Unexpected surface chemistry in capillaries for electrophoresis.

Good and reproducible capillary quality is needed to develop robust methods and to facilitate method transfer in CE. Physical surface defects no longer play a major role in variability of fused-silica capillaries. Nevertheless, problems are frequently being reported when buffers in the pH range between 4 and 7 are used. Thus the surface chemistry has been studied by X-ray photoelectron spectroscopy. Silicon-carbon bindings have been found on inner capillary surfaces for electrophoresis. This binding type is not completely removed by pre-conditioning with 1 M NaOH for 30 min. This corresponds to the result, that capillaries provide more stable migration times, especially in the pH range 4-7, when they are pre-conditioned for longer than 1 h. The origin of this Si-C bond is still not quite clear. They could be caused by graphite which is used during the fabrication of the raw cylinders prior to capillary drawing. Further investigations are intended in order to understand if there are any differences in surface carbon content from batch to batch and if this can influence experimental results in CE. A better understanding of the surface chemistry should not only improve robustness in CE, but also help to facilitate and accelerate capillary pre-conditioning and rinsing procedures to remove strongly adsorbed analytes or matrices.

Bandage soft contact lens barrier function: a clinical research note.

Corneal thickness pre- and post-operatively was measured on 18 volunteer subjects within the context of a clinical investigation of laser refractive surgery. All measurements were taken with regard for time of day, in order to counter any complicating diurnal influence on data accuracy. Of the 18 subjects, six lost or had accidently displaced their overnight bandage soft contact lenses the first night immediately after surgery, and 12 retained theirs. The individuals with lost bandage lenses exhibited uniformly thick, swollen corneas. In contrast, the other 12 subjects, with retained lenses, exhibited a stable corneal thickness map, displaying the characteristic relatively thick periphery that transitions to a thinner central region. Moreover, in the six affected subjects, application of a new overnight bandage lens resulted in recovery of the normal thickness pattern on day 2, as opposed to the uniform swelling or oedema of the previous day. In combination, these findings indicate a fluid barrier function on behalf of the bandage soft contact lenses, which allowed the corneal endothelial pump mechanism to counteract any extreme swelling or fluid accumulation. This previously unreported phenomenon helps explain the historical effectiveness of this treatment regimen for corneal bullous, or excessive fluid-retention, conditions.

Fused-silica capillaries for capillary electrophoresis and gas chromatography: inner surface corrosion, within-batch differences, and influence of drawing parameters studied by atomic force microscopy.

Fused-silica capillaries for capillary electrophoresis (CE) and gas chromatography (GC) were investigated by atomic force microscopy (AFM). Differences from batch to batch and within one batch were often observed. Surface heterogeneity can be caused by bulk material, manufacturing parameters, or by aging effects. One batch of a fused-silica capillary was stored in water for three years at room temperature. The significant increase in surface roughness (measured as rms = root mean square) during this time is demonstrated. The effect of different drawing temperatures was investigated. Other drawing parameters were kept constant using one capillary batch. If the chosen drawing temperature was too low, the roughness values more than doubled. This increase in roughness did not affect the separation efficiency. However, the relative standard deviation (RSD%) of migration times and peak areas increased at the same time. Three capillary batches for gas chromatography of different inner diameters (250 microm, 320 microm, 530 microm) were also investigated. In all cases the higher rms values for surface roughness could be found at the beginning of the drawing process, although all values were close to atomic flatness.

Orbscan pachymetry: implications of a repeated measures and diurnal variation analysis.

