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Biomedical subjects

E Y Zavala

Publications and source records attributed to E Y Zavala.

At least 19 recordsLinked to original sources
PubMed2000

Economic cost of expanded criteria donors in cadaveric renal transplantation: analysis of Medicare payments.

BACKGROUND: The use of expanded criteria donors (ECDs) in cadaveric renal transplantation is increasing in the US. We assess the economic impact of the use of ECDs to the Medicare end stage renal disease program. METHODS: The United Nations for Organ Sharing renal transplant registry was merged to Medicare claims data for 42,868 cadaveric renal transplants performed between 1991-1996 using USRDS identifiers. Only recipients for whom Medicare was the primary payer were considered, leaving 34,534 transplants. An ECD was defined as (1) age < or =5 or > or =55 years, (2) nonheart-beating donors, donor history of (3) hypertension or (4) diabetes. High-risk recipients (HRR) were age >60 years, or a retransplant. Medicare payments from the pretransplant dialysis period were projected forward to provide a financial "breakeven point" with transplantation. RESULTS: There were 25,600 non-HRR transplants, with 5,718 (22%) using ECDs, and 8,934 HRR transplants, of which 2,200 (25%) used ECDs. The 5-year present value of payments for non-ECD/non-HRR donor/recipient pairings was $121,698 vs. $143,329 for ECD/non-HRR pairings (P<0.0001) and, similarly was $134,185 for non-ECD/HRR pairings vs. $165,716 for ECD/HRR pairings (P<0.0001). The break even point with hemodialysis ranged from 4.4 years for non-ECD/ non-HRR pairings to 13 years for the ECD/HRR combinations but was sensitive to small changes in graft survival. Transplantation was always less expensive than hemodialysis in the long run. CONCLUSIONS: The impact of ECDs on Medicare payments is most pronounced in high-risk recipients. Cadaveric renal transplantation is a cost-saving treatment strategy for the Medicare ESRD program regardless of recipient risk status or the use of ECDs.

Aged↗
PubMed1988

Clinical pathology of non-freeze lamellar refractive keratoplasty.

We studied two corneal specimens obtained following corneal transplantation for loss of best corrected vision after planar lamellar refractive keratoplasty. The epithelium appeared slightly undifferentiated in both cases. Peripheral bends and occasional breaks were found in the periphery of Bowman's layer. In one case there were areas of subepithelial fibrosis as well as ultrastructural fractures in Bowman's layer. The keratocyte population appeared to be slightly decreased in one case. In both specimens the optical interface contained active fibroblasts in the periphery. The planar lamellar refractive keratoplasty technique theoretically eliminates many of the adverse morphologic features encountered following the standard Barraquer cryolathe techniques, but clinical studies will be needed to determine if this form of lamellar keratoplasty is clinically superior to currently practiced techniques.

Aged↗
PubMed1987

An ultrastructural and histochemical study of long-term wound healing after radial keratotomy.

Using correlative microscopy and plant lectins conjugated to fluorescent dyes, we studied two human corneal specimens obtained 66 and 70 months after radial keratotomy. In one case a second radial keratotomy had been performed 11 months before we obtained the corneal specimen, which allowed us to compare wounds 11 and 66 months old in the same specimen. The 11-month-old incisions demonstrated morphologic features consistent with incomplete wound healing, whereas the incisions examined 66 and 70 months postoperatively demonstrated complete wound healing. A different lectin binding pattern of wheat germ agglutinin and concanavalin-A was observed in the 11-month-old wounds, compared with the 66-month-old wounds. Published and unpublished morphologic studies of 17 human keratotomy specimens have demonstrated incomplete wound healing up to 47 months postoperatively. The present study documents complete corneal wound healing 66 months after radial keratotomy.

Adult↗
PubMed1987

Why do some epikeratoplasties fail?

We performed a morphologic analysis of nine epikeratoplasty lenticules that were removed due to nonhealing epithelial defects, interface opacity, and/or haze of the donor lenticule. Structural abnormalities were found in all layers of the donor lenticules, with the major changes being present in the surface epithelium and Bowman's layer. Significant changes in the stromal collagen were documented. Similar changes were found in a previous analysis of never-used, factory-prepared lenticules that had been prepared following the use of a corneal press and a lyophilization process. This study suggests that the presently used process of tissue preparation may be deleterious to the structure of the donor lenticule and may adversely affect surface reepithelialization. The placement of the lenticule above the recipient's Bowman layer may be an additional retardant to postoperative reepithelialization.

Adult↗
PubMed1987

Laboratory evaluation of freeze vs nonfreeze lamellar refractive keratoplasty.

