Terahertz scanning of the rabbit cornea with experimental UVB-induced damage: in vivo assessment of hydration and its verification.

SIGNIFICANCE: Water content plays a vital role in the normally functioning visual system; even a minor disruption in the water balance may be harmful. Today, no direct method exists for corneal hydration assessment, while it could be instrumental in early diagnosis and control of a variety of eye diseases. The use of terahertz (THz) radiation, which is highly sensitive to water content, appears to be very promising. AIM: To find out how THz scanning parameters of corneal tissue measured by an experimental setup, specially developed for in vivo contactless estimations of corneal reflectivity coefficient (RC), are related to pathological changes in the cornea caused by B-band ultraviolet (UVB) exposure. APPROACH: The setup was tested on rabbit eyes in vivo. Prior to the course of UVB irradiation and 1, 5, and 30 days after it, a series of examinations of the corneal state was made. At the same time points, corneal hydration was assessed by measuring RC. RESULTS: The obtained data confirmed the negative impact of UVB irradiation course on the intensity of tear production and on the corneal thickness and optical parameters. A significant (1.8 times) increase in RC on the 5th day after the irradiation course, followed by a slight decrease on the 30th day after it was revealed. The RC increase measured 5 days after the UVB irradiation course generally corresponded to the increase (by a factor of 1.3) of tear production. RC increase occurred with the corneal edema, which was manifested by corneal thickening (by 18.2% in the middle area and 17.6% in corneal periphery) and an increased volume of corneal tissue (by 17.6%). CONCLUSIONS: Our results demonstrate that the proposed approach can be used for in vivo contactless estimation of the reflectivity of rabbit cornea in the THz range and, thereby, of cornea hydration.

Treatment of Severe Acute Bacterial Keratitis in Rabbits Using Continuous Topical Ocular Instillation with Norvancomycin.

PURPOSE: Efficacy of norvancomycin (NVCM) through continuous topical ocular instillation drug delivery (CTOIDD) system for treating severe acute bacterial keratitis infection with Staphylococcus aureus was investigated. METHODS: Rabbits with bacterial keratitis were treated using CTOIDD with NVCM (n=13), topical NVCM eye drops (n=11), and CTOIDD with saline (n=8). Clinical signs of keratitis in all groups were assessed consecutively for a week. Bacterial quantification of excised corneas was counted on the fourth and eighth days. Histopathologic examinations were performed to assess inflammatory cell infiltration on the eighth day. RESULTS: All signs of bacterial keratitis were alleviated in CTOIDD with NVCM according to criteria, and the CTOIDD-NVCM group had significantly less inflammation than CTOIDD-saline (p<0.05), and eye drop-NVCM (p<0.05). Two eyes in the eye drop-NVCM group, four eyes in the CTOIDD-saline group had corneal perforation (CP), while none of the rabbits showed CP in the CTOIDD-NVCM group. Bacterial counts were significantly less in the CTOIDD with NVCM group in comparison to the eye drop-NVCM (p<0.05), and CTOIDD-saline (p<0.05) groups. Severe inflammation and marked inflammatory cell infiltration were found in histopathologic examinations in the CTOIDD-saline and eye drop-NVCM groups, while significantly less inflammation was documented in the CTOIDD-NVCM (p<0.05) group. CONCLUSION: CTOIDD with NVCM effectively reduced the severity and treated acute bacterial S. aureus keratitis infection in a rabbit model. The presented approach of CTOIDD with NVCM appears to be a promising therapeutic approach for severe acute bacterial keratitis.

The penetration and distribution of topical atropine in animal ocular tissues.