INTRODUCTION: Corneal thickness changes reflect alterations in hydration and metabolism. Ultrasound pachymetry determinations may be adversely influenced by fluctuations in tissue hydration, whereas optical systems are apparently unaffected by these fluxes. A recently marketed, optical-based, topographic mapping system (Orbscan; Orbtek, Inc.) uses anterior and posterior corneal surface data to calculate corneal thickness. OBJECTIVE: This new instrumentation presents as a potentially useful pachymetry tool for evaluation of corneas under hydration flux or challenge (e.g., postphotorefractive keratectomy [PRK] healing studies) and was therefore evaluated for accuracy and variability. MEASUREMENTS: Three calibrated standards were measured in repeated fashion. Additionally, 1 test subject was measured 30 times in 1 day (5 measurements each at 8:00, 9:30, and 11:00 AM and at 1:00, 2:30, and 4:00 PM). Corresponding measurements were made at 8:00 and 11:00 AM and at 4:00 PM on 3 separate days to assess repeatability. Grouped data from 18 volunteer subjects were compared to the data of the test subject as well. RESULTS: Pachymetry accuracy on a calibrated standard was determined to be +/-2 microm (standard deviation, n = 12). Repeated measures on the subject demonstrated a mean standard deviation of 9.08 microm for 750 thickness data points across the central 7 mm of the cornea; peripheral measurement points exhibited progressively greater variability than at the apex (analysis of variance; P<0.0001). A plot of thickness by corneal location and time of day exhibited a diurnal pattern, with the peripheral cornea exhibiting progressively greater thickness changes than the central cornea (two-way analysis of variance; P<0.00001). The data significantly correlated across days when all times of day were considered (r = 0.999). However, thickness values obtained at 8:00 AM were significantly different across days (t test; P<0.0002). The subject's data correlated very well (r = 0.9996) with the grouped volunteer data. CONCLUSIONS: These data show this system to be useful in corneal research and in clinical settings. The data confirm early morning pachymetry to be highly variable. Additionally, the data not only indicate a diurnal variation of corneal hydration over time, but also imply the presence of a diurnal-based hydration gradient across the peripheral cornea, both of which can have significance for PRK, since excimer tissue ablation effectiveness is influenced by tissue hydration.

Topographic detection of photorefractive keratectomy.

PURPOSE: This study aimed to evaluate the sensitivity and specificity of subjective review of corneal topography to detect patients who have undergone photorefractive keratectomy (PRK). METHODS: Topographic maps from 3 different devices were obtained from 19 patients with postoperative PRK and 9 control subjects with emmetropia and 10 control subjects with myopia. Each image was printed in an absolute and relative scale (total of 228 maps) and graded for overall shape and pattern. Fifteen masked reviewers independently rated each map as either postoperative PRK or not. RESULTS: The overall sensitivity (ability to detect PRK) and specificity rates (ability to exclude control subjects) by reviewers were 65% and 93%, respectively. Sensitivity was influenced independently by the scale (relative, 68%; absolute, 62%; P < 0.01), experience of reviewer (experienced, 77%; inexperienced, 53%; P < 0.001), and device (Alcon, 67 +/- 29.9; Eyesys, 75 +/- 29.4%; and Tomey, 54 +/- 31.7%; P < 0.001). Low levels of preoperative myopia were consistently more difficult to detect than higher levels (low myopia -1.50 to -2.99 diopters [D] sensitivity: 53 +/- 34.5%; medium level -3.00 to -4.49 D: 67 +/- 28.9%; and high level -4.50 to -6.00 D: 77 +/- 21.1%; P < 0.0001). Differences in specificity between experienced and inexperienced reviewers were obtained when maps had a homogeneous topographic pattern (97 +/- 5.6% and 85 +/- 13.7%, respectively; P < 0.05). Several control topography patterns (e.g., homogeneous, focal, and keyhole) were disproportionately more difficult to correctly identify on the Eyesys device. CONCLUSIONS: Topographic experience is a significant factor influencing the correct identification of PRK. Techniques also can be used to enhance detection, such as the use of different devices and scales. However, if subjective review of topography is used as the only method of detection, many patients with PRK will not be identified properly. In addition, the most prevalent preoperative myopic category in the general population (myopia < -3.00 D) also is the most difficult to detect after treatment. This reduces the usefulness of topography as a screening tool. Other techniques are needed to improve the detection of patients with postoperative PRK.

Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel.

PURPOSE: To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel. METHODS: Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare. RESULTS: At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure. CONCLUSIONS: Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.

[The effect of preculture on disinfectant testing]. / Der Einfluss der Vorkultur auf die Desinfektionsmittelprüfung.

For organisational reasons, it is often necessary to work with pre-cultures from a refrigerated incubator after a weekend or holidays. It was investigated, whether the cold storage of cultures before the incubation technique had an effect on disinfectant testing. The work with the germs from the refrigerated incubator showed an increased resistance of the bacteria in tests with a phenolic disinfectant. In comparison to control cultures there was a 3 log (10(3) difference in the reduction factors. The decreased performance of the disinfectant did not correspond to a difference in the number of germs. The germ count from the refrigerated incubator was 10(9) cfu/ml which is the required amount for the DGHM-test-methods. The exceptionally high survival rate of the pre-cultures from the refrigerated incubator must have through their pre-test handling led to the increased resistance against the phenolic test product.