Elizabeth A. Mindrup

Polysulfone corneal lenses.

ABSTRACT Polysulfone is a thermoplastic compound first synthesized in 1965. A unique characteristic of polysulfone is its high refractive index (1.633), which allows very thin optical lenses to be manufactured. Over the last five years, D. Peter Choyce has surgically implanted over 40 polysulfone lenses into eyes of his patients. Analysis of his data indicates that polysulfone intraocular lenses are capable of correcting large refractive errors. Based on his work, a multicenter study was undertaken to evaluate the safety and efficacy of polysulfone as an intracorneal lens material in laboratory models. Four monkeys, eight baboons, and 24 cats were used as laboratory models; 5.0‐mm to 6.0‐mm diameter hyperopic (+28.5 diopter) and myopic (‐17.0 and ‐25.5 diopter) lenses were surgically implanted within the corneal stroma in one eye of each of the laboratory models while a sham lamellar dissection was performed in the other eye. One hundred percent (4/4) of monkey eyes, 12.5% (1/8) of baboon eyes, and 70.0% (18/24) of cat eyes maintained clear media by ophthalmoscopic examination at follow‐ups ranging from three to six months. Complications included both visually and nonvisually significant interface opacities, lens extrusion, anterior corneal necrosis, refractile particles, and epithelial thinning.

Minnesota system corneal preservation.

The clinical and laboratory results with a modified Minnesota system of organ culture corneal preservation are presented. A refinement of our preservation technique using a closed system, as well as the addition of chondroitin sulphate to the medium is presented. Laboratory results show preservation of corneal endothelial integrity for at least 21 days with maintenance of normal corneal thickness. In addition, a 10-day quarantine system reduces the risk of donor contamination and secondary endophthalmitis. Preliminary results of the 34 degrees C and 4 degrees C closed Minnesota corneal preservation system using chondroitin sulphate show that it is safe and efficacious and allows intermediate to long-term maintenance of sterile thin tissue prior to corneal transplantation.

Betadine decontamination of donor globes

Between May 1983 and December 1989, 2,921 donor eyes received by the Minnesota Lions Eye Bank underwent a decontamination protocol using 10% Betadine (1% povidone- iodine) solution. Positive pretreatment limbal cultures were obtained on 52.1% of donor eyes. Posttreatment limbal cultures demonstrated a 76.1% reduction in microbial growth, including an 85.7% reduction in Candida species. Streptococcus species were reduced by 76.7% and coagulase-negative Staphylococcus were reduced by 76.1%. In addition, of 250 donor rims obtained at the time of surgery, two had coagulase-negative. Staphylococcus present that were also present after the decontamination procedure. In no cases did endophthalmitis occur during this study. This study demonstrates that this protocol using 10% Betadine solution is extremely effective in decontaminating donor globes of aerobic bacteria and fungi. However, gentamicin-resistant organisms survived this protocol, emphasizing the need to develop storage media containing a broader-spectrum antibiotic agent than gentamicin.

Increased Endothelial Cell Loss After Transplantation of Corneas Preserved by a Modified Organ-culture Technique

Forty-seven donor corneas were preserved in McCarey-Kaufman (M-K) medium at 4 degrees C for 1 day, then in organ culture at 34 degrees C for approximately 1 month, then in M-K medium at 4 degrees C for an additional two days before transplantation. The central donor endothelium was examined by specular microscopy before and after organ culture and 2 months after keratoplasty. No significant change in central endothelial cell density occurred during organ culture. The 47 transplants were compared with 47 grafts preserved only in M-K medium at 4 degrees C for approximately 36 hours. All transplants were performed by the same surgeon over the same period, and the two groups contained similar types of surgical procedures. The organ-cultured grafts were thicker on the first post-operative day and took longer to epithelialize . Two months after keratoplasty all of the 94 grafts were clear and thin, but the mean central endothelial cell loss was 28% in the 47 organ-cultured transplants and 10% in the 47 transplants preserved only in M-K medium (P less than 0.0001). These results indicate that the endothelium of corneas preserved by organ culture at 34 degrees C and then placed in M-K medium at 4 degrees C for 2 days may be more susceptible to surgical trauma than those preserved only in M-K medium at 4 degrees C.

Safety and efficacy of 2% methylcellulose in cat and monkey cataract-implant surgery

We evaluated the safety and efficacy of 2% methycellulose as an adjunct for cataract extraction with implantation in cat and monkey models. When used intraoperatively, methylcellulose reduced the iridovitreal bulge during surgery. No significant increase in clinical inflammation occurred nor was there statistically significant intraocular pressure elevation at 24 hours, 7 days, or 90 days. In the cat model, the central corneal thickness increased at day seven in both control and methylcellulose eyes; this thickness persisted to 90 days. The endothelial cell loss decreased significantly at day 90 in methylcellulose eyes. In the monkey model, no statistically significant increase in corneal thickness occurred in control or methylcellulose eyes at day seven. The endothelial cell loss was greater than in the cat model in both control and methylcellulose eyes; there was no statistically significant difference between the two. Two percent methylcellulose was safe in both the cat and monkey models. It facilitated surgery in both models and reduced the endothelial cell loss in the cat eye.

