title: Reverse-geometry gas-permeable lens design for pellucid marginal degeneration.
abstract: OBJECTIVE
  To report a case of treating a patient with pellucid marginal degeneration (PMD) by using a reverse-geometry gas-permeable lens design.
  
  
  METHODS
  A 38-year-old Hispanic man was referred for having reduced visual acuity secondary to distorted corneas. The patient was diagnosed with PMD after an extensive slitlamp examination showed a thinning of the inferior peripheral cornea in both eyes. Corneal topography (Orbscan II) was performed to help confirm the diagnosis. A Reverse Aspheric Ortho Focus (RAOF) gas-permeable lens was fitted on this patient.
  
  
  RESULTS
  The Orbscan II corneal topography showed distinct peripheral steepening, a pronounced astigmatic pattern (greater in the left eye than in the right), and thinner corneas in the inferior periphery than centrally. The fluorescein pattern of the RAOF 5 lenses showed central alignment, good edge lift 360 degrees, mid peripheral bearing with 0.5 mm vertical movement on blinking, and good centration. The patient's distance visual acuity with the lenses was 20/20-1 in the right eye and 20/20 in the left.
  
  
  CONCLUSIONS
  The Orbscan II was an important tool in making the diagnosis of early PMD, because few clinical signs were observed. Not only does the Orbscan II provide the clinician with a topographic map of the cornea, but it also measures the corneal thickness, which aided in the diagnosis of this patient. In addition, the posterior float measurement provided by the Orbscan II may be instrumental in making a differential diagnosis. A reverse-geometry gas-permeable lens provided the patient with improved peripheral fit over conventional designs, adequate comfort, and optimal visual acuity.
authors.affiliation: Texas Eye Research and Technology Center, College of Optometry, University of Houston, Houston, TX 77204-2020, USA. jliu@optometry.uh.edu
authors.forename: Jill
authors.initials: J
authors.lastname: Liu
authors.forename: Norman E
authors.initials: NE
authors.lastname: Leach
authors.forename: Jan P G
authors.initials: JP
authors.lastname: Bergmanson
mesh_terms: D000328:Adult; D003261:Contact Lenses; D003316:Corneal Diseases / Q000175:diagnosis / Q000628:therapy*; D019781:Corneal Topography; D004108:Dilatation, Pathologic; D006801:Humans; D008297:Male; D011474:Prosthesis Design