Intravitreal injection of therapeutic agents

Regulation of the Ocular Cell/Tissue Response by Implantable Biomaterials and Drug Delivery Systems

Therapeutic advancements in the treatment of various ocular diseases is often linked to the development of efficient drug delivery systems (DDSs), which would allow a sustained release while maintaining therapeutic drug levels in the target tissues. In this way, ocular tissue/cell response can be properly modulated and designed in order to produce a therapeutic effect. An ideal ocular DDS should encapsulate and release the appropriate drug concentration to the target tissue (therapeutic but non-toxic level) while preserving drug functionality. Furthermore, a constant release is usually preferred, keeping the initial burst to a minimum. Different materials are used, modified, and combined in order to achieve a sustained drug release in both the anterior and posterior segments of the eye. After giving a picture of the different strategies adopted for ocular drug release, this review article provides an overview of the biomaterials that are used as drug carriers in the eye, including micro- and nanospheres, liposomes, hydrogels, and multi-material implants; the advantages and limitations of these DDSs are discussed in reference to the major ocular applications.

Intravitreal injection of resveratrol inhibits laser-induced murine choroidal neovascularization

AIM

To determine the effects of intravitreal resveratrol (RSV) on murine laser-induced choroidal neovascularization (CNV).

METHODS

The toxicity of RSV to choroidal endothelial cell (CEC) was measured using thiazolyl blue tetrazolium bromide (MTT) assay. Effects of RSV on choroidal endothelial cell (CEC) migration were evaluated with a modified Boyden chamber assay, while tube formation was evaluated in a 2-D gel assay. CNV was induced by laser photocoagulation in mice. The effects of intravitreal injection of RSV on CNV development were evaluated by fluorescein angiography (FA), confocal analysis of isolectin B4 labeled choroidal flat mounts, and histologic examination of CNV membranes. Immunostaining was used to analyze the expression and phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2).

RESULTS

No significant cell toxicity was observed in CEC if the concentration of RSV was less than 200 µmol/L (P>0.05). RSV inhibited vascular endothelial growth factor (VEGF)-induced CEC migration (P<0.05) and tube formation (P<0.05) in vitro. Furthermore, intravitreal injection of RSV significantly inhibited laser induced CNV formation in mice. The FA leakage, CNV volume and CNV area analysis revealed that there were 41%, 45%, and 58% reduction in RSV-treated eyes (1.691±0.1032, 178 163±78 623 µm³ and 6508±619.0 µm², respectively) compared with those in control (2.724±0.08447, 379 676±98 382 µm³ and 16 576±2646 µm², respectively; P<0.05). Phospho-VEGFR2 expression was much weaker in the sections of CNV lesions in RSV injected mice compared with that in control (P<0.05).

CONCLUSION

Intravitreal injection of RSV exerts an inhibitory effect on CNV, which may through suppressing endothelial cell migration, tube formation and VEGFR2 phosphorylation.

Focused ultrasound as a novel strategy for noninvasive gene delivery to retinal Müller glia

Müller glia are specialized retinal cells with stem cell properties in fish and frogs but not in mammals. Current efforts to develop gene therapies to activate mammalian Müller glia for retinal repair will require safe and effective delivery strategies for recombinant adeno-associated viruses (AAVs), vectors of choice for clinical translation. Intravitreal and subretinal injections are currently used for AAV gene delivery in the eye, but less invasive methods efficiently targeting Müller glia have yet to be developed. Methods: As gene delivery strategies have been more extensively studied in the brain, to validate our vectors, we initially compared the glial tropism of AAV-PHP.eB, an AAV9 that crosses the blood-brain and blood-retinal barriers, for its ability to drive fluorescent protein expression in glial cells in both the brain and retina. We then tested the glial transduction of AAV2/8-GFAP-mCherry, a virus that does not cross blood-brain and blood-retinal barriers, for its effectiveness in transducing Müller glia in murine retinal explants ex vivo. For in vivo assays we used larger rat eyes, performing invasive intravitreal injections, and non-invasive intravenous delivery using focused ultrasound (FUS) (pressure amplitude: 0.360 - 0.84 MPa) and microbubbles (Definity, 0.2 ml/kg). Results: We showed that AAV-PHP.eB carrying a ubiquitous promoter (CAG) and green fluorescent protein (GFP) reporter, readily crossed the blood-brain and blood-retinal barriers after intravenous delivery in mice. However, murine Müller glia did not express GFP, suggesting that they were not transduced by AAV-PHP.eB. We thus tested an AAV2/8 variant, which was selected based on its safety record in multiple clinical trials, adding a glial fibrillary acidic protein (GFAP) promoter and mCherry (red fluorescent protein) reporter. We confirmed the glial specificity of AAV2/8-GFAP-mCherry, showing effective expression of mCherry in astrocytes after intracranial injection in the mouse brain, and of Müller glia in murine retinal explants. For in vivo experiments we switched to rats because of their larger size, injecting AAV2/8-GFAP-mCherry intravitreally, an invasive procedure, demonstrating passage across the inner limiting membrane, leading to Müller glia transduction. We then tested an alternative non-invasive delivery approach targeting a different barrier - the inner blood-retinal-barrier, applying focused ultrasound (FUS) to the retina after intravenous injection of AAV2/8 and microbubbles in rats, using magnetic resonance imaging (MRI) for FUS targeting. FUS permeabilized the rat blood-retinal-barrier and allowed the passage of macromolecules to the retina (Evans blue, IgG, IgM), with minimal extravasation of platelets and red blood cells. Intravenous injection of microbubbles and AAV2/8-GFAP-mCherry followed by FUS resulted in mCherry expression in rat Müller glia. However, systemic delivery of AAV2/8 also had off-target effects, transducing several murine peripheral organs, particularly the liver. Conclusions: Retinal permeabilisation via FUS in the presence of microbubbles is effective for delivering AAV2/8 across the inner blood-retinal-barrier, targeting Müller glia, which is less invasive than intravitreal injections that bypass the inner limiting membrane. However, implementing FUS in the clinic will require a comprehensive consideration of any off-target tropism of the AAV in peripheral organs, combined ideally, with the development of Müller glia-specific promoters.

Intravitreal Injections with Vascular Endothelial Growth Factor Inhibitors: A Practical Approach

Intravitreal injections with vascular endothelial growth factor inhibitors constitute the most prevalent ophthalmic procedure in developed countries. Historically, there has been steady growth in the number of treatments performed of this kind, and projection studies estimate further growth in such treatments in the future. We provide a practical approach to intravitreal injections and discuss important aspects relating to the setting, the patient, the procedure, and the information given to the patient.

