Comparing Lubricating Eye Drops Using a Tribometer

Eye drop solutions are employed to ease symptoms which come as a result of a variety of eye problems. They can be utilized to treat minor eye irritation (e.g. redness and dryness) treat infections, or delay the onset of glaucoma for example.

The majority of eye drop solutions which are sold over-the-counter are used to treat dryness. The effectiveness of these solutions in lubricating the eye can be measured and compared via a coefficient of friction test.

Importance of Testing Eye Drop Solutions

Many factors can lead to dry eyes, being outdoors in extreme weather conditions or computer eye strain for example. Good lubricating eye drops help to supplement and maintain the moisture on the outer surface of the eyes. This alleviates burning, discomfort, or redness and irritation related to dry eyes. By measuring the coefficient of friction (COF) of an eye drop solution, its lubricating efficiency and how it measures up to other solutions can be established.

Measurement Objectives

By utilizing the pin-on-disk setup on the Nanovea T50 Tribometer the coefficient of friction (COF) of three different lubricating eye drop solutions was measured.

Eye-drop solution sample on Nanovea T50 Tribometer.

Eye-drop solution sample on Nanovea T50 Tribometer.

Measurement Parameters

With each eye drop solution behaving as the lubricant between the two surfaces, a 6 mm diameter spherical pin made from alumina was applied to a glass slide. Table 1 below shows the test parameters employed for all experiments.

Note that the alumina pins and glass slides employed in this study were selected because of their availability at the time of testing. A large variety of materials and lubricants can be utilized in order to simulate real life applications, or tailor the below experiment.

Table 1: Test parameters for COF measurements.

Test Parameters
Load 1 N
Duration of test 3 min
Rotational rate 200 rpm
Radius of track 2 mm
Revolutions 600
Ball Diameter 6 mm
Ball Material Alumina
Lubricant Samples A, B, C, D
Temperature 23 °C (room)

Samples of eye-drop solutions.

Samples of eye-drop solutions.

Results and Discussion

The average, minimum, and maximum coefficient of friction values for the three different eye drop solutions tested are tabulated in Table 2 below. The COF v. Revolutions graphs for each eye drop solution can be seen in Figures 2 - 4. During each test, the COF stayed relatively constant for the majority of the total test duration. The lowest average COF was seen in Sample A, which indicated that it had the best lubrication properties.

Table 2: The measure coefficient of friction values for Samples A, B, and C.

Sample Max COF Min COF Avg COF
A 0.578 ± 0.205 0.18 ± 0.277 0.317 ± 0.121
B 1.05 ± 0.02 0.121 ± 0.071 0.78 ± 0.024
C 1.09 ± 0.06 0.085 ± 0.069 0.84 ± 0.103

Change in COF over number of revolutions for Sample A.

Figure 2: Change in COF over number of revolutions for Sample A.

Change in COF over number of revolutions for Sample B.

Figure 3: Change in COF over number of revolutions for Sample B.

Change in COF over number of revolutions for Sample C.

Figure 4: Change in COF over number of revolutions for Sample C.

Conclusion

In this study the capability of the Nanovea T50 Tribometer is showcased by measuring the coefficient of friction of three eye drop solutions. It is demonstrated that Sample A had a lower coefficient of friction and so shows better lubrication when compared to the other two samples, based on these values.

Nanovea Tribometers provides repeatable and precise friction and wear testing by utilizing ASTM and ISO compliant linear and rotative modules. They also supply optional high temperature lubrication, wear, and tribo-corrosion modules available in one pre-integrated system.

This versatility enables users to simulate the real application environment better and enhance fundamental understanding of the wear mechanism and tribological characteristics of numerous materials.

This information has been sourced, reviewed and adapted from materials provided by Nanovea.

For more information on this source, please visit Nanovea.

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