Magnetic resonance imaging study of current and ion delivery into the eye during transscleral and transcorneal iontophoresis

PURPOSE: The objectives were to determine by nuclear magnetic resonance imaging (MRI) the target sites of ion delivery in the eye during iontophoresis, compare transscleral and transcorneal ocular iontophoresis, and monitor the distribution of a probe ion in the anterior chamber and vitreous after iontophoretic delivery. METHODS: Thirty-minute 2-mA anodal constant current transscleral and transcorneal iontophoresis (current density, 10 mA/cm(2)) was performed on three New Zealand White rabbits in vivo. Intravitreal injection and passive delivery were the controls. Transscleral and transcorneal iontophoresis experiments were conducted with the electrode device placed in the superior cul-de-sac away from the limbus and on the cornea adjacent to the limbus, respectively. During iontophoresis, the current delivered into the eye was monitored using a probe ion (Mn(2+)) with MRI. The distributions of the ion in the aqueous and vitreous humor after iontophoresis, passive delivery, and intravitreal injection were also determined by MRI. RESULTS: With the short application time, passive diffusion did not deliver a significant amount of the ion into the eye. Whereas transscleral iontophoresis delivered the ion into the vitreous, transcorneal iontophoresis delivered the ion into the anterior chamber. The current pathways during iontophoresis were mainly from the electrode into the eye, perpendicular to the electrode-eye interface beneath the electrode. Electric current along the surface of the globe was relatively minimal. With the present transscleral iontophoresis protocol, the ion penetrated the sclera and traveled as far as 1.5 mm from the electrode-conjunctiva interface into the vitreous. For transcorneal iontophoresis, the ion penetrated the cornea and filled the entire anterior chamber. CONCLUSIONS: MRI can be a useful technique in the study of the penetration of probe compounds in the eye during and after iontophoresis, such as in iontophoresis protocol and device testing. Ocular pharmacokinetic studies using MRI are noninvasive and provide real-time data without perturbation and compound redistribution that can occur during dissection and assay in traditional pharmacokinetic studies. With MRI, it was shown that transscleral iontophoresis, transcorneal iontophoresis, and intravitreal injection deliver ions to different parts of the eye.     

Methotrexate delivery to the eye using transscleral hydrogel iontophoresis

PURPOSE: To evaluate methotrexate penetration and distribution profile in ocular structures after short low current transscleral hydrogel iontophoresis. METHODS: Methotrexate iontophoresis was studied in rabbits using drug-loaded hydrogels mounted on a portable iontophoretic device. Drug distribution profile was evaluated 2, 4, and 8 hours after iontophoretic treatment of 1.6 mA/cm2 for 4 min. Ocular drug levels were also determined two hours after iontophoretic treatment of 5 mA/cm2, compared to mock iontophoresis and intravitreal injection of methotrexate. RESULTS: Therapeutic drug levels were maintained for at least 8 h at the sclera and retina and for 2 h at the aqueous humor following the iontophoretic treatment. After increasing the current density, a twice-higher concentration was achieved at the vitreous and 8 to 20 time higher concentrations at the retina and sclera. CONCLUSIONS: A short low current non-invasive iontophoretic treatment using methotrexate-loaded hydrogels has a potential clinical value in treating ocular inflammatory diseases and intraocular lymphoma.     

A rabbit model for assessing the ocular barriers to the transscleral delivery of triamcinolone acetonide

