Peggy D. Lamar

Efficacy of various drugs in the prevention of posterior capsule opacification: Experimental study of rabbit eyes

Purpose: To assess the efficacy of various drugs in the prevention of posterior capsule opacification (PCO) in a closed capsular bag technique. Setting: Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, USA. Methods: Lens material was removed using phacoaspiration or phacoemulsification through a microcapsulorhexis according to the hardness of the crystalline lens correlated with the weight and age of the rabbits. A mixture of an ophthalmic viscosurgical device (sodium hyaluronate 1.4% [SHA]) and a drug was injected into the empty capsular bag, allowed to remain inside for 3 minutes, and removed. The capsular bag was rinsed with balanced salt solution (BSS®) and refilled with SHA. In a group of rabbits, the capsulorhexis was sealed with a minicapsulorhexis valve (MCV). Rabbits were treated with 1 of the following: SHA (control), BSS, mitomycin‐C (MMC, 0.2 mg/mL), ethylenediaminetetraacetic acid (EDTA) (10 mM and 15 mM), 5‐fluorouracil (5‐FU, 33 mg/mL), acetic acid (3%, 0.3%, and 0.003%), and distilled water. Results: Upon completion of the study, the control and treated eyes had PCO and new lens material (not residual). Anterior capsule proliferation was observed in eyes treated with 5‐FU. The order of PCO appearance (earliest to latest) was as follows: 15 mM EDTA, SHA, MMC, acetic acid 0.3%, acetic acid 3%, BSS, distilled water (small animals; no MCV), acetic acid 0.003%, 5‐FU, 10 mM EDTA, and distilled water (large animals; MCV). The earliest appearance was day 1 postoperatively and the latest, day 47. Conclusions: Distilled water and 10 mM EDTA treatments were the most efficient in retarding the appearance of PCO.

Preparation and hydration control of corneal tissue strips for experimental use.

Purpose The purpose of this study was to develop an experimental protocol to maintain corneal tissue strips at normal hydration and avoid swelling or dehydration during experimental studies on corneal biomechanics and thermal stability. Methods The corneal thickness of 9 whole Eye-Bank eyes was brought back to normal values by immersion in a 25% dextran solution for 24 hours. Corneal buttons were then removed and cut into 2 × 6 mm strips. The 9 strips were immersed successively in Dextran solutions at 25%, 22.5%, and 20% concentration at 35°C. The thickness of the immersed strip in solution was measured every 5 minutes for 1 hour using a modified optical comparator. Results The mean final thickness for the nine corneal strips after one hour in 25%, 22.5%, and 20% dextran solution was 508 ± 38, 563 ± 56, and 592 ± 33 &mgr;m, respectively. Average swelling in 25%, 22.5%, and 20% dextran solutions was 1.06 ± 0.03, 1.20 ± 0.07, and 1.24 ± 0.07 times the initial thickness, respectively. Conclusion The hydration of corneal tissue strips is maintained at normal values when the strips are immersed in 25% Dextran solution. Corneal strips swell to thicknesses above normal values in solutions with lower molecular weights.

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-μm-thick optical zone, 100-μm-thick outer flange) was implanted after 45 ± 5 days. The keratoprostheses were implanted with their central optic part positioned on a completely exposed Descemets 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.

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.

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 μm 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 α-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.

