Petrographic and spectroscopic characterization of phosphate-stabilized mine tailings from Leadville, Colorado.

The use of soluble PO4(3-) and lime as a heavy metal chemical stabilization agent was evaluated for mine tailings from Leadville, Colorado. The tailings are from piles associated with the Wolftone and Maid of Erin mines; ore material that was originally mined around 1900, reprocessed in the 1940s, and now requires stabilization. The dominant minerals in the tailings are galena (PbS), cerrusite (PbCO3), pyromorphite (Pb5(PO4)3Cl), plumbojarosite (Pb0.5Fe3(SO4)2(OH)6), and chalcophanites ((Pb,Fe,Zn,Mn)Mn2O5 x 2H2O). The tailings were treated with soluble PO4(3-) and lime to convert soluble heavy metals (principally Pb, Zn, Cu, Cd) into insoluble metal phosphate precipitates. The treatment process caused bulk mineralogical transformations as well as the formation of a reaction rind around the particles dominated by Ca and P. Within the mineral grains, Fe-Pb phosphosulfates, Fe-Pb sulfates (plumbojarosite), and galena convert to Fe-Ca-Pb hydroxides. The Mn-Pb hydroxides and Mn-(+/-Fe)-Pb hydroxides (chalcophanites) undergo chemical alteration throughout the grains during treatment. Bulk and surface spectroscopies showed that the insoluble reaction products in the rind are tertiary metal phosphate (e.g. (Cu,Ca2)(PO4)2) and apatite (e.g. Pb5(PO4)3Cl) family minerals. pH-dependent leaching (pH 4,6,8) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 150 for many metals; particularly Pb2+, Zn2+, Cd2+, and Cu2+. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca2+, PO4(3-) Pb2+, Zn2+, Cd2+, and Cu2+ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids.

Management of increased vitreous pressure during penetrating keratoplasty using pars plana anterior vitreous aspiration.

PURPOSE: To describe the technique, outcomes, and complication rates for a method of pars plana vitreous aspiration to control excessive vitreous pressure during penetrating keratoplasty. METHODS: All cases of penetrating keratoplasty were reviewed retrospectively in a large cornea subspecialty private practice over a 5-year period, and 70 cases of penetrating keratoplasty complicated by excessive posterior pressure were identified. Study eyes were treated with a pars plana vitreous aspiration technique to relieve excessive posterior vitreous pressure. The main study parameters included preoperative best corrected visual acuity (BCVA), postoperative BCVA at the last recorded follow-up visit, refractive cylinder at 1 year, complications related to surgery, and other conditions that may have influenced visual function. The mean follow-up period was 24.5 months with a range of 1 to 61.1 months. RESULTS: Adverse outcomes during the extended period of follow-up included rejection in 11 of 70 eyes, graft failure in 7 of 70 eyes, glaucoma in 4 of 70 eyes, and postoperative cystoid macular edema (CME) in 5 of 70 eyes. Posterior capsulotomies using the neodymium-yttrium aluminum garnet laser were necessary in 10 of 70 patients during the follow-up period. The average magnitude of refractive astigmatism at 1 year after surgery was 3.73 diopters (D) with a range of 0 to 8 D. There were no known retinal complications other than CME and no complications that could be directly attributed to the pars plana vitreous aspiration technique. CONCLUSIONS: Pars plana anterior vitreous aspiration is a safe and effective technique for controlling increased vitreous pressure, which can complicate penetrating keratoplasty.

A modified technique for conjunctival transplant.

An improved technique for the harvesting and placement of conjunctival autograft in complex, advanced and recurrent pterygia is presented. A paper template, fashioned to the approximate size of the pterygium excision site, is used to mark and subsequently transfer the conjunctival graft to the recipient bed. The template creates a strong, steady scaffold on which to orient and align the floppy conjunctival graft. This permits easier suturing and more accurate placement of the graft. We report a series of 30 eyes in which all transplants were taken from the superior or superotemporal bulbar conjunctiva of the same eye. There were no intraoperative or postoperative complications. No graft failures or graft retractions were seen. Although there have been several cases of partial recurrence, we have not had to resort to repeat surgery. We present this modification of a technique originally developed by Thoft and later refined by Vastine and Kenyon, as an effective way to correct complex, advanced, and recurrent pterygia.

