title: Evaluation of FD2 (Frisby Davis distance) stereotest in surgical management of intermittent exotropia.
abstract: OBJECTIVE
  To evaluate Frisby Davis distance (FD2) stereotest for determining the timing of surgical intervention in intermittent exotropia (X(T)).
  
  
  METHODS
  A prospective case-control study was conducted including 30 patients with X(T) and 30 age-matched controls. Stereoacuity was measured preoperatively and 3 months postoperatively using FD2 for distance and TNO and Randot for near.
  
  
  RESULTS
  Preoperative distance stereoacuity was 43.83 ± 35.51 arcsec (median 30 arcsec; range 10-120) which improved postoperatively to 27 ± 33.74 arcsec (median 15 arcsec; range 5-120) (p=0.001). Cases with FD2 stereoacuity worse than 70 arcsec did not show significant improvement. Mean preoperative near stereoacuity by TNO was 94.00 ± 79.48 arcsec (median 60 arcsec) and Randot was 50.33 ± 39.23 arcsec (median 30 arcsec) which improved to 80.00 ± 80.08 arcsec (median 60 arcsec) and 34.17 ± 57.00 arcsec (median 20 arcsec), respectively, after surgery (both p=0.001). The controls had a mean distance stereoacuity of 14.66 ± 4.13 arcsec (median 15 arcsec; range 5-20) and near stereoacuity of 63.00 ± 