Four pairs of human eyes were operated on to correct 10 diopters of myopia. One eye underwent standard myopic keratomileusis, and the mate underwent planar lamellar refractive keratoplasty (PLRK). Cryolathing produced morphologic alterations in all layers. Planar lamellar refractive keratoplasty produced a smoother stromal surface in the optic zone. Peripheral triangular surface depressions in the lenticule, corresponding to fixation facets on the PLRK unit, were the only morphologic alterations noted. It appears that PLRK eliminates many adverse features associated with tissue freezing and lyophilization.

Cornea↗
PubMed1986

Combined morphologic effects of cryolathing and lyophilization on epikeratoplasty lenticules.

A correlative microscopic analysis of factory-prepared epikeratoplasty lenticules, corneas stored in McCarey-Kaufman medium for two to four days, and fresh human corneas disclosed ultrastructural abnormalities in Bowman's membrane and in the corneal stroma of the lyophilized lenticules that were not present in the control corneas. These features included mottling of Bowman's membrane, with large interfibrillar spaces; a roughness to its surface; and wide interlamellar lacunae within the corneal stroma, with significant changes in interfibrillar collagen distance and fibril diameter. The morphologic features of a clinical specimen excised three months following myopic epikeratoplasty were similar to those found with the factory-prepared lenticules. Our patient's corneal curvature steepened almost 3 diopters following lenticule removal. Our results suggest that additional studies of lyophilized epikeratoplasty lenticules should be performed.

Cornea↗
PubMed1985

Delayed corneal wound healing following radial keratotomy.

Four human corneal specimens obtained 5 to 47 months following radial keratotomy were evaluated by correlative microscopy. Repeat radial keratotomies had been performed in two cases. We documented gaping keratotomy incisions, epithelial plugs, and epithelial-lined incisions. In all cases, Bowman's layer was malapposed with slight to moderate fibroblastic activity at the incision sites. Epithelial and endothelial radial ridges were seen in two cases. No endothelial damage was seen under the radial incisions. The morphological evaluation of these specimens show the potential for a poor wound-healing response when corneas with previous corneal surgery and/or pathologic states undergo radial keratotomy.

Adult↗
PubMed1984

Refractive keratoplasty. Keratophakia in a nonhuman primate.

We performed 11 keratophakia procedures in a baboon (Papio cynocephalus) model using the same instruments and techniques that are presently clinically employed. We requested 10 diopters of correction in nine cases and 14 D in two cases. We were able to achieve a mean (+/- SD) keratometric steepening correction of 5.8 +/- 1.5 D using fresh and 9.3 +/- 5.0 D using prefrozen donor corneas. The overall change was 8.0 +/- 4.3 D. Morphologic results and corneal clarity were consistent with the excellent clinical results. The keratophakia lenticles were sparsely repopulated with keratocytes up to six months following surgery, but at 12 months, partial keratocyte repopulation of one lenticle did occur. We recommend that the baboon model be used for evaluation of all lamellar refractive surgical procedures.

Animals↗
PubMed1984

Alloplastic implants for the correction of refractive errors.

Convex-shaped, hydrophilic lenticles of various water content were implanted into microkeratome-dissected corneal pockets in a baboon model. Freshly trephined, cryolathed, and factory-lathed hydrogels were evaluated for periods exceeding 15 months, documenting clinical response, corneal curvature shifts, and morphologic features. Previously implanted hydrogels were subsequently removed, documenting the reversibility of the procedure while allowing the corneas to return to their preoperative condition. Various alloplastic materials were then reimplanted into the same intrastromal pockets. Medium and high water content lenses produced good results without affecting the recipient cornea, whereas thick or low water content materials extruded or produced severe anterior segment inflammation. The use of medium and high water content, convex-shaped lenticles for the correction of aphakia is possible using current techniques.

Animals↗
PubMed1984

Refractive keratoplasty: myopic keratomileusis in baboons.

We performed 8 myopic keratomileusis procedures in a baboon (Papio cynocephalus) model using the same instruments and techniques which are presently clinically employed. We requested 10 diopters of refractive correction and were able to achieve a mean keratometric correction of 5.5 diopters (range 2.4-8.4) in 6 eyes. Keratometric data in the two remaining eyes was not obtained, because of distortion of corneascope photographs. We did not encounter any technical problems at surgery or during the 2-1/2 to 6 month postoperative period of followup. Morphologic analysis demonstrated subclinical, focal breaks in Bowman's membrane in all specimens and keratocyte repopulation in 7 of 8 eyes. We did find a wide range in the central thickness of the excised corneas which can account for the undercorrections achieved. We consider the baboon model to be excellent for the evaluation of myopic keratomileusis.

Animals↗
PubMed1984

Keratocyte attachment to hydrogel materials.