Validation of hyaluronic acid-agar-based hydrogels as vitreous humor mimetics for in vitro drug and particle migration evaluations

Artificial vitreous humor holds immense potential for use in in vitro intravitreal drug delivery assays. In this study, we investigated rheological properties and drug or nanoparticle migration in hyaluronic acid (HA) - agar based hydrogels and compared these characteristics with bovine vitreous humor. Gel compositions identified in literature containing HA (0.7-5.0 mg/ml) and agar (0.95-4.0 mg/ml) were classified as either high (VH), medium (VM) or low (VL) polymer load. Viscoelastic behavior was evaluated using oscillatory rheology, and migration of differently sized and charged polystyrene nanoparticles (NPs) through the different gels was determined via multiple particle tracking. Comparable rheological behaviour was observed between VL and bovine vitreous. Tracking evaluations revealed that increasing particle size and gel viscosity slowed NP migration. Additionally, 100 nm anionic NPs migrated slower than neutral NPs in VL and VM, while cationic NPs were immobile in all gels. Finally, distribution and clearance of sodium fluorescein was used to model drug mobility through the gels using a custom-built eye model. Flow and angular movement only influenced drug migration in VL and VM, but not VH. Finally, VL and VM demonstrated to have the most similar sodium fluorescein clearance to that of bovine vitreous humor. Together, these evaluations demonstrate that low viscosity HA-agar gels can be used to approximate nanoparticle and drug migration through biological vitreous humor.

[Protocol of intravitreal drug delivery. Consensus of the Expert Counsil of Retina and Optic Nerve Diseases of the All-Russian Public Organasation «Association of Ophthalmologists»]

Intravitreal drug administration is a procedure that has become widespread in modern ophthalmology. However, there is no global consensus on certain aspects of this manipulation, and practitioners feel the need for guidelines. In the Russian Federation, until now, such a document was not available. The expert council on diseases of the retina and optic nerve of All-Russian public organization «Association of Ophthalmologists», with participation of invited specialists, has studied and analyzed the existing foreign guidelines for performing intravitreal injections, as well as the regulatory framework in Russia. As a result, this Protocol was developed and approved for use in the healthcare system of the Russian Federation. The document regulates the requirements for specialists and organizations, the conditions for performing the procedure and the necessary material resources and presents an algorithm for performing intravitreal drug administration, a patient examination check-list for various conditions of the procedure, as well as parameters for evaluating and monitoring the quality of the procedure.

Rapid pathogen identification and antimicrobial susceptibility testing in in vitro endophthalmitis with matrix assisted laser desorption-ionization Time-of-Flight Mass Spectrometry and VITEK 2 without prior culture

PURPOSE

Prompt clinical diagnosis and initiation of treatment are critical in the management of infectious endophthalmitis. Current methods used to identify causative agents of infectious endophthalmitis are mostly inefficient, owing to suboptimal sensitivity, length, and cost. Matrix Assisted Laser Desorption-Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) can be used to rapidly identity pathogens without a need for culture. Similarly, automated antimicrobial susceptibility test systems (AST, VITEK 2) provide accurate antimicrobial susceptibility profiles. In this proof-of-concept study, we apply these technologies for the direct identification and characterization of pathogens in vitreous samples, without culture, as an in vitro model of infectious endophthalmitis.

METHODS

Vitreous humor aspirated from freshly enucleated porcine eyes was inoculated with different inocula of Staphylococcus aureus (S. aureus) and incubated at 37°C. Vitreous endophthalmitis samples were centrifuged and pellets were directly analyzed with MALDI-TOF MS and VITEK 2 without prior culture. S. aureus colonies that were conventionally grown on culture medium were used as control samples. Time-to-identification, minimum concentration of bacteria required for identification, and accuracy of results compared to standard methods were determined.

RESULTS

MALDI-TOF MS achieved accurate pathogen identification from direct analysis of intraocular samples with confidence values of up to 99.9%. Time from sample processing to pathogen identification was <30 minutes. The minimum number of bacteria needed for positive identification was 7.889x106 colony forming units (cfu/μl). Direct analysis of intraocular samples with VITEK 2 gave AST profiles that were up to 94.4% identical to the positive control S. aureus analyzed per standard protocol.

CONCLUSION

Our findings demonstrate that the direct analysis of vitreous samples with MALDI-TOF MS and VITEK 2 without prior culture could serve as new, improved methods for rapid, accurate pathogen identification and targeted treatment design in infectious endophthalmitis. In vivo models and standardized comparisons against other microbiological methods are needed to determine the value of direct analysis of intraocular samples from infectious endophthalmitis with MALDI-TOF MS and VITEK 2.

Assessment of Patient Pain Experience During Intravitreal Ranibizumab and Aflibercept Injection

PURPOSE:

The aim of this study was to compare the pain scores of the patients during intravitreal injection of ranibizumab and aflibercept based on patient feedback.

MATERIALS AND METHODS:

Seventy-two eyes of 72 patients, who had not previously undergone any intravitreal injection procedures, were included in this study. Thirty-eight patients received ranibizumab, and 34 patients received aflibercept injections. The pain was measured by visual analog scale (VAS). Patients were asked to rate their pain experienced during the injection between 0 (no pain) and 10 (worst pain ever felt) on VAS just after the injection.

RESULTS:

VAS pain scores in ranibizumab and aflibercept groups were 3.28 ± 2.45 and 4.20 ± 2.30, respectively. There was a significant difference in average VAS pain scores between groups (P = 0.04).

CONCLUSION:

VAS pain scores in aflibercept group were found to be significantly higher than the scores in the ranibizumab group.

Ocular Drug Delivery: Present Innovations and Future Challenges

Ocular drug delivery has always been a challenge for ophthalmologists and drug-delivery scientists due to the presence of various anatomic and physiologic barriers. Inimitable static and dynamic ocular barriers not only exclude the entry of xenobiotics but also discourage the active absorption of therapeutic agents. Designing an ideal delivery scheme should include enhanced drug bioavailability and controlled release of drug at the site of action, which can overcome various ocular barriers. Conventional ophthalmic medications include the use of topical eye drops and intravitreal injections of anti-vascular endothelial growth factor agent for treatment of anterior and posterior segment disorders, respectively. Current inventions for anterior ocular segment disorders such as punctum plugs, ocular implants, drug-eluting contact lenses, and ocular iontophoresis represent state-of-the-art inventions for sustained and controlled drug release. Parallel efforts for ocular drug delivery technologies for back of the eye disorders have resulted in the approval of various intravitreal implants. Novel drug-delivery technologies, including nanoparticles, nanomicelles, dendrimers, microneedles, liposomes, and nanowafers, are increasingly studied for anterior and posterior disorders. To achieve patient compliance for back of the eye disorders, novel approaches for noninvasive delivery of potent therapeutic agents are on the rise. In this review article, we discuss past successes, present inventions, and future challenges in ocular drug-delivery technologies. This expert opinion also discusses the future challenges for ocular drug-delivery systems and the clinical translatable potential of nanotechnology from benchtop to bedside.

