Urinary stones as a novel matrix for human biomonitoring of toxic and essential elements.

Monitoring of body burden of toxic elements is usually based on analysis of concentration of particular elements in blood, urine and/or hair. Analysis of these matrices, however, predominantly reflects short- or medium-term exposure to trace elements or pollutants. In this work, urinary stones were investigated as a matrix for monitoring long-term exposure to toxic and essential elements. A total of 431 samples of urinary calculi were subjected to mineralogical and elemental analysis by infrared spectroscopy and inductively coupled plasma mass spectrometry. The effect of mineralogical composition of the stones and other parameters such as sex, age and geographical location on contents of trace and minor elements is presented. Our results demonstrate the applicability of such approach and confirm that the analysis of urinary calculi can be helpful in providing complementary information on human exposure to trace metals and their excretion. Analysis of whewellite stones (calcium oxalate monohydrate) with content of phosphorus <0.6 % has been proved to be a promising tool for biomonitoring of trace and minor elements.

Association of minor and trace elements with mineralogical constituents of urinary stones: a hard nut to crack in existing studies of urolithiasis.

The role of metals in urinary stone formation has already been studied in several publications. Moreover, urinary calculi can also be used for assessing exposure of humans to minor and trace elements in addition to other biological matrices, for example, blood, urine, or hair. However, using urinary calculi for biomonitoring of trace elements is limited by the association of elements with certain types of minerals. In this work, 614 samples of urinary calculi were subjected to mineralogical and elemental analysis. Inductively coupled plasma mass spectrometry and thermo-oxidation cold vapor atomic absorption spectrometry were used for the determination of major, minor, and trace elements. Infrared spectroscopy was used for mineralogical analysis, and additionally, it was also employed in the calculation of mineralogical composition, based on quantification of major elements and stoichiometry. Results demonstrate the applicability of such an approach in investigating associations of minor and trace elements with mineralogical constituents of stones, especially in low concentrations, where traditional methods of mineralogical analysis are not capable of quantifying mineral content reliably. The main result of this study is the confirmation of association of several elements with struvite (K, Rb) and with calcium phosphate minerals, here calculated as hydroxylapatite (Na, Zn, Sr, Ba, Pb). Phosphates were proved as the most important metal-bearing minerals in urinary calculi. Moreover, a significantly different content was also observed for Fe, Zr, Mo, Cu, Cd, Se, Sn, and Hg in investigated groups of minerals. Examination of such associations is essential, and critical analysis of mineral constituents should precede any comparison of element content among various groups of samples.

Simultaneous flue gas bioremediation and reduction of microalgal biomass production costs.

A flue gas originating from a municipal waste incinerator was used as a source of CO(2) for the cultivation of the microalga Chlorella vulgaris, in order to decrease the biomass production costs and to bioremediate CO(2) simultaneously. The utilization of the flue gas containing 10-13% (v/v) CO(2) and 8-10% (v/v) O(2) for the photobioreactor agitation and CO(2) supply was proven to be convenient. The growth rate of algal cultures on the flue gas was even higher when compared with the control culture supplied by a mixture of pure CO(2) and air (11% (v/v) CO(2)). Correspondingly, the CO(2) fixation rate was also higher when using the flue gas (4.4 g CO(2) l(-1) 24 h(-1)) than using the control gas (3.0 g CO(2) l(-1) 24 h(-1)). The toxicological analysis of the biomass produced using untreated flue gas showed only a slight excess of mercury while all the other compounds (other heavy metals, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and dibenzofurans, and polychlorinated biphenyls) were below the limits required by the European Union foodstuff legislation. Fortunately, extending the flue gas treatment prior to the cultivation unit by a simple granulated activated carbon column led to an efficient absorption of gaseous mercury and to the algal biomass composition compliant with all the foodstuff legislation requirements.

Correlation of intraocular pressure and central corneal thickness in normal myopic eyes and after laser in situ keratomileusis.