Transscleral delivery of triamcinolone acetonide into the vitreous using sub-Tenon's injections may be a safer alternative to reduce the sight-threatening complications of direct intravitreal injections. However, sub-Tenon's injections have demonstrated low and poorly sustained vitreous drug levels in animal studies. To improve our understanding of the clearance mechanisms of corticosteroids, we evaluated vitreous drug levels following sub-Tenon's injection of triamcinolone acetonide in rabbits with selective elimination of conjunctival lymphatic/blood vessels and the choroid. Pigmented rabbits were given a sub-Tenon's injection of a preservative-free triamcinolone acetonide formulation of either a 10- or 20-mg dose in the superotemporal quadrant. The effect eliminating both conjunctival and choroidal clearance was evaluated by injecting the drug, followed by immediate euthanasia, effectively terminating both lymph and blood flow in the conjunctiva and choroid. To inhibit only the clearance from conjunctival lymphatics/blood vessels of a sub-Tenon's injection of triamcinolone acetonide, a group of rabbits had a 'conjunctival window' created by incising an 7 mmx7 mmx7 mm square through the conjunctiva to bare sclera in the superotemporal quadrant. To eliminate only the clearance of drug from the choroidal circulation, cryotherapy was performed in another group of rabbits creating a chorioretinal scar in the superotemporal quadrant. Following the sub-Tenon's drug injection, the eyes were enucleated in all groups after 3 hr and vitreous drug levels were measured with HPLC. In normal animals, a 10-mg sub-Tenon's injection showed no detectable vitreous drug levels; however, a 20-mg injection showed positive vitreous drug levels. This suggested that collectively, the transscleral clearance mechanisms inhibiting delivery into the vitreous may be saturated with a drug depot that has a higher release rate. A 10-mg sub-Tenon's drug depot was able to deliver drug into the vitreous when both the conjunctival and choroidal drug clearance was eliminated by euthanizing the animal immediately following the drug injection. In rabbits that had only a 'conjunctival window', selectively eliminating conjunctival drug clearance, vitreous drug levels were detected. However, in rabbits that had only cryotherapy, selectively eliminating choroidal drug clearance, vitreous drug levels were not detected suggesting that the conjunctival lymphatics/blood vessels may be an important barrier to the transscleral delivery of triamcinolone acetonide. Variability in the vitreous drug levels between rabbits in each group precluded statistical testing. In summary, the rabbit appeared to demonstrate saturable ocular barriers to transscleral delivery of triamcinolone acetonide into the vitreous following a sub-Tenon's injection. The results suggested that the conjunctival lymphatics/blood vessels may be an important barrier to the delivery of triamcinolone acetonide to the vitreous in this rabbit model. The barrier location and clearance abilities of the ocular tissues are important to consider when developing a successful transscleral drug delivery system. Animal models, retaining the dynamics of blood and lymph flow, may improve the basic understanding of the ocular barriers involved with transscleral drug transport and warrants further investigation.     

Methylprednisolone delivery to the back of the eye using hydrogel iontophoresis.

AIM: The aim of this study was to evaluate methylprednisolone penetration into ocular structures after low-current trans-scleral hydrogel iontophoresis, as compared with the common intravenous (i.v.) treatment. METHODS: Methylprednisolone hemisuccinate (MPH) iontophoresis was studied in rabbits, using drug-loaded hydrogels mounted on a portable iontophoretic device. Cathodal iontophoresis of 2.6 mA/cm(2) was applied for 5 min at two opposite sites on the sclera or for 10 min at the same site. Ocular drug levels were determined 2 h after iontophoretic treatment, then compared to mock iontophoresis and i.v. infusion of 10 mg/kg methylprednisolone. RESULTS: Significantly higher methylprednisolone levels were found in ocular tissues after iontophoresis, compared with the control groups, except for the sclera concentrations, which were similar to the concentrations achieved after mock iontophoresis. Two (2) h after the trans-scleral iontophoretic treatment, 178.59 +/- 21.63 microg/g, 6.74 +/- 2.38 microg/ml, and 2.71 +/- 0.57 microg/mL were found in the retina, aqueous humor, and vitreous, respectively. No significant differences were found between one or two site treatments of trans-scleral iontophoresis. Nondetectable concentrations were found 2 h after the i.v. infusion of 10 mg/kg of methylprednisolone in all evaluated ocular tissues and fluids. CONCLUSIONS: A short, low-current noninvasive iontophoretic treatment, using methylprednisolone-loaded hydrogels, has potential clinical value in treating ocular inflammatory diseases.     

