Tear Turnover Research Articles

Ocular drug delivery: a clue from nanotechnology

Topical administration is the most common route of ocular drug delivery. Despite its apparent easy accessibility, the eye is well protected from foreign materials and drugs by a number of very efficient mechanisms such as blinking, induced lacrimation, tear turnover, nasolacrimal drainage, which cause rapid removal of substances from the eye surface and by the cornea, which forms the physical-biological barrier (Figure ​(Figure1).1). Consequently, these protective mechanisms and structural obstacle may cause subtherapeutic drug levels at the tissue target, particularly at retinal level. Delivery of drugs to the posterior eye is challenging, and there is an increasing need for managing rapidly progressing for posterior eye diseases, such as diabetic retinopathy, age-related macular degeneration, and optic neuropathy (Bucolo et al., 2012a,b; Musumeci et al., 2012). Currently, the intravitreal route is widely used to deliver therapeutic molecules to the retina. However, frequent administration of drugs via this route can lead to retinal detachment, endophthalmitis and increased intraocular pressure. For this reason ophthalmic drug delivery, particularly targeted to posterior segment, is one of the most challenging endeavors facing the ocular pharmacologists. Topical route represents a safer administration, therefore a major challenge to the scientists is to overcome the ocular barriers and reach the tissue target. Systemic route (e.g., oral, parenteral) is also used to reach the eye, though the drug transport across the ocular barriers (blood-aqueous barrier and blood-retinal barrier) is quite difficult.

Ocular drug delivery for bioactive proteins

Recent advances in biotechnology enabled commercial production of humanized monoclonal antibodies. In the field of ophthalmology, ranibizumab and bevacizumab, anti-VEGF antibodies, are highly recognized as first-choice drugs to treat age-related macular degeneration, which is one of the major causes of legal blindness in developed countries. Infliximab is a monoclonal antibody against TNF-α and is effective in treating autoimmune diseases such as Behçet’s disease. Thus, these drugs proved the potential of antibodies as molecularly targeted therapies for the treatment of a variety of ocular diseases. A variety of cytokines may also possess great potential as therapeutics, exemplified by interferon for the treatment of chronic hepatitis C, multiple sclerosis, and other systemic diseases. However, intraocular delivery of bioactive proteins remains a critical problem to be overcome. The cornea, sclera, tear turnover, frontward current of aqueous humor, the blood–aqueous barrier and blood–retinal barrier strictly limit penetration and diffusion of the drug into the chorioretinal tissue. Therefore, ranibizumab and bevacizumab are intravitreally injected, with the possibility of rare but serious adverse events such as endophthalmitis. Moreover, repeated injections are required to keep therapeutic concentrations in the eye. In addition, intravitreal injections may be less effective on eyes after vitrectomy because the residence time of intravitreally injected drugs is remarkably shortened. Generally, cytokines have a short half-life of bioactivity in the body, which may limit their suitability as a drug. One of strategies to overcome these limitations may be the development of intraocular drug-delivery systems. However, previously developed devices may be applicable only to deliveries of steroids and other small compounds. In this review, we aim to summarize possible strategies involving controlled release and drug targeting of bioactive proteins on the basis of polyion complexation or metal coordination and other gelling agents to prolong residence time of intravitreally injected drugs.

