title: Quantifying silicone oil emulsification in patients: are we only seeing the tip of the iceberg?
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Room 301, Level 3, Block B, Cyberport 4, 100 Cyberport Road, Pokfulam, Hong Kong.|Department of Mechanical Engineering, Faculty of Engineering, University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Yau Kei
authors.initials: YK
authors.lastname: Chan
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Room 301, Level 3, Block B, Cyberport 4, 100 Cyberport Road, Pokfulam, Hong Kong.|Singapore Eye Research Institute, National University of Singapore, City-State, Singapore.|Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia.
authors.forename: Ning
authors.initials: N
authors.lastname: Cheung
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Room 301, Level 3, Block B, Cyberport 4, 100 Cyberport Road, Pokfulam, Hong Kong.
authors.forename: Wing Suet Catherine
authors.initials: WS
authors.lastname: Chan
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Room 301, Level 3, Block B, Cyberport 4, 100 Cyberport Road, Pokfulam, Hong Kong. shdwong@hku.hk.
authors.forename: David
authors.initials: D
authors.lastname: Wong
mesh_terms: D000328:Adult; D000368:Aged; D004322:Drainage / Q000379:methods; D004655:Emulsions / Q000032:analysis*; D058450:Endotamponade; D005260:Female; D006801:Humans; D008297:Male; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D008863:Microspheres; D008875:Middle Aged; D010316:Particle Size; D012827:Silicone Oils / Q000737:chemistry*; D014821:Vitrectomy; D057586:Vitreoretinal Surgery
chemical_list: D004655:Emulsions; D012827:Silicone Oils
keywords: Coulter counter; Emulsification; Silicone oil; Tamponade