Electrically assisted delivery of macromolecules into the corneal epithelium

Electrically assisted delivery is noninvasive and has been investigated in a number of ocular drug delivery studies. The objectives of this study were to examine the feasibility of electrically assisted delivery of macromolecules such as small interfering RNA (siRNA) into the corneal epithelium, to optimize the iontophoresis and electroporation methods, and to study the mechanisms of corneal iontophoresis for macromolecules. Anodal and cathodal iontophoresis, electroporation and their combinations were the methods examined with mice in vivo. Cyanine 3 (Cy3)-labeled glyceraldehyde-3-phosphate dehydrogenase (GAPDH) siRNA and fluorescein isothiocyanate (FITC)-labeled dextran of different molecular weights (4–70 kDa) were the macromolecules studied. Microscopy and histology after cryostat sectioning were used to analyze and compare the delivery of the macromolecules to the cornea. Iontophoresis was effective in delivering siRNA and dextran up to 70 kDa into the cornea. The electroporation method studied was less effective than that of iontophoresis. Although both iontophoresis and electroporation alone can deliver the macromolecules into the cornea, these methods alone were not as effective as the combination of iontophoresis and electroporation (iontophoresis followed by electroporation). The significant enhancement of dextran delivery in anodal iontophoresis suggests that electroosmosis can be a significant flux-enhancing mechanism during corneal iontophoresis. These results illustrate the feasibility of electrically assisted delivery of macromolecules such as siRNA into the cornea.     

Pharmacokinetics of systemic versus focal Carboplatin chemotherapy in the rabbit eye: possible implication in the treatment of retinoblastoma

PURPOSE: To characterize the pharmacology and toxicity of intravenous versus focal carboplatin delivery in the rabbit eye. METHODS: Pharmacological distribution of carboplatin was examined in New Zealand White Rabbits after a single intravenous infusion of carboplatin (18.7 mg/kg of body weight), a single subconjunctival carboplatin injection (5.0 mg/400 microL), or a single application of carboplatin delivered by Coulomb-controlled iontophoresis (CCI; 14 mg/mL carboplatin, 5.0 mA/cm(2), 20 minutes). After each treatment, animals were euthanatized, and the eyes analyzed at 1, 2, 6, or 24 hours by atomic absorption spectroscopy to determine carboplatin concentration in ocular structures. Potential toxicity of focally delivered carboplatin was assessed by histology after six cycles of 5.0 mg carboplatin delivered by subconjunctival injection or six transscleral carboplatin CCI applications at 72-hour intervals (14.0 mg/mL, 20 minutes at 2.5 mA). RESULTS: Determination of concentrations through atomic absorption spectroscopy in the retina, choroid, vitreous humor, and optic nerve after subconjunctival injection or iontophoretic carboplatin delivery revealed significantly higher levels than those achieved with intravenous administration. Carboplatin concentrations in the blood plasma were found to be significantly higher after intravenous delivery than after focal delivery by subconjunctival injection or CCI. No evidence of ocular toxicity was detected after focally delivered Carboplatin. CONCLUSIONS: Focal administration of carboplatin using subconjunctival or noninvasive CCI safely and effectively transmits this chemotherapeutic drug into the target tissues of the retina, choroid, vitreous, and optic nerve. These results suggest that focal carboplatin delivery may effectively increase intraorbital carboplatin concentrations while decreasing systemic exposure to this cytotoxic drug.     

Regional ocular gentamicin levels after transcorneal and transscleral iontophoresis

Transcorneal and transscleral iontophoresis were compared to subconjunctival injection (control) in the delivery of gentamicin into rabbit eyes. Gentamicin levels in the corena, aqueous, and vitreous were measured by a fluorescence polarization assay at various time intervals after treatment. A mean peak corneal concentration of 376.1 micrograms/ml was achieved 2 hr after transcorneal iontophoresis. This was significantly higher than the level obtained in control eyes (P = 0.016). A mean peak aqueous humor concentration of 54.8 micrograms/ml occurred 2 hr after transcorneal iontophoresis. This was significantly higher than the peak level of 14.2 micrograms/ml after subconjunctival injection (P = 0.003). Inhibitory levels (approximately 5 micrograms/ml) were maintained in both aqueous and cornea for 8 hr after transcorneal iontophoresis. After transscleral iontophoresis, the mean peak vitreous humor concentration was 53.4 micrograms/ml at 16 hr and remained inhibitory through 24 hr; the peak aqueous level was 23.2 micrograms/ml and remained inhibitory for 24 hr. Peak drug concentrations in the vitreous were significantly higher than control (P = 0.026). Therapeutic vitreous humor levels were not achievable after transcorneal iontophoresis or subconjunctival injection. Potential corneal toxicity of transcorneal iontophoresis was demonstrated by measuring corneal thickness and endothelial cell counts prior to and 3 days after transcorneal iontophoresis of gentamicin and balanced saline solution (BSS) (control). No significant differences existed between eyes treated with gentamicin compared to those treated with BSS or when pre- versus postiontophoresis of gentamicin in the same eyes were compared. Transcorneal and transscleral iontophoresis may be an effective noninvasive method of delivering inhibitory levels of gentamicin to the cornea, aqueous humor, and vitreous for the treatment of intraocular infections.     