We have developed an in-vitro model for keratocyte interactions with hydrogel materials. With the aid of inverted phase contrast microscopy and scanning electron microscopy, we observed the growth of baboon stromal keratocytes on the surface of various hydrogel materials. In this study, the Bioflex lens (0.5% hydration) surface was extensively covered with keratocytes, whereas 1% to 25% of the surfaces of Crofilcon A (40% hydration) and Perfilcon A (70% hydration) lenses were covered with keratocytes. The Bufilcon A (55% hydration) lens was free of keratocyte attachment. Keratocytes attached to the surfaces of the lenses produced extracellular collagenous material as evidenced by positive staining with alcian green-metanil yellow. These in-vitro results correlate with our non-human primate studies using Bioflex, Crofilcon A and Bufilcon A lenses as intracorneal implants.

Animals↗
PubMed1984

Morphology of hydrogel implants used for refractive keratoplasty.

The pathology of 14 keratophakia procedures in nine nonhuman primates using various hydrogel lenses as donor lenticles is presented. The lenses were treated as if they were human donor corneas using currently practiced keratophakia procedures. This included microkeratome resection of the recipient cornea, staining of the lenses before cryolathing and, in most instances, lathing according to a modified computer program after which the lenses were inserted into the previously dissected recipient lamellar bed. There was no histologic evidence of an inflammatory reaction to the hydrogels. The major pathologic feature was the presence of activated keratocytes lining the dissected intrastromal pockets.

Animals↗
PubMed1984

Epikeratophakia: clinical evaluation and histopathology of a non-human primate model.

We performed four aphakic and two myopic epikeratophakia procedures in a non-human primate model using two fresh and three prefrozen corneas and one glycerin-preserved cornea. The experiments were terminated 4 to 5 months postoperatively, and the eyes examined with correlative microscopy. The glycerin-preserved cornea sloughed and was not available for analysis. All but one prefrozen specimen demonstrated donor keratocyte repopulation. Active keratocytes were noted lining the optical interface. Focal areas of missing Bowman's layer were present in three recipient corneas. Epithelial interface ingrowth occurred in two specimens. The recipient corneas were otherwise normal.

Animals↗
PubMed1983

Acute morphologic features of radial keratotomy.

We performed eight partially penetrating incisions in 19 eye-bank, 12 nonhuman primate, and 34 canine eyes. Evaluation of the posterior corneal surface by vital staining, correlative microscopy, with corneal incisions set from 80% to 110% of central pachymetric thickness, in three eyes demonstrated damage to the endothelium without anterior chamber perforation. Posterior folds in Descemet's membrane under an incision site was present in all specimens. Potential optical aberrations could be produced about the visual axis depending on the direction of the corneal incisions. Based on this study, the radial keratotomy procedure performed with up to eight deep incisions may produce optic defects. We recommend animal studies to assess the long-term effects of this procedure on the cornea and especially the endothelium.

Adult↗
PubMed1983

Refractive keratoplasty. Tissue dyes and cryoprotective solutions.

The cryoprotective dye solution KM-26 (0.25% kiton green, 8% glycerin, and 4% dimethyl sulfoxide), which is presently used for all lamellar refractive surgical procedures, was evaluated and compared to other dyes that can stain corneal tissue. With the use of canine and human eye bank tissue, we found kiton green and light green to produce the least tissue alteration and to destain readily. Glycerin with or without dimethyl sulfoxide or dye was deleterious to the endothelium in the area under the keratectomized recipient bed. On the basis of our findings, glycerin and dimethyl sulfoxide should be deleted from the cryoprotective solution and a 0.1% concentration of light green in balanced salt solution or M-K medium should be used and the frozen tissue should be thawed in a balanced salt solution or M-K medium to eliminate potential damage to the recipient corneal endothelium.

Animals↗
PubMed1982

The histopathology of a case of keratophakia.

We studied a human cornea that was obtained at the time of penetrating keratoplasty four months after a keratophakia procedure and cataract extraction. We found endothelial cell loss with corneal edema, interface epithelial ingrowth, absence of keratocytes, and an abnormality in the collagen structure of the donor homograft (lenticule) and abnormal host keratocytes in the recipient lamellar (host) bed. We suspect that the cause of keratocyte and collagen injury was associated with the cryopreservation process. We recommend that if a combined cataract extraction and keratophakia procedure is contemplated, the lens extraction be performed in an intracapsular fashion if the keratophakia procedure has been completed or in an extracapsular fashion before the replacement of the donor lenticule and anterior part of the host cornea.

Aged↗
PubMed1982

Refractive keratoplasty: microkeratome evaluation.

We performed routine microkeratome and freehand lamellar keratectomies in 65 canine eyes and 24 human eye-bank eyes. The microkeratome technique produced more predictable resections compared with the freehand technique and at the same time produced a wound that would allow for better wound coaptation. Neither technique damaged the corneal endothelium. We conclude that one of the reasons for the success of the refractive keratoplasty procedures is the refined microkeratome technique.

Animals↗