Bernard E. McCarey

Cohesive tensile strength of human LASIK wounds with histologic, ultrastructural, and clinical correlations.

PURPOSE To measure the cohesive tensile strength of human LASIK corneal wounds. METHODS Twenty-five human eye bank corneas from 13 donors that had LASIK were cut into 4-mm corneoscleral strips and dissected to expose the interface wound. Using a motorized pulling device, the force required to separate the wound was recorded. Intact and separated specimens were processed for light and electron microscopy. Five normal human eye bank corneas from 5 donors served as controls. A retrospective clinical study was done on 144 eyes that had LASIK flap-lift retreatments, providing clinical correlation. RESULTS The mean tensile strength of the central and paracentral LASIK wounds showed minimal change in strength over time after surgery, averaging 2.4% (0.72 +/- 0.33 g/mm) of controls (30.06 +/- 2.93 g/mm). In contrast, the mean peak tensile strength of the flap wound margin gradually increased over time after surgery, reaching maximum values by 3.5 years when the average was 28.1% (8.46 +/- 4.56 g/mm) of controls. Histologic and ultrastructural correlative studies found that the plane of separation always occurred in the lamellar wound, which consisted of a hypocellular primitive stromal scar centrally and paracentrally and a hypercellular fibrotic stromal scar at the flap wound margin. The pathologic correlations demonstrated that the strongest wound margin scars had no epithelial cell ingrowth-the strongest typically being wider or more peripherally located. In contrast, the weakest wound margin scars had epithelial cell ingrowth. The clinical series demonstrated the ability to lift LASIK flaps without complications during retreatments up to 8.4 years after initial surgery, correlating well with the laboratory results. CONCLUSIONS The human comeal stroma typically heals after LASIK in a limited and incomplete fashion; this results in a weak, central and paracentral hypocellular primitive stromal scar that averages 2.4% as strong as normal comeal stroma. Conversely, the LASIK flap wound margin heals by producing a 10-fold stronger, peripheral hypercellular fibrotic stromal scar that averages 28.1% as strong as normal comeal stromal, but displays marked variability.

Improved Corneal Storage For Penetrating Keratoplasties in Man

Twenty-six of 28 human corneas stored for up to seven days in a simple tissue culture medium (dextran dissolved in tissue culture medium with streptomycin-penicillin mixture) remained clear and thin after keratoplasty. Temperature reversal phenomenon and electron microscopy demonstrated high quality of such tissue after storage. The method is inexpensive, requires limited technical assistance, and provides the surgeon with excellent tissue at regular operation hours.

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.

Intrastromal Crystalline Deposits Following Hydrogel Keratophakia in Monkeys

Intrastromal corneal crystals developed in 11 of 49 monkey eyes with hydrogel intracorneal lenticules followed over a 4 year period. All of the eyes, except one, underwent synthetic keratophakia via a microkeratome incision. The diagnosis of crystal formation was initially made by slit-lamp examination and confirmed with specular microscopy (from 21 to 150 days post-hydrogel keratophakia). The crystals were noted to lie in a plane adjacent to the hydrogel lenticule and specular microscopy revealed polychromatic, hyperrefringent crystals with either a rectangular or linear morphology. Prior to intrastromal crystal formation, these corneas developed early postoperative stromal edema (*3 weeks). We hypothesize that early stromal edema in combination with the hydrogel intracorneal lenticule induced the production of lipid crystals by stromal keratocytes.

Eight years experience with Permalens® intracorneal lenses in nonhuman primates

BACKGROUND For the past 8 years, three independent laboratories have been researching the biocompatibility and performance of Permalens intracorneal lens implants in the corneas of nonhuman primates. Both myopic and hyperopic corrections have been achieved. This article describes the evolution of the intracorneal lens design and manufacturing process. METHODS During this time period, 63 surgeries were performed on various species of nonhuman primates. Follow-up examination extended between 30 months and 8.2 years. Objective measures of refractive performance, as well as biocompatibility were made using slit lamp, retinoscopy, autorefractor, specular microscope, etc. Additionally, histopathology was performed on many of the specimens, both acute and chronic. RESULTS Surgically successful implants were achieved in between 60% and 100% of eyes in the various series of lens implants outlined in the article. Levels of contamination in the preparation of hydrogels were felt to be responsible for many of the surgical failures. The removal of silicone and other contaminants seems to have significantly improved the biocompatibility of these materials within the cornea. The major histopathological finding was that there appeared to be some epithelial thinning over the implants, but in general excellent biocompatibility was obtained over the 8-year period outlined in this paper. CONCLUSIONS Although extensive studies of biocompatibility have been completed, the future of the performance of these materials remains to be proven in the human subject. Additionally, empirical relationships between lens implant power and refractive results will have to be determined in humans, prior to their general clinical usage.