PURPOSE: To determine the relationship of intraocular pressure (IOP) and central corneal thickness (CCT) in normal myopic eyes and after laser in situ keratomileusis (LASIK). SETTING: TLC The Windsor Laser Center, Windsor, Ontario, Canada. METHODS: Intraocular pressure measured by Goldmann applanation tonometry and CCT by ultrasonic pachymetry were determined in a group of untreated corneas of 120 patients (203 eyes) and in 50 patients (85 eyes) pre- and post-LASIK. Statistical analyses were performed with the Pearson correlation coefficient and paired Student t test. RESULTS: In the untreated group of 288 eyes, mean CCT was 544.0 microns +/- 37.3 (SD) (range 461 to 664 microns) and mean IOP, 15.6 +/- 2.7 mm Hg (range 10 to 24 mm Hg). The correlation between IOP and CCT in this group was highly significant (r = 0.44; P < .0001). The slope was 0.032 mm Hg/micron of CCT or an approximate decrease of 1 mm Hg, for a reduction in CCT of 31.3 microns. In the post-LASIK group, mean CCT dropped approximately 73.0 microns to 479.5 +/- 41.2 microns (range 408 to 503 microns) and IOP dropped to a mean of 13.6 +/- 3.3 mm Hg (range 7 to 22 mm Hg). A significant correlation was found between IOP and CCT after LASIK (r = 0.33; P < .002). The difference between the mean pre- and post-LASIK measurements of applanation IOP was 2.5 mm Hg, which was significant (P < .0001). The post-LASIK slope was 0.027 mm Hg/micron, or a decrease of 1.0 mm Hg per 37.8 microns reduction in CCT. CONCLUSION: Central corneal thickness is an important variable in the evaluation of applanation IOP and should be included in the assessment of any case of potential glaucoma or ocular hypertension, particularly in eyes with previous photoablative refractive surgery.

Removal of flap striae following laser in situ keratomileusis.

While laser in situ keratomileusis (LASIK) offers advantages over photorefractive keratectomy (PRK), creation of the corneal flap has been associated with postoperative flap striae. These result from misalignment of the corneal flap after flap replacement, movement of the corneal flap during the first postoperative day, or the "tenting effect" of the corneal flap over the ablated stromal bed. Flap striae become more difficult to remove as the postoperative course progresses; therefore, identifying the striae on the first postoperative day is imperative. We describe techniques of flap hydration, refloating, stretching, and smoothing that we use to remove visually significant flap striae.

Mathematics of laser in situ keratomileusis for high myopia.

PURPOSE: To determine the maximal ablation that can be safely performed with laser in situ keratomileusis (LASIK) to maintain long-term corneal integrity. SETTING: TLC The Windsor Laser Center, Windsor, Canada. METHODS: The pretreatment protocols for the VISX Star, Summit Omnimed, and Chiron Technolas 116 excimer lasers generally apply 1 to 2 microns per diopter (D) at an optical zone of 3.0 mm or less to avoid the postoperative central islands that can occur with broad-beam excimer lasers. The ablation depth per diopter for the VISX Star, Summit Omnimed, Chiron Technolas 116, and Chiron Technolas 217 excimer lasers ranges from 10 to 24 microns per diopter depending on the size and number of ablation zones and the excimer laser used. RESULTS: Previous experience with lamellar surgery suggests that at least 250 microns of central posterior stromal tissue should be preserved to maintain long-term corneal integrity and avoid postoperative corneal ectasia. If a 160 microns flap is created for LASIK, the average 550 microns cornea will have 140 microns of corneal stroma available for ablation. Depending on the excimer laser and ablation nomogram used, the maximal LASIK correction for the average cornea ranges from 9.8 to 15.0 D. CONCLUSION: The preoperative corneal thickness and the depth of the excimer laser ablation must be evaluated before LASIK to ensure that adequate posterior corneal stroma is preserved.

Conservative photorefractive keratectomy for residual myopia following radial keratotomy.

