Corneal UV Protective Effects of a Topical Antioxidant Formulation: A Pilot Study on In Vivo Rabbits.

This study aimed to evaluate the protective effect of a topical antioxidant and ultraviolet (UV) shielding action formulation containing riboflavin and D-α-tocopherol polyethylene glycol succinate (TPGS) vitamin E against corneal UV-induced damage in vivo rabbit eyes. In vivo experiments were performed using male albino rabbits, which were divided into four groups. The control group (CG) did not receive any UV irradiation; the first group (IG) was irradiated with a UV-B-UV-A lamp for 30 min; the second (G30) and third (G60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with one drop of the antioxidant and shielding formulation every 15 min, starting one hour before irradiation, until the end of UV exposure. The cornea of the IG group showed irregular thickening, detachment of residual fragments of the Descemet membrane, stromal fluid swelling with consequent collagen fiber disorganization and disruption, and inflammation. The cornea of the G30 group showed edema, a mild thickening of the Descemet membrane without fibrillar collagen disruption and focal discoloration, or inflammation. In the G60 group, the cornea showed a more severe thickening, a more abundant fluid accumulation underneath the Descemet membrane with focal detachment, and no signs of severe tissue alterations, as were recorded in the IG group. Our results demonstrate that topical application of eye drops containing riboflavin and TPGS vitamin E counteracts UV corneal injury in exposed rabbits.

Intraocular pressure reduction with once-a-day application of a new prostaglandin eye drop: a pilot placebo-controlled study in 12 patients.

PURPOSE: To assess the ocular hypotensive effect of 15-keto fluprostenol, the oxidized metabolite of travoprost, on glaucoma patients, through a randomized double-masked placebo-controlled study. METHODS: Twelve patients with ocular normal tension glaucoma (NTG) (intraocular pressure [IOP] < 22 mmHg) were enrolled. In order to ensure patient compliance to treatment, all study subjects were hospitalized. In each patient, the eye to be submitted to the treatments was randomly chosen. After hospital admission (day 1), those patients received for 5 days at 8 P.M. either one drop of 15-keto fluprostenol (35 µg/ml) or one drop of placebo. IOP evaluation was performed within 8 A.M. and 8 P.M. for 6 days. Furthermore, we performed a determination of cardiovascular parameters before and after the treatments. RESULTS: Starting with the first IOP measurement after the first treatment (8 A.M. on day 2), IOP was reduced of about 14% in the eyes treated 15-keto fluprostenol, in comparison with baseline IOP values of 15-keto fluprostenol-treated patients. The IOP reduction in the 15-keto fluprostenol-treated group was significantly compared to placebo group (p < 0.05) starting from day 3 till day 6 of the study. Except for mild hyperemia in one 15-keto fluprostenol-treated eye, no other side effects were observed or reported by the enrolled patients. CONCLUSIONS: The travoprost metabolite 15-keto fluprostenol was effective in decrease IOP and maintained IOP reduction along 5 days of treatment. The 15-keto fluprostenol can be developed as a good candidate for once-a-day NTG patients' treatment.

A Novel Vitamin E TPGS-Based Formulation Enhances Chlorhexidine Bioavailability in Corneal Layers.

Keratitis is a severe condition characterized by inflammation of the cornea following a local trauma. The most common ocular disease is the bacterial one, which requires an antibiotic treatment. The major limitation of this therapy is the resistance of the antibiotic. For this reason, alternative procedures have been developed and consist of antimicrobial molecules. One of the most used is the chlorhexidine gluconate, which has shown activity versus Gram-positive and Gram-negative bacteria and fungi. In addition to its efficiency, chlorhexidine shows low toxicity levels for mammalian cells and is a low-cost molecule. Despite its multiple benefits, chlorhexidine, if used at concentrations higher than 0.02% (w/w), can cause local eye irritation. Additionally, its poor penetrability through the cornea makes necessary frequent instillation of eye drops for a prolonged time. Due to these limitations, alternative drug delivery strategies are required. Here, we report a novel formulation based on the combination of d-alpha-tocopherol polyethylene glycol 1000 succinate with chlorhexidine, which results in higher accumulation of the drug in human corneas measured by liquid chromatography and strong antimicrobial activity. Moreover, this formulation does not cause any toxic effect on human cells and is well tolerated by rabbit eyes. Therefore this novel formulation represents a good candidate for the treatment of keratitis that overcomes the risk of antibiotic resistance.

