Is pulse synchronized pneumotonometry more reproducible than routine pneumotonometry and more in agreement with Goldmann applanation tonometry?

PURPOSE: This study compared the variability of intraocular pressure (IOP) measurements taken with pulse synchronized pneumotonometry (PNT) and with routine PNT (without pulse synchronization) and evaluated the agreement between PNT and Goldmann applanation tonometry (GAT). METHODS: In this prospective study, 148 eyes from 78 patients were enrolled. Patients were randomized into two groups. In the first group (A), the sequence of measurements was pulse synchronized PNT, routine PNT, and GAT. In the second group (B), the sequence of measurements was routine PNT, pulse synchronized PNT, and GAT. The mean of three measurements was averaged for PNT and GAT. All the measurements were performed by the same investigator, who was masked to GAT measurements. The mean IOP measurements and intrapatient standard deviations among the three tonometers were compared using analysis of variance measurement. Bland & Altman plots were used to assess the agreement between PNT and GAT. RESULTS: The variability of IOP measurements taken with pulse synchronized PNT was significantly lower than with routine PNT in both groups (1.2+/-0.7 vs 1.3+/-0.7 mmHg in group A and 1.1+/-0.9 vs 1.3+/-1.0 mmHg in group B [p<0.001], respectively). PNT measurements with and without pulse synchronization were on average +/-2 mmHg higher than GAT measurements in both groups (p<0.001). The 95% limits of agreement between PNT and GAT varied between -3.8 and 8.5 mmHg. CONCLUSIONS: Pulse synchronized PNT gives more reproducible measurements than routine PNT. The agreement between PNT and GAT is poor.

Pachymetry before or after applanation tonometry: does it matter?

We examined prospectively 60 healthy volunteers to evaluate if the accuracy of central corneal thickness (CCT) measurement is influenced by Goldmann applanation tonometry (GAT) and vice versa. The sequence of the examinations in the right eye was CCT--GAT--CCT, in the left eye GAT--CCT--GAT and the measurements were done consecutively. Two tonometry and five pachymetry measurements were averaged each time. Pearson correlation coefficients and Bland-Altman plots were used to assess the correlation between the measurements. In the right eye the mean CCT measurement before and after GAT was 565.22 +/- 32.99 micro and 566.04 +/- 33.50 micro (p = 0.34, r = 0.98) respectively. In the left eye the mean GAT before and after pachymetry was 19.38 +/- 4.71 mmHg and 19.16 +/- 4.32 mmHg (p = 0.43, r = 0.86) respectively. The study suggests that the sequence of the two examinations doesn't matter.

Needling-revision of failed filtering blebs.

PURPOSE: To investigate the efficacy and safety of needling-revision of failed blebs after trabeculectomy. METHODS: A retrospective chart review of 28 eyes of 28 patients who underwent a trabeculectomy with subsequent needling-revision between January 2002 and December 2003. The mean follow-up was 15 months after the first needling-revision. All interventions were conducted by the same surgeon. Absolute success was defined as an IOP <18 mmHg without medication or as an IOP reduction > 20% without medication if the preoperative IOP was < or = 21 mmHg. Relative success was defined as meeting these criteria with or without medication. RESULTS: The mean interval between trabeculectomy and the first needling-revision was 5 months. Repeated needling-revision (up to 3 times) was performed as clinically necessary. In 90% of the needling-revisions 5-FU was used to prevent postoperative fibrosis. The mean +/- SD IOP before needling-revision and at the last follow-up was respectively 24.7 +/- 6 and 15.7 +/- 3 mmHg (p<0.001) Needling-revision was an absolute success in 39% (11/28) and a relative success in 68% (19/28). Minor complications attributed to needling-revision occurred in 32% including self reabsorbing subconjunctival bleeding (1), filamental (1) and punctate keratitis (1), transient choroidal effusion (3), wound leak (4) and hyphaema (2). Progression of cataract occurred in 1 patient. A serious complication occurred in 1 case (hypotony with persistent macular oedema). CONCLUSIONS: Bleb needling-revision can prevent more invasive intervention in a significant number of patients with failed trabeculectomy blebs. Complications are similar to those seen after trabeculectomy.

The use of a pinhole aperture during the recording of pattern reversal visual evoked potentials.

