A 4 1/2-year-old boy with congenital hereditary endothelial dystrophy underwent successful bilate... more A 4 1/2-year-old boy with congenital hereditary endothelial dystrophy underwent successful bilateral penetrating keratoplasties. Visual acuity in both eyes was restored to 6/18 (20/60). Correlative microscopic analysis of the corneal button obtained from the first transplant showed an irregular epithelium, a continuously thickened Bowman's layer, fragmentation and homogenization of the anterior stromal lamellae, a mildly enlarged stromal fibril diameter, abnormal collagen layers posterior to Descemet's membrane, atrophic paracentral corneal endothelium, and absent central endothelium. The endothelial cells from the second corneal button were placed in tissue culture and failed to demonstrate any growth characteristics of differentiation into normal appearing cells after 14 days. We concluded that the endothelial cells in congenital hereditary endothelial dystrophy are functionally and morphologically abnormal. Early penetrating keratoplasty can be successful in such cases.
The increasing use of scanning electron microscopy in pathology has provided new avenues of obser... more The increasing use of scanning electron microscopy in pathology has provided new avenues of observation and evaluation for the pathologist and researcher. The cell surface changes noted by scanning electron microscopy can contribute to an overall understanding of the pathoanatomy and pathophysiology of disease states v~hen correlated with light microscopy and transmission electron microscopy. Our laboratory routinely evaluates corneal pathology specimens by correlative light, transmission and scanning electron microscopy. This procedure has provided new and in some cases previously undocumented corneal pathologic surface morphology of epithelial downgrowth, experimental epithelial-endothelial interactions and ichthyosiform erythroderma.
Using correlative microscopy and plant lectins conjugated to fluorescent dyes, we studied two hum... more 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.
The use of expanded criteria donors (ECDs) in cadaveric renal transplantation is increasing in th... more 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. 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. 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. 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.
Approximately 10000 deceased donor organs are available yearly for 85 000 US patients awaiting ki... more Approximately 10000 deceased donor organs are available yearly for 85 000 US patients awaiting kidney transplant. Living kidney donation is essential to close this gap and offers better survival rates. However, nationally, 80% of potential donors evaluated fail to donate. Nurse coordinators who perform predonation screening and education need additional insight into the large number of potential donors who fail to complete the donation process. Reasons for nondonation in donor candidates undergoing medical evaluation, and variables affecting nondonation at Vanderbilt University Medical Center between 2004 and 2009 are examined. Multivariable logistic regression models are used to test the effects of age and race on donation status and reasons for nondonation. Summary data are frequencies, percentages, and means (SD). The sample included 706 candidates (63% female, 80% white; mean age, 40 [SD, 12] years). Almost half (46%) received clearance to donate. Undiagnosed hypertension (14%), abnormal glucose tolerance (10%), and protein-urea (9%) were the most prevalent medical reasons for nondonation. About 13% of candidates changed their minds during evaluation. Analyses demonstrated an increased likelihood of older candidates (P < .001) and a decreased likelihood of white candidates (P = .007) being excluded from donation. Within the nondonation group, increased age was associated with undiagnosed hypertension and abnormal glucose tolerance (both race-adjusted, P = .01). Younger candidates (race-adjusted, P = .003) and African Americans (age-adjusted, P = .04) were more likely to decide against donation. The most prevalent medical reasons for nondonation could be identified through enhanced prescreening, and improved preevaluation education could decrease nondonation rates.
Four human corneal specimens obtained 5 to 47 months following radial keratotomy were evaluated b... more 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. [
Convex-shaped, hydrophilic lenticles of various water content were implanted into microkeratome-d... more 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.
We performed 8 myopic keratomileusis procedures in a baboon (Papio cynocephalus) model using the ... more 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.
We have developed an in-vitro model for keratocyte interactions with hydrogel materials. With the... more 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.
We performed sixteen keratophakia procedures in nine non-human primates using various hydrogel le... more We performed sixteen keratophakia procedures in nine non-human primates using various hydrogel lenses (38% to 79% water) as donor corneas (lenticules). The lenses were treated as if they were donor human corneas using currently practiced keratophakia procedures including microkeratome resection of the recipient cornea, staining of the lenses before cryolathing and, in some cases, lathing according to a modified computer program after which the lenses were inserted into a previously dissected recipient lamellar pocket. This technique was able to produce steepening of the cornea up to 44.8 diopters and was well tolerated for over three months. The use of hydrogel lenses could potentially eliminate many of the negative aspects of the use of human donor corneas for the surgical correction of aphakia.
We performed four aphakic and two myopic epikeratophakia procedures in a non-human primate model ... more 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.
We studied two corneal specimens obtained following corneal transplantation for loss of best corr... more 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.
