title: Fixation and its role in the causation, laterality and location of pterygium: a study in amblyopes and non-amblyopes.
abstract: OBJECTIVE
  To evaluate the role of fixation in causing pterygium and determining its laterality and location.
  
  
  METHODS
  This is a prospective, observational, case-control study. Cases were defined as patients with primary pterygium who had unilateral amblyopia with eccentric fixation. Controls were age-matched patients with primary pterygium, but without amblyopia and eccentric fixation. All patients underwent complete ocular, orthoptic, and systemic examination and a detailed risk-factor assessment (latitude of residence, exposure to sunlight, sand, and a high-reflectance environment). The role of fixation in the causation, laterality and location of pterygium was evaluated. Fisher's exact test, the unpaired t-test, and odds ratio (OR) were carried out to determine the significance of the observations.
  
  
  RESULTS
  The mean age of subjects was 47.1±5.25 years in cases (n=107) and 48.2±4.75 years in controls (n=310; P=0.78). As far as known risk factors were concerned, both groups were evenly matched. Among the cases, 88 (82.2%) patients demonstrated suppression of the amblyopic eye and 19 (17.8%) patients had abnormal retinal correspondence (ARC). Patients with suppression had a unilateral pterygium in the better (fixating) eye, whereas those with ARC had bilateral pterygia. Among the controls, 192 (61.9%) eyes had bilateral pterygia and 118 (38.1%) eyes had unilateral pterygium. In controls, the dominant eye had a higher prevalence of pterygium. All patients in both groups had a nasal pterygium. Pterygium and fixation were strongly associated (P=0.007; Fisher's exact test; OR -15.98; P=0.008).
  
  
  CONCLUSIONS
  Fixation appears to have an important role in causing pterygium and determining its location and laterality.
authors.affiliation: M & J Institute of Ophthalmology, Ahmedabad, India. adityasudhalkar@yahoo.com
authors.forename: A
authors.initials: A
authors.lastname: Sudhalkar
mesh_terms: D000328:Adult; D000550:Amblyopia / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D005403:Fixation, Ocular; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011446:Prospective Studies; D011625:Pterygium / Q000209:etiology* / Q000473:pathology*; D012307:Risk Factors