title: Intraocular fluid dynamics and retinal shear stress after vitrectomy and gas tamponade.
abstract: OBJECTIVE
  To evaluate fluid dynamics and fluid shear stress on the retinal wall in a model eye after vitrectomy and gas tamponade in relation to saccadic eye movements and sudden head movements and to correlate the results with gas fill fraction (GF). Methods. Analyses was undertaken using high-resolution computational fluid dynamic software. The fluid volume within the eye was discretized using 6 × 10(5) elements and solved with a volume-of-fluid
  
  
  METHODS
  The eye was abstracted to a sphere. Vertical and horizontal saccades and sudden rectilinear displacement of the head were examined. GF was varied from 20% to 80% of the eye height filled with gas.
  
  
  RESULTS
  Maximum shear stress during horizontal and vertical saccades was 1.0 Pa (Pascal) and 2.5 Pa, respectively, and was dependent on GF. Rapid rectilinear acceleration of the head caused a maximum shear stress of 16 Pa, largely independent of GF. Fluid sloshing within the eye decayed within 0.1 second. Stresses were maximum at the contact line and equator of the eye and were parallel to the direction of motion.
  
  
  CONCLUSIONS
  This study predicts that saccadic eye movements and normal head movements after vitrectomy and gas tamponade generate only small fluid shear stresses on the retina that are below published norms for retinal adhesion strength. Sudden, jerking head movements generate fluid shear forces similar to retinal adhesion strength that localize to the area of gas-fluid interface. Fluid sloshing occurs after movement, but rapidly decays on cessation of movement. These results suggest that restrictive posturing after vitrectomy and gas tamponade may be unnecessary. Patients should avoid sudden head movements.
authors.affiliation: Moorfields Eye Hospital, National Health Service (NHS) Foundation Trust, London, UK. romesh.indika@gmail.com
authors.forename: Romesh I
authors.initials: RI
authors.lastname: Angunawela
authors.forename: Ali
authors.initials: A
authors.lastname: Azarbadegan
authors.forename: G William
authors.initials: GW
authors.lastname: Aylward
authors.forename: Ian
authors.initials: I
authors.lastname: Eames
mesh_terms: D003198:Computer Simulation; D058450:Endotamponade; D020342:Finite Element Analysis; D005740:Gases; D019416:Head Movements / Q000502:physiology; D006801:Humans; D057446:Hydrodynamics; D008962:Models, Theoretical; D012160:Retina / Q000378:metabolism*; D012163:Retinal Detachment / Q000601:surgery; D012438:Saccades / Q000502:physiology; D033081:Shear Strength; D013312:Stress, Physiological / Q000502:physiology*; D014821:Vitrectomy; D014822:Vitreous Body / Q000378:metabolism*
chemical_list: D005740:Gases