Ocular surface analysis in patients affected with rheumatic diseases

The international criteria for primary Sjögren's Syndrome (SS I) diagnosis (Vitali et al. 2002) include the Schirmer test I and vital dye staining as tests for ocular surface involvement, but diagnosis can be reached also when the item for ocular signs is not satisfied. The purpose of our study was to evaluate the ocular surface in patients with Sjögren's Syndrome, non-Sjögren's autoimmune diseases and Sicca Syndrome, to understand whether the SS I diagnosis can be targeted also on other tests related to the ocular surface status. Clinical and cytological data were collected from 122 patients: 40 patients had diagnosis of Primary Sjögren's Syndrome, 51 a non Sjögren's autoimmune disease and 31 had symptoms of dry eye. A validated questionnaire on symptoms was filled by each patient; clinical tests included: Schirmer test I, Jones test, Ferning test, Break Up Time, corneal aesthesiometry, tear clearance test, vital dye staining of the ocular surface, scraping and impression conjunctival cytology. Data were statistically evaluated by using SPSS software and Mann-Whitney analysis on unpaired data. Data show that the subjective symptoms score, tear production, tear turnover, corneal sensitivity and ocular surface integrity are affected in SS I patients, with a statistically significant difference when matched to the other two groups. Our results suggest to enlarge the spectrum of ocular surface analysis, to support and orient a differential diagnosis among the autoimmune diseases.

Differential control and selective down regulation of cytokines but not chemokines in the normal and pathological tear fluid

AbstractPurpose Overnight eye closure results in a near cessation in tear turnover and the induction of a sub‐clinical inflammation as evidenced by PMN cell recruitment and degranulation and the accumulation of pro‐inflammatory cytokines and chemokines. What prevents cytokine induced damage to the cornea was investigated.Methods Methods: Open (O) and Closed (C) tears from Ns were subjected to multiple micro well array assays to obtain quantitative data on the distribution of >80 low abundance proteins. Samples were also separated by molecular sieve HPLC and the eluent profiled for the presences of chemokines, cytokines and interactive proteins. Cytokine‐protein complexes were identified using a laboratory‐developed multiplex assays.Results Micro‐well array assay reveal a marked increase in the concentrations of a wide range of inflammatory and immune modulating cytokines as well as chemokines in the closed eye tears. This was accompanied by increased levels of s‐receptors at concentrations greatly exceeding that of the targeted proteins along with the accumulation of α2‐M. Protein‐protein binding studies and analysis of the HPLC eluent reveals that most inflammatory, angiogenic and immune cytokines eluent in the form of macromolecular complexes bound to s‐receptor and α2‐M. This serves to inactivate these entities and tags them for up take by macrophages and other cells that express the α2‐M receptor. In contrast chemokines which lack s‐receptors remain free and bioactive.Conclusion s‐receptors and α2‐M co‐operatively function in the down–regulation of cytokine and growth factor induced inflammation. Data will also be presented showing its functional role in the control of inflammation elsewhere.

Biomedical soft contact-lens sensor for in situ ocular biomonitoring of tear contents

A soft contact-lens biosensor (SCL-biosensor) for novel non-invasive biomonitoring of tear fluids was fabricated and tested. Wearing a biosensor on eye enabled the in situ monitoring of tear contents. The biosensor has an enzyme immobilized electrode on the surface of a polydimethyl siloxane (PDMS) contact lens. The SCL-biosensor was fabricated using microfabrication techniques for functional polymers (PDMS and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer). In investigation of in vitro characterization, the SCL-biosensor showed excellent relationship between the output current and glucose concentration from 0.03 to 5.0mmol·L(-1), with a correlation coefficient of 0.994. The calibration range covered the reported tear glucose concentrations (0.14mmol·L(-1)). Based on the result, ocular biomonitoring with the SCL-biosensor was carried out. The SCL-biosensor well worked both in the static state and the dynamic state. The tear glucose level of rabbit was estimated to 0.12mmol·L(-1) at first and then the tear turnover was successfully calculated to be 29.6 ± 8.42% min(-1). The result indicated that SCL-biosensor is useful for advanced biomonitoring on eye.