Transport barriers in transscleral drug delivery for retinal diseases

Transscleral delivery has emerged as an attractive method for treating retinal disorders because it offers localized delivery of drugs as a less invasive method compared to intravitreal administration. Numerous novel transscleral drug delivery systems ranging from microparticles to implants have been reported. However, transscleral delivery is currently not as clinically effective as intravitreal delivery in the treatment of retinal diseases. Transscleral drug delivery systems require drugs to permeate through several layers of ocular tissue (sclera, Bruch's membrane-choroid, retinal pigment epithelium) to reach the neuroretina. As a result, a steep drug concentration gradient from the sclera to the retina is established, and very low concentrations of drug are detected in the retina. This steep gradient is created by the barriers to transport that hinder drug molecules from successfully reaching the retina. A review of the literature reveals 3 types of barriers hindering transscleral drug delivery: static, dynamic and metabolic. While static barriers have been examined in detail, the literature on dynamic and metabolic barriers is lacking. These barriers must be investigated further to gain a more complete understanding of the transport barriers involved in transscleral drug delivery.     

Ocular pharmacokinetic study of a corticosteroid by F MR

Traditional ocular pharmacokinetic studies are invasive and cannot be easily applied to humans in vivo. To acquire in vivo ocular pharmacokinetic data noninvasively, ¹⁹F MR on a 3T clinical scanner was used to follow the real time dynamics of a corticosteroid in the eye. ¹H MR was also performed to locate the site of administration. Triamcinolone acetonide phosphate (TAP) was the model drug, administered by intravitreal and subconjunctival injections. TAP pharmacokinetics were monitored by changes in the ¹⁹F spectrum of the intraocular drug in real time. The elimination half-lives of TAP in the eye after intravitreal and subconjunctival injections were 8 and 0.5 h in vivo and 17 and 6.0 h postmortem, respectively. The half-lives associated with clearance were 14 h for intravitreal injection and 0.5 h for subconjunctival injection.     

Electrically assisted delivery of macromolecules into the corneal epithelium

Electrically assisted delivery is noninvasive and has been investigated in a number of ocular drug delivery studies. The objectives of this study were to examine the feasibility of electrically assisted delivery of macromolecules such as small interfering RNA (siRNA) into the corneal epithelium, to optimize the iontophoresis and electroporation methods, and to study the mechanisms of corneal iontophoresis for macromolecules. Anodal and cathodal iontophoresis, electroporation and their combinations were the methods examined with mice in vivo. Cyanine 3 (Cy3)-labeled glyceraldehyde-3-phosphate dehydrogenase (GAPDH) siRNA and fluorescein isothiocyanate (FITC)-labeled dextran of different molecular weights (4–70 kDa) were the macromolecules studied. Microscopy and histology after cryostat sectioning were used to analyze and compare the delivery of the macromolecules to the cornea. Iontophoresis was effective in delivering siRNA and dextran up to 70 kDa into the cornea. The electroporation method studied was less effective than that of iontophoresis. Although both iontophoresis and electroporation alone can deliver the macromolecules into the cornea, these methods alone were not as effective as the combination of iontophoresis and electroporation (iontophoresis followed by electroporation). The significant enhancement of dextran delivery in anodal iontophoresis suggests that electroosmosis can be a significant flux-enhancing mechanism during corneal iontophoresis. These results illustrate the feasibility of electrically assisted delivery of macromolecules such as siRNA into the cornea.     

