Relationship between rheological properties and transverse relaxation time (T2) of artificial and porcine vitreous humour.

Vitreous liquefactive processes play an integral role in ocular health. Knowledge of the degree of liquefaction would allow better monitoring of ocular disease progression and enable more informed therapeutic dosing for an individual patient. Presently this process cannot be monitored in a non-invasive manner. Here, we evaluated whether magnetic resonance imaging (MRI) could predict the viscoelasticity and in turn liquefactive state of artificial and biological vitreous humour. Gels comprising identical concentrations of hyaluronic acid and agar ranging from 0.125 to 2.25 mg/ml of each polymer were prepared and their T2 was measured using a turbo-spin echo sequence via 3T clinical MRI. The gels were subsequently subjected to rheological frequency and flow sweeps and trends between T2 and rheological parameters were assessed. The relationship between T2 and vitreous humour rheology was further assessed using ex vivo porcine eyes. An optimised imaging technique improved homogeneity of obtained artificial vitreous humour T2 maps. Strong correlations were observed between T2 and various rheological parameters of the gels. Translation to porcine vitreous humour demonstrated that the T2 of biological tissue was related to its viscoelastic properties. This study shows that T2 can be correlated with various rheological parameters within gels. Future investigations will assess the translatability of these findings to live models.

Ex vivo evaluation of the stability, safety and antibacterial efficacy of an extemporaneous povidone-iodine preparation for ophthalmic applications.

BACKGROUND: Povidone-iodine is used as a cost-effective broad-spectrum antiseptic in the prophylaxis and treatment of certain ocular infections. In this study, the stability, ophthalmic irritation potential and antibacterial efficacy of an extemporaneous povidone-iodine preparation was determined using established ex vivo and in vitro assays. METHODS: Extemporaneous iodine was prepared by simple dilution in normal saline. Preparation stability was evaluated by monitoring concentration and pH. Ocular safety was determined using the bovine cornea opacity and permeability assay. Efficacy was assessed by determining the minimum inhibitory and minimum bactericidal concentration of the preparation on Staphylococcus aureus and Pseudomonas aeruginosa. RESULTS: Diluted povidone-iodine maintained its stability over the 28-day evaluation. The formulation caused mild ocular irritation at the lowest prepared concentration (0.5 per cent w/v), with irritation noticeably increased at higher concentrations. The preparation showed minimum bactericidal and inhibitory concentrations of 0.078 and 0.3 per cent w/v on S. aureus and P. aeruginosa, respectively. CONCLUSIONS: This study confirms the stability and broad-spectrum antibacterial efficacy of povidone-iodine, while addressing the ocular irritation potential of this chemical.