Lipid Deposits Posterior to Impermeable Intracorneal Lenses in Rhesus Monkeys: Clinical, Histochemical, and Ultrastructural Studies

Synthetic materials are being evaluated for their potential long-term use in corneal refractive surgery. Clinical and histopathologic studies were performed with polymethylmethacrylate (PMMA) and polysulfone intracorneal lenses in rhesus monkey eyes that were followed for up to 3 years. The 5 mm diameter lenses were placed in the deep posterior corneal stroma of four eyes. Fine, polychromatic crystalline deposits formed a layer posterior to the implants. Enucleated eyes had the corneas either frozen for histochemistry or fixed for electron microscopy. Special stains included oil red 0 and filipin on fresh frozen tissue. The cornea, with a PMMA intracorneal lens showed myriad crystalline aggregates in the deep corneal stroma behind the implant. These crystalline deposits stained positively with oil red 0 and with filipin indicating the presence of neutral fat as well as unesterified cholesterol. The polysulfone implant showed no evidence of crystalline deposits histologically but was surrounded by homogeneous aggregates that could represent nonspecific reaction to the lens material or protein deposits. Electron microscopy of all four corneas revealed dissolved lipid aggregates and laminated electron dense material that were most abundant posterior to the implant where the keratocytes appeared disintegrated. The PMMA lens appeared to induce lipid keratopathy.

Improved corneal storage: Penetrating keratoplasties in rabbits

Abstract In the present study, rabbit corneas were stored in McCarey-Kaufman corneal bathing media (M-K media) at 4°C for up to 14 days and used as donor material in penetrating keratoplasties. These results were compared to penetrating keratoplasties with corneas stored in refrigerated moist chambers. Evaluation of the graft clarity shows that all the M-K media stored corneas were clear from the day of surgery. This contrasted with the 14-day moist chamber stored grafts which were hazy for the first week then either became opaque or remained hazy. Electron microscopy of postoperative grafts of 14-day M-K stored donor corneas, show the endothelial ultrastructure to be normal by the third day postoperative.

Comparison of the effect of moxifloxacin and gatifloxacin on corneal epithelial wound healing in the rabbit model

Purpose: Corneal epithelial wound closure rates in rabbit eyes were compared after topical applications of moxifloxacin 0.5% ophthalmic solution, gatifloxacin 0.3% ophthalmic solution, and BSS Sterile Irrigating Solution. Methods: Thirty rabbits were divided into 3 randomization groups of 10 rabbits each. Animals in each randomization group were predosed 4 times a day with a different test article in each eye for 1 day before surgery. Group 1 animals received BSS in 1 eye and moxifloxacin in the other eye; group 2 animals received BSS in 1 eye and gatifloxacin in the other eye; and group 3 animals received moxifloxacin in 1 eye and gatifloxacin in the other eye, resulting in each test articles being administered to 20 eyes. Rabbits underwent a bilateral procedure to remove the full thickness of the central corneal epithelium within a 5-mm trephine mark. After wounding, the eyes were dosed 4 times a day with the same respective predose test articles, and epithelial wound closure was recorded using slit-lamp photography. The data were analyzed to determine the rate of wound closure. Results: The mean wound radius closure rate was 71.1 ± 11.7 μm/h for BSS-treated eyes, 67.6 ± 7.1 μm/h for moxifloxacin-treated eyes, and 65.9 ± 8.0 μm/h for gatifloxacin-treated eyes. Conclusions: The relative order of wound healing rates was BSS > moxifloxacin > gatifloxacin; however, differences between treatment groups were not considered significant.