REDUCTION OF POSTINTRAVITREAL INJECTION PAIN USING ICE: An Open-Label Interventional Randomized Controlled Trial

PURPOSE

Intravitreal injections of intraocular therapeutic agents are a common and effective treatment for various retinal pathologies. Patient discomfort related to injection is a potential barrier to treatment. Our aim in this study was to evaluate whether cooling the eye using topical ice compresses before intravitreal injection will reduce pain or bleeding.

METHODS

This randomized controlled open-label study included 42 patients. All patients received a standard topical anesthesia protocol and then were randomly assigned to either receive a placement of ice packs (intervention group) or a room-temperature pack (control group) on the eyelid, 2 minutes before the intravitreal injection. Patients' discomfort, itching, burning and pain (using visual analog scale), and bleeding size (using photographs) were measured 1 and 10 minutes after the injection. Tolerability was calculated by averaging patients' discomfort, itching, burning, and pain scores.

RESULTS

At 1 minute, pain (1.95 vs. 4.27, P = 0.01) and overall tolerability (1.66 vs. 2.98, P = 0.03) were significantly lower in patients receiving ice packs. At 10 minutes, pain (1.6 vs. 3.73, P = 0.02), burning (0.9 vs. 3.09, P = 0.007), discomfort (2.1 vs. 4.27, P = 0.008), and overall tolerability (1.23 vs. 2.87, P = 0.004) were all significantly lower in the ice group compared with the controls. Bleeding size (area or circumference) was not statistical different between groups.

CONCLUSION

Topical ice patch administered before intravitreal injection significantly decreased pain and overall tolerability. This simple and inexpensive method may be used to ameliorated pain and improve tolerability.

In vitro and in vivo evaluation of benzathine foscarnet microcrystals as a potential intravitreal drug depot

Sodium foscarnet is an antiviral drug against cytomegalovirus retinitis, and clinically it is used via frequent intravitreal injection which causes various ocular complications. Here we propose to use benzathine foscarnet in a new salt form with much lower aqueous solubility, and as a potential long-acting intravitreally injectable solid form for foscarnet. Benzathine foscarnet (1 : 1) microcrystals were synthesized and evaluated both in vitro and in vivo. The aqueous solubility of benzathine foscarnet was 14.2 mM, which is in between those of the currently-used sodium foscarnet and our previously-reported calcium foscarnet salt. In a rabbit model, the injected microcrystals last for about 3 weeks in the vitreous, suggesting its solubility and dissolution profile is appropriate for its intended use. However, the injected benzathine foscarnet microcrystals also caused adverse effects in vivo.

Benzathine foscarnet microcrystals as a potential intravitreal drug depot.

An Eye on Staphylococcus aureus Toxins: Roles in Ocular Damage and Inflammation

Staphylococcus aureus (S. aureus) is a common pathogen of the eye, capable of infecting external tissues such as the tear duct, conjunctiva, and the cornea, as well the inner and more delicate anterior and posterior chambers. S. aureus produces numerous toxins and enzymes capable of causing profound damage to tissues and organs, as well as modulating the immune response to these infections. Unfortunately, in the context of ocular infections, this can mean blindness for the patient. The role of α-toxin in corneal infection (keratitis) and infection of the interior of the eye (endophthalmitis) has been well established by comparing virulence in animal models and α-toxin-deficient isogenic mutants with their wild-type parental strains. The importance of other toxins, such as β-toxin, γ-toxin, and Panton-Valentine leukocidin (PVL), have been analyzed to a lesser degree and their roles in eye infections are less clear. Other toxins such as the phenol-soluble modulins have yet to be examined in any animal models for their contributions to virulence in eye infections. This review discusses the state of current knowledge of the roles of S. aureus toxins in eye infections and the controversies existing as a result of the use of different infection models. The strengths and limitations of these ocular infection models are discussed, as well as the need for physiological relevance in the study of staphylococcal toxins in these models.

Intravitreal injections in clinical practice: results of a survey of eye surgeons in the Ural federal district

Introduction. Intravitreal i njections ( IVI) are widespread in modern ophthalmology as a method of drug delivery in various posterior segment pathologies. Despite the accumulated experience, some aspects of the procedure remain debatable. In addition, in the literature there are no data on the practical aspects of IVI performance in real clinical conditions in Russia. This article presents the results of an anonymous survey of 74 ophthalmologists of the Ural Federal District of the Russian Federation, conducted in 2018 using an original questionnaire, which included 20 questions. It was revealed that respondents generally share the traditional for Russia approach to IVI as to major ophthalmic surgery. The survey revealed a lack of common approaches and incomplete adherence to modern guidelines in certain aspects of the procedure, and therefore correcting measures were proposed.

Prefilled syringes for intravitreal drug delivery

Intravitreal injections of anti-vascular endothelial growth factor (VEGF) medications play an increasingly critical role in numerous retinal vascular diseases. Initially, anti-VEGF medications came in vials that had to be drawn up by the physician into a syringe for administration. In 2018, the US Food and Drug Administration (US FDA) approved the ranibizumab 0.3 mg prefilled syringe (PFS), and in October 2016, the US FDA approved the ranibizumab 0.5 mg PFS. This article discusses the advantages of the PFS, including reduced injection time, possible reduced risk of endophthalmitis, reduction in intraocular air bubbles and silicone oil droplets, and improved precision in the volume and dose of intravitreal ranibizumab administered, along with possible disadvantages. Implications of the innovation of the PFS on intravitreal injection technique and clinical practice pattern are discussed and reviewed.

Efficacy and safety of intravitreal drug injections using a short 34-gauge needle

PURPOSE

To evaluate the efficacy and safety of intravitreal drug injections using a short 34-gauge needle.

STUDY DESIGN

Retrospective study.