Tear physiology in dry eye associated with chronic GVHD

The purpose of this study was to compare tear physiology characteristics of chronic GVHD (cGVHD)-associated dry eye to dry eye caused by Sjogren's syndrome (SS), a extreme form of aqueous-deficient dry eye, and meibomian gland dysfunction (MGD), the major cause of evaporative dry eye. Tear turnover rate, evaporation and osmolarity along with meibomian gland dropout and lipid layer interferometric patterns were assessed in the right eyes of 12 patients with dry eye associated with cGVHD, 12 age-matched patients with SS and 12 age-sex matched subjects with MGD. In cGVHD, the decrease in tear turnover rate was similar (P=0.33), but the number of non-functioning meibomian glands was significantly higher (P<0.01) than in SS. Tear evaporation rate in cGVHD dry eye was found to be similar to that in MGD (P=0.36) and significantly higher than in SS (P<0.01). The lipid layer was most unstable in cGVHD compared with other groups. There was no variation in tear volume across all groups. Although statistical significance was not detected, the mean tear osmolarity (333.51±14.67mOsm/L) was highest in cGVHD. Major aspects of tear physiology were severely impaired in cGVHD-associated dry eye.

Polymeric ocular hydrogels and ophthalmic inserts for controlled release of timolol maleate.

Background:Ophthalmic drug delivery systems are the challenging subject for the researchers because of delicate nature of ocular membrane and preventive barriers leading to less than 1 % of Bioavailability. Reasons for reduced bioavailability are due to rapid pre corneal elimination, tear turnover, lacrimal drainage, blinking and degradation by enzymes. Less bioavailability causes short duration of action and increased frequency of administration.Materials and Methods:Timolol maleate was used as model drug. Dynamic drug release studies were used to study the polymeric hydrogels and ophthalmic inserts. Rheological studies were carried out by Brookfield Viscometer LVDV- II+.Result and Discussion:Viscosity value lies in the range of 4.08 to 31.8 cps. Drug release data was fitted to various kinetic equations such as First order plots, Higuchi plots, Peppa's exponential plots. The results shows fairly linear curve and the slope value of the Peppa's equation is less than 0.5 and hence follows the fickian diffusion.Conclusion:The developed hydrogels and inserts were therapeutically effacious, stable, non irritant and provide a sustained release of drug over 8 hours time period.

Emulsions and microemulsions for ocular drug delivery

Ocular drug delivery through aqueous eye drops is the most common approach for administering ophthalmic drugs, in spite of the low residence time of a few minutes, which limits the bioavailability to less than 5 %. A number of drug delivery approaches have been explored to overcome the drawbacks of the aqueous eye drops including addition of colloidal particles to the eye drops. Emulsions and microemulsions are particularly appealing for delivering hydrophobic drugs to the cornea because of the possibility of loading the drugs in the oil particles. There are some other potential advantages such as the possibility of increasing the residence time through binding between the surfactant covered oil drops and the cornea, or through designing systems that undergo phase transition to a liquid crystalline system with high viscosity. Additionally, some researchers have dispersed microemulsions in contact lenses to further increase the residence time. The benefits of the emulsions and microemulsions listed above are at least partially offset by potential toxicity issues, and also formulation issues such as shelf life. Furthermore, issues related to the ocular physiology including tear biochemistry, and rapid tear turnover also sometimes limit the potential benefits of using microemulsions and emulsions. This review paper focuses on summarizing recent research on ophthalmic delivery through emulsions and microemulsions, with a particular focus on mechanistic and formulation issues.

A Clinical Alternative to Fluorophotometry for Measuring Tear Production in the Diagnosis of Dry Eye

