Episcleral Surface Research Articles

Hollow Microcapsules as Periocular Drug Depot for Sustained Release of Anti-VEGF Protein.

Diseases affecting the posterior segment of the eye such as age-related macular degeneration and diabetic retinopathy are leading causes of blindness all over the world. The current treatment regimen for such diseases involves repeated intravitreal injections of anti- Vascular Endothelial Growth Factor (VEGF) proteins. This method is highly invasive and can lead to severe complications. In an attempt to develop less invasive alternatives, we propose the use of a controlled release system consisting of anti-VEGF loaded hollow microcapsules that can be administered periocularly to form drug eluting depots on the episcleral surface. The microcapsules with either positive or negative surface charge were prepared by a layer by layer approach and showed pH responsive permeability switching. An ex vivo experiment using porcine sclera indicated positively charged microcapsules remained on the episcleral surface over four days while the negatively charged microcapsules were washed away. These positively charged microcapsules were then loaded with anti-VEGF protein ranibizumab using pH dependent permeability switching and protein release from the microcapsules were studied using an in vitro setup. An ex vivo experiment utilizing porcine sclera demonstrated sustained release of ranibizumab over seven days with zero-order kinetics.

Differences in the Region- and Depth-Dependent Microstructural Organization in Normal Versus Glaucomatous Human Posterior Sclerae

This study quantitatively investigated differences in the regional- and depth-dependent human posterior scleral microstructure in glaucomatous (G) and nonglaucomatous (NG) donors. Twenty-five posterior poles from six G and seven NG donors were analyzed using small angle light scattering (SALS) to investigate the organization of scleral fibers around the optic nerve head. Eccentricity (Ecc), fiber splay (FS), and percent equatorial fibers (PEF) were quantified. Regional statistically significant differences between G and NG groups existed in Ecc (P < 0.0001), FS (P < 0.005), and PEF (P < 0.005). Distinct and substantial variation through the depth occurred in all three end points. Region-specific differences in Ecc existed at the episcleral surface; however, by 40% into the depth, all regions converged to a similar value. Fiber splay increased in all regions by an average of 0.14 from the episcleral surface to the intraocular surface. The percentage of equatorial fibers decreased universally through the depth from approximately 61% to 33%. Generally, the inferior and superior regions had a lower Ecc and PEF compared to the nasal and temporal regions. Region and depth of the posterior sclera are important factors that should be included when comparing scleral microstructure of G and NG tissue in experimental and computational work. The dramatic changes in the depth of the sclera may represent baseline properties that affect predisposition to primary open angle glaucoma (POAG), and necessitate that further research include depth as a factor in assessing how observed structural differences contribute to or are a result of POAG.

The Efficacy and Safety of Episcleral Pigmentation Removal From Pig Eyes

To evaluate the efficacy and safety of removing episcleral pigmentation from pig eyes using a 532-nm Q-switched Nd:YAG laser. Forty-four porcine eyes with episcleral pigmentation were enucleated approximately 3 hours after death. After conjunctival dissection, 0.5×1.0 cm-sized segments of pigmented episcleral surface underwent laser treatment. To determine the minimal energy fluence required for effective episcleral pigmentation removal, the laser output was set to 2, 3.2, 4, 5, and 6 J/cm for 20 eyes. To investigate thermal effects, the surface temperatures of the episclera were measured in the remaining 24 eyes before and after laser treatment in which the minimal energy fluence required to effectively remove episcleral pigmentation was used. Episcleral pigmentation began to fade immediately with a laser setting of 2 J/cm and was satisfactorily removed immediately with a laser setting of 4 J/cm. The increase in surface temperature was 0.90±0.37°C from baseline with a laser setting of 4 J/cm (P>0.05). Light-microscopic analysis showed that levels of melanin granules decreased by laser treatment in all tested episcleral tissues. The retinal pigment epithelium and the choroid were not affected by treatment. However, the collagen fiber structure was damaged after laser treatment with settings of more than 5 J/cm, as showed by the loss of straight profiles, although the damage was confined to the outer one third of the scleral stroma. 532-nm Q-switched Nd:YAG laser treatment is effective and safe for the removal of episcleral pigmentation in pig eyes. Our findings indicate that the laser system may be effective for the removal of episcleral pigmentation in cases of oculodermal melanocytosis, and further investigation is necessary to evaluate long-term safety of laser treatment.

