Abstract
Purpose: :
The aim of this study was to compare dynamic distribution of different artificial tears using real–time optical coherence tomography (OCT).
Methods: :
A real–time corneal OCT was used to image the tear film and tear menisci around upper and lower eyelids before and immediately after the instillation of different artificial tears. Three artificial tears (Refresh Liquigel, RL, Allergan, viscosity 70 cps; Refresh Tears, RT, Allergan, viscosity 3 and Systane, S, Alcon, viscosity 18) and control (Normal Saline, NS, viscosity 1) were tested on both eyes separately on two consecutive days on 20 subjects (total 8 visits). OCT imaging was repeated at 5, 20, 40 and 60 minutes after instillation (35µl). Custom software was used to process OCT images to obtain results, which included tear film thickness and tear meniscus curvature, height and area around both upper and lower eyelids.
Results: :
After the instillation of artificial tears and NS, all variables increased significantly (Re–ANOVA, p<0.001). Tear film thickness changed significantly during the study period (Re–ANOVA, F(5, 95)=175.3, p<0.001, averaged data) with significant increases immediately after the instillation and at 5 minutes (post hoc tests: p<0.001). No significant differences of all parameters among drops were found at 20 minutes and afterwards (post hoc tests, p>0.05). Immediately after instillation, both tear film thickness and the lower tear meniscus parameters were related to product viscosity, with RL > S > RT > NS. Upper tear meniscus parameters did not follow this relationship (S > RL > RT = NS). When total volume of tears on the ocular surface was estimated, it was dominated by the volume carried in the lower meniscus.
Conclusions: :
This is the first study to demonstrate the feasibility of measuring the dynamic behavior of artificial tears using OCT. The differences observed between upper and lower tear meniscus parameters suggest that the volume of tears held in these two compartments might be determined by different properties (such as viscosity and surface tension) of the tears. The observations of volume retention time of tears following instillation between 5 and 20 minutes, depending on tear composition, are consistent with prior reports of the residence time of aqueous drops on the ocular surface. (This study has been supported by research grants from NEI, Allergan, Rochester Eye Bank and RPB).
Keywords: cornea: tears/tear film/dry eye • lacrimal gland