To determine the utility of the tear function index (Liverpool modification TFI) in assessing tear turnover rate (TTR), evaluate association of tear clearance rate (TCR) and TFI with measurements of TTR by fluorophotometry, and determine effectivity of these test measures in dry eye (DE) diagnosis. Forty-one subjects with DE and 15 control subjects participated. Tests included symptoms, fluorophotometry (by automated scanning fluorophotometry), and TCR and TFI from a prepared Liverpool modification TFI strip. Significant differences between subjects with DE and control subjects were found for all tests. Although wetting length values gave highest sensitivity (SS) and specificity (SP) (71% and 73%, respectively), this resulted from a high degree of selection bias because the Schirmer test was one of the inclusion criteria for patients entering the study. Therefore, the best tear production test was found to be TTR (SS 71% and SP 60%). The TTR test is not readily available in clinical settings; therefore, associations between the TTR test and other tests were determined. Significant correlations were found between TTR and wetting length/TCR/TFI, indicating these latter clinical tests useful as surrogates. The strongest correlations, TTR/TCR at 0.69 (P = 0.000) and TTR/TFI at 0.65 (P = 0.000), indicate TCR/TFI with the Liverpool test can be used as an alternative to TTR by fluorophotometry. The diagnostic effectiveness between these tests was compared, with both TCR and TFI found to have equal effectivity of 78% SS and 40% SP (TCR) and 83% SS and 40% SP (TFI). TCR measured by the commercially available Liverpool modification TFI strip is an acceptable alternative to TTR by fluorophotometry as a measure of tear production. It is effective as a single test for the discrimination of those with DE from those without the condition.

Ion- and pH-activated novel in-situ gel system for sustained ocular drug delivery

Poor bioavailability (<1%) of drugs from conventional eye drops is mainly due to the various precorneal loss factors which include rapid tear turnover, systemic drug absorption through naso-lachrymal duct, transient residence time of the drug solution in the cul-de-sac and the relative impermeability of the drugs to corneal epithelial membrane. The present study describes the formulation and evaluation of chitosan and gellan gum based novel in-situ gel system activated by dual physiological mechanisms. Chitosan (a pH-sensitive polymer) in combination with gellan gum (an ion-activated polymer) were used as gelling agent. Timolol maleate, the drug which is frequently used for glaucoma therapy was used as model drug to check the efficacy of the formulation. The developed formulation was characterized for various in vitro parameters, for example, clarity, gelation pH, isotonicity, sterility, viscosity, transcorneal permeation profile, and ocular irritation. Ocular retention was studied by gamma scintigraphy and a significant increase in retention time was observed. The formulation was also found to be nonirritant and well tolerable. The developed system can be a viable alternative to conventional eye drops for the treatment of various ocular diseases and is suitable for clinical application.

Tear volume, turnover rate, and flow rate in ophthalmologically normal horses

To determine tear volume, turnover rate, and flow rate in ophthalmologically normal horses by use of fluorophotometry. 12 mares free of ophthalmic disease. 2 microL of 10% sodium fluorescein was instilled onto 1 eye of each horse, and tear samples were collected via microcapillary tubes from the inferonasal conjunctival culde-sac at 0, 2, 4, 6, 10, 15, and 20 minutes after instillation. Collected tear samples were then measured for fluorescein concentrations with a computerized scanning ocular fluorophotometer. A decay curve plot of concentration changes over time was used to determine tear flow rate and volume through 2 different mathematical treatments of the data (the including method and the excluding method). Fluorescein concentration in tears decreased in a first-order manner. The including method yielded a mean tear volume of 360.09 microL, a turnover rate of 12.22%/min, and a flow rate of 47.77 microL/min. The excluding method yielded values of 233.74 microL, 13.21%/min, and 33.62 microL/min, respectively. Mean +/- SD correlation coefficients for the natural logarithm of the fluorescein concentration versus time were 0.93 +/- 0.12 for the including method and 0.98 +/- 0.03 for the excluding method. The excluding method yielded more accurate results. A tear flow rate of 33.62 microL/min and a tear volume of 233.74 microL imply a complete recycling of the tear volume in approximately 7 minutes and suggest that increased dosing regimens or constant infusion methods for topical administration of ophthalmic drugs may be indicated when treating horses for corneal disease in which high ocular surface concentrations are needed.

