Long-term follow-up of a supradescemetic keratoprosthesis in rabbits: an immunofluorescence study.

OBJECTIVE: To evaluate the long-term clinical and immunohistological outcome of two different non-penetrating keratoprosthesis (KPro) implanted in non-injured rabbit corneas. MATERIALS AND METHODS: Three rabbits underwent implantation of a pHEMA-MMA(34) synthetic cornea in the supradescemetic space, and PMMA synthetic corneas in the supradescemetic space and within the central stroma. Animals were followed for at least 24 months before euthanasia. Periodic evaluation was performed with slit-lamp examination and photography. At the end of the follow-up, histological examination including hematoxylin eosin staining and immunocharacterization against collagen IV, alpha smooth muscle actin (α-SMA) and macrophages was performed. RESULTS: The pHEMA-MMA(34) implant was not extruded, and remained transparent until the end of follow-up. This material did not induce any cell infiltration, corneal scarring or tissue remodeling in the surrounding stroma as shown by immunofluorescence. In contrast, synthetic corneas made of PMMA-induced myofibroblast differentiation, stromal remodeling and macrophage infiltration. This reaction was even more significant in the rabbit with the PMMA implant within the corneal stroma. CONCLUSION: pHEMA-MMA(34) was clinically biocompatible, and did not induce any inflammatory reaction or scarring when implanted in the supradescemetic space. This material showed more promising biocompatibility results than for PMMA, whether implanted within the central cornea stroma or in the supradescemetic space.

Comparison of macular function and visual fields after membrane blue or infracyanine green staining in vitreoretinal surgery.

BACKGROUND: To compare possible toxic effects of membrane blue and infracyanine green used as vital stains in macular surgery. Vital stains are used in vitreoretinal surgery to perform peeling of the internal limiting membrane and idiopathic epiretinal membrane. There are many controversial studies about their toxicity, safety, and their effects on the retinal pigment epithelium and the neuroretinal elements. To compare possible toxicities of the two vital stains membrane blue and infracyanine green in vivo, we conducted a prospective, randomized, clinical trial. METHODS: A prospective, randomized clinical trial including 30 eyes of 30 patients with either full-thickness macular hole or idiopathic epiretinal membrane were included and randomized 1:1 to receive either membrane blue or infracyanine green during vitreoretinal surgery. Complete ophthalmic examinations, including optical coherence tomography and peripheral visual field were performed preoperatively, and 1, 3, and 6 months postoperatively in our clinic. The main outcome measure was the peripheral visual field. Data was analysed with Student's t-test and Pearson's correlation coefficient. RESULTS: Three months after surgery there was a significant difference in increase in visual field in the superior region in favor of the membrane blue group (p = 0.021). Eight eyes (53%) of the infracyanine group had a decrease in temporal visual fields of at least 5 degrees . CONCLUSION: Although there was a significant difference in visual fields between the groups after 3 months in the superior region, there were no more significant differences between the two groups after 6 months. However, due to the decrease in the temporal visual field in some eyes, we conclude that membrane blue is less toxic.

Corneal stroma regeneration in felines after supradescemetic keratoprosthesis implantation.

PURPOSE: To show corneal regeneration in 3 cats that underwent lamellar keratectomy (90%) depth during supradescemetic keratoprosthetic implantation. METHODS: Three 2-year-old cats that underwent spontaneous keratoprosthesis extrusion between 15 and 150 days after implanting a supradescemetic prosthesis into their right eyes were studied. Corneal structures and stroma thickness were evaluated by slit-lamp photographs, pachymetry, and confocal microscopy. Regenerated corneal epithelial cells, stroma matrix, and keratocyte morphology were studied with histology and transmission electron microscopy. Epithelial and stromal cell immunocharacterization was performed. RESULTS: Corneas progressively regained normal thickness and improved clarity within 40 to 60 days. Slit-lamp photographs and pachymetry showed gains in stromal thickness until 600 microm or more. In vivo confocal microscopy showed the restoration of normal epithelium and stroma in all cats. Corneal nerves were seen in the regenerated stroma of 2 cats. Immunostaining showed absent alpha-smooth muscle actin (SMA) expression and a keratin K3-expressing epithelium. Electron microscopy showed regeneration of normal epithelium with a well-formed basement membrane, organized corneal lamellae, and the presence of normal keratocytes. CONCLUSION: Felines are capable of regenerating corneal structures including epithelium and reinnervated stroma matrix after deep lamellar keratectomy. The use of feline models in corneal keratoprosthesis is therefore questionable.

Ex vivo evaluation of Tono-Pen and pneumotonometry in cat eyes.

PURPOSE: To evaluate the validity and intraobserver reliability of intraocular pressure (IOP) measurements with both pneumotonometry and the Tono-Pen in a closed ex vivo system in cat eyes. METHODS: IOP was increased step by step in 5 enucleated cat eyes, while taking IOP measurements with the Tono-Pen and pneumotonometry. The outcomes were compared to readings of a digital manometer simultaneously measuring the actual pressure in the anterior chamber. RESULTS: Pneumotonometry overestimated IOP below 15 mm Hg and underestimated pressures above 20 mm Hg. Tono-Pen tonometry considerably underestimated IOP over the whole spectrum in all of the eyes tested. The pneumotonometer was identified as the more valid and reliable instrument for cat eyes. CONCLUSION: Both tonometers are clinically useful tools to assess IOP for glaucoma studies using a cat animal model. However, one has to consider underestimation of IOP in the upper ranges. A correction formula can be used to calculate the actual IOP.

