A First Approach to Non-Contact Volume Measurements of Drops of Collyrium Instilled From Single-Dose Vials

Eye drops are a commonly employed treatment for a wide range of ophthalmic diseases due to their ease of administration, limited toxicity, and affordability. The main issue with this medical practice pertains to the uncertainty associated with the correct amount of drug instilled into the eye, which can lead to pharmacological excess or deficiency, as well as potential adverse or insufficient effects. This paper presents an optical method for measuring the volume of drops of collyrium instilled from commercial single-dose vials. For such a purpose, a measurement method was implemented to estimate the size of single drops through the analysis of digital images. First, two different instillation approaches were compared: one carried out by a patient and the other by a specifically designed automatic system. Successively, the uncertainty associated with the implemented image analysis-based method was estimated by a Monte Carlo simulation for both dispensing approaches. The results indicate that the geometric characteristics of the drop depend on the dispensing modality exclusively for a few percentage points. However, the manual approach exhibits a significant dispersion in terms of standard deviation (i.e., 110% and 48% for the radius and the height of the drop, respectively), with an expanded uncertainty about three times higher than that estimated when using the automatic system.