Hyaluronic acid modified chitosan nanoparticles for effective management of glaucoma: development, characterization, and evaluation

In clinical practices, solution of dorzolamide hydrochloride (DH) and timolol maléate (TM) is recommended for the treatment of glaucoma. However, low drug-contact time and poor ocular bioavailability of drugs due to drainage of solution, tear turnover and its dilution or lacrimation limits its uses. In addition, systemic absorption of TM may induce undesirable cardiovascular side effects. Chitosan (CS) is a polycationic biodegradable polymer which provides sustained and local delivery of drugs to the ocular sites. Hyaluronic acid (HA) also provides synergistic effect for mucoadhesion in association with chitosan. In the present study, hyaluronic acid modified chitosan nanoparticles (CS-HA-NPs) loaded with TM and DH were developed and characterized. The CS-HA-NPs were evaluated for size, shape, zeta potential, entrapment efficiency, and mucoadhesive strength. The in vitro release study was also performed in PBS pH 7.4. The ocular irritation potential of CS-HA-NPs was estimated using draize test on albino rabbits. A significant reduction in IOP level was obtained using CS-HA-NPs as compared to plain solution of drug and a comparable higher reduction in IOP level was observed as to CS-NPs. These results suggest that HA potentialy enhance the mucoadhesiveness and efficiency of CS-NPs and may be promising carrier for ocular drug delivery.

Tear Physiology of Aqueous Deficiency and Evaporative Dry Eye

To determine the differences in tear physiology between aqueous deficiency dry eye (ADDE) and evaporative dry eye (EDE), and evaluate their utility in diagnosis. Fifty-six dry eye patients were classified into 30 ADDE and 26 EDE according to the recently published Dry Eye Workshop criteria. A range of tear physiology measures comprising of tear evaporation, turnover rate (TTR), distribution, volume and osmolarity, and meibomian gland dropout were measured in these patients. The effectiveness of the tests, singly and in combinations, in differentiating between the dry eye subtypes was evaluated by retrospective allocation into groups and by Receiver Operative Characteristics (ROC) curve analysis. Statistically significant differences were seen for TTR and tear evaporation (with lower values for ADDE) between ADDE and EDE, but no significant differences were seen for tear osmolarity, volume, distribution, and meibomian gland dropout scores. Differentiation of ADDE and EDE by a cut-off value of 11%/min for TTR was found to have a sensitivity of 86%, specificity of 75%, positive predictive value 89%, negative predictive value 69%, and overall accuracy 83%. The area under the curve on the ROC curve was 0.83. For tear evaporation, a cut-off of 60 g/mh was found to have a sensitivity of 77%, specificity of 55%, positive predictive value 38%, negative predictive value 80%, and overall accuracy 58% in subtype differentiation. The area under the curve was 0.59 on the ROC curve. The distribution curve of the evaporation rates for ADDE and EDE, showed an overlap coefficient of 0.76 indicating that tear evaporation is within a similar range in these two dry eye subtypes. Tear turnover is significantly lower in ADDE than EDE, but there is considerable overlap of tear evaporation between the two dry eye subtypes. Tear osmolarity and turn over tests can be conducted sequentially to effectively diagnose dry eye and its subtypes.

Inputs and Outputs of the Lacrimal system: Review of Production and Evaporative Loss

Meta-analyses were carried out of studies of tear production (by fluorophotometry, tear turnover rate [TTR]) and evaporation (from capture of fluid loss from the eye). TTR was reduced in dry eye relative to normal at 9.26 ± 5.08%/min (0.54 ± 0.28 μl/min) vs 16.19 ± 5.1%/min (1.03 ± 0.39 μl/min); with values of 7.71 ± 1.02 %/min (0.4 ± 0.10 μl/min) in aqueous deficiency dry eye (ADDE) and 11.95 ± 4.25%/min (0.71 ± 0.25 μl/min) in evaporative dry eye (EDE). Evaporation was increased in dry eye at 21.05 ± 13.96 × 10−7g/cm2/s (0.21 ± 0.13 μl/min) vs 13.57 ± 6.52 × 10−7g/cm2/s (0.14 ± 0.07 μl/min) in normals; with values of 17.91 ± 10.49 × 10−7g/cm2/s (0.17 ± 0.1 μl/min) in ADDE and 25.34 ± 13.08 × 10−7g/cm2/s (0.26 ± 0.16 μl/min) in EDE. Evaporation rate from tear film thinning was also considered, and possible reasons and consequences for the much higher rates thereby reported are discussed. A new statistical approach determined diagnostic efficacy of cut-offs for dry eye derived from the meta-analyses; sensitivities and specifications ranging from 69.5 to 98.6% and 58.7 to 96.8% (TTR) and 45.5 to 61.2% and 79.8 to 90.6% (evaporation). Indices of tear dynamics were reconsidered, and ratios of evaporation and TTR suggest that an increase of between 2 and 3 times may be associated with dry eye.