Topography and Pachymetry Guided, Rapid Epi-on Corneal Cross-Linking for Keratoconus: 7-year Study Results.

PURPOSE: To evaluate custom fast cross-linking (cfCXL) treatment of keratoconus. METHODS: "Custom fast cross-linking" or "cfCXL" is a keratoconus treatment algorithm featuring no epithelial disruption, 15 minutes of corneal presoaking with a riboflavin-vitamin E TPGS solution, and a 370-nm ultraviolet A radiation beam centered on the most highly curved corneal region. Ultraviolet A radiation beam fluence, total energy, and exposure time are significantly less than those in the Dresden protocol. In this study, refraction, spectacle-corrected distance visual acuity, Kmax, and corneal hysteresis were monitored in 81 eyes of 81 patients for 7 years with 100% follow-up. Pretreatment Kmax and patient age averaged 53.01 ± 4.87 D and 25.9 ± 4.7 years, respectively. RESULTS: Average refractive cylinder magnitude was reduced by 26.1% at 1 month postoperatively and by 44.2% at 7 years postoperatively. Logarithm of the minimum angle of resolution average spectacle-corrected distance visual acuity (best spectacle-corrected distance visual acuity) improved from +0.26 ± 0.34 (20/36.4) to +0.15 ± 0.23 (20/28.25), +0.05 ± 0.20 (20/22.4), and +0.06 ± 0.20 (20/22.96) at 1 month, 1 year, and 7 years postoperatively, respectively. Best spectacle-corrected distance visual acuity improved in 54.3%, 74.1%, 84.0%, 87.7%, 84.0%, 84.0%, and 82.7% of patients at postoperative months 1, 3, 6, 12, 24, 48, and 84, respectively. Kmax did not increase in 96.3% of patients at 1 month, 97.5% at 1 year, and 98.8% at 7 years postoperatively, with average corneal apex flattening at 1 month and 7 years of -2.79 ± 1.70 D and -4.00 ± 2.40 D, respectively. CONCLUSIONS: Custom fast cross-linking, epi-on, rapid, narrowed beam apex-centered treatment of keratoconus with riboflavin-vitamin E TPGS produced a significant, rapid, and lasting cone progression stoppage, astigmatism reduction, and visual acuity improvement.

Effectiveness and Safety of Topical Chlorhexidine and Vitamin E TPGS in the Treatment of Acanthamoeba Keratitis: A Survey on 29 Cases.

This study aimed to test the effectiveness of a solution of chlorhexidine (CHX) and D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) in the treatment of Acanthamoeba keratitis (AK) via a prospective, interventional case series study. Twenty-nine consecutive patients with AK were enrolled. At baseline, best-corrected visual acuity (BCVA), slit lamp examination, confocal microscopy, and polymerase chain reaction (PCR) were performed. Topical therapy with CHX 0.02% and VE-TPGS 0.2% was administered hourly/24 h for the first day, hourly in the daytime for the next three days, and finally, every two hours in the daytime up to one month. BCVA and ocular inflammation were recorded after two weeks, four weeks, and three months from baseline. Mean logMAR BCVA significantly improved at two weeks (0.78) compared to baseline (1.76), remaining stable over time (0.80 at four weeks, 0.77 at three months). Ocular inflammation improved in 14 eyes at 2 weeks, with further slow improvements in all cases. At three months, no patient had signs of corneal inflammation. The presence of corneal scars was first recorded at the two-week follow-up, with an enlargement at the four-week follow-up. At the three-month follow-up, 19 eyes still showed corneal opacities. In conclusion, the tested solution was shown to be effective for the treatment of AK. Furthermore, it might represent a good first-line treatment.

Customized Corneal Cross-Linking-A Mathematical Model.