Trabecular meshwork alteration and intraocular pressure change following pulsed near-infrared laser trabeculoplasty in cats.

BACKGROUND AND OBJECTIVE: To comparatively assess the safety and variation in intraocular pressure (IOP) of two pulsed near-infrared lasers (titanium:sapphire and alexandrite) for laser trabeculoplasty versus conventional blue-green argon laser trabeculoplasty in an animal model. MATERIALS AND METHODS: The left eyes of 15 healthy cats received a 180 degree laser trabeculoplasty treatment: 5 with a titanium:sapphire laser, 5 with an alexandrite laser, and 5 with an argon laser. Preoperatively and postoperatively, all animals underwent tonometry, gonioscopy, and slit-lamp examination. The cats were observed up to 12 weeks. Scanning electron microscopy and histologic examination were performed to evaluate potential alterations in the trabecular meshwork structure. RESULTS: IOP at 1 hour, 1 day, and 1 week following treatment was remarkably lower, irrespective of the laser source used. Following treatment with both near-infrared lasers, gonioscopy showed depigmentation underneath the area of the treated trabecular meshwork and histologic evaluation showed a decrease in pigment density. On scanning electron microscopy, damage to the trabecular meshwork structure could not be detected after treatment with near-infrared lasers. CONCLUSIONS: Near-infrared laser trabeculoplasty was found to be effective to temporarily lower IOP in cats. The lasers selectively altered pigment-containing cells, avoiding structural damage of the trabecular meshwork anatomy.

Biocompatibility of a nonpenetrating synthetic cornea in vascularized rabbit corneas.

PURPOSE: This study was designed to assess feasibility and biocompatibility of a lamellar, nonperforating supraDescemetic Synthetic Cornea (sDSC) implanted in rabbit eyes after a corneal injury. METHODS: Corneal vascularization and scarring was induced in the right eye of 15 rabbits by application of 1-heptanol and complete surgical removal of the limbus. An sDSC (7-mm diameter, 450-microm-thick optical zone, 100-microm-thick outer flange) was implanted after 45 +/- 5 days. The keratoprostheses were implanted with their central optic part positioned on a completely exposed Descemet's membrane (DM) while the outer flange was located in deep stroma. Three different materials were tested: hydrophobic PMMA (n = 5) and hydrophilic HEMA-MMA (n = 5) and HEMA-NVP (n = 5) with a water content of 34% and 75%, respectively. The corneal surface was covered with a conjunctiva-Tenon flap. Central flap trephination was performed after 63 +/- 7 days. DM vascularization and scarring was assessed and graded after flap opening and weekly thereafter. RESULTS: In all 15 consecutive cases implantation could be completed successfully without perforation of DM. Repair of the conjunctival flap had to be performed in five rabbits. Four months postoperatively, the flaps were opened. Four of five corneas (80%) with a PMMA implant and three of five (60%) with a HEMA-NVP75 implant had retained their original transparency. The others had developed significant neovascularization in the Descemet-sDSC optic interface. All corneas (100%) that received an sDSC made of HEMA-MMA34 displayed a completely clear DM without any vessels or scarring. DM was found firmly attached to the posterior surface of the optic. CONCLUSION: Implantation of a nonperforating synthetic cornea on top of an exposed DM is feasible. HEMA-MMA34 showed the most promising results. Because opening of the anterior chamber is not required, a lamellar supraDescemetic Synthetic Cornea would theoretically reduce some of the risks attributed to penetrating keratoprostheses.

Biological response to a supraDescemetic synthetic cornea in rabbits.

OBJECTIVE: To evaluate the biocompatibility of a novel nonpenetrating keratoprosthesis (supraDescemetic synthetic cornea) in a rabbit model. METHODS: Seven rabbits received a supraDescemetic synthetic cornea (7-mm diameter, 350-microm-thick optical zone, 100-microm-thick peripheral flange) in their healthy right eyes. A surgical technique was developed that allowed implantation of the device on top of the bare Descemet membrane. Three rabbits received a supraDescemetic synthetic cornea made of hydroxyethyl methacrylate-methyl methacrylate(26), 1 received a hydroxyethyl methacrylate-N-vinyl pyrrolidone(75) mesoplant, and 3 were implanted with devices made of polymethyl methacrylate. All rabbits were euthanized after 8 weeks; the eyes were enucleated and examined by conventional histological and immunohistochemical evaluations. RESULTS: All eyes became quiet within several days. The Descemet membrane remained transparent during the observation period. Indirect ophthalmoscopy performed through the prosthesis allowed accurate examination of the posterior pole. Histological evaluation of the implanted corneas displayed no signs of an acute or chronic inflammatory reaction to the supraDescemetic synthetic cornea in 5 eyes; a few inflammatory cells were detected in the corneas of 2 rabbits. The interface between the Descemet membrane and the mesoplant displayed ingrowth of very thin (<10-microm) tissues colonized by keratocytes in 3 of the 7 corneas. CONCLUSIONS: This study validates the biocompatibility of this new type of nonpenetrating keratoprosthesis. Because opening of the anterior chamber is not required with the supraDescemetic synthetic cornea, the risk for intraocular infection is minimal, and the implantation procedure is less traumatic compared with a penetrating device.