title: ToF-SIMS analysis of dexamethasone distribution in the isolated perfused eye.
abstract: OBJECTIVE
  To illustrate the ability of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to characterize and demonstrate the spatial distribution of dexamethasone within ocular tissues.
  
  
  METHODS
  Dexamethasone sodium phosphate was administrated to perfused and nonperfused ovine eyes via intravitreal injections. The vitreous humor, the lens, and the retina of the eyes were then removed and divided into front, middle, and back sections. ToF-SIMS analysis was performed on each cross-section of the vitreous humor using Bi(3+) cluster source and images of drug distribution within the sections generated.
  
  
  RESULTS
  In the positive ion spectra, four key drug fragment peaks were identified and in the negative ion spectra, one key drug peak was identified. All five important drug peaks were successfully imaged in each tissue section and their distribution within the section illustrated. The drug was shown in the nonliving eye to move by diffusion alone, whereas in the living eye the drug was shown to distribute faster within the vitreous and penetrate through to the back of the retina and also into the lens.
  
  
  CONCLUSIONS
  The results illustrate the ability of ToF-SIMS to characterize and provide spatial information about drug distribution within ocular tissues. Key differences in drug movement through the vitreous humor, toward both the anterior and the posterior tissues, in the living eye and the nonliving ovine eye were demonstrated, showing that dexamethasone sodium phosphate distribution through the vitreous is not determined by diffusion alone.
authors.affiliation: Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, Scotland.
authors.forename: Jenifer
authors.initials: J
authors.lastname: Mains
authors.forename: Clive G
authors.initials: CG
authors.lastname: Wilson
authors.forename: Andrew
authors.initials: A
authors.lastname: Urquhart
mesh_terms: D000818:Animals; D003907:Dexamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005123:Eye / Q000378:metabolism*; D005938:Glucocorticoids / Q000008:administration & dosage / Q000493:pharmacokinetics*; D058449:Intravitreal Injections; D034561:Sheep, Domestic; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D014018:Tissue Distribution
chemical_list: D005938:Glucocorticoids; D003907:Dexamethasone