In vitro transcorneal and transscleral diffusion of radiolabeled compounds in human and rabbit cornea and in human, monkey, dog, and rabbit sclera

Abstract Purpose To determine the in vitro diffusion of selected compounds across the cornea or sclera of humans, monkeys, dogs, and rabbits. Methods Human and NZW rabbit corneas were obtained and the epithelium was removed from one cornea of each pair. Corneas were mounted in chambers with 3H‐water or 3H‐dexamethasone on the epithelial side and BSS solution on the endothelial side. Serial aliquots were taken from each chamber and assayed by LSC. Scleral sections from human, NZW rabbit, dog, or monkey eyes were mounted in perfusion chambers. Adjacent sclera was used for H&amp;E histology. 3H‐water, 3H‐dexamethasone, or 70kD‐14C‐dextran were added to the episcleral surface while perfusing BSS across the choroidal side. Serial aliquots were collected up to 5 hrs and assayed by LSC. Scleral permeability (ktrans) was calculated. H&amp;E slides were used to determine scleral thickness. Results 3H‐water diffused through cornea faster than 3H‐dexamethasone, especially with denuded epithelium. Scleral thickness and molecular weight were determinant of diffusion in sclera. Monkey sclera was thinnest, followed by dog, rabbit, and human. ktrans for 70kD‐14C‐Dextran and 3H‐dexamethasone were greatest in monkey, followed by dog, rabbit, and human. ktrans values for 3H‐water were similar in all species, and greater than values for 14C‐dextran and 3H‐dexamethasone. Conclusion These studies demonstrate permeability of cornea and sclera in human and animal models with compounds of varied molecular weights representative of drugs being developed for treatment of ocular diseases. The results of this study indicate that these techniques are valuable as screening tools in the development of ocular drugs.

Transscleral Permeability of Fluorescent-Labeled Antibiotics

To determine the in vitro transscleral permeability of antibiotics for posterior segment infection. Scleral sections from moist chamber-stored human globes were mounted in a 2-compartment perfusion chamber. Fluorescent-labeled vancomycin, polymyxin B, or penicillin G was added to the episcleral surface, while the choroidal side was slowly perfused with balanced salt solution (Alcon Laboratories, Inc., Ft. Worth, TX). The perfusate was collected and fluorescence was measured using a fluorometer. From the measurements, permeability (Ktrans) was calculated. Photomicrographs were taken with a fluorescent microscope to evaluate tissue absorption. The Ktrans values (cm/s, mean +/- standard error) were 6.66 +/- 1.46 x 10(-7) for vancomycin, 3.90 +/- 0.59 x 10(-7) for polymyxin B, and 1.89 +/- 0.21 x 10(-6) for penicillin G. The percent of antibiotic that diffused across the sclera from the donor chamber in 24 hours was 20.6 +/- 4.2 for vancomycin, 12.6 +/- 2.0% for polymyxin B, and 50.8 +/- 4.8% for penicillin G. This study shows that human sclera is more permeable to lower molecular weight, water-soluble penicillin G than to vancomycin or polymyxin B. The data suggests that a local, noninvasive, transscleral drug-delivery method may be reasonable for treating intraocular infections.

In Vitro Sustained Human Transscleral Drug Delivery of Fluorescein-Labeled Dexamethasone and Methotrexate with Fibrin Sealant

Purpose: To study the use of fibrin sealant as a drug delivery system for the sustained transscleral delivery of dexamethasone and methotrexate. Methods: Scleral sections excised from moist-chamber-stored human globes were mounted in a perfusion chamber. Dexamethasone-fluorescein or methotrexate-fluorescein in either fibrin sealant or balanced salt solution (BSS) was applied to the episcleral surface. BSS was perfused to the choroidal side, fluorescence was measured in perfusate fractions, and an apparent scleral permeability PA was calculated for each solute-vehicle combination. Results: PA for both compounds was significantly lower with fibrin sealant delivery compared to delivery in BSS (p < 0.001). However, the fibrin sealant vehicle provided a more sustained release of both drugs through 24 hr. Conclusions: Incorporating dexamethasone and methotrexate into a fibrin sealant provided a more gradual drug delivery and a more uniform delivery compared to dissolving these drugs in BSS. Fibrin sealant could be useful for transscleral delivery for posterior segment disease.

Scleral Permeability of a Small, Single-Stranded Oligonucleotide

Developing more effective ocular drug delivery systems is essential to improving the treatment of posterior segment eye disease. The large target area provided by the sclera and potentially less vision threatening complications are advantages of transscleral administration compared to more traditional modalities of drug delivery to the posterior segment. We aimed to determine the permeability coefficient for the in vitro diffusion of a small, single-stranded, oligonucleotide across human sclera. Transscleral permeability was measured by placing 100 microL of 2.96 x 10(-4) mol single-stranded, fluorescein-labeled oligonucleotide (MW = 7998.3) on the episcleral surface of sclera mounted in a perfusion chamber. Fractions of choroidal perfusate were collected hourly for 24 hours. The permeability constant or K(trans) for the transscleral diffusion of the naked, single-stranded, fluorescein-labeled oligonucleotide was 7.67 +/- 1.8 x 10(-7) cm/s (mean +/- SEM, N = 7). The permeability constant or K(trans) after intrascleral injection of the same fluorescein-labeled oligonucleotide was 1.32 +/- 0.42 x 10(-7) (mean +/- SEM, N = 4). This analysis demonstrates that diffusion of a naked, 24-base, single-stranded, fluorescein-labeled oligonucleotide can be accomplished by both of the described methods. The ability to deliver single-stranded oligonucleotides across the sclera may prove to be advantageous given the development of several novel therapeutic strategies that use similar molecules.

