title: [Advantage of higher oxygen transmissibility material Piggyback lens for keratoconus correction].
abstract: OBJECTIVE
  To evaluate the oxygen transmissibility of new material Piggyback lens combined with silicone hydrogel lens and higher Dk RGPCL. To investigate the improving of visual acuity, ocular shape and comfortable, also orthokeratology results and safety of this new system for keratoconus correction.
  
  
  METHODS
  Calculating the oxygen transmission (Dk/t) of the new Piggyback system involves Ohm's Law. Compare the changes of ocular surface curves and astigmatism with or without Si-SCL fitting, RGPCL vision and Piggyback lens vision. Investigate the comfortable improving and ocular complications, and changes of corneal shape after fitted with Piggyback lens by using corneal topography.
  
  
  RESULTS
  Selected silicone hydrogel lens was pure vision (B&L PV, 36% water, Dk/t 110) lens, RGPCL material was Menicon Z, Dk/t 95.9 and Boston XO, Dk/t 58.8. It was calculated to 44.4 Dk/t and 34.4 Dk/t with these two combinations. Twenty two moderate and severe keratoconus patients (28 eyes) fitted with the Piggyback lens successfully. Corneal K reading and astigmatism decreased significantly after wore the Si-SCL. Compared with RGPCL vision(4.82 ± 0.11), Piggyback lens vision (4.93 ± 0.08) was significant increased (t = -10.395, P < 0.01) 90% cases improved comfort vs prior RGPCL wear alone. Only few cases appeared slight conjunctival hyperemia and corneal staining. Corneal topography showed corneal flatter, spherical and regular reshaping results after 6 months wore the Piggyback lens.
  
  
  CONCLUSIONS
  By fitting Piggyback systems using new Si-SCL and higher Dk RGPCL materials may help problematic keratoconic patients improve visual acuity, comfort and safety, increase wearing time and orthokeratology results further.
authors.affiliation: Bei Yi Optometry & Ophthalmology Center, Beijing 100028, China. xpy@b-d.ac.cn
authors.forename: Pei-Ying
authors.initials: PY
authors.lastname: Xie
authors.forename: Hui
authors.initials: H
authors.lastname: Chi
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D000328:Adult; D001672:Biocompatible Materials / Q000737:chemistry*; D003261:Contact Lenses; D019781:Corneal Topography; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000628:therapy*; D008297:Male; D010100:Oxygen / Q000502:physiology*; D014792:Visual Acuity; D055815:Young Adult
chemical_list: D001672:Biocompatible Materials; D010100:Oxygen