Designing Minimally Invasive Preocular Contact Tips for Potential Application in Tear Collection

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Purpose:Basal tear fluid has drawn great attention as a medium for many disease markers and, hence, for its potential to be used in self-diagnosis. However, collection of basal tear fluid is difficult because a conventional tear collector, such as a glass capillary tube, may inflict irritation or damage on the sensitive ocular surface. Therefore, we sought to design a tip for contact with the preocular surface [a preocular contact tip (PCT)] that minimizes damage to the ocular surface.Methods:We designed the shape of the tip to have rounded boundaries and no sharp edges. We then tested different tip areas, each of which was contacted with the inferior palpebral conjunctiva of rabbit eyes at varying depths to demonstrate their feasibility in vivo. The area of damaged tissue and the time required for tissue recovery were monitored according to the pressure applied through the tips.Results:Our findings revealed that a contact area of the PCT greater than 2.36 mm2 caused relatively little damage to the inferior palpebral conjunctival tissue, which could recover within 4 hours after contact at all pressing depths. In contrast, a glass capillary tube caused relatively severe damage, which did not recover for more than 8 hours. The PCT (3.14 mm2) was embedded with a microchannel as a prototype tear collector, which could collect 0.3 μL of tears with minimal tissue damage.Conclusions:The PCT proposed in this study can be a promising tool for minimally invasive collection of basal tears from the inferior palpebral conjunctiva.

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