OBJECTIVE: To evaluate the efficacy, predictability, stability and safety of a conservative approach to photorefractive keratectomy (PRK) (treating only 60% to 70% of the residual myopia) for residual myopia following radial keratotomy (RK). DESIGN: Case series. SETTING: Laser eye surgery centre in Windsor, Ont. PATIENTS: Thirty-three eyes of 27 patients with an average age of 40.1 years who underwent PRK between January 1993 and July 1995, 12 months or more after RK. All were followed for at least 12 months after PRK. OUTCOME MEASURES: Efficacy and safety were assessed by changes in the uncorrected and best corrected visual acuity. Predictability was determined by the proximity of the final result to emmetropia. The stability of the refractive outcome was assessed over the follow-up period. RESULTS: At 12 months 12 eyes (36%) had 20/20 or better uncorrected visual acuity and 29 eyes (88%) had 20/40 or better uncorrected acuity. Twenty-seven eyes (82%) were within 0.50 D of emmetropia, and 30 eyes (91%) were within 1.00 D of emmetropia. There was a significant change in the mean postoperative spherical equivalent between 1 and 3 months (p < 0.001); however, there was no significant change after this time. Six eyes (18%) had a loss of 2 or more lines of best corrected visual acuity due to corneal haze; however, retreatment reduced this incidence to 9% at 12 months. CONCLUSIONS: Our results show that conservative PRK for residual myopia following RK is efficacious and predictable and produces stable results. However, the risk of postoperative haze reduces the safety of this procedure.

Excimer laser keratectomy for the correction of myopia.

We present the preliminary refractive and visual results in 46 sighted eyes that had undergone excimer photorefractive keratectomy. Although our sample size was small and the follow-up relatively limited (3-6 months), a few important conclusions were drawn. The visual and refractive results compare quite favorably to the preliminary results with radial keratotomy. Thirty-four of 46 patients (74%) were within 1 D of emmetropia; and 45 (98%) were within 2 D at the end of the follow-up period. Forty-four patients (96%) achieved at least 20/40 vision, with more than half achieving 20/20 or better. We encountered no significant vision threatening complications. Twenty of 46 patients (43%) complained of night vision disturbances, but symptoms improved in all patients by 6 months. The majority of patients developed trace epithelial haze; however, corneal haze did not produce reductions in visual acuity. Though the preliminary results of our study of the safety and efficacy of excimer photorefractive keratectomy are promising, further study of long-term vision stability and corneal clarity is clearly needed.

Double-blind corticosteroid trial in identical twins following photorefractive keratectomy.

The use of topical corticosteroids following excimer laser photorefractive keratectomy (PRK) is widespread, but the role of corticosteroids remains poorly defined. The purpose of this study was to evaluate the use of different corticosteroid postoperative regimens following 193-nanometer excimer PRK in identical twins. Preoperatively, cycloplegic refraction of the left eye of each twin measured -3.00 D sphere. The full correction was treated utilizing the identical technique within the same 30 minute period. The study was conducted in a double-blind fashion and the refraction, corneal clarity, uncorrected and best spectacle corrected visual acuity, and keratometry were assessed over the 6-month study period. Both twins were placed on an identical regimen, tapering their drops over a 3-month period. Corneal clarity was remarkably well preserved with essentially clear corneas observed in both twins. Similarly, both twins achieved 20/15 vision with a cycloplegic refraction of +0.75 D at 6 months. The only difference in the healing pattern was the slightly more rapid visual recovery in twin A. The code was revealed upon the cessation of corticosteroid regimen. Twin A had received fluoromethalone 0.1% and Twin B received dexamethasone 0.1%. Keratometry demonstrated identical flattening. There were no corticosteroid induced intraocular pressure rise or other complications noted. Identical twins presented a unique opportunity to better understand wound healing following laser keratectomy. The results of this limited study indicated that for at least lower degrees of myopia the need for full strength topical corticosteroids remains questionable.

Photorefractive keratectomy for myopia: preliminary results in 147 eyes.

Excimer photorefractive keratectomy (PRK) was performed on 100 consecutive patients (147 eyes) for the correction of myopia. The follow up period ranged from 3 to 16 months (mean, 8). Preoperative myopia ranged from -1.75 to -8.75 D (mean -3.90 D). Patients were divided into three groups for analysis based upon their degree of preoperative myopia: mild (< or = 2.90 D), moderate (-3.00 to -5.90 D), and severe (> or = -6.00 D). Uncorrected visual acuity was 20/40 or better in 88.4% (130/147) overall; 97% of mild, 91% of moderate, and 68% of severely myopic patients. Preoperative astigmatism remained the primary cause of reduced uncorrected visual acuity. Postoperatively, 68% of patients overall had a spherical equivalent refraction within +/- 1.00 D. The majority of treated corneas had trace (53%) to mild (29%) subepithelial haze. One patient with severe myopia developed significant subepithelial opacification postoperatively with partial regression and loss of one line of best spectacle corrected visual acuity.