Quantifying silicone oil emulsification in patients: are we only seeing the tip of the iceberg?

Abstract

Purpose: Emulsification of silicone oil in the eye is a difficult problem. In an effort to find an objective way to quantify emulsification, we used the Coulter principle to measure silicone oil emulsified droplets from the washings of a series of patients.

Methods: Aqueous washouts after silicone oil removal were obtained from nine patients (nine eyes). We used the Coulter counter Multisizer® 4 to obtain the size distribution of the oil droplets.

Results: Over 65 % of the emulsified silicone oil droplets in the clinical samples had a diameter smaller than is detectable by light microscopy (2 μm). The median size of the droplets was between 1.1 and 1.9 μm. Based on the Spearman's correlation coefficient (r), there was a strong correlation between the number of the droplets that cannot be seen (between 1 and 2 μm) and those that can be seen (7-30 μm) (r = 0.817, p = 0.007).

Conclusion: Once emulsification was detected clinically in the anterior chamber, extensive emulsification would have already occurred in the posterior chamber, with most of the emulsified droplets that were too small in size to be seen on clinical examination. Ostwald ripening might explain why there were so many small droplets. The predominance of small droplets might account for some of the clinical complications associated with silicone oil use.

Keywords: Coulter counter; Emulsification; Silicone oil; Tamponade.