PURPOSE: To conduct a multi-tissue investigation on the penetration and distribution of topical atropine in myopia treatment, and determine if atropine is detectable in the untreated contralateral eye after uniocular instillation. METHODS: Nine mature New Zealand white rabbits were evenly divided into three groups. Each group was killed at 5, 24 and 72 hr, respectively, following uniocular instillation of 0.05 ml of 1% atropine. Tissues were sampled after enucleation: conjunctiva, sclera, cornea, iris, ciliary body, lens, retina, aqueous, and vitreous humors. The assay for atropine was performed using liquid chromatography-mass spectrometry (LC-MS), and molecular tissue distribution was illustrated using matrix-assisted laser desorption ionization-imaging mass spectrometry (MALDI-IMS) via an independent experiment on murine eyes. RESULTS: At 5 hr, the highest (mean ± SEM) concentration of atropine was detected in the conjunctiva (19.05 ± 5.57 ng/mg, p < 0.05) with a concentration gradient established anteriorly to posteriorly, as supported by MALDI-IMS. At 24 hr, preferential binding of atropine to posterior ocular tissues occurred, demonstrating a reversal of the initial concentration gradient. Atropine has good ocular bioavailability with concentrations of two magnitudes higher than its binding affinity in most tissues at 3 days. Crossing-over of atropine to the untreated eye occurred within 5 hr post-administration. CONCLUSION: Both transcorneal and transconjunctival-scleral routes are key in atropine absorption. Posterior ocular tissues could be important sites of action by atropine in myopic reduction. In uniocular atropine trials, cross-over effects on the placebo eye should be adjusted to enhance results reliability. Combining the use of LC-MS and MALDI-IMS can be a viable approach in the study of the ocular pharmacokinetics of atropine.

Safety study of intravitreal and suprachoroidal Laponite clay in rabbit eyes.

PURPOSE: To study the safety and biocompatibility of Laponite clay (LAP) within an intravitreal and suprachoroidal administration in rabbit eyes. METHODS: Thirty-two New Zealand albino rabbits were divided into two experimental groups to test intravitreal (IVT group) and suprachoroidal (SCS group) administration of a 100-µl and 50-µl Laponite suspension respectively. Following injection, the eyes were monitored by ocular tonometry, slit-lamp eye examination and indirect ophthalmoscopy, at 24 h, 1, 4, 12, and 14 weeks post administration. Histological examination was also performed to determine whether any ocular pathological change had occurred. Throughout the study, LAP presence in vitreous was estimated by complexometric titration with ethylenediaminetetraacetic acid (EDTA), taking advantage of the Laponite high content of magnesium ions. RESULTS: Neither significant differences in the intraocular pressure, nor relevant ocular complications were found in the two experimental groups after LAP administration. The histology of the retina remained unchanged. LAP presence in vitreous could be indirectly confirmed by complexometric titration until 14 weeks post administration in eyes of IVT group. CONCLUSION: Laponite could be considered as a vehicle for potential clinical use in ocular drug administration, due to its proven ocular biocompatibility and its transparency in gel state.

Study on phototherapeutic keratotomy for bacterial corneal lesions in rabbit / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To study the effect of phototherapeutic keratectomy (PTK) on rabbit bacterial corneal ulcer model and explore the clinical potential of this method. METHODS:Totally 48 eyes from all the 24 New Zealand rabbits were inoculated with Staphylococcus aureus and bacterial corneal ulcer model was established successfully. At 1d after inoculation,48 eyes were given levofloxacin eye drops when corneal ulcer was confirmed. Then slit lamp inspection and optical coherence tomography ( OCT) were performed to measure the central corneal ulcer depth. All the rabbits right eyes were treated with PTK, as an observation group,left eyes were not treated as a control group. The eye section were observed by slit lamp and central thickness of corneal ulcer was measured by OCT at 3 and 7d after this operation. Rabbits were sacrificed and the cornea was removed for pathological section 7d later. RESULTS: The corneal ulcers in both groups had a tendency to heal, showing a decrease in ulcer area and smoothness of the surface. There was no significant difference in the depth of corneal ulcer between the observation group and the control group before PTK (t=0.706,P=0.484). The difference between the two groups of eyes at 3 and 7d after PTK was obviously (P<0.05). CONCLUSION: PTK can effectively cure rabbit Staphylococcus aureus corneal ulcer and promote ulcer wound healing,which may be used for clinical treatment of patients with bacterial corneal lesions.

Variations in the endogenous fluorescence of rabbit corneas after mechanical property alterations.