METHODS

This study included patients with age-related macular degeneration, diabetic macular edema, or macular edema associated with retinal vein occlusion. We reviewed the medical records of consecutive patients with one of those three diseases treated with antivascular endothelial growth factor (VEGF) agents using an 8-mm-long 34-gauge needle. Sustained intraocular pressure (IOP) elevations were defined as IOP exceeding 21 mmHg or 6-mmHg or higher increases from baseline on 2 consecutive visits at least 1 month apart. The main outcome measures were improved best-corrected visual acuity (BCVA), central retinal thickness (CRT), IOP changes, and incidence of complications related to the 34-gauge needle.

RESULTS

Six hundred ninety-eight injections were administered to 243 consecutive patients (mean age, 74.0 years) and reviewed. The mean follow-up time was 30.2 ± 15.9 weeks. The mean number of intravitreal injections/eye was 2.7 ± 1.8 (range, 1-9). The mean BCVA improved significantly (P < .0001), from 0.43 ± 0.4 logarithm of the minimum angle of resolution (logMAR) units at baseline to 0.36 ± 0.41 logMAR units at the last visit. The mean CRT decreased significantly (P < .0001), from 426.9 ± 168.5 microns at baseline to 297.6 ± 121.1 microns at the last visit. The mean IOP decreased significantly (P < .0001), from 13.6 ± 3.0 mmHg at baseline to 12.9 ± 3.1 mmHg at the visit after the first injection. A retinal tear occurred in 0.14%/injection (1/698). A sustained IOP elevation occurred in 1.29%/injection (9/698).

CONCLUSION

Despite a few complications, the short 34-gauge needle was efficacious and safe for anti-VEGF intravitreal injections.

Novel Long-acting Pharmacotherapy for Exudative Age Related Macular Degeneration

Exudative age-related macular degeneration (AMD) is a major indication for the administration of intravitreal injections of anti-VEGF agents, which have been established as a very effective pharmacotherapy for this disease. However, treatment with anti-VEGF agents requires several patient visits for monitoring and treatment. Strategies for achieving a longer duration of pharmacological action are currently being developed. These include the development of longer-acting drugs, and of novel technologies to increase the duration of action of administered agents. This manuscript will review the novel drugs and technologies currently being developed for achieving a longer-action pharmacotherapy for exudative AMD.

Updates on thermosensitive hydrogel for nasal, ocular and cutaneous delivery

Thermosensitive hydrogels are in situ gelling systems composed of hydrophilic homopolymers or block copolymers which remain as solutions at room temperature and form gels after administration into the body. Its application in advanced drug delivery has gained significant attention in recent years. The tunable characteristics of thermosensitive hydrogels make them versatile and capable of incorporating both hydrophilic and lipophilic compounds and macromolecules. The drug molecules can be included as free molecules or preformulated into nano- or micro-particles or liposomes. Although there were several reviews on the materials of thermosensitive hydrogels, the compatibility between the drug and thermosensitive material as well as its in vitro release mechanisms and in vivo performance have barely been investigated. The current review is proposed aiming to not only provide an update on the recent development in thermosensitive hydrogel formulations for nasal, ocular and cutaneous deliveries, but also identify the relationship between the drug characteristics and the loading strategies, and their impacts on the release mechanisms and the in vivo performance. Our current update for the first time highlights the essential features for successful development of in situ thermosensitive hydrogels to facilitate nasal, ocular or cutaneous drug deliveries.

Temporal Distribution Patterns of Alexa Fluor 647-Conjugated CeNPs in the Mouse Retina After a Single Intravitreal Injection

Intravitreal (IVT) injection of ophthalmic therapeutics is the most widely used drug delivery route to the posterior segment of the eye. We employed this method to deliver our inorganic, catalytic antioxidant, cerium oxide nanoparticles (CeNPs), to rodent models of retinal degeneration. A single IVT of CeNPs delays disease progression. Even though we have shown that our synthesized CeNPs are retained in the retina for over a year, we still do not know which cell types in the retina preferentially take up these nanoparticles. In this study, we examined the temporal and spatial distribution of fluorescently labeled CeNPs in retinal sections after IVT. We detected elevated fluorescent signals in all the layers where retinal neurons and glia reside and retinal pigment epithelium (RPE) up to 90 days post injection. Additionally, we found that free fluorochrome accumulated in retinal vasculature instead of retinal cells. These data suggested that CeNP-conjugation mediated the targeting of the fluorochrome to retinal cells. We propose that CeNPs can be deployed as ophthalmic carriers to the retina.

Objective evaluation of lens clarity after the intravitreal injection of sustained-release dexamethasone implant

PURPOSE

To evaluate the lens densitometry values in eyes with macular edema secondary to retinal vein occlusion that were treated with intravitreal dexamethasone implants and to compare these data with those of fellow healthy control eyes.

SETTING

Ulucanlar Eye Training and Research Hospital, Ankara, Turkey.

DESIGN

Prospective case series.

METHODS

Patients with unilateral macular edema secondary to retinal vein occlusion who were to be treated with intravitreal dexamethasone implants were recruited. The lens densitometry values measured with Scheimpflug imaging before and 3 months after the injection were compared with those in fellow healthy eyes.

RESULTS

Thirty-seven patients (22 with branch retinal vein occlusion and 15 with central retinal vein occlusion) with a mean age of 61.5 years ± 11.4 (SD) (range 37 to 82 years) were included. The mean lens densitometry value at Pentacam densitometry zone 1 was significantly increased in the study eyes at 3 months compared with baseline values (baseline 9.44 ± 0.99; 3 months 9.68 ± 1.24; P = .015). At zones 2 and 3, the mean and maximum lens densitometry values in study eyes and lens thickness were similar at baseline and 3 months after injection (P > .05). The densitometry values in fellow healthy eyes were also similar at baseline and at 3 months.

CONCLUSION

The mean lens densitometry value at zone 1 significantly increased from baseline in the study eyes 3 months after the injection of the dexamethasone implant for the treatment of macular edema secondary to retinal vein occlusion.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Which quadrant is less painful for intravitreal injection? A prospective study

PURPOSE

To evaluate the relationship between injection site and pain severity following intravitreal injection of bevacizumab (IVB).

DESIGN

Prospective, randomized, four-armed, clinical trial.

METHODS

The present study was a prospective, randomized, four-armed clinical trial, which included 1004 eyes from 1004 patients. Patients receiving IVB were randomly assigned into four groups: superotemporal (ST); superonasal (SN); inferotemporal (IT); and inferonasal (IN) injections. The visual analog scale (VAS) was used to assess pain. Primary study variables were the relationship between pain severity and injection site, number of previous injections, age, sex, and indication for injection. Secondary variables included best-corrected visual acuity (BCVA) and central macular thickness (CMT) changes 1 month post IVB.