The Castroviejo square graft: a retrospective study.

We examined 19 eyes of 12 patients who had undergone penetrating keratoplasty utilizing the Castroviejo square graft technique. The visual acuities at the time of examination for inclusion in the study ranged from 20/30 to counting fingers. Of the 19 original square grafts, eight were judged clear centrally with varying degrees of peripheral stromal haze, and one was hazy. The remaining eight failed with varying degrees of irreversible corneal edema. The eight corneas obtained following repeat penetrating keratoplasty were studied with light and electron microscopy. The donor/recipient corneal stromal lamellae were continuous at the graft-host junction, particularly in the mid-stromal area. Disruptions in Descemet's membrane were present at the wound; transmission electron microscopy revealed differences in the composition of Descemet's membrane between the graft and the host. Two additional square grafts had failed, and the patients were awaiting keratoplasty. Nine of the 19 grafts were judged functionally clear, with six of the nine requiring contact lens correction.

Histologic study of a pair of human corneas after anterior radial keratotomy.

Two corneas were obtained from a man who underwent anterior radial keratotomy in both eyes less than three months before his death. The corneas were obtained and fixed 16 hours after death and prepared for histologic evaluation four days later. Both corneas showed epithelial ingrowth in the surgical wounds, epithelial inclusion cysts in some areas, and ridges or protrusions of the posterior cornea beneath the incisions. The incisions ranged in depth from 48% to 63% of the full thickness of the cornea in the right eye and from 69% to 98% in the left eye, demonstrating the difficulties involved in maintaining a precise and predictable depth of incision, which may, in turn, be related to variations in visual results. Signs of endothelial stress, in the form of collagen and fibrils on the posterior Descemet's membrane, apparently predated the refractive surgery. Precautions such as specular microscopy may be needed to rule out this kind of surgery in patients with the early signs of some types of potential corneal disease.

Histopathology of a case of radial keratotomy.

A patient underwent a radial keratotomy (RK) to reduce residual astigmatism that occurred after a corneal transplant. The patient enjoyed immediate good vision, but later intense glare, photophobia, and pain forced him to quit work. Five months later the graft became cloudy, and superficial vascularization developed in the radial scars. An 8.5-mm penetrating keratoplasty was performed 5 1/2 months after RK. Analysis of the corneal button revealed diffuse epithelial edema, epithelial ingrowth into the incisions, an irregularly thickened epithelial basement membrane, immature hemidesmosomes, focal malapposition of Bowman's layer, marked cellularity of the stroma around the margins of the incisions, and posterior folds in Descemet's membrane. Our analysis of this specimen suggests RK may carry a risk of optical and visual aberrations by producing multiple defects in the anterior and posterior aspects of the cornea.

Automated pattern analysis of corneal endothelium.

A proper understanding of the endothelial cell morphology of the cornea is of great significance to the corneal surgeon. Specular microscopy allows direct visualization of endothelial cell morphology and a proper analysis of these data needs automated computerized type of systems. Automated pattern analysis seems to offer a good option in this direction. From our experience it appears that such systems can be used with great advantage in the analysis of endothelial cell morphology. The data obtained from such analysis help to develop some indices for various facets of endothelial cell morphology.

Endothelial cell morphology and corneal deturgescence.

In a series of 46 patients accepted for cataract removal and intraocular lens implantation, 23 showed visibly obvious variation in endothelial cell size (polymegethism) according to specular microscopic examination. In this group, mean increase in postoperative corneal thickness was 52.7% on the first postoperative day, 35.4% on the third, and 18.0% after 4 weeks. Mean corneal swelling was consistently and significantly less in the 23 patients exhibiting apparently normal endothelial cell patterns (homomegethism). In homomegethous corneas, preoperative cell density was significantly correlated with age (inversely) and postoperative cell loss (directly). Preoperative cell density in polymegethous corneas showed significant, direct correlation with age, suggesting that endothelial cell density may remain relatively constant in this condition. There was no correlation with postoperative cell loss. Significant differences in endothelial functional capability identified within each morphologically-defined group indicate a structure-function continuum. Since 15 homomegethous corneas and only one polymegethous cornea returned to preoperative thickness within 4 weeks, it appears clinically valid to use morphological criteria in predicting functional capability.

