Systemic inflammatory conditions frequently affect both the small joints of the hand and the eye. Uveitis and scleritis is common in this group and patients are required to apply regular eye drops. Ophthalmic conditions are also common in patients with Osteoarthritis of the thumb CMCJ who have weakness and pain on pinch grip. Poor compliance with therapy due to difficulties in administering eye drops can cause permanent ocular and visual morbidity.

A laboratory based biomechanical study was performed to replicate the pinch forces applied to the 20 most frequently used eye drops. The minimum force required to disperse a drop from a full bottle held in the inverted vertical position was assessed on three occasions by placing the eye drop bottles between a finger and thumb simulator attached to a load cell. Recordings of two bottle types were repeated using 2 different ergonomic ‘aids’ produced by the pharmaceutical companies.

The data was compared to published data for pinch strength of general ophthalmology patients and to collected data for patients with thumb base CMCJ osteoarthritis.

Compressive forces varied significantly between different eye drop types from 6.4 newtons (Systane) to 20.8 newtons (Minims). The highest values were found in minims which is the most frequently used eye drop. The use of the Xalatan aid appeared to increase the force required from 7.7(+/−0.64) to 12.9 (+/−3.93) but this difference did not reach significance, p=0.08, the results for Allegan aid showed no significant difference 11.3(+/−0.91) to 9.9 (+/−1.18)p=0.17. The forces required to disperse a drop increased as the bottles became less full.

Forces required to disperse eye drops from bottles varies considerably and can be greater than the maximum pinch pressure of some patient groups which may be a cause of poor compliance. Some ergonomic aids designed to help with the application of drops do not appear to reduce the forces required.