RESULTS

Overall mean pain score was 2.86 ± 2.2. Indications for injection were diabetic macular edema (84.1%), neovascular age-related macular degeneration (7.7%), and macular edema secondary to retinal vein occlusion (8.2%). The mean VAS scores in the SN, IN, ST, and IT groups were 1.5 ± 1.7, 3 ± 2.3, 4 ± 2, and 3 ± 2.1, respectively. Pain severity was significantly correlated with injection site (p < 0.001) and sex (p < 0.001); females showed higher pain scores. A negative correlation existed between pain score and number of previous injections (p = 0.03). Pain severity was not associated with age (p = 0.659), lens status (p = 0.478), vitreous reflux (p = 0.648), or indication for injection (p = 0.390). No significant complications were observed.

CONCLUSIONS

ST quadrant was the most painful and SN quadrant was the least painful sites for IVB. Pain severity score was significantly associated with injection site, number of injections, and sex.

Evolution of Intravitreal Therapy for Retinal Diseases-From CMV to CNV: The LXXIV Edward Jackson Memorial Lecture

PURPOSE

To present the evolution of intravitreal therapy for retinal diseases and its impact on clinical practice.

DESIGN

Retrospective literature review and personal perspective.

METHODS

Retrospective literature review and personal perspective.

RESULTS

Pharmacotherapeutic advances in retinal disease have been remarkable over the last 25 years. Almost all of the new drugs developed have required intravitreal administration to be highly effective, leading to an exponential increase in the annual number of intravitreal injections given. The use of intravitreal antibiotic injections to treat endophthalmitis, usually on a one-time basis, first familiarized ophthalmologists with this method of drug delivery. Ganciclovir was the first widely available, relatively inexpensive compounded drug that was used for repeat intravitreal injection to treat a chronic retinal disease, followed by triamcinolone for diabetic macular edema and bevacizumab for neovascular age-related macular degeneration. Ganciclovir was formulated for sustained-release drug delivery to avoid frequent intravitreal injections, a goal that has been more elusive for anti-VEGF drugs. Political obstacles encountered while conducting some of the trials to evaluate these treatments were substantial. Addressing the issues they raised led to important national policy changes that will impact the conduct of future clinical trials. The first comparative efficacy trial of intravitreal therapies was the Comparison of AMD Treatments Trials (CATT). The primary results from CATT and the many publications that followed continue to shape the use of intravitreal therapy today.

CONCLUSION

Intravitreal therapy has proven highly effective for the treatment of many retinal diseases. The treatment burden for patients from numerous injections, the cost to health care systems, and the impact on workflows in clinical practice have been substantial. Efforts to develop effective intravitreal therapies with reduced treatment burden and cost are ongoing.

Ocular drug delivery targeted by iontophoresis in the suprachoroidal space using a microneedle

Treatment of many posterior-segment ocular indications would benefit from improved targeting of drug delivery to the back of the eye. Here, we propose the use of iontophoresis to direct delivery of negatively charged nanoparticles through the suprachoroidal space (SCS) toward the posterior pole of the eye. Injection of nanoparticles into the SCS of the rabbit eye ex vivo without iontophoresis led to a nanoparticle distribution mostly localized at the site of injection near the limbus and <15% of nanoparticles delivered to the most posterior region of SCS (>9 mm from the limbus). Iontophoresis using a novel microneedle-based device increased posterior targeting with >30% of nanoparticles in the most posterior region of SCS. Posterior targeting increased with increasing iontophoresis current and increasing application time up to 3 min, but further increasing to 5 min was not better, probably due to the observed collapse of the SCS within 5 min after injection ex vivo. Reversing the direction of iontophoretic flow inhibited posterior targeting, with just ~5% of nanoparticles reaching the most posterior region of SCS. In the rabbit eye in vivo, iontophoresis at 0.14 mA for 3 min after injection of a 100 μL suspension of nanoparticles resulted in ~30% of nanoparticles delivered to the most posterior region of the SCS, which was consistent with ex vivo findings. The procedure was well tolerated, with only mild, transient tissue effects at the site of injection. We conclude that iontophoresis in the SCS using a microneedle has promise as a method to target ocular drug delivery within the eye, especially toward the posterior pole.

2018 Update on Intravitreal Injections: Euretina Expert Consensus Recommendations

Intravitreal injections (IVI) have become the most common intraocular procedure worldwide with increasing numbers every year. The article presents the most up-to-date review on IVI epidemiology and techniques. Unfortunately, important issues related to pre-, peri- and postinjection management lack randomized clinical trials for a final conclusion. Also, a great diversity of approaches exists worldwide. Therefore, expert consensus recommendations on IVI techniques are provided.

Nanoparticle-Mediated Delivery of Neuroprotective Substances for the Treatment of Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a major complication of diabetes, characterized by extensive vascular pathology leading to vision loss. Neuronal suffering and death are also present in the diabetic retina as a result of different molecular mechanisms that are compromised or modified in response to high glucose. The aim of this paper is to highlight recent data indicating that neurodegeneration is likely to play a primary role in the development of DR and that strategies based on nanomedicine may be exploited to deliver neuroprotection to the retina.

METHODS

An extensive analysis of the publications dealing with the role of neuroprotection in DR and with nanoparticle-mediated drug delivery to the retina has been conducted using PubMed, with particular attention to the most recent papers.

RESULTS

There are important limitations related to possible systemic side effects of neuroprotective substances and to drug bioavailability in the retina such as, for instance, the amount of drug reaching the retina, the need of keeping to a minimum the number of administrations (especially, for example, in the case of intraocular injections) and the need of assuring a long-lasting, graded intraocular drug delivery. In recent years, a variety of investigations have been aimed at the exploitation of approaches of nanomedicine to enhance the pharmacokinetics and pharmacodynamic activity of intraocularly delivered drugs. In particular, we provide some preliminary results that we have obtained about the feasibility of delivering magnetic nanoparticles functionalized with a neuroprotectant to mouse eyes through intraocular injections.

CONCLUSION

We propose that nanoparticles functionalized with neuroprotective substances may be used to protect the diabetic retina, thus causing an impact in the design of future pharmacologic treatments for DR.