PURPOSE: To improve the safety, reproducibility, and depth of effect of corneal cross-linking with the ultraviolet A (UV-A) exposure time and fluence customized according to the corneal thickness. METHODS: Twelve human corneas were used for the experimental protocol. They were soaked using a transepithelial (EPI-ON) technique using riboflavin with the permeation enhancer vitamin E-tocopheryl polyethylene glycol succinate. The corneas were then placed on microscope slides and irradiated at 3 mW/cm for 30 minutes. The UV-A output parameters were measured to build a new equation describing the time-dependent loss of endothelial protection induced by riboflavin during cross-linking, as well as a pachymetry-dependent and exposure time-dependent prescription for input UV-A fluence. The proposed equation was used to establish graphs prescribing the maximum UV-A fluence input versus exposure time that always maintains corneal endothelium exposure below toxicity limits. RESULTS: Analysis modifying the Lambert-Beer law for riboflavin oxidation leads to graphs of the maximum safe level of UV-A radiation fluence versus the time applied and thickness of the treated cornea. These graphs prescribe UV-A fluence levels below 1.8 mW/cm for corneas of thickness 540 µm down to 1.2 mW/cm for corneas of thickness 350 µm. Irradiation times are typically below 15 minutes. CONCLUSIONS: The experimental and mathematical analyses establish the basis for graphs that prescribe maximum safe fluence and UV-A exposure time for corneas of different thicknesses. Because this clinically tested protocol specifies a corneal surface clear of shielding riboflavin on the corneal surface during UV-A irradiation, it allows for shorter UV-A irradiation time and lower fluence than in the Dresden protocol.

Corneal Cross-Linking: Evaluating the Potential for a Lower Power, Shorter Duration Treatment.

PURPOSE: To determine the cross-linking effect of a riboflavin ultraviolet-A (UV-A) corneal cross-linking treatment that is both shorter and has lower energy than the Dresden protocol. METHODS: In a first experiment, 12 human corneas were presoaked with riboflavin and then irradiated with UV-A at 3 mW/cm after clearing the surface of riboflavin, with no added riboflavin during irradiation. Percent UV-A transmission through the corneas was measured at intervals up to 30 minutes. A second experiment involved 24 porcine corneas. Eight were de-epithelialized, presoaked in riboflavin for 30 minutes, and irradiated at 1.5 mW/cm for 10 minutes. An additional 8 were riboflavin treated and similarly irradiated, but with epithelium intact and a final 8 corneas were not treated. Young modulus was measured in all 24 corneas at the end of the experiment. RESULTS: The first experiment showed essentially complete riboflavin oxidation after only 10 minutes. Based on these results, a shortened UV-A exposure cross-linking experiment was designed using a reduced UV-A fluence of 1.5 mW/cm, an endothelial exposure within safety limits in humans. With this protocol Young modulus was the same in the irradiated porcine corneas but with epithelium intact as in the untreated corneas. In contrast, Young modulus increased by a factor of 1.99 in the UV-A cross-linked corneas at 1.5 mW/cm for 10 minutes with the epithelium removed. CONCLUSIONS: A shorter, lower energy protocol than the Dresden protocol seems to provide a significant increase in Young modulus, similar to published results with higher energy, longer exposure protocols.

Enhancement of corneal permeation of riboflavin-5'-phosphate through vitamin E TPGS: a promising approach in corneal trans-epithelial cross linking treatment.

Corneal accumulation of riboflavin-5'-phosphate (riboflavin) is an essential step in the so called corneal cross-linking (CXL), an elective therapy for the treatment of progressive keratoconus, corneal ectasia and irregular astigmatism. CXL is usually performed after surgical debridement of corneal epithelium, since it impedes the stromal penetration of riboflavin in a relatively short time. d-Alpha-tocopheryl poly(ethylene glycol) 1000 succinate (VE-TPGS) is an effective permeation enhancer used to increase adsorption of drugs trough different biological barriers. Moreover, belonging to the group of tocopherol pro-drugs, VE-TPGS exerts a protective effect on biological membrane against free-radical damage. The aim of this work is the evaluation of VE-TPGS effects on riboflavin corneal permeability, and the assessment of its protective effect against free-radicals generated during CXL procedures. Different solutions containing riboflavin (0.125% w/w), dextran (20.0% w/w) and increasing concentration of VE-TPGS were tested. Corneal permeation was evaluated in vitro by the use of modified Franz-cell type diffusion cells and freshly excised porcine corneas as barrier. The effect of VE-TPGS on riboflavin corneal penetration was compared with a standard commercial solution of riboflavin in dextran at different times. Accumulation experiments were conducted both on epithelized and non-epithelized corneas. Moreover, epithelized porcine corneas, treated with the tested solutions, were subjected to an in vitro CXL procedure versus non-epithelized corneas, treated with a commercial solution of riboflavin. Differences were measured by means of corneal rigidity using Young's modulus. The photo-protective effect of tested solutions on corneal epithelium was, finally, evaluated. CXL treatment was applied, in vitro, on human explanted corneas and resulting morphology of corneal epithelium was investigated by scanning electron microscopy.