Precorneal residence times of sodium hyaluronate solutions studied by quantitative gamma scintigraphy

Abstract

SummarySodium hyaluronate solutions have been advocated in the management of a variety of dry-eye states. By virtue of their non-Newtonian rheological properties, for mulations exhibiting high zero-shear viscosities may be used as an artificial tear with the expectation of prolonged precorneal residence times and improved tolerance.Quantitative gamma scintigraphy was used to evaluate the residence times of 0.2% and 0.3% sodium hyaluronate solutions and a polymer-free solution of buffered saline in 12 patients with keratoconjunctivitis sicca and a group of six normal volun teers. Using several indices of residence time, mean values for the sodium hyalur. onate solutions were significantly longer than those for buffered saline. Parallel changes in tear film thickness were also demonstrated using a technique based on laser interferometry.Although a variety of therapeutic strategies can be utilised in the management of dry-eye disorders,1.2 the basis of therapy remains the artificial tear. The principal limitation of currently available tear substitutes is the short duration of symptom control experienced by some patients. A number of approaches have, therefore, been adopted to prolong the time they remain in contact with the ocular surface including the use of high viscosity formula tions,"· slow-release artificial tears' and occlusion of the lacrimal puncta.1> However, none of these methods have met with uniform success.Polymer solutions formulated at high vis cosity have longer residence times, 7 .H but are poorly tolerated because of transmitted 'University of Oxford, Department of Ophthalmology.shearing forces associated with blinking and rapid eye movements. It is in this respect that formulations of polymers that display non Newtonian or pseudoplastic properties offer a potential therapeutic advantage over conven tional artificial tears. At concentrations of 0. 2% and 0.3% , sodium hyaluronate solu tions exhibit high static. or zero-shear, vis cosities but undergo dramatic reduction in viscosity with increasing shear rate� (Fig. 1), thereby offering significantly less resistance to the movement of the lid over the globe than viscous Newtonian formulations. It is the expectation of prolonged residence time asso ciated with high zero-shear viscosities, and of patient acceptance owing to its shear-thinning behaviour, that has lead to the investigation of

Sodium Hyaluronate Decreases Ocular Surface Toxicity Induced by Benzalkonium Chloride–Preserved Latanoprost: An In Vivo Study

“…29 Moreover, viscoelastic properties and long ocular surface residence time of SH have rendered it effectively increase tear film stability and corneal wettability, and reduce the tear evaporation rate. 30 It was recently reported that a hyaluronate receptor, CD44, is expressed in human and rabbit corneas. 31,32 SH promoted human cornea epithelial cell migration by the adhesion between CD44 receptor.…”

Tear break-up time for tear film evaluation: Are moistening solutions interchangeable?

“…On the other hand S3, which resulted in the longest TBUT values, contains hyaluronic acid, which has been reported as a high-viscosity agent equivalent to mucus glycoprotein, with the ability to adhere to epithelial cells [19]. Previous research on surface residence time found that solutions containing sodium hyaluronate had a mean half-life on the ocular surface of 321 s, significantly longer than others with hydroxypropyl methyl cellulose, which is a viscosity agent for S4, or a buffered saline solution such as S1 and S2 [20,21]. Other reports disclosed that tear substitutes with sodium hyaluronate provide better tear film stability, as determined by NIBUT values, than those with hydroxypropyl methyl cellulose [22], and resulted in better patient reported comfort [23].…”

Mechanistic modeling of ophthalmic drug delivery to the anterior chamber by eye drops and contact lenses

“…Increasing the rate of evaporation of the tear film would reduce the time to equilibrium for the volume. For this reason, the time for removal of the drug from the system is also over predicted, with experimental results taking 900-1000 s for a tracer compound in a 25 μL drop to reach 1% of its original value [48,49] while the model predicts this time to be 1454 s. Again, increasing the rate of evaporation would result in the model predicting a lower value. When the rate of evaporation was set at 4 times the value originally used in the model, the time for removal of the drug decreased by ~9% [40].…”