Nanotechnology for Omics-Based Ocular Drug Delivery

Millions of people suffer from ocular diseases that impair vision and can lead to blindness. Advances in genomics and proteomics have revealed a number of different molecular markers specific for different ocular diseases, thereby optimizing the processes of drug development and discovery. Nanotechnology can increase the throughput of data obtained in omics-based studies and allows for more sensitive diagnostic techniques as more efficient drug delivery systems. Biocompatible and biodegradable nanomaterials developed through omics-based research are able to target reported molecular markers for different ocular diseases and offer novel alternatives to conventional drug therapy. In this chapter, the authors review the pathophysiology, current genomic and proteomic information, and current nanomaterial-based therapies of four ocular diseases: glaucoma, uveal melanoma, age-related macular degeneration, and diabetic retinopathy. Omics-based research can be used to elucidate specific genes and proteins and develop novel nanomedicine formulations to prevent, halt, or cure ocular diseases at the transcriptional or translational level.

Macular oedema as manifestation of diabetic retinopathy

Diabetes mellitus is the third most dangerous disease of our time preceded by cardiovascular diseases and oncologic pathology. According to the International Diabetes Federation (January 1, 2016), worldwide approximately 415 million people aged 2079 years suffer from diabetes. The most significant manifestations of diabetes mellitus are lesions of the retina and blood vessels, which manifest as diabetic retinopathy and macular oedema, which lead to the inevitable loss of vision and disability in patients of working age. The existence of multile diagnostic methods and a broad classification provide an evidence of the complex nature of the pathological process of the macular zone in diabetes mellitus. However, to date, a single, generalised and accepted classification does not exist. Difficulties in the treatment of diabetic maculopathy are attributed to various forms of retinal lesions and ambiguities in the approach used to choose the disease management. It determines the importance of the development of diagnostic methods for the further correction of the standard treatment approach. New directions of surgical treatment allow relying on the best results of diabetic maculopathy treatment.

Concomitant Intravitreal Ganciclovir and Dexamethasone Therapy in the Management of Acute Retinal Necrosis in a Patient Previously Treated with Oral Famciclovir

Several treatments have been reported for acute retinal necrosis (ARN). We report a case of treatment with intravitreal injection of ganciclovir and dexamethasone in addition to oral valacyclovir in a patient who was previously treated with oral famciclovir for ipsilateral herpes zoster ophthalmicus (HZO).

Protocol for a randomised, double-masked, sham-controlled phase 4 study on the efficacy, safety and tolerability of intravitreal aflibercept monotherapy compared with aflibercept with adjunctive photodynamic therapy in polypoidal choroidal vasculopathy: the ATLANTIC study

PURPOSE

The purpose of this study is to compare the efficacy and safety of intravitreal aflibercept (IVA) with sham photodynamic therapy (sPDT) versus IVA with verteporfin PDT (vPDT) in a Caucasian population with treatment-naive polypoidal choroidal vasculopathy (PCV), enrolling into a treat and extend (T&E) regimen.

METHODS AND ANALYSIS

Randomised, double-masked, sham-controlled, multicentre phase 4 investigator-driven clinical trial. The primary outcomes are (1) change in best-corrected visual acuity (BCVA) from baseline and (2) polyp regression at week 52, assessed by indocyanine green angiography (ICGA). Fifty patients with treatment-naive PCV will be recruited from Portuguese and Spanish clinical sites. Eligible patients will receive monthly IVA for 3 months (week 0, week 4 and week 8). At week 16, all patients will repeat ICGA and undergo central randomisation (1:1 ratio) into one of the following groups: Group 1-IVA T&E + vPDT; Group 2-IVA T&E + sPDT. PDT will be performed at week 16, week 28 and week 40 in the presence of active polyps. After week 16, the presence of macular fluid on optical coherence tomography will determine the schedule of observations. When present, the interval between visits/injections will decrease 2 weeks (minimum 6 weeks). When not, the interval between visits/injections will increase 2 weeks (maximum 12 weeks). Efficacy will be evaluated based on BCVA, central retinal thickness and polyp regression. Safety parameters will include assessment of intraocular pressure, adverse events and serious adverse events.

ETHICS AND DISSEMINATION

This study was designed and shall be implemented and reported in accordance with the International Conference on Harmonisation (ICH) Harmonised Tripartite Guidelines for Good Clinical Practice, with applicable local regulations and with the ethical principles laid down in the Declaration of Helsinki. The study received approval from Comissão de Ética para a Investigação Clínica and Comité Ético de investigación Clínica del Hospital Universitari de Bellvitge.

TRIAL REGISTRATION NUMBER

This study is registered under the EudraCT number: 2015-001368-20 and the ClinicalTrials.gov Identifier: NCT02495181.

Intravitreal Injections of Bevacizumab: The Impact of Needle Size in Intraocular Pressure and Pain

Aim

To compare the effect of 30-gauge vs 27-gauge needle size on intraocular pressure (IOP) rise and patients’ pain experience after intravitreal injection (IVI) of bevacizumab.

Materials and methods

Cross-sectional, randomized, double-armed study. Patients were randomized to IVI with 30-gauge or 27-gauge needle. The IOP was measured pre and post IVI. Patients’ pain was graded using the visual analog scale (VAS).

Results

A total of 54 eyes were included. The IVI caused a significant IOP rise in both groups (p < 0.001). In the 30-gauge group, the mean pre- and postinjection IOP was 16.3 ± 3.6 mm Hg and 24.1 ± 9.0 mm Hg. The corresponding figures in the 27-gauge group were 18.0 ± 2.54 (p = 0.26) and 23.1 ± 7.5 mm Hg (p = 0.66). In the 30-gauge group, the mean VAS pain score was 3.2 ± 2.6 compared to 3.0 ± 2.5 in the 27-gauge group (p = 0.78).

Conclusion

The IVI caused a significant rise in IOP after the injection, independently of the needle size used. The 27-gauge needle coursed with lower postinjection IOP without prejudice of the patient comfort.

Clinical significance

The IVI with 27-gauge may be considered for glaucomatous eyes (higher risk eyes), for which IOP spikes are not recommended.

How to cite this article

Loureiro M, Matos R, Sepulveda P, Meira D. Intravitreal Injections of Bevacizumab: The Impact of Needle Size in Intraocular Pressure and Pain. J Curr Glaucoma Pract 2017;11(2):38-41.