Transscleral and transcorneal iontophoresis of ketoconazole in the rabbit eye

The authors assessed the efficacy of transscleral and transcorneal iontophoresis of ketoconazole as a method of drug delivery to the aqueous humor, vitreous, and cornea of the rabbit eye. Transscleral iontophoresis (4-6 mAmps for 15 minutes) achieved peak ketoconazole concentrations in the aqueous 1 hour after treatment (10.2 micrograms/ml) and remained at fungicidal therapeutic concentrations for 8 hours; in the vitreous, a peak concentration of 0.1 microgram/ml occurred between 1 and 2 hours posttreatment. Transcorneal iontophoresis (1.5 mAmps for 15 minutes) achieved peak corneal concentration of 27.6 micrograms/ml and peak aqueous concentrations of 1.4 micrograms/ml, both 1 hour after iontophoresis. Fungicidal therapeutic drug concentrations were sustained for 2 hours both in the cornea and in the aqueous. These concentrations were compared with those obtained after subconjunctival injection (peak values): 0.8 microgram/ml in aqueous, 5.9 micrograms/ml in cornea, and 0.7 microgram/ml in vitreous, all within 1 hour of injection. Aqueous and corneal concentrations were significantly higher after transscleral and transcorneal iontophoresis than subconjunctival injection (P less than 0.05). Iontophoresis is proposed as an effective means of delivering high concentrations of ketoconazole to the anterior segment of the eye.     

Downregulation of endotoxin-induced uveitis by intravitreal injection of vasoactive intestinal Peptide encapsulated in liposomes

PURPOSE: To reestablish the immunosuppressive microenvironment of the eye, disrupted by ocular inflammation during endotoxin-induced uveitis (EIU), by means of intravitreal injection of vasoactive intestinal peptide (VIP) in saline or encapsulated in liposomes, to increase its bioavailability and efficiency. METHODS: EIU was induced in Lewis rats by subcutaneous injection of lipopolysaccharide (LPS). Simultaneously, animals were intravitreally injected with saline, saline/VIP, VIP-loaded liposomes (VIP-Lip), or unloaded liposomes. EIU severity and cellular infiltration were assessed by clinical examination and specific immunostaining. VIP concentration was determined in ocular fluids by ELISA. Ocular expression of inflammatory cytokine and chemokine mRNAs was detected by semiquantitative RT-PCR. Biodistribution of rhodamine-conjugated liposomes (Rh-Lip) was analyzed by immunohistochemistry in eyes and regional cervical lymph nodes (LNs). RESULTS: Twenty-four hours after intravitreal injection of VIP-Lip, VIP concentration in ocular fluids was 15 times higher than after saline/VIP injection. At that time, EIU clinical severity, ocular infiltrating polymorphonuclear leukocytes (PMNs), and, to a lesser extent, ED1(+) macrophages, as well as inflammatory cytokine and chemokine mRNA expression, were significantly reduced in VIP-Lip-injected rats compared with rats injected with saline/VIP, unloaded liposomes, or saline. Rh-Lip was distributed in vitreous, ciliary body, conjunctiva, retina, and sclera. It was internalized by macrophages and PMNs, and VIP colocalized with liposomes at least up to 14 days after injection. In cervical LNs, resident macrophages internalized VIP-Rh-Lip, and some adjacent lymphocytes showed VIP expression. CONCLUSIONS: VIP was efficient at reducing EIU only when formulated in liposomes, which enhanced its immunosuppressive effect and controlled its delivery to all tissues affected by or involved in ocular inflammation.     

Determination and pharmacokinetic profile of liposomal foscarnet in rabbit ocular tissues after intravitreal administration

The treatment of ocular diseases affecting the posterior segment of the eye, such as cytomegalovirus (CMV) retinitis, requires the access of the drugs to the vitreous humor. Foscarnet inhibits replication of herpesviruses, including CMV. The drug's encapsulation in liposomes is meant not only to increase activity and to prolong the effect of the drug, but also to reduce its toxicity. The aims of the present study were to evaluate foscarnet levels and its pharmacokinetic parameters in vitreous humor and retinal tissue of rabbits after the administration of an intravitreal injection of both liposomal foscarnet and foscarnet commercial solution. Liposomes were prepared by the reverse-phase evaporation method. The amount of encapsulated foscarnet (F) was 63% wt. The in vitro diffusion assays showed that F was released more slowly when formulated in liposomes than in the commercial solution. The in vivo studies showed that, as opposed to commercial solution F, liposomal F achieves stable and durable therapeutic levels in retina, going beyond 72 h, reaching the vitreous humor with adequate levels to accomplish the aims of intravitreal therapy. Lyophilization also increased stability and dispersion of liposomes in aqueous medium, although not improving the pharmacokinetic results over those from non-lyophilized liposomes.     

