title: Incidence of corneal pigmented arc and factors associated with its appearance in orthokeratology.
abstract: OBJECTIVE
  To determine the incidence of the corneal pigmented arc in orthokeratology (ortho-k) lens wearers over 12 months of lens wear and the factors associated with its appearance.
  
  
  METHODS
  Thirty-five ortho-k subjects were recruited; refractive and corneal changes after lens wear (single-lens protocol) were monitored over 12 months. The incidence of the pigmented arc after 3, 6 and 12 months of lens wear was determined.
  
  
  RESULTS
  The incidence of corneal pigmented arc was 17% (27%), 49% (49%) and 90% (93%) after 3, 6 and 12 months lens wear respectively in the left and right eyes. For subjects with arcs observed in the left eye within the first 6 months of lens wear, the mean +/- S.D. period of lens wear before initial detection of the arc was 14 +/- 7.4 weeks, and no correlation was found between this factor and the baseline spherical and cylindrical refractive errors (i.e. refractive sphere and cylinder, respectively), spherical equivalent refractive error (SERE), the target myopia reduction, the amount of refractive sphere (or SERE) reduction and changes in central and peripheral corneal curvatures after 6 months of lens wear. Baseline refractive sphere, baseline SERE, target, amount of myopia reduction, and change in central corneal curvature were significantly larger (p < 0.05) in those subjects with pigmented arcs after about 6 months of lens wear. The intensity of the observed pigmented arcs after about 6 months of lens wear was significantly related to the time when it was first observed (p = 0.003). Significant correlation was also found between the intensity of the arcs and the following parameters: baseline refractive sphere and SERE, target, change in central corneal curvature, and amount of myopia reduction (p < 0.006). After about 12 months of lens wear, the intensity of observed arcs was significantly related to the baseline refractive sphere, SERE and the target (p < 0.006).
  
  
  CONCLUSIONS
  The incidence of ortho-k-associated pigmented arc increases from 17% after 3 months of lens wear to over 90% after 12 months of lens wear. The intensity of the arc is related to the time when the arc first appeared. Both the incidence and the intensity of the arc are related to the period of lens wear, baseline refractive sphere, SERE and the target.
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
authors.forename: S W
authors.initials: SW
authors.lastname: Cheung
authors.forename: John
authors.initials: J
authors.lastname: Mountford
authors.forename: W S
authors.initials: WS
authors.lastname: Chui
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects*; D003315:Cornea / Q000473:pathology*; D003316:Corneal Diseases / Q000473:pathology*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D009216:Myopia / Q000473:pathology / Q000628:therapy; D009907:Optometry / Q000379:methods; D010859:Pigmentation Disorders / Q000473:pathology*; D013997:Time Factors