Nanocarriers in Ocular Drug Delivery: An Update Review

Controlled drug delivery to eye is one of the most challenging fields of pharmaceutical research. Low drug-contact time and poor ocular bioavailability due to drainage of solution, tear turnover and its dilution or lacrimation are the problems associated with conventional systems. In addition, anatomical barriers and physiological conditions of eye are also important parameters which control designing of drug delivery systems. Nanosized carriers like micro/nano-suspensions, liposome, niosome, dendrimer, nanoparticles, ocular inserts, implants, hydrogels and prodrug approaches have been developed for this purpose. These novel systems offer manifold advantages over conventional systems as they increase the efficiency of drug delivery by improving the release profile and also reduce drug toxicity. Conventional delivery systems get diluted with tear, washed away through the lacrimal gland and usually require administering at regular time intervals whereas nanocarriers release drug at constant rate for a prolonged period of time and thus enhance its absorption and site specific delivery. This review presents an overview of the various aspects of the ocular drug delivery, with special emphasis on nanocarrier based strategies, including structure of eye, its barriers, delivery routes and the challenges/limitations associated with development of novel nanocarriers. The recent progresses in therapy of ocular disease like gene therapy have also been included so that future options should also be considered from the delivery point of view. Recent progress in the delivery of proteins and peptides via ocular route has also been incorporated for reader benefit.

Role of Transporters in Ocular Drug Delivery System

A number of sight threatening diseases affect the anterior and posterior segments of the eye. Various therapeutic agents have been discovered to treat these disorders, but the challenge still lies in effectively delivering these drugs to the eye, primarily due to the unique anatomy and physiology of the ocular structures. Topical mode of administration is the most preferred and convenient delivery method, but ocular bioavailability of most topically applied drugs is less than 5%. Drug loss is primarily due to precorneal factors such as solution drainage, blinking, tear turnover rate and absorption by adjacent tissues i.e., conjunctiva, resulting in the loss of drug to systemic circulation. Low ocular bioavailability has also been attributed to the lipoidal nature of the corneal epithelium and the water-laden stroma which act as rate limiting barriers for hydrophilic and lipophilic molecules, respectively. In addition, the physicochemical properties of the drug itself limit its permeability across ocular barriers. Recently, transporter-targeted prodrug approach has received significant attention and a number of membrane transporters have been discovered in various ocular tissues such as cornea, conjunctiva and retina. These transporters are involved in the translocation of essential nutrients and xenobiotics across biological membranes. Ocular transporters include carriers for peptides, amino acids, glucose, lactate and nucleosides/nucleobases and are primarily localized on the epithelia of cornea, conjunctiva and retina. Prodrugs or analogues designed to target these transporters can significantly enhance the absorption of poorly permeating parent drug. Both solubility and membrane permeability can be improved by proper selection of the promoiety. These prodrugs are recognized by the membrane transporters as substrates and are translocated across the epithelia. Subsequently, the prodrugs are enzymatically cleaved to release the parent drug and the ligand which in most cases is a nutrient and thereby non-toxic. Amongst various nutrient transporters that are expressed on the corneal epithelium, the peptide and amino acid transporters have been classified as high capacity low affinity transporters. The current theme section contains an article, which deals with improving the corneal permeability of a poorly permeable hydrophilic drug, acyclovir (ACV), for the treatment of herpetic keratitis, by chemically derivatizing it into a prodrug (L-aspartate-acyclovir, L-Asp-ACV). L-Asp-ACV was shown to be a substrate of the corneal B 0,+ amino acid transporter and it resulted in a fourfold increase in the transcorneal permeability of ACV. However, D-Asp-ACV did not increase the corneal permeability relative to ACV, suggesting that the L-form of the amino acid is necessary for transporter recognition. Hence, targeting such nutrient transporters on the corneal epithelium is a viable strategy to enhance corneal permeability of hydrophilic therapeutic agents (1). In addition to the tight junctions expressed by the corneal epithelium, more recently, efflux pumps such as P-glycoprotein (P-gp) have also shown to play a role in restricting ocular

