The Relationship of Residence Time and Visual Effect of Optive and Systane in Dry Eye Subjects

The benefits of artificial tears to relieve dry eye symptoms include, but are not limited to: stabilizing the tear film layer, fluid supplement action, improving visual acuity, and comfort. Studies have found a relationship between some of these benefits. For example, stabilization of the tear film is important not only to increase the tear break up time (TBUT), but is key in improving and maintaining visual acuity. These studies have alluded to the fact that there may or may not be a relationship between residence time and visual performance. Viscosity is one reason behind the uncertainty. Some solutions contain polymers which influence the ocular surface when contacted. This can impact residence time and ultimately visual performance. No prior research has explored the direct relationship between residence time and visual performance.

Residence time refers to the duration at which the artificial tear resides on the eye. Methods have been developed to assess residence time by admixing fluorescent tracers to the solution and then measuring the amount of fluorescence over time. The caveat to methods using certain tracers has lead to uncertainty in elimination measurements due to corneal penetration or differing molecular weights (MW) from the active vehicle ingredient in the solution. For example, low-MW tracers can be eliminated at a different rate than higher-MW polymers. In addition, the low-MW tracers may be able to penetrate the corneal epithelium giving a false pre-corneal residence time. Meadows, Paugh, Joshi, and Mordaunt addressed this issue by developing a technique using a polymer which did not penetrate the cornea and had the same MW as the active ingredient in the solution FITC-dextran. Based on the assumption that similar weights are eliminated at the same rate, this technique has shown to be more economic, manageable, and amendable than previous procedures measuring residence time.

Any ophthalmic drop has the potential to impact visual acuity upon instillation due to the effect it has on the tear layer components. Studies have observed that taking artificial tears continuously over time tends to stabilize the tear layer thus minimizing the immediate drop in contrast sensitivity upon instillation. Measuring the visual effect of artificial tears, using contrast sensitivity as a measure, provides valuable information about the therapeutic effect of artificial tears that are meant to stabilize the tear film, thus improving visual acuity in dry eye patients.

But what about the patient? There is a difference between residence time and retention of effect- which is often what matters the most for patients. Retention of effect refers to the beneficial effect of the drop. Currently there is no real measure of retention of effect. Doctors can assess the tear film objectively, but there have been no strong correlations between subjective dry symptoms and tear film stability. A possible reason for the lack of correlation may be due to the fact that subjectivity is difficult to quantify. However, scales like the Visual Analog Scale (VAS) and Numerical Rating Scale (NRS) have been established in an attempt to quantify subjective experiences such as visual quality. We will be using the NRS to gauge the comfort of the drop upon the initial application to get a general idea of the comfort the drop provides to the user.

Although there have been several studies done on residence time and visual effect of ophthalmic formulations separately, there is no current research correlating these two aspects of therapeutic efficacy. This study will be the first to concurrently investigate residence time (using FITC-dextran) and visual effect of an ophthalmic formulation.