In vitro human scleral permeability of fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein and rhodamine 6G and the use of a coated coil as a new drug delivery system.

To determine the in vitro human scleral permeability of several dyes and drugdye combinations with varying molecular weights (MW) and lipid solubilities (fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein, and rhodamine). Coils coated with rhodamine were also evaluated for scleral permeability and sustained release. Scleral sections excised from moist chamber stored human globes were mounted in a 2-compartment perfusion chamber. A small depot of drug/dye (100 microl of 10(-4) M fluorescein, dexamethasone-fluorescein, methotrexate-fluorescein or rhodamine) or a coated coil in 100 microl of BSS was added to the episcleral surface while perfusing BSS to the choroidal side. The perfusate was collected and measured for fluorescence. Permeability was calculated as Ktrans from the flux measurements. Ktrans values (cm/sec, mean +/- SE) for the studied dyes and drug-dye combinations were 5.21 +/- 0.71 x 10(-6) for fluorescein, 1.64 +/- 0.17 x 10(-6) for dexamethasone-fluorescein, 3.36 +/- 0.62 x 10(-6) for methotrexate-fluorescein, 1.86 +/- 0.39 x 10(-6) for rhodamine and 2.18 +/- 0.23 x 10(-6) for the rhodamine from the coils. We found a significant difference between the permeability of the sclera to fluorescein and dexamethasone-fluorescein (P < 0.001), methotrexate-fluorescein (P < 0.05) and rhodamine (P < 0.001). Steady state flux was observed from the rhodamine coil. The rank order of scleral permeability to the studied dyes is as follows: fluorescein > methotrexate-fluorescein > rhodamine coil > rhodamine 6G > dexamethasone-fluorescein. Differences in scleral permeability are related to MW and lipid solubility. Prolonged transscleral diffusion of rhodamine delivered by solution and by coil are similar.

Trabeculectomy with mitomycin-c in the treatment of pediatric glaucomas

PurposeTo evaluate the effectiveness and safety of trabeculectomy with mitomycin-C (MMC) in the management of childhood glaucomas. DesignRetrospective, noncomparative case series. ParticipantsAll patients less than 18 years of age who underwent trabeculectomy with MMC from June 1991 through October 1997 were included. MethodsThe medical records of 29 consecutive patients (29 eyes) were reviewed. Data collected during routine patient follow-up were analyzed. Surgical outcome was evaluated using Kaplan-Meier life-table analysis. Main outcome measuresClinical outcome assessment included intraocular pressure (IOP) control, visual acuity, and identification of complications. Successful IOP control was defined as 5 mmHg ≤ final IOP ≤ 21 mmHg, with or without antiglaucoma medications and without further glaucoma surgery or loss of light perception. Outcomes for the group of patients with primary infantile glaucoma were compared with those for the group with secondary glaucomas. ResultsMean patient age was 6.4 ± 4.4 years (range, 0.2–15.3 years). A variety of primary and secondary glaucomas were represented. Mitomycin-C (0.5 mg/ml) on a surgical sponge was applied to the episcleral surface for an average of 3.8 ± 1.0 minutes (range, 1.5–5.0 minutes). Mean follow-up time for patients categorized as successes was 25.1 ± 16.0 months (range, 5.5–59.7 months). The 12-, 24-, and 36-month life-table success rates for IOP control were 82%, 59%, and 59% respectively. There was no difference between the primary infantile glaucoma group and the secondary glaucoma group with respect to length of follow-up, rate of successful IOP control, and incidence of complications. Five patients (17%) experienced late bleb-related infection (BRI) at an average of 27.9 ± 18.1 months (range, 5.4–55.5 months) after surgery. Other complications included hyphema, retinal detachment, late-onset bleb leak, flat anterior chamber, chronic hypotony, decompression retinopathy, suture abscess, and phthisis. ConclusionsTrabeculectomy with MMC may be useful in the management of childhood glaucomas in which goniotomy, trabeculotomy, or both have failed. However, the high incidence of BRI in this series over an extended follow-up interval dictates caution in using MMC as an adjunct in pediatric trabeculectomy.