Dry Eye Diagnosis

To determine the most effective objective tests, applied singly or in combination in the diagnosis of dry eye disease. Two groups of subjects--41 with dry eye and 32 with no ocular surface disease--had symptoms, tear film quality, evaporation, tear turnover rate (TTR), volume and osmolarity, and meibomian gland dropout score assessed. The subjects with dry eye had TTR, tear evaporation, and osmolarity significantly different from that of healthy normal subjects. Cutoff values between the groups were determined from distribution curves for each aspect of tear physiology, and the effectiveness of the cutoff was determined from receiver operator characteristic (ROC) curves. Values of 12%/min for TTR, 33 g/m(-2)/h for evaporation, and 317 mOsmol/L for osmolarity were found to give sensitivities, specificities, and overall accuracies of 80%, 72%, and 77%; 51%, 96%, and 67%; and 78, 78%, and 79%, respectively when applied singly as diagnostic criteria in dry eye. In combination, they yielded sensitivities, specificities, and overall accuracy of 100%, 66%, and 86% (in parallel) and 38%, 100%, and 63% (in series), respectively. Discriminant function analysis incorporating these three factors in an equation allowed diagnosis with a sensitivity of 93%, specificity of 88%, and overall accuracy of 89%. Tear osmolarity is the best single test for the diagnosis of dry eye, whereas a battery of tests employing a weighted comparison of TTR, evaporation, and osmolarity measurements derived from discriminant function analysis is the most effective.

Ocular Gelling Microspheres: In Vitro Precorneal Retention Time and Drug Permeation Through Reconstituted Corneal Epithelium

The model drug norfloxacin (NOR) was encapsulated into trehalose (TRH) and hydroxyethylcellulose (NAT) microspheres to obtain a novel gelling ophthalmic delivery system for prolonged release on corneal tissue. We assessed NOR release from microspheres, prepared by the emulsion-solvent evaporation method. A new in vitro tear turnover model, including inserts containing reconstituted human corneal epithelium (RHC), was designed to evaluate the TRH/NAT microspheres' precorneal retention time. Bioadhesive properties of TRH/NAT microspheres were validated by using drug-loaded microspheres prepared with gelatine (GLT) commonly used as reference material in adhesion studies. In vitro drug release showed a typical trend of swelling systems. Precorneal retention tests showed that TRH/NAT microspheres maintained fluorescence in tear fluid for 81.7 min, whereas TRH/GLT microspheres and water solution maintained fluorescence for 51.8 and 22.3 min, respectively. NOR released from microspheres permeated throughout RHC slower (J(s) = 23.08 microg/cm(2)h) than NOR from commercial eye drops (J(s) = 42.77 microg/cm(2)h) used as the control. Adequate drug concentrations in aqueous humor could be prolonged after the administration of TRH/NAT/NOR microspheres. Good bioadhesive properties of the system and slow drug release on corneal surface might increase ocular NOR bioavailability.