Eine neue, nicht penetrierende synthetische Hornhaut

ZusammenfassungBei penetrierenden Keratoprothesen (KPro) kommt es häufig zu postoperativen Komplikationen die bis zum Verlust des Auges führen können. Um diese Komplikationen zu verringern, wurde eine neue supradescemetsche, nicht penetrierende, Keratoprothese entwickelt.Sie wird durch eine zirkuläre Schürze, die intrastromal verankert wird, befestigt, und liegt auf der Descemet Membran auf. Vier verschiedene biokompatible Polymere wurden in Augen von Hasen (NZW) implantiert. Dazu wurde eine neue Delaminationstechnik und Trepanation entwickelt. In acht Augen wurde je eine KPro (2X PMMA, 2X Hema-NVP, 2X Hema-MMA und 2X Hema-EMA) implantiert. Der postoperative Verlauf war komplikationslos, die Prothesen blieben klar und in situ und erlaubten einen ausgezeichneten Einblick in den Fundus. Die Nachbeobachtungszeit von einem Monat ist jedoch zu kurz um über die Stabilität und den Einsatz dieser KPro für den humanen Gebrauch zu entscheiden.SummaryPostoperative complications of transcorneal fixated keratoprosthesis (KPro) are frequent and severe and may lead to the loss of the eye. To avoid these problems, a novel supra-Descemetic, non penetrating mesoplant was developed. It is locked in place by an annular skirt and is placed over Descemet’s membrane. Four different biocompatible polymers were implanted in eyes of New Zealand white rabbits (NZW). A new delamination and trephination technique was developed.In 8 eyes the new KPro (2X PMMA, 2X Hema-NVP, 2X Hema-MMA and 2X Hema-EMA) were implanted. There were no postoperative complications, the KPros stayed clear and in place and allowed an excellent view of the fundus. The follow-up of one month is nevertheless too short to determine stability and possible use of this new KPro in humans.

Assessment of the strength of minicapsulorhexes

PURPOSE: To evaluate the effect of age, size, position, and species on the strength of minicapsulorhexes. SETTING: Surgical Suite and Laser Laboratory, Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA. METHODS: Capsulorhexes 0.7 to 2.3 mm in diameter were made centrally or peripherally in 35 eye‐bank eyes and 32 rabbit eyes. A custom‐made instrument stretched the capsulorhexes until rupture. Load and stretch at rupture were recorded. RESULTS: Maximum load and stretch were 26.3 mN ± 20.3 (SD) and 50% ± 18% for central and 50.8 ± 20.5 mN and 69% ± 17% for peripheral capsulorhexes in eye‐bank eyes and 19.8 ± 15.2 mN and 38% ± 13% for central and 13.5 ± 9.5 mN and 30% ± 7% for peripheral capsulorhexes in rabbit eyes. Peripheral capsulorhexes were stronger and more elastic than central capsulorhexes in eye‐bank eyes, and maximum load and stretch increased statistically with the capsulorhexis diameter. CONCLUSIONS: Peripheral minicapsulorhexes were more resistant to rupture than central capsulorhexes in eye‐bank eyes, probably because of increased lens capsule thickness at the periphery. An increase in capsulorhexis diameter increased the resistance to rupture.

Entwicklung einer neuen Implantationstechnik zur supraDescemetalen Implantation einer lamellären Keratoprothese