Microneedles for enhanced transdermal and intraocular drug delivery

Microneedle mediated delivery based research has garnered great interest in recent years. In the past, the initial focus was delivery of macromolecules of biological origin, however the field has now broadened its scope to include transdermal delivery of conventional low molecular weight drug molecules. Great success has been demonstrated utilising this approach, particularly in the field of vaccine delivery. Current technological advances have permitted an enhancement in design formulation, allowing delivery of therapeutic doses of small molecule drugs and biomolecules, aided by larger patch sizes and scalable manufacture. In addition, it has been recently shown that microneedles are beneficial in localisation of drug delivery systems within targeted ocular tissues. Microneedles have the capacity to modify the means in which therapeutics and formulations are delivered to the eye. However, further research is still required due to potential drawbacks and challenges. Indeed, no true microneedle-based transdermal or ocular drug delivery system has yet been marketed. Some concerns have been raised regarding regulatory issues and manufacturing processes of such systems, and those in the field are now actively working to address them. Microneedle-based transdermal and ocular drug delivery systems have the potential to greatly impact not only patient benefits, but also industry, and through diligence, innovation and collaboration, their true potential will begin to be realised within the next 3-5 years.

Challenges for the pharmaceutical technical development of protein coformulations

Objectives

This review discusses challenges to stability, analytics and manufacturing of protein coformulations. Furthermore, general considerations to be taken into account for the pharmaceutical development of coformulated protein drug products are highlighted.

Key findings

Coformulation of two or more active substances in one single dosage form has recently seen increasing use offering several advantages, such as increased efficacy and/or the overall reduction of adverse event incidents in patients. Most marketed coformulated drug products are composed of small molecules. As proteins are not only comparatively large but also complex molecules, the maintenance of their physicochemical integrity within a formulation throughout pharmaceutical processing, storage, transport, handling and patient administration to ensure proper pharmacokinetics and pharmacodynamics in vivo already represents various challenges for single-entity products. Thus, nowadays, only sparse biologics-based coformulations can be found, as additional complexity during development is given for these products.

Summary

The complexity of the dosage form and the protein molecules results into additional challenges to formulation, manufacture, storage, transport, handling and patient administration, stability and analytics during the pharmaceutical development of protein coformulations. Various points have to be considered during different stages of development in order to obtain a safe and efficacious product.

Foscarnet calcium microcrystals as the intravitreal drug depot

Foscarnet sodium is an antiviral drug for the treatment of CMV retinitis, currently in the form of twice-weekly intravitreal injection. Here we developed foscarnet calcium microcrystals as the drug depot, and using the rabbit model we demonstrated that the injected microcrystals maintained a therapeutically relevant drug concentration in the vitreous for more than 3 months.

Evaluation of Intracameral Pentablock Copolymer Thermosensitive Gel for Sustained Drug Delivery to the Anterior Chamber of the Eye

PURPOSE

To investigate PTSgels (Pentablock copolymers) as an injectable formulation technology for sustained ocular drug delivery. Drug release profile, tolerability, and polymer degradation for one of the thermosensitive, biodegradable, and biocompatible compositions were investigated through intracameral (IC) injection in rabbits.

METHODS

New Zealand White rabbit eyes were injected IC (50 μL) with 100 μg near-infrared-immunoglobulin G (NIR-IgG) in balanced salt solution (BSS) or 20% PTSgel; or with PTSgel or BSS alone. Ocular irritation scoring, intraocular pressure (IOP), and corneal thickness (CT) measurement, as well as color and infrared photography, were performed for up to 28 days postinjection. Upon euthanasia at 7, 14, or 28 days, eyes underwent ex vivo imaging (Xenogen IVIS) followed by tissue fixation and histopathology.

RESULTS

IC injection of PTSgel (liquid at room temperature) was performed without difficulty using a 31G needle. The polymer quickly gelled in the IC space resulting in an inferior anterior chamber deposit. The tested PTSgel was well tolerated, with no significant changes in IOP or CT. Eyes injected with NIR-IgG in PTSgel had visible NIR-IgG through 9 days postinjection, and ex vivo imaging detected a strong NIR-IgG signal in the anterior chamber through day 28. The gel deposit steadily decreased in size over time and was nearly eliminated by 28 days.

CONCLUSIONS

The PTSgel released IgG for 28 days and was well tolerated. The polymer degraded in parallel with drug release. These results demonstrate the potential of intracameral PTSgel formulations for sustained delivery of biologic therapies to the ocular anterior segment.

Endophthalmitis after intravitreal injections. Incidence, management and prognosis

OBJECTIVE

To assess the rate of endophthalmitis after intravitreal injection (IVI) in a «clean room» of a single health centre, following the guidelines of the Spanish Vitreo-Retinal Society (SERV). An analysis was performed on the culture specimens, response to treatment, and final outcomes (guidelines).

MATERIAL AND METHODS

A retrospective, observational study was conducted on a consecutive case series of patients diagnosed with infectious endophthalmitis after IVI in a single health centre between 2010 and 2015. Intravitreal and systemic treatment was given following the SERV guidelines. The patients were followed up the case was resolved.

RESULTS

There were 5 cases of endophthalmitis out of 9467 IVI (incidence 0.053%). Positive cultures were obtained in aqueous and/or vitreous fluid in all cases, with Staphylococcus epidermidis being involved in 4 out of 5 cases. In 2 cases, final visual acuity was non-light perception due to intractable retinal detachments after resolution of the infectious process.

CONCLUSIONS

IVI performed in a «clean room» have a low incidence of endophthalmitis. The most common infectious agent was Staphylococcus species. In 2 cases the functional prognosis was poor.

Nanotechnology for Omics-Based Ocular Drug Delivery

Millions of people suffer from ocular diseases that impair vision and can lead to blindness. Advances in genomics and proteomics have revealed a number of different molecular markers specific for different ocular diseases, thereby optimizing the processes of drug development and discovery. Nanotechnology can increase the throughput of data obtained in omics-based studies and allows for more sensitive diagnostic techniques as more efficient drug delivery systems. Biocompatible and biodegradable nanomaterials developed through omics-based research are able to target reported molecular markers for different ocular diseases and offer novel alternatives to conventional drug therapy. In this chapter, the authors review the pathophysiology, current genomic and proteomic information, and current nanomaterial-based therapies of four ocular diseases: glaucoma, uveal melanoma, age-related macular degeneration, and diabetic retinopathy. Omics-based research can be used to elucidate specific genes and proteins and develop novel nanomedicine formulations to prevent, halt, or cure ocular diseases at the transcriptional or translational level.

