Microcapillary Tear Measurement Device with Silicone Coating
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Solution Overview
Problem
Current technologies for dry eye diagnostics, particularly for tear flow measurement, lack reliability and precision, leading to inaccurate assessments and potential irritation to the eye.
Innovation Solution
A biocompatible polymer microcapillary with a hydrophobic inner surface at the exit end and a hydrophilic or neutral surface elsewhere, coated with silicone rubber, is used to trap and measure tear fluid, minimizing irritation and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Schirmer test uses absorbent filter paper strip to measure tear flow, then tear flow measurement is achieved, but eye irritation and reactive tears occur causing inaccurate readings
Solution Approach 1:
The patent uses a flexible microcapillary tube with a soft silicone rubber coating on its outer surface. This thin flexible film covers the potentially irritating microcapillary, allowing it to gently contact the eye surface without causing irritation or reactive tears, while still enabling accurate tear flow measurement through the capillary action of the untreated inner surface.
Solution Approach 2:
The microcapillary tube features localized hydrophobic treatment only at the exit end (distal tip), while the entrance end (proximal end) and body remain hydrophilic. This local differentiation allows the entrance to wick tears effectively through capillary action while the hydrophobic exit prevents tear leakage and allows air passage, optimizing both measurement accuracy and comfort.
2Object-affected harmful factors
If topical anesthetic is applied to counter irritation during Schirmer test, then eye irritation is reduced, but tear flow measurement results are affected
Solution Approach 1:
The soft silicone rubber coating on the microcapillary tube provides a cushiony interface with the eye that reduces irritation without requiring topical anesthetics. This physical cushioning approach eliminates the need for chemical anesthetics that would interfere with tear flow measurement, thereby maintaining measurement accuracy while still protecting against eye irritation.
3Ease of manufacture
If filter paper with randomly sized interstitial spaces is used for Schirmer strip, then manufacturing is simple, but calibration between strips is inconsistent
Solution Approach 1:
The patent employs microcapillary tubes with precisely controlled inner diameters (e.g., 50-200 micrometers) that provide consistent capillary action. This parameter control ensures uniform tear wicking rates across all devices, eliminating the calibration inconsistencies found in filter paper with random interstitial spaces, while maintaining manufacturing feasibility through standard capillary tube production methods.
4Measurement precision
If microcapillary has hydrophobic inner surface at exit end, then tear liquid is trapped for measurement, but air passage may be blocked
Solution Approach 1:
The microcapillary tube features a localized hydrophobic treatment only at the distal tip (exit end), while the proximal end and body remain hydrophilic. This local hydrophobicity creates a one-way valve effect: the hydrophobic tip prevents tear liquid from escaping backward into the tube, while the small aperture and surface tension effects allow air to pass through unencumbered. This simple local modification eliminates the need for complex air-liquid separation mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a reliable and precise method for tear flow measurement, reducing eye irritation and enabling accurate assessment of tear production and quality, which can aid in diagnosing and managing dry eye conditions.
Implementation Method 1
the microcapillary has a hydrophobic inner surface treatment for a short portion at the opposite end
Implementation Method 2
The rest of the inner surface is either neutral or hydrophilic
Implementation Method 3
At the 1- to 1000-micron (μm) scale involved, the hydrophobic surface at the exit end exerts enough influence on any nearby liquid to prevent its escape out of the exit end
Data Source
AI summary
A lacrimal tear flow measurement device, and methods of manufacture and use, are described that includes a polymer microcapillary tube or similar structure having at least one end coated on the outside with soft silicone rubber and one end treated on the inside to be hydrophobic. The hydrophobic end keeps liquid from escaping or entering that end while allowing air to pass. The rest of the tube's insides may be hydrophilic or a neutral hydrophobe. As a Schirmer's test strip replacement, the entrance end of the device can be touched to the lacrimal lake of a patient's eye to collect suck up, or merely collect, tear fluid within the collection tube for weighing, volume measurement, or other analysis. Long-term collection devices for wear between doctors' visits can have a bypass channel allowing liquid to flow back onto the eye.