Morphological appearance of the healing corneal endothelium.

We studied endothelial cell patterns in both the central and the superior regions of the cornea in 43 cases of cataract extraction and intraocular lens implantation. During the early postoperative period, the central endothelial cells maintained their preoperative appearance. The endothelium within 3 to 4 mm of the superior limbus, however, demonstrated large dark areas where no cell outlines were visible, bounded by large cells. During the late postoperative period, there was an increase in the size and a reduction in the density of the central endothelial cells. In the periphery the previously acellular areas were populated with cells of varying diameter. These changes are consistent with postoperative spreading and sliding of existing cells to cover the traumatized cell-free areas. Central endothelial cell density in the early postoperative period does not accurately reflect the actual degree of cell loss.

The functional reserve of corneal endothelium.

With recent advances in our knowledge of corneal physiology, coupled with the development and increasing availability of the specular microscope as a clinical instrument, valid observations relating the morphologic appearance of the corneal endothelium to its functional capacity are within our reach. Manual methods of data analysis are cumbersome, time consuming, and associated with human error and investigator bias. The Omnicon pattern analysis system lends itself to objective analysis of morphologic features, offers the possibility of quantifying the data obtained and, hopefully, will lead to a better understanding of the many aspects of endothelial cell morphology which, in total, relate to the functional reserve of a given cornea.

A technique for treating positive vitreous pressure during intraocular lens implantation in intracapsular surgery.

Positive vitreous pressure during intraocular lens implantation is treated by early recognition and instillation of an air bubble to deepen the anterior chamber, and subsequently to prevent contact between the intraocular lens and the corneal endothelium. A technique is presented which has proven successful in 20 cases.

Intraocular lens implantation combined with penetrating keratoplasty.

A restrospective analysis was conducted of 27 cases of penetrating keratoplasty associated with intraocular lens implantation. Although not statistically significant, the results indicated an 80% success rate when penetrating keratoplasty, cataract extraction and intraocular lens implantation were combined in a single operation. Secondary implantation of intraocular lenses in cases of previous keratoplasty were unsuccessful in all three cases.

Pneumococcal endophthalmitis following grafting of corneal tissue from a (cadaver) kidney donor.

In order to stress the need for continued vigilance in maintaining the highest standards of quality control for corneal tissue used for transplantation, we are presenting 2 cases of pneumococcal endophthalmitis which occurred in tissue transplanted from a young donor who died following acute trauma. The patient had been on cardiovascular support for over 26 hours and had suffered from a febrile illness which on autopsy revealed bronchial pneumonia. Both kidney recipients from the same donor died of myocardial infarctions on the same day in separate cities, 2 days after kidney transplantation surgery. Several recommendations are made which should assist all eye banks in providing the highest quality tissue and in preventing the occurrence of infection transmitted donor tissue.

Thermokeratoplasty in the treatment of persistent corneal hydrops.

Thermokeratoplasty (TKP) was used to treat six cases of chronic corneal hydrops previously refractory to traditional therapy. In all instances TKP resulted in a clearing of the hydrops within three weeks. In four cases the resultnat comfort and clarity precluded the necessity for transplantation, while in the remaining two cases subsequent penetrating keratoplasty was successfully performed. Thermokeratoplasty is advocated in chronic hydrops refractive to standard therapy, in acute hydrops to accelerate recovery, in recurrent hydrops to assist in healing of breaks in Descemet membrane, thus preventing recurrences, in cases with extensive hydrops to deturgesce the peripheral cornea prior to transplantation, and as definitive therapy in cases where transplantation is contraindicated.

Alterations in corneal morphology following thermokeratoplasty.

Fifteen corneal buttons were removed at keratoplasty from patients with keratoconus who had previously undergone thermokeratoplasty (TKP). The buttons were studied with light microscopy, in an attempt to analyze the type of changes produced by TKP. The principal histologic findings in patients with retarded epithelial healing (8 of 15) included epithelial thinning, bullous keratopathy, thickening of the epithelial basement membrane, and frequent destruction of Bowman's membrane. More severely affected patients showed asceptic stromal necrosis and fibrinous iritis with hypopyon. A poor visual result in patients with normal epithelial healing (7 of 15) was caused by superficial stromal scarring or persistent inflammatory infiltrate. Vascularization was seen in only one patient.