Keratoconus is an eye disease in which the cornea progressively deforms due to loss of cornea mechanical rigidity, and thus causes deterioration of visual acuity. Techniques to characterize the mechanical characteristics of the cornea are important to better monitor changes and response to treatments. To investigate the feasibility of using the endogenous fluorescence of cornea for monitoring alterations of its mechanical rigidity, linear tensiometry was used to quantitate stiffness and Young's modulus (YM) after treatments that increase cornea stiffness (collagen photocross-linking) or decrease stiffness (enzymatic digestion). The endogenous ultraviolet fluorescence of cornea was also measured before and after these treatments. The fluorescence excitation/emission spectral ranges were 280 to 430/390 to 520 nm, respectively. A correlation analysis was carried out to identify fluorescence excitation/emission pairs whose intensity changes correlated with the stiffness. A positive correlation was found between variations in fluorescence intensity of the 415-/485-nm excitation/emission pair and YM of photocross-linked corneas. After treatment of corneas with pepsin, the YM decreased as the fluorescence intensity at 290-/390-nm wavelengths decreased. For weakening of corneas with collagenase, only qualitative changes in the fluorescence spectrum were observed. Changes in the concentration of native or newly created fluorescent molecular species contain information that may be directly or indirectly related to the mechanical structure of the cornea.

Ocular penetration of topically applied 1% tigecycline in a rabbit model.

AIM: To evaluate ocular penetration of topically applied 1% tigecycline. METHODS: Forty-two New Zealand White rabbits were divided into 3 groups. A 50 µL drop of 1% tigecycline was administered in group 1. In groups 2 and 3, the drop was administered every 15min for 60min (keratitis protocol). Aqueous humor samples in groups 1 and 2 were collected under general anesthesia at 15, 30, 45, 60, 120, and 180min after the last drop. All animals in group 3 were euthanatized. Cornea, vitreous and blood samples were collected 60 and 120min after the last drop. Tigecycline concentrations were measured using high performance liquid chromatography-mass spectrometry (LC-MS/MS). RESULTS: The peak aqueous humor tigecycline concentration [mean 0.73±0.14 mg/L (SD) and 2.41±0.14 mg/L, respectively] occurred 45min after topical drug application in groups 1 and 2. Group 3 mean values in the cornea, and vitreous, were 3.27±0.50 µg/g, and 0.17±0.10 mg/L at 60min and 3.17±0.77 µg/g and 0.20±0.07 mg/L at 120min, respectively. Tigecycline serum concentrations were negligible. CONCLUSION: Tigecycline levels in the aqueous humor in groups 1 and 2, and in the cornea in group 3 exceeded the minimum inhibitory concentrations of most gram-positive organisms that cause bacterial keratitis and endophthalmitis.

Phase-transition W/O Microemulsions for Ocular Delivery: Evaluation of Antibacterial Activity in the Treatment of Bacterial Keratitis.

PURPOSE: Moxifloxacin (MXN) is widely prescribed for the treatment of bacterial keratitis. The conventional MXN solution has several limitations, including short precorneal residence time and poor intrastromal bioavailability, requiring frequent instillation of the drug to achieve the desired therapeutic effect. To circumvent this problem, the W/O (water-in-oil) microemulsion (ME) system was utilized for sustained release and improved precorneal retention. METHODS: The pseudo-ternary phase diagrams were developed and various MEs were prepared using two non-ionic surfactants, Tween 80 and Span 20, with isopropyl myristate and acetate buffer. Physicochemical parameters, in vitro drug release and in vitro antibacterial activity were studied. The in vivo antimicrobial efficacy of optimized microemulsion (ME 10) was studied in an experiment on bacterial keratitis in rabbit eyes and compared with that of the marketed eye drops. RESULTS: The optimized microemulsion (ME 10) displays as an average globule size of <40 nm. The developed MEs showed acceptable physico-chemical behaviour, good stability for 3 months and exhibited sustained drug release. Greater efficacy in experimental bacterial keratitis in rabbit eyes was also observed in comparison with marketed drug solution. CONCLUSIONS: The developed MEs are a viable alternative to conventional eye drops, because of its ability to enhance bioavailability through its longer precorneal residence time and its ability to sustain the release of the drug.