Effect of topically administered platelet-derived growth factor on corneal wound strength

Since the cornea is an avascular tissue, the wound healing process is lengthy, with a need for sutures to stabilize the wound for a long time. Platelet-derived growth factor (PDGF) has been shown to accelerate wound healing in rat dermal models. Accelerated healing, if unaccompanied by side effects may reduce suture related complications such as astigmatism and infectious keratitis. This study evaluated the effect of PDGF on wound strength in corneal laceration and penetrating keratoplasty models using New Zealand white albino rabbits. Twenty-two rabbits were used in the corneal laceration model and sixteen rabbits in the penetrating keratoplasty model. The treated rabbits received 385 picomoles/drop of PDGF-BB dissolved in balanced salt solution six times on day 1 and three times a day for the remainder of the study. The control rabbits received balanced salt solution in the same dosing schedule. The pressure required to rupture the wound was measured using a pressure transducer. In the laceration model the PDGF treated group had mean (+/- standard deviation) average pressures on day 7 of 360 +/- 102 mm Hg for wound rupture compared to 210 +/- 102 mm Hg in the control group. (p = 0.005). The average pressures in the penetrating keratoplasty model on day 17 were 707 +/- 201 mm Hg for the controls and 1042 +/- 292 mm Hg for the PDGF treated group (p = 0.026). Histopathological evaluation of eyes not subjected to bursting showed increased fibroblasts at the wound junction with an increase in types III and type IV collagen production.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole globe enucleation versus in situ corneal excision: a study of tissue trauma and contamination.

Twenty-four pair of eyes donated to the Minnesota Lions Eye Bank were studied to determine the effect of corneal procurement methods on tissue quality. Eyes studied were ineligible for transplantation because of a preexisting medical condition other than sepsis or age of > years. The procurement technique was randomized for each donor. One cornea was procured in situ (IS), whereas the fellow eye was enucleated and processed in the laboratory (EN). Procurement protocols were standard Eye Bank Association of America methods. Tissue characteristics were scored according to standard eye bank protocols. Cultures were performed at the time of tissue procurement and following storage for 7 days in Dexol media. With the exception of endothelial striae, no statistical difference was found between groups for any tissue characteristics. The average score for endothelial striae in the IS group was greater than twice that of the EN group. Initial cultures were positive in 10 of 24 in the IS group and four of 24 in the EN group. Each group had three positive end-storage cultures. These results demonstrate superior tissue decontamination after initial processing and less endothelial cell trauma with standard enucleation when compared to in situ corneal excisions.

The fate of experimental organ-cultured corneal xenografts.

Human, chicken, and guinea pig corneas organ cultured (O.C.) from 1 to 4 weeks were transplanted intralamellarly into rabbits. Chicken and guinea pig corneal xenografts O.C. 3 to 4 weeks had statistically significant delayed rejection times compared to fresh controls. In addition, 22% of chicken xenografts O. C. 4 weeks did not reject. Histologically, O.C. xenografts with delayed rejection or nonrejection were hypocellular. Chicken xenografts O.C. 4 weeks in which recipient (autochthonous) rabbit serum replaced the calf serum routinely used in the media also had a significant delay in rejection time when compared to fresh controls or chicken xenografts stored in pooled (allogeneic) rabbit serum. The rejection time of human corneal xenografts O.C. for periods up to 4 weeks was not delayed. These data suggest that in this model, prolonged survival of xenografts after O.C. is species specific and represents a form of immunological modification, possibly reduced antigenicity secondary to donor hypocellularity.

Suppression of graft rejection using 15-deoxyspergualin in the allogeneic rat penetrating keratoplasty model.

We tested the ability of 15-deoxyspergualin (DSG), a new immunosuppressant, to inhibit corneal allograft rejection in the rat penetrating keratoplasty model. Fifty-six inbred Lewis rats were recipients of orthotopic corneal allografts from Brown Norway rats. Allogeneic groups received daily intramuscular injections of DSG 2, 3, 4, or 10 mg/ kg/day. The animals treated with 2 mg/kg/day had four out of 10 grafts rejected; in the 3 mg/kg/day group none of the six grafts rejected; whereas in the 4 mg/kg/day group one out of 15 grafts rejected. The animals treated with 10 mg/kg/day became emaciated and died during the second and third postoperative weeks with relatively clear grafts. All corneas rejected following discontinuation of the drug. We conclude that the systemic administration of DSG at 3 or 4 mg/kg/day results in effective suppression of corneal allograft rejection in the rat penetrating keratoplasty model.

Macrophage migration inhibition factor activity in the aqueous humor during experimental corneal xenograft and allograft rejection.

Macrophage migration inhibition factor (MIF), a soluble mediator of delayed hypersensitivity, was assayed for in the aqueous humor of rabbits undergoing corneal graft rejection. Penetrating and interlamellar xenografts and interlamellar allografts were performed in rabbits, and aqueous humor early in the course of xenograft and allograft rejection, and MIF activity was present during the course of the active rejection. This activity returned to near normal after the active rejection resolved. No significant MIF activity could be measured during the nonspecific inflammations produced by alkali burns, multiple paracenteses, intracorneal clove oil, mechanical debriding of the endothelium.