两种不同注射方法眼局部注射鼠神经生长因子后兔眼内药物分布

目的 观察兔玻璃体腔注射与球周注射~(125)I-神经生长因子(NGF)后眼部各组织药物含量分布.方法 45只家兔分别于左眼玻璃体腔(A组)和右眼球周(B组)注射~(125)I-NGF 30 μg/100μl.于注药后15、30 min,1、3、6、8、12、24、48 h取眼房水、玻璃体等眼内容物,角膜、巩膜等眼球外壁组织,虹膜睫状体、视网膜、脉络膜等眼球内壁组织进行γ-计数,计算~(125)I-NGF的含量.结果 A组药物在眼内容物及眼球内壁各组织弥散较快,玻璃体内含量呈梯度下降,其它眼内组织含量呈正态曲线变化;房水、虹膜睫状体、视网膜、脉络膜达峰值时间均为给药后3 h,巩膜、角膜分别为6、8 h;B组眼内各组织药物含量呈正态曲线变化,药物达眼内峰值时间较慢,除房水在给药后3 h达峰值,其他组织均在6 h达峰值;A组各组织~(125)I-NGF峰值含量也明显高于B组;A组除玻璃体直接注射导致高药物含量外,视网膜药物含量最高.结论 玻璃体腔注射~(125)I-NGF较球周注射更能在眼内各组织达到高药物含量.     

Effect of benzalkonium chloride on transscleral drug delivery

PURPOSE: To investigate the effect and safety of benzalkonium chloride on transscleral drug delivery in the rabbit after continuous intrascleral administration. METHODS: Betamethasone 21-phosphate (BP) aqueous solutions, with or without benzalkonium chloride (BAK), were continuously administered to albino rabbit sclera with an osmotic pump for 1 week. The BP concentrations in the aqueous humor, vitreous, and retina-choroid were measured by high-performance liquid chromatography (HPLC). To investigate the effect of BAK on scleral permeability of BP in vitro, penetration of BP aqueous solution with or without BAK across the rabbit sclera was evaluated using a two-chamber Ussing apparatus. To determine the effects of BAK on transscleral delivery of large molecules, 20- and 70-kDa fluorescein isothiocyanate (FITC)-dextran (FD-20 and -70, respectively) aqueous solutions, with or without BAK, were continuously administered to the sclera by an osmotic pump. The intensity of fluorescence in the aqueous humor, vitreous, and retina-choroid was measured by fluorescence spectrophotometry at 1 week after implantation of the pump. The retinal toxicity of BAK was evaluated electrophysiologically and histologically. RESULTS: BAK increased concentrations of BP in the vitreous and retina-choroid compared with the control. BP was not detected in the aqueous humor. In the in vitro study, BAK did not increase the scleral permeability of BP. In the retina-choroid, BAK significantly increased concentrations of FD-20 but did not increase those of FD-70. The addition of BAK did not increase concentrations of FD-20 or -70 in the vitreous. No substantial toxic reactions were observed in the retina in electrophysiological or histologic examinations after the addition of BAK. CONCLUSIONS: The results of this study demonstrate that BAK may improve the ocular penetration of a drug in a transscleral drug delivery system without producing toxic reactions.     

An improved apparatus for transscleral iontophoresis of gentamicin.

The authors previously found that positively charged substances are less well-transported into the vitreous humor by transscleral iontophoresis than are negatively charged substances. There was more bubble formation in the eye cup with positively charged than with negatively charged substances. The authors hypothesized that these bubbles might account for the poorer conductance of the positively charged species by causing interruptions of the current. Therefore, the authors developed a modified eye cup in which the diameter of the fluid column was larger than that in the old device (1.0 rather than 0.5 mm). This modification allowed larger voltage to be applied than with the older device, because bubbles could be more easily cleared from the conjunctiva than with the narrower-bore eye cup. Although the efficiency of the apparatus was the same with the two eye cups (micrograms per milliliter in vitreous humor divided by milliampere minutes of current applied), vitreal concentrations of gentamicin with the modified eye cup were fourfold higher than with the older eye cup (83 versus 19 micrograms/ml; P < 0.001). These studies suggest that modifying the eye cup to permit easier removal of bubbles resulted in improved delivery of gentamicin into the ocular humors.     

Scleral indentation following cryotherapy and repeat cryotherapy enhance release of viable retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells are an important component of intravitreal and epiretinal membranes in proliferative vitreoretinopathy (PVR) that contract and cause recurrent retinal detachment. Cryotherapy has been shown to enhance release of viable RPE cells into the vitreous cavity. This study demonstrates that repeat cryotherapy (refreezing) releases viable RPE cells in even larger numbers. Repeated indentation of the sclera after transscleral cryotherapy also releases more viable RPE cells than does cryotherapy alone or scleral indentation preceding cryotherapy. These findings suggest that refreezing should be avoided, and repeated indentation of the sclera should be minimized after cryotherapy.     