Evaluation of the effect of fasudil hydrochloride on outflow facility in enucleated eyes of different animals / 眼科新进展

Objective To evaluate the influence of a selective Rho-associated protein kinase inhibitor (fasudil hydrochloride) on outflow facility in enucleated porcine,rabbit and bovine eyes.Methods At the constant perfusion pressure of 15 mm-Hg (1 kPa =7.5 mmHg),the baseline coefficient of outflow facility (C0) of the isolated porcine,rabbit and bovine eyes was recorded respectively.The enucleated porcine eyes were divided into two groups randomly (n =6),and they were control group and experimental group.The same grouping method was also used-C0 the ribbit and bovine eyes.The control group was subjected to GPBS perfusion,while the experimental group was treated with 100 μmol · L-1 fasudil solution,followed by recording the experimental coefficient of outflow facility (C1),as well as calculating ΔC (ΔC =C1-C0) and ΔC％ (ΔC％ =ΔC/C0).Finally,the paired t test and one-way analysis of variance were performed using SPSS 17.0.Results As for porcine eyes,the ΔC％ of the control group was (17.83 ± 3.84) ％ while the experimental group was (44.00 ± 6.44) ％;as for rabbit eyes,the ΔC％ of the control group was (15.50 ± 2.93) ％,while the experimental group was (31.67 ±6.54)％;as for bovine eyes,the ΔC％ of the control group was (11.67 ± 1.17)％,while the experimental group was (37.17 ± 4.48)％.The ΔC％ in the experimental group was significantly increased when compared with the control group in three animals,with significant difference (all P ＜ 0.05).There was no statistical difference in ΔC％ of three experimental groups among different kinds of animals (all P ＜ 0.05).Conclusion Fasudil can improve outflow facility in enucleated eyes of animals,and it can redistribute aqueous humor drainage to a wider area through directly regulating the cytoskeleton of cells and matrix,resulting in increased coefficient of outflow facility.

Episcleral drug film for better-targeted ocular drug delivery and controlled release using multilayered poly-ε-caprolactone (PCL).

UNLABELLED: Triamcinolone acetonide (TA) and poly-ε-caprolactone (PCL) were engineered into a micro drug film for episcleral application to better manage chronic vitreoretinal diseases such as proliferative vitreoretinopathy (PVR). Compared to an intravitreal drug injection, this drug film is much safer without breaking into ocular barriers. Compared to a traditional subtenon injection, this drug film demonstrated superior therapeutic duration, better drug bioavailability in the choroid and retina, and better-targeted drug delivery ability. The rabbit eye study demonstrated that using the PCL-TA film led to 5.6 and 3.4 times higher drug AUC in the choroid and the retina respectively than in eyes following a subtenon drug injection. The mean drug residence time in the rabbit choroid was also doubled by using the episcleral TA film (86days versus 43days). Remaining TA in the drug film was consistently higher than that in the subtenon space, indicating controlled release of TA by the PCL-TA film. The pharmacokinetics of triamcinolone in the choroid and retina were optimized from typical first-order kinetics to a more sustained release by use of this film. This episcleral film system worked better on rabbit eyes than on guinea pig eyes, indicating that scleral thickness and eye size may be crucial aspects to consider when choosing an animal model or when designing a transscleral delivery device for human use. This engineered drug film may be very useful in preventing and managing PVR associated with open globe trauma or surgical repair for retinal detachment. STATEMENT OF SIGNIFICANCE: This study demonstrated a novel micro episcleral drug film that is made from the engineering of triamcinolone acetonide (TA) into poly-ε-caprolactone (PCL). The film can be conveniently placed at the injury or disease site during primary surgery and provide controlled release of TA for four months that covers the high-risk time window for developing proliferative vitreoretinopathy (PVR). This engineered drug film may be very useful in preventing and managing PVR associated with open globe trauma or intraocular surgery.

Therapeutic Effectiveness in the Treatment of Experimental Bacterial Keratitis with Ion-activated Mucoadhesive Hydrogel.