Breakdown Evaluation of Corneal Epithelial Barrier Caused by Antiallergic Eyedrops Using an Electrophysiologic Method

The aim of this study was to examine the usefulness of an electrophysiologic method for predicting corneal epithelial breakdown by antiallergic eyedrops and comparing the results with those in other appraisal methods. Six kinds of antiallergic eyedrops, including benzalkonium chloride (BK) as an ophthalmic preservative and two kinds of BK-free antiallergic eyedrops, were used in this study. Eyedrops were applied to excise rabbit corneas and monitoring was performed according to an electrophysiologic method, using a commercially available chamber system to mimic human tear turnover. Changes in transepithelial electrical resistance (TEER) in the corneal surface were recorded. The cytotoxicity of each kind of eyedrops in a normal rabbit corneal epithelial (NRCE) cell line and a human endothelial cell line EA.hy926 was also examined. The extent of decrease in the corneal TEER after applying antiallergic eyedrops was dependent on the concentration of the BK included as a preservative, but it was also affected by the different kinds of drugs when the BK concentration was low. Higher cytotoxicity of the eyedrops against the NRCE and EA.hy926 cell lines was observed with a reduction of TEER. Monitoring changes in the corneal TEER, according to the electrophysiologic method with the application of antiallergic eyedrops, is useful for predicting corneal epithelial breakdown caused by their instillation.

An open-label, investigator-masked, crossover study of the ocular drying effects of two antihistamines, topical epinastine and systemic loratadine, in adult volunteers with seasonal allergic conjunctivitis

Background: Systemic antihistamines such as loratadine are efficacious in the treatment of many allergic conditions. However, their use has been associated with drying effects, particularly of the ocular surface. Objective: The purpose of this study was to compare the ocular drying effects of topical treatment with epinastine hydrochloride ophthalmic solution 0.05 % twice daily and systemic treatment with loratadine 10 mg once daily in patients with seasonal allergic conjunctivitis through the use of several standard clinical tests for dry eye. Methods: This was a single-center, 4-visit, open-label, investigator-masked crossover study in healthy adult volunteers with a history of seasonal allergic conjunctivitis. Participants received 4 days of treatment with topical epinastine administered as 1 drop per eye twice daily and 4 days of treatment with systemic loratadine once daily, with a 10-day washout between treatments. Fluorophotometry was conducted at the baseline visit, at the crossover visit, and after 4 days of each treatment to assess tear volume, tear flow, and tear turnover rate. Decreases from baseline in tear volume, tear flow, or tear turnover rate were considered indicative of a drying effect. Keratitis, global (corneal and conjunctival) fluorescein staining (scale from 0–20 points), and tear film break-up time (TFBUT) were assessed after fluorophotometry at each visit. An increase in keratitis (as measured by global fluorescein staining) and conjunctival lissamine green staining, and a decrease in TFBUT were considered further evidence of a drying effect. Results: Eighteen subjects were enrolled in and completed the study (78% female; 94% white; age range, 18–55 years). After 4 days of twice-daily use, topical epinastine was associated with no significant changes in tear volume, tear flow, or global fluorescein staining. After 4 days of once-daily use, systemic loratadine was associated with a 33.7% reduction in tear volume (mean reduction, 4.5 μL; range, −7.53 to 22.36 μL; P < 0.05), a 35.0% reduction in tear flow (mean reduction, 0.93 μL/min; range, −2.57 to 2.73 μL/min; P < 0.05), and a 21.7% increase in global fluorescein staining (mean increase, 0.74 point; range, −2.5 to 6.5 points; P < 0.05). No significant change in TFBUT was observed with either treatment. Conclusions: These healthy adult volunteers with a history of seasonal allergic conjunctivitis had no clinical signs of ocular drying after 4 days of twice-daily treatment with topical epinastine. After 4 days of once-daily dosing, systemic loratadine was associated with clinical signs of ocular dryness, including decreased tear volume and tear flow. Use of loratadine was also associated with an increase in global fluorescein staining, indicating an increase in ocular surface damage.