title: Quantifying scatter in Shack-Hartmann images to evaluate nuclear cataract.
abstract: OBJECTIVE
  Quantify and localize lenticular forward scatter using Shack-Hartmann wavefront sensing (SHWS) as single-valued metrics and a scatter map, and to examine the relationships between forward scatter and backscatter metrics and visual acuity.
  
  
  METHODS
  We obtained SHWS images from 148 patients in the Texas Investigation of Cataract Optics study. Patient age was 22 to 84 years, with Lens Opacities Classification System III (LOCS III) nuclear opalescence (NO) scores ranging from 0.8 to 5.6. Visual acuities were measured at photopic (280 cd/m2) high (VA(PHC)) and low contrast (VA(PLC)) and mesopic (0.75 cd/m2) high (VA(MHC)) and low contrast (VA(MLC)). Scattering was described in a scatter map and by five single-valued metrics characterizing SHWS lenslet point spread functions. The relationships between scatter and visual acuity were tested using linear regression.
  
  
  RESULTS
  Visual acuities decreased proportional to both LOCS III NO (R2=up to 39%) and scatter metrics (R2=up to 21%). Stepwise multiple linear regression improved visual acuity prediction by including a backscatter and a forward scatter metric (R2 up to 51.2%). For the subjects over age 60 years (N=46, 68.8+/-6.12 years), the forward scatter metrics explain as much variance in visual acuities (R2=up to 29%) as LOCS III NO (R2=up to 26%). Combined they accounted for up to 48.8% of visual acuity variance.
  
  
  CONCLUSIONS
  Forward light scatter can be quantified using SHWS and the resulting metrics explain significant variance in visual acuity, especially in the aging eye. Together with a backscatter metric they explain approximately 50% of the variance in VA.
authors.affiliation: Visual Optics Institute, College of Optometry, University of Houston, Houston, TX 77204-2020, USA. wdonnelly.2001@alumni.opt.uh.edu
authors.forename: William J
authors.initials: WJ
authors.lastname: Donnelly
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
authors.forename: Jason D
authors.initials: JD
authors.lastname: Marsack
authors.forename: Edwin J
authors.initials: EJ
authors.lastname: Sarver
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Applegate
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002386:Cataract / Q000175:diagnosis* / Q000503:physiopathology*; D015331:Cohort Studies; D019781:Corneal Topography; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D008875:Middle Aged; D012542:Scattering, Radiation; D014785:Vision, Ocular; D014792:Visual Acuity