PURPOSE: To investigate the therapeutic effectiveness of ion-activated mucoadhesive hydrogel system in the treatment of experimental bacterial keratitis. MATERIALS AND METHODS: Mucoadhesive systems were prepared using gellan or sodium alginate alone and combined with sodium carboxymethylcellulose (NaCMC) to enhance the gel bioadhesion properties. The in vivo antimicrobial efficacy of selected mucoadhesive systems was studied in an experiment on bacterial keratitis in rabbit's eyes and compared with that of the marketed conventional eyedrops. RESULTS: Ocular tolerance was studied in the eye of albino rabbits and tested formulations were non-irritant with no sign of inflammation. Better improvement in experimental bacterial keratitis in rabbit eyes was observed in animals treated with mucoadhesive hydrogel formulation (GG5 and GS5) compared with marketed drug solution. CONCLUSION: The developed system is a viable alternative to conventional eyedrops of GTN due to its ability to enhance bioavailability through its longer precorneal residence time.

Safety and pharmacodynamics of suprachoroidal injection of triamcinolone acetonide as a controlled ocular drug release model.

Suprachoroidal injection is an emerging technique for drug delivery to the posterior segment, which is hard to reach by non-invasive approaches. However, the injection technique varies and the associated ocular safety is not well understood. In addition, it is not clear if drug formulation is a major factor in optimizing pharmacodynamics using this technique. The current study was designed to compare the suprachoroidal injection of different drug formulations and to characterize the safety and pharmacodynamics of triamcinolone acetonide (TA) delivered by this technique. Both indocyanine green (ICG) solution and TA suspension, at 50µL, 100µL, and 150µL, were suprachoroidally injected and intraocular pressure (IOP) tonometry, fundus photography, and electroretinography were performed over multiple time points up to eight weeks. After 50µL TA (Kenalog-40) suprachoroidal injection, 4-5 animals at 7 time points were sacrificed for aqueous, vitreous, retina, and plasma collections. TA was quantitated using ultra-performance liquid chromatography tandem mass spectrometry. For comparative efficacy study, 50µL (2mg) suprachoroidal TA versus 20mg subtenon TA were performed 4weeks before induction of experimental uveitis with 10ng of intravitreal lipopolysaccharide. After suprachoroidal injection, IOP had an acute elevation, higher volume caused higher IOP (p<0.0001). Equivalent volume of ICG solution led to a significantly smaller IOP elevation than after TA suprachoroidal injection. This finding suggests better distribution of ICG solution than TA suspension in the suprachoroidal space. Following a 50µL suprachoroidal injection, peak TA concentration in the aqueous was below 1ng/mL. In contrast, the posterior vitreous and retina had 1912ng/mL and 400,369ng/mL TA, respectively. Maximum TA in plasma was 11.6ng/mL. Drug exposure to the posterior retina was 523,910 times more than that to the aqueous and 29,516 times more than systemic TA exposure. In the treatment of lipopolysaccharide-induced uveitis, compared with 20mg subtenon injection, suprachoroidal 2mg TA demonstrated much better efficacy with significantly less aqueous humor cells and lower vitreous opacity scores (p<0.05). Histology showed much less vitreous inflammation in the suprachoroidal injection group (p<0.0001). It seems that a 50µL suprachoroidal injection of TA was well tolerated in rabbit eyes and demonstrated excellent penetration into the posterior retina, providing better therapeutic effect than subtenon 20mg TA.

Sustained release of triamcinolone acetonide from an episcleral plaque of multilayered poly-ε-caprolactone matrix.