Intravitreal infusion: A novel approach for intraocular drug delivery

Intraocular injection has become an increasingly important intervention in the treatment of posterior segment diseases. However, an acute intraocular pressure (IOP) elevation after intravitreal injection is a common concern. This study aimed to evaluate the efficacy of intravitreal infusion in maintaining stable IOP in a rabbit model. Trypan blue (TB) 0.06% with an external pump was used to evaluate intravitreal infusion in rabbit eyes. Groups A (50 μL), B (100 μL), C (150 μL), and D (200 μL) were slowly infused over 30 minutes with TB. As a control, Group E underwent conventional intravitreal injection of 100 μL of TB. Group F received a bolus infusion of 100 μL of TB within 1 minute. The mean increases in IOP during infusion for each group were: Group A (7.93 ± 3.80 mmHg), B (13.97 ± 3.17 mmHg), C (19.91 ± 6.06 mmHg) and D (29.38 ± 8.97 mmHg). Immediately post-injection in group E the mean increase in IOP amounted to 34.33 ± 6.57 mmHg. The mean increase in IOP of group F after bolus infusion was 49.89 ± 1.71 mmHg. Intravitreal infusion maintains a stable IOP and provides a controlled infusion speed compared with intravitreal injection.

TOPICAL APRACLONIDINE REDUCES PAIN AFTER INTRAVITREAL INJECTIONS: A Double-Blind Randomized Controlled Trial

PURPOSE

To evaluate the efficacy of topical apraclonidine in reducing pain and subconjunctival hemorrhage (SCH) after intravitreal injections (IViT).

METHODS

A prospective, randomized, double-blinded study. Thirty-nine patients were examined twice, at each monthly IViT of 1.25 mg/0.05 mL bevacizumab. Patients were randomly assigned to receive either topical apraclonidine 0.5% or placebo to the treated eye, 30 minutes before the first IViT. At their second IViT, the intervention was switched. Thirty minutes after the injection, SCH size was measured by a slit lamp, and pain was assessed by the numerical rating scale (NRS-11).

RESULTS

Mean pain score was 1.69 (SD ±1.44) in the apraclonidine group and 3.28 (SD ±2.27) in the control group (P < 0.001). Phakic patients had a greater pain reduction after topical apraclonidine (P < 0.001). Subconjunctival hemorrhage incidence was 41% in the apraclonidine group and 51.3% in the control group (P = 0.503). Mean SCH size was 1.71 mm (SD ±5.83) in the apraclonidine group and 3.25 mm (SD ±6.41) in the control group (P = 0.253). After topical apraclonidine, there was a smaller reduction in SCH size in patients with choroidal neovascularization or hypertension (P = 0.003 and 0.044, respectively), and a greater reduction in phakic patients (P = 0.048).

CONCLUSION

Topical apraclonidine 0.5%, administered 30 minutes before IViT, significantly decreased pain by a factor of 1.94. It did not decrease the incidence or size of SCH in the entire cohort, but only in several subpopulations.

A national survey of Canadian ophthalmologists to determine awareness of published guidelines for the management of uveitis

Background

The objectives of this study are to assess Canadian ophthalmologists’ awareness of established uveitis treatment guidelines and clinical management of uveitis and to assess the frequency of government applications for immunomodulatory therapy (IMT) and identify primary prescribers.

A 25-item questionnaire was sent to 759 practicing Canadian ophthalmologists. Six questions assessed demographics including the year of residency completion, training by uveitis specialists during residency, and fellowship training. Five questions assessed application of guidelines to clinical scenarios, and 12 questions assessed referral patterns and success of obtaining coverage for IMT.

Results

Of 144 respondents, 12 (8.3 %) were uveitis specialists; 45.1 % of respondents had uveitis training during residency by a uveitis specialist. Sixty-one percent reported awareness of management guidelines. Recent graduates (2001–2012) referred patients to uveitis specialists (55.3 %) less frequently than earlier graduates. Recent graduates also managed uveitis patients more frequently with corticosteroid injections (15.6 %) than those who graduated before 1980 (9.75 %). The majority (93.6 %) of respondents submitted less than six IMT funding applications for provincial drug coverage yearly, and 5.5 % reported prescribing IMT themselves, rather than referring to other specialists.

Conclusions

Although greater than half of respondents reported awareness of uveitis treatment guidelines, Canadian ophthalmologists’ awareness of uveitis treatment guidelines and application of the guidelines to patient care could be improved. Few applications are made for IMT, and the majority of applications are sent by non-ophthalmologists. This suggests the need for further education of ophthalmologist about uveitis treatment guidelines and for more ophthalmologists trained to manage uveitis with IMT.

Electronic supplementary material

The online version of this article (doi:10.1186/s12348-016-0102-3) contains supplementary material, which is available to authorized users.

Extended ocular drug delivery systems for the anterior and posterior segments: biomaterial options and applications

INTRODUCTION

The development of new therapies for treating various eye conditions has led to a demand for extended release delivery systems, which would lessen the need for frequent application while still achieving therapeutic drug levels in the target tissues. Areas covered: Following an overview of the different ocular drug delivery modalities, this article surveys the biomaterials used to develop sustained release drug delivery systems. Microspheres, nanospheres, liposomes, hydrogels, and composite systems are discussed in terms of their primary materials. The advantages and disadvantages of each drug delivery system are discussed for various applications. Recommendations for modifications and strategies for improvements to these basic systems are also discussed. Expert opinion: An ideal sustained release drug delivery system should be able to encapsulate and deliver the necessary drug to the target tissues at a therapeutic level without any detriment to the drug. Drug encapsulation should be as high as possible to minimize loss and unless it is specifically desired, the initial burst of drug release should be kept to a minimum. By modifying various biomaterials, it is possible to achieve sustained drug delivery to both the anterior and posterior segments of the eye.

Modeling intraocular bacterial infections

Bacterial endophthalmitis is an infection and inflammation of the posterior segment of the eye which can result in significant loss of visual acuity. Even with prompt antibiotic, anti-inflammatory and surgical intervention, vision and even the eye itself may be lost. For the past century, experimental animal models have been used to examine various aspects of the pathogenesis and pathophysiology of bacterial endophthalmitis, to further the development of anti-inflammatory treatment strategies, and to evaluate the pharmacokinetics and efficacies of antibiotics. Experimental models allow independent control of many parameters of infection and facilitate systematic examination of infection outcomes. While no single animal model perfectly reproduces the human pathology of bacterial endophthalmitis, investigators have successfully used these models to understand the infectious process and the host response, and have provided new information regarding therapeutic options for the treatment of bacterial endophthalmitis. This review highlights experimental animal models of endophthalmitis and correlates this information with the clinical setting. The goal is to identify knowledge gaps that may be addressed in future experimental and clinical studies focused on improvements in the therapeutic preservation of vision during and after this disease.