A 4 1/2-year-old boy with congenital hereditary endothelial dystrophy underwent successful bilate... more A 4 1/2-year-old boy with congenital hereditary endothelial dystrophy underwent successful bilateral penetrating keratoplasties. Visual acuity in both eyes was restored to 6/18 (20/60). Correlative microscopic analysis of the corneal button obtained from the first transplant showed an irregular epithelium, a continuously thickened Bowman's layer, fragmentation and homogenization of the anterior stromal lamellae, a mildly enlarged stromal fibril diameter, abnormal collagen layers posterior to Descemet's membrane, atrophic paracentral corneal endothelium, and absent central endothelium. The endothelial cells from the second corneal button were placed in tissue culture and failed to demonstrate any growth characteristics of differentiation into normal appearing cells after 14 days. We concluded that the endothelial cells in congenital hereditary endothelial dystrophy are functionally and morphologically abnormal. Early penetrating keratoplasty can be successful in such cases.
The increasing use of scanning electron microscopy in pathology has provided new avenues of obser... more The increasing use of scanning electron microscopy in pathology has provided new avenues of observation and evaluation for the pathologist and researcher. The cell surface changes noted by scanning electron microscopy can contribute to an overall understanding of the pathoanatomy and pathophysiology of disease states v~hen correlated with light microscopy and transmission electron microscopy. Our laboratory routinely evaluates corneal pathology specimens by correlative light, transmission and scanning electron microscopy. This procedure has provided new and in some cases previously undocumented corneal pathologic surface morphology of epithelial downgrowth, experimental epithelial-endothelial interactions and ichthyosiform erythroderma.
Using correlative microscopy and plant lectins conjugated to fluorescent dyes, we studied two hum... more 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.
The use of expanded criteria donors (ECDs) in cadaveric renal transplantation is increasing in th... more 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. 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. 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. 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.
Approximately 10000 deceased donor organs are available yearly for 85 000 US patients awaiting ki... more Approximately 10000 deceased donor organs are available yearly for 85 000 US patients awaiting kidney transplant. Living kidney donation is essential to close this gap and offers better survival rates. However, nationally, 80% of potential donors evaluated fail to donate. Nurse coordinators who perform predonation screening and education need additional insight into the large number of potential donors who fail to complete the donation process. Reasons for nondonation in donor candidates undergoing medical evaluation, and variables affecting nondonation at Vanderbilt University Medical Center between 2004 and 2009 are examined. Multivariable logistic regression models are used to test the effects of age and race on donation status and reasons for nondonation. Summary data are frequencies, percentages, and means (SD). The sample included 706 candidates (63% female, 80% white; mean age, 40 [SD, 12] years). Almost half (46%) received clearance to donate. Undiagnosed hypertension (14%), abnormal glucose tolerance (10%), and protein-urea (9%) were the most prevalent medical reasons for nondonation. About 13% of candidates changed their minds during evaluation. Analyses demonstrated an increased likelihood of older candidates (P < .001) and a decreased likelihood of white candidates (P = .007) being excluded from donation. Within the nondonation group, increased age was associated with undiagnosed hypertension and abnormal glucose tolerance (both race-adjusted, P = .01). Younger candidates (race-adjusted, P = .003) and African Americans (age-adjusted, P = .04) were more likely to decide against donation. The most prevalent medical reasons for nondonation could be identified through enhanced prescreening, and improved preevaluation education could decrease nondonation rates.
Four human corneal specimens obtained 5 to 47 months following radial keratotomy were evaluated b... more 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. [
Convex-shaped, hydrophilic lenticles of various water content were implanted into microkeratome-d... more 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.
We performed 8 myopic keratomileusis procedures in a baboon (Papio cynocephalus) model using the ... more 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.
We have developed an in-vitro model for keratocyte interactions with hydrogel materials. With the... more 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.
We performed sixteen keratophakia procedures in nine non-human primates using various hydrogel le... more We performed sixteen keratophakia procedures in nine non-human primates using various hydrogel lenses (38% to 79% water) as donor corneas (lenticules). The lenses were treated as if they were donor human corneas using currently practiced keratophakia procedures including microkeratome resection of the recipient cornea, staining of the lenses before cryolathing and, in some cases, lathing according to a modified computer program after which the lenses were inserted into a previously dissected recipient lamellar pocket. This technique was able to produce steepening of the cornea up to 44.8 diopters and was well tolerated for over three months. The use of hydrogel lenses could potentially eliminate many of the negative aspects of the use of human donor corneas for the surgical correction of aphakia.
We performed four aphakic and two myopic epikeratophakia procedures in a non-human primate model ... more 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.
We studied two corneal specimens obtained following corneal transplantation for loss of best corr... more 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.
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Papers by Edward Zavala