was more negative in the 0.50go and 0.75go probability trials than in the 0.25go probability trials. CONCLUSIONS: The results of the present study confirm the hypothesis that differences between go and nogo event-related potentials are not dependent on overt movement-related potentials. It could be speculated that the probability effect on the N2 amplitude in go trials in the manual condition has to be explained in terms of a modulation of the strength of motoric preparation processes varying as a positive function of the probability of the go stimulus.

Response priming in a go/nogo task: do we have to explain the go/nogo N2 effect in terms of response activation instead of inhibition?

OBJECTIVES: In the present study, we examined the effects of response priming on the event-related potentials (ERPs) evoked by target stimuli in a go/nogo task. METHODS: In each trial, subjects were presented a cue and a target stimulus. The cue informed subjects about the following target in that trial, and therefore, also about the kind of response (right-hand response, left-hand response, no overt response) potentially to be given in that trial. RESULTS: The traditional N2 and P3 go/nogo effects were replicated: the ERPs to nogo targets were negative compared to the ERPs evoked by go targets in the N2 latency range at frontal electrode sites, and the nogo P3s were more anteriorly distributed than the go P3s. Comparing the ERPs evoked by nogo targets, we found the P3, but not the N2, to be modulated by response priming. CONCLUSIONS: These results seem to indicate that the P3, but not the N2, is associated with response inhibition, or with an evaluation/decision process with regard to the expected and/or given response. It could be speculated that the traditional go/nogo N2 effect has to be explained in terms of response activation instead of response inhibition.

Habituation: an event-related potential and dipole source analysis study.

The goal of this study was to investigate habituation processes in the brain, and in particular, to identify the brain structures involved in these processes. Therefore, event-related potentials (ERPs) were recorded in response to a series of repeated, task-irrelevant, salient stimuli presented against the background of a cognitive task which required the subjects to attend to a fixation sign on a TV screen. Stimuli were presented randomly in one of four possible quadrants of the TV screen. Dipole analyses were performed in order to localize the source of stimulus repetition effects (habituation). As expected, there was a decrease in amplitude of the N1 and P3 components as a function of stimulus repetition; habituation of N1 occurred faster than that of the P3 component. It is suggested from the results of dipole analyses that the N1 effect concerns diffuse cortical activation. The P3 habituation effect seemed to involve the temporal cortex especially.

Localization of spatial attention processes with the aid of a probe technique.

A sudden visual onset is thought to 'attract attention to its location' within less than 100 ms. We attempted to measure the effect of this attentional process on the event-related potential (ERP) to a probe presented about 140 ms after the onset, and to delineate the spatiotemporal characteristics of such an effect, if any. ERPs were recorded from 30 channels from 6 subjects while they performed a target detection task. Both targets and probes could be located in each of the 4 quadrants (eccentricities 6.1 degrees and 7 degrees, respectively). For a given single target, the subsequent probe was either presented near the location of the target ('valid target') or at the diagonal opposite ('invalid target'). Appropriate 'neutral' conditions (probes preceded by no target, or by simultaneous targets in all quadrants) were applied, and ERPs to probes were corrected for the contribution of the ERPs to targets. The earliest effect of (in)validity was found at about 120 ms after probe onset for lower field probes. This effect consisted of enhanced posterior positivity for valid relative to neutral relative to invalid conditions. This positivity was superposed on a contralateral, extrastriate negative ongoing wave peaking at about 150 ms ('N150'). Source localization suggested that the (in)validity effects originate from deep medial parietal areas. The source corresponding to the N150 activity was not influenced by (in)validity. An earlier deflection to the probe at 80 ms ('NP80') depended on location, but not on (in)validity, and seemed to be of striate origin. Results are discussed in terms of a model postulating an attention-independent 'input module' from which activation is fed to a 'location module' embodying the actual attention mechanism.