A statistically significant variability in the force needed to squeeze a drop from common glaucoma medications was observed in a study published in the Journal of Glaucoma.
A team of researchers aimed to determine the force requirements to dispense a single drop from common brand and generic topical glaucoma medications and to correlate these findings with pinch strength in a representative patient population. The study tested four bottles of each medication with two in vertical orientation and two in horizontal orientation. The bottles were held in a customized force gauge apparatus intended to mimic ballpoint fingertip contact with a bottle tip. Each of the first 10 drops was tested and then tests were conducted in increments of 10 until the bottle was empty. The maximum force and displacement were electronically measured for every tested drop.
Eighty-four total bottles from 21 bottle designs were tested. Study authors noted a significant variability across the designs, with approximately a 7-fold (0.67–4.49kgf) and 4-fold (0.81–3.00kgf) difference in force requirements in the vertical and horizontal orientations, respectively. Of the enrolled patients in the glaucoma clinic (n=53), the mean pinch strength was 5.05kgf (range 1.23–10.4kgf) for the right hands and 4.82kgf (range 1.47–10.67kgf) for the left hands.
Overall, the sampling of glaucoma patients suggests that many likely have difficulty with the force requirements of several bottle designs. The findings support a need for standardization of topical glaucoma drug delivery and design.
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