title: Resultant vertical prism in toric soft contact lenses.
abstract: OBJECTIVE
  Rotational stability of toric soft contact lenses (TSCLs) is achieved using a range of designs. Designs utilising prism or peripheral ballast may result in residual prism in the optic zone. This study quantifies the vertical prism in the central 6mm present in TSCLs with various stabilisation methods.
  
  
  METHODS
  Vertical prism was computed using published refractive index and vertical thickness changes in the central optic zone on a full lens thickness map. Thickness maps were measured using scanning transmission microscopy. Designs tested were reusable, silicone hydrogel and hydrogel TSCLs: SofLens(®) Toric, PureVision(®)2 for Astigmatism, PureVision(®) Toric, Biofinity(®) Toric, Avaira(®) Toric, clariti(®) toric, AIR OPTIX(®) for ASTIGMATISM and ACUVUE OASYS(®) for ASTIGMATISM; with eight parameter combinations for each lens (-6.00DS to +3.00DS, -1.25DC, 90° and 180° axes).
  
  
  RESULTS
  All TSCL designs evaluated had vertical prism in the optic zone except one which had virtually none (0.01Δ). Mean prism ranged from 0.52Δ to 1.15Δ, with three designs having prism that varied with sphere power. Vertical prism in ACUVUE OASYS(®) for ASTIGMATISM was significantly lower than all other TSCLs tested.
  
  
  CONCLUSIONS
  TSCL designs utilising prism-ballast and peri-ballast for stabilisation have vertical prism in the central optic zone. In monocular astigmats fitted with a TSCL or those wearing a mix of toric designs, vertical prism imbalance could create or exacerbate disturbances in binocular vision function. Practitioners should be aware of this potential effect when selecting which TSCL designs to prescribe, particularly for monocular astigmats with pre-existing binocular vision anomalies, and when managing complaints of asthenopia in monocular astigmats.
authors.affiliation: Johnson & Johnson Vision Care, Wokingham, UK. Electronic address: asulley1@its.jnj.com.
authors.forename: Anna
authors.initials: A
authors.lastname: Sulley
authors.affiliation: nLight Corp., USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Hawke
authors.affiliation: Johnson & Johnson Vision Care, Inc., Jacksonville, FL, USA.
authors.forename: Kathrine Osborn
authors.initials: KO
authors.lastname: Lorenz
authors.affiliation: Johnson & Johnson Vision Care, Inc., Jacksonville, FL, USA.
authors.forename: Youssef
authors.initials: Y
authors.lastname: Toubouti
authors.affiliation: Johnson & Johnson Vision Care, Inc., Jacksonville, FL, USA.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Olivares
mesh_terms: D016880:Anisotropy; D003263:Contact Lenses, Hydrophilic / Q000145:classification*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D012031:Refractometry
keywords: Binocular vision; Monocular astigmats; Toric soft contact lenses; Vertical prism