ZusammenfassungHintergrundDie Implantation einer „künstlichen Hornhaut“ (Keratoprothese) stellt bei beidseitigen schweren Hornhauterkrankungen mitunter die letzte Möglichkeit zur Wiederherstellung eines akzeptablen Sehvermögens dar. Bei penetrierenden Keratoprothesen fuhren jedoch manchmal schwere postoperative Komplikationen zu einem neuerlichen Visusabfall. Als Alternative wurde eine lamelläre Keratoprothese (supraDescemetale Synthetische Cornea, sDSC) entwickelt, die der Descemet’schen Membran (DM) aufliegt.Material und MethodenDie Implantationstechnik wurde am Tiermodell (New Zealand White Rabbits) entwickelt und getestet. Nach paralimbaler Incision der peripheren Hornhaut (∼ 85% der Hornhautdicke), Präparation einer Hornhauttasche und Trepanation (3,7 mm Ø) der vorderen Hornhautanteile, erfolgte die vorsichtige Resektion des verbliebenen Hornhautstromas bis zum vollständigen Freiliegen der Descemet’schen Membran. Die sDSC wurde derart positioniert, dass die Haptik im tiefen Hornhautstroma und die zentrale Optik direkt auf der DM zu liegen kamen. Bei insgesamt 41 Hasenaugen wurde eine Operation durchgeführt. In 25 Fällen wurde die Operation an einer gesunden und klaren Hornhaut durchgeführt, 16 Hornhäute waren zum Operationszeitpunkt vaskularisiert.ErgebnisseVon den ersten 22 Fällen konnten 15 Operationen erfolgreich beendet werden, in 7 Fällen war eine Perforation der DM zu verzeichnen. Durch Modifikation der Methode und Verminderung des intraokularen Drucks durch Ablassen von Kammerwasser konnte die Perforationsrate drastisch gesenkt werden. Bei keiner der folgenden Operationen trat in der Folge diese schwerwiegende Komplikation auf. Histologisch konnte das Erreichen der DM bewiesen werden.SchlussfolgerungDa die Vorderkammer bei Implantation einer derartigen „supradescemetalen“ synthetischen Cornea (sDSC) nicht eröffnet werden muss, könnte mit einem vergleichsweise geringerem Risiko für schwere Komplikationen gerechnet werden.SummaryBackgroundImplantation of a keratoprosthesis (KPro) or ‘synthetic cornea’ is the last resort in regaining useful vision in patients with corneal blindness not amenable to conventional corneal transplantation. Complications in these penetrating devices are common and sometimes severe, therefore a non-penetrating, lamellar KPro was developed.MethodsThe technique for implantation was developed and tested in an animal model (New Zealand White Rabbits). A paralimbal corneal incision was performed at 85% thickness, followed by preparation of an intracorneal pocket and trephination (3.7 mm) of the anterior lamella. The remaining stroma was removed by blunt dissection. The sDSC was positioned with its central optic part on bare Descemet’s membrane (DM) and with its peripheral haptic in deep corneal stroma. The operation was performed in the right eye of 41 rabbits. 25 corneas were clear and healthy, 16 corneas were vascularized at time of surgery.ResultsImplantation of the sDSC could be performed successfully in 15 of the first 22 consecutive cases, perforation of DM occurred in 7 eyes. Minor modification of the surgery (reduction of the intraocular pressure via paracentesis) significantly improved the success. In none of the following 19 cases a perforation of DM occurred. Implantation depth was evaluated by histology, showing a bare DM.ConclusionAs the anterior chamber is not altered during sDSC surgery, the complication rate could be less compared to implantation of a penetrating devive.

Synthetic cornea: biocompatibility and optics

Purpose. Experimentally find a method to provide a safe surgical technique and an inexpensive and long lasting mesoplant for the restoration of vision in patients with bilateral corneal blindness due to ocular surface and stromal diseases. Methods. Identify the least invasive and the safest surgical technique for synthetic cornea implantation. Identify the most compatible biomaterials and the optimal shape a synthetic cornea must have to last a long time when implanted in vivo. Results. Penetrating procedures were deemed too invasive, time consuming, difficult and prone to long term complications. Therefore a non-penetrating delamination technique with central trephination was developed to preserve the integrity of Descemets membrane and the anterior segment. Even though this approach limits the number of indications, it is acceptable since the majority of patients only have opacities in the stroma. The prosthesis was designed to fit in the removed tissue plane with its skirt fitted under the delaminated stroma. To improve retention, the trephination wall was made conical with the smallest opening on the anterior surface and a hat-shaped mesoplant was made to fit. The skirt was perforated in its perimeter to allow passage of nutrients and tissues ingrowths. To simplify the fabrication procedure, the haptic and optic were made of the same polymer. The intrastromal biocompatibility of several hydrogels was found superior to current clinically used PMMA and PTFE materials. Monobloc mesoplants made of 4 different materials were implanted in rabbits and followed weekly until extrusion occurred. Some remained optically clear allowing for fundus photography. Conclusions. Hydrogel synthetic corneas can be made to survive for periods longer than 1 year. ArF excimer laser photoablation studies are needed to determine the refractive correction potential of these mesoplants. A pilot FDA clinical trial is needed to assess the mesoplant efficacy and very long-term stability.