In young children, mentally retarded persons or in malingering persons, determining the optimal refraction is not always evident. Because of the importance of this optimal refraction during the recording of pattern-reversal visual evoked potentials, we tried in this study to overcome these refraction errors by the use of a pinhole.

Short-term intra-individual variability in heidelberg retina tomograph II.

We determined the short-term intra-individual variability for each parameter of the Heidelberg Retina Tomograph II (HRT II). Therefore we examined prospectively 20 healthy volunteers 3 times within 2 weeks. The variability was expressed as the coefficient of variation for each parameter. The short-term intra-individual variability in normal subjects was < or = 12% in all but 3 parameters. Rim Area was the least variable parameter (2 +/- 1%). Cup Volume had the highest variability (25 +/- 38%).

Different strategies for Humphrey automated perimetry: FASTPAC, SITA standard and SITA fast in normal subjects and glaucoma patients.

PURPOSE: To evaluate the influence on examination time and test quality of the recently introduced SITA strategies of the Humphrey Field Analyzer. METHODS: The sample consisted of 41 subjects (19 normal subjects and 22 glaucoma patients), all experienced in automated perimetry, ranging in age from 24 to 83 years. One eye of each patient was examined with the HC30-2 program using the FASTPAC (FP) and SITA Standard (SS) or SITA Fast (SF) strategy on the same day, in random order. Examination time was evaluated as a function of the strategy. To evaluate the test quality both regional and global visual field parameters were analyzed. Global parameters included mean deviation (MD) and pattern standard deviation (PSD). Regional parameters (mean and maximum loss) were calculated to estimate the extent and the depth of localized visual field defects. For this purpose each visual field was divided in 4 quadrants and in 10 clusters as defined in the glaucoma hemifield test. RESULTS: 1. There is a considerable test time reduction from FASTPAC over SITA Standard to SITA Fast for comparable MD and PSD values. On average, the SITA Fast test duration is half that of the FASTPAC procedure. For each strategy, the test duration increases for increasing visual field loss. 2. Between all three strategies, there is a good correlation for the global indices (MD, PSD) 3. For the regional indices (mean loss, maximum loss) the same high correlation exists. CONCLUSION: The SITA strategy causes a significant test time reduction without decreasing the test quality.

Recording of the fast oscillations in the human electro-oculogram.

The fast oscillations (FO) of the electro-oculogram were recorded in 102 eyes of 51 normal subjects. We evaluated the normal range and variability of FO parameters, i.e. Rf, which is the average ratio in percentage of the average amplitude in the dark period (AD) and the average amplitude in the light period (AL), and df, which is the average difference between AD and AL in microV. The standing potential was recorded continuously during six subsequent cycles, each consisting of a one minute period in the dark and one minute period in the light. The mean +/- standard error for Rf was 112.9 +/- 1.3% and 69.6 +/- 5.3 microV for df. There was no statistically significant difference between both genders or different age groups. Rf and df were calculated using a different number of dark-light cycles. In normal subjects both the Rf and df show no difference when only 4 dark-light cycles are used in calculating these values. Therefore there seems no additional advantage in performing as many as 6 cycles. Using 4 dark-light cycles reduces the duration of the examination (8 vs. 12 min) of the fast oscillations and in particular when examining both fast and slow oscillations successively it might be useful to reduce the time of the examination.

Visually evoked potentials evoked by moving unidimensional noise stimuli: effects of contrast, spatial frequency, active electrode location, reference electrode location, and stimulus type.

We determined the relative importance of electrode derivation, stimulus type, spatial frequency and contrast in determining the relative size of the late negative and early positive responses of motion elicited VEPs. Seven subjects aged 22-48 years with normal vision were tested binocularly. Motion onset and motion reversal were employed as modes of stimulus presentation. For both, pseudo-random one-dimensional noise patterns whose peak power was at 5.2, 2.6, 1.3, 0.325 and 0.1625 cycles per degree (cpd) were stimuli. Contrasts were 70% and 5%. Active electrodes were placed at Oz, 5 cm to the left of Oz, 5 cm to the right of Oz and a frontal midline position (Fpz) and referenced to linked mastoids. Transient motion reversal elicited a prominent positive response present in all subjects and at low contrasts. Motion onset VEPs have a complex waveform which may be either predominantly positive or negative. The most important variables in determining whether a prominent positivity or negativity is present in the motion onset VEP are the contrast and the spatial frequencies. Data such as these are first efforts in developing recommendations for the motion VEP.