title: The acoustic lighthouse effect. An ultrasonic response met in eyes after vitreoretinal surgery with silicone oil.
abstract: OBJECTIVE
  To discuss and possibly explain the ultrasonic lighthouse effect, a metaphor suggested for an artifact-like phenomenon sometimes found by B-scan in eyes having had intra-ocular perfluorocarbon and/or silicone oil injected as part of vitreoretinal surgery.
  
  
  METHODS
  Analysis of the ultrasonic findings with a view to the specific gravities of the above injected substances. Compared to water, perfluorocarbon has a higher and silicone oil a lower gravity; they are heavy and light, respectively.
  
  
  RESULTS
  The elicited lighthouse effect may appear localized or 'mobile'. When evoked only from specific positions on the globe, most likely it is explained by a lens-like accumulation of material trapped at the vitreous base just under the transducer. When mobile it depends on head position; there is a gravitational shift in position of the material, as evident in particular when becoming visible in the anterior chamber.
  
  
  CONCLUSIONS
  In case reports in literature slit-lamp verified anterior segment perfluorocarbon remnants have caused acoustic disturbances of a similar nature. In this study we found evidence that also silicone oil can underlie the acoustic lighthouse effect.
authors.affiliation: Rigshospitalet, University Eye Clinic, Copenhagen, Denmark.
authors.forename: H C
authors.initials: HC
authors.lastname: Fledelius
authors.forename: E
authors.initials: E
authors.lastname: Scherfig
mesh_terms: D000328:Adult; D000368:Aged; D000869:Anterior Eye Segment / Q000000981:diagnostic imaging*; D016477:Artifacts; D003937:Diagnosis, Differential; D005260:Female; D005466:Fluorocarbons / Q000627:therapeutic use; D006801:Humans; D007223:Infant; D007267:Injections; D008297:Male; D015203:Reproducibility of Results; D012163:Retinal Detachment / Q000000981:diagnostic imaging* / Q000601:surgery; D012827:Silicone Oils / Q000627:therapeutic use*; D014463:Ultrasonography; D014821:Vitrectomy; D014823:Vitreous Hemorrhage / Q000000981:diagnostic imaging* / Q000601:surgery
chemical_list: D005466:Fluorocarbons; D012827:Silicone Oils