生物可降解载药微球经巩膜向眼内给药的研究

由于眼部复杂的生理结构和诸多屏障,使得全身给药后药物到达眼后段的量有限,疗效甚微。眼局部药物使用方便,但药物难以传递到视网膜。玻璃体内给药侵袭性大,危险性高。经巩膜给药有诸多优势,如巩膜表面积大,且位置表浅、操作简单,也不引起眼内屏障的损害。但要求药物在巩膜表面有适当的浓度,这个浓度过高会导致大量药物进入全身系统,引起全身不良反应;如果药物在巩膜表面浓度太低,通过巩膜进入脉络膜和视网膜所需的药物浓度梯度就难以建立。所以绝大部分 药物溶液不适合经巩膜给药。为了满足巩膜表面合适药物浓度的要求,科研工作者尝试研发并使用生物材料药物微球或巩膜表面给药装置进行经巩膜给药。相比于巩膜表面给药装置,微球不需要手术植入,简单注射即可,使用较为方便。     

Transscleral delivery of bioactive protein to the choroid and retina

PURPOSE: To investigate the feasibility of transscleral drug delivery to the choroid and retina. METHODS: An osmotic pump was used to deliver IgG across the sclera of pigmented rabbits, and levels were measured in the choroid, retina, vitreous humor, aqueous humor, orbit, and plasma over 28 days. This method was then used to deliver an anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibody (mAb), and its effect on inhibiting vascular endothelial growth factor (VEGF)-induced leukostasis in the choroid and retina was determined by measuring tissue myeloperoxidase (MPO) activity. RESULTS: Levels of retinal and choroidal IgG were significantly higher than baseline at all points up to 28 days (P < or = 0.01). IgG levels in the orbit, vitreous humor, aqueous humor, and plasma were negligible (P > 0.05). MPO activity in the choroid of eyes treated with anti-ICAM-1 mAb was 80% less (P = 0.01) than in eyes receiving an equal rate of delivery of an isotype control antibody. Inhibition of MPO activity in the retina was 70% (P = 0.01). The plasma concentration of anti-ICAM-1 mAb was 31,000-fold less than the concentration in the osmotic pump. CONCLUSIONS: Minimally invasive transscleral delivery can be used to deliver therapeutic levels of bioactive drugs to the choroid and retina with negligible systemic absorption. This method of ocular drug delivery may be used in the treatment of a variety of chorioretinal disorders.     

Clearance of intravitreal voriconazole

Purpose To investigate the elimination rate of voriconazole after intravitreal injection in rabbits. METHODS: Intravitreal injections of 35 microg/0.1 mL voriconazole were administered to rabbits. Vitreous and aqueous humor levels of voriconazole were determined at selected time intervals (1, 2, 4, 8, 16, 24, and 48 hours), and the in vitreous half-life was calculated. Four to six eyes per time point after injection were enucleated and immediately stored at -80 degrees C. Aqueous humor samples were withdrawn before enucleation, and vitreous samples were obtained from ocular dissection and isolation at various time intervals. Voriconazole concentrations in vitreous and aqueous humor were assayed with high-performance liquid chromatography (HPLC). RESULTS: The concentration of intravitreal voriconazole at various time points exhibited exponential decay with a half-life of 2.5 hours. The mean vitreous concentration was 18.912 +/- 2.058 microg/mL 1 hour after intravitreal injection; this declined to 0.292 +/- 0.090 microg/mL at 16 hours. The mean aqueous concentration was much lower and showed a decline from 0.240 +/- 0.051 microg/mL at 1 hour to undetectable levels 8 hours after injection. CONCLUSIONS: Vitreous concentrations achieved during the first 8 hours were greater than the previously reported minimum inhibitory concentrations (MICs) of organisms most involved in fungal endophthalmitis. A rapid decline of intravitreal concentration suggests that supplementation of intraocular voriconazole to maintain therapeutic levels may therefore be required in clinical settings. Further studies are needed to determine the elimination rate of voriconazole after intravitreal injection in humans.