A subtenon injection of triamcinolone acetonide (TA) is a widely used treatment modality for various chorio-retinal diseases. Although it is less invasive than intravitreal injection, it can produce dose-associated ocular complications and has the disadvantages associated with systemic TA exposure. In this study we have developed and evaluated an episcleral film consisting of TA and poly-ε-caprolactone (PCL). The films were prepared by spraying a mixture of PCL in dichloromethane and TA in acetone. The films were produced as 6mm wide and 12 mm long episcleral plaques. X-ray diffraction demonstrated an even distribution of TA crystals in PCL, although the TA was less crystalized than a native TA control. Fourier transform infrared spectroscopy revealed effective integration of TA within the PCL matrix. An in vitro study of the release of TA from the episcleral plaques showed that TA release rate was only 40-50% that of the equivalent native TA control. An in vivo study demonstrated that the plaques were well tolerated in rabbit eyes with significantly less systemic TA exposure. The episcleral plaques provided therapeutic vitreous TA levels for 3 months, while TA levels in the vitreous were detectable for only 1 month following an equivalent dose by subtenon TA injection. The PCL-TA 30-60 episcleral plaque may be further developed as a better alternative treatment for many chronic vitreo-retinal diseases, providing longer and controlled release and fewer drug-associated complications than those associated with a conventional subtenon injection of TA.

Application of sustained delivery microsphere of cyclosporine A for preventing posterior capsular opacification in rabbits.

AIM: To explore the inhibitory effect of a sustained cyclosporin A (CsA) delivery microsphere (CsA-MS) on posterior capsular opacification (PCO) in rabbit eyes after cataract extraction. METHODS: Twenty New Zealand white rabbits accepted cataract extraction plus intraocular lens implantation and their left eyes were intraoperatively injected CsA-MS prepared using polymer polylactioglycolic acid (PLGA) as a carrier and their right eyes were injected with empty MS. The changes in cornea, anterior chamber reaction, intraocular pressure, PCO and CsA concentration in aqueous humor were examined postoperatively and all the eyes were enucleated 3 months after surgery for histopathological and morphological examination with light microscopy and electron microscopy. RESULTS: Conjunctival hyperemia, corneal edema, intraocular pressure and anterior chamber response of experimental and control eyes were similar, while PCO in CsA-MS injected eyes was greatly improved compared with that in control eyes. Posterior capsules in CsA-MS injected eyes were smooth and lens epithelial cells (LEC) did not proliferate significantly (P>0.05), while LEC in posterior capsule of control eyes had different degrees of proliferation and cortical regeneration. LEC in CsA-MS injected eyes were not functionally active and underwent apoptosis, whereas LEC in control eyes were functionally active (F-test, P=0.025). In addition, the corneal ultrastructure showed no differences between CsA-MS and MS injected eyes. CONCLUSION: CsA-MS has high bioavailability in rabbit eyes and could inhibit postoperative PCO occurrence and development during the study period, suggesting that CsA-MS may be a promising, effective and safe administration route to prevent PCO in clinic.

Histologic Study after 5-Fluorouracil Injection into the Bleb in Ahmed Valve Implanted Rabbit Eyes

PURPOSE: To study the effect of the 5-fluorouracil (5-FU) injection into the bleb after the Ahmed glaucoma valve implant in rabbits. METHODS: Ahmed valve was implanted in normal 10 rabbits without previous ophthalmic history. In 4 of 10 rabbits, 5-FU (50 mg/ml, 0.1ml) was injected into filtering bleb in every two weeks for two times at postoperative 1 month and others were followed up as a control group. We obtained histological findings in 2 rabbis of control group at postoperative 1 month. In the control group and 5-FU injected 4 rabbit eyes, each 2 rabbit eyes were enucleated at postoperative 3 months and 6 months in both groups. The dissected bleb was examined through light microscopy with hematoxyline and eosin (H and E) stain and Masson-Trichrome (M-T) stain, and electron microscopy. RESULTS: The bleb was relatively avascular on gross and histological examination in the 5-FU injected group, and collagen fibers of the 5-FU injected group were less compact than that of the control group at postopeative 3 months. The number of inflammatory cells, fibroblasts and capillaris in outer layer was decreased in the 5-FU injected group. Under the electron microscopic examination, the density of collagen fibers was decreased and the space among them was widened. This change was more prominent in the 5-FU injected group. CONCLUSIONS: We found that the histological changes of blebs were made by the influx of aqueous humor through the Ahmed glaucoma valve and more stimulated by injection of 5-FU into the bleb after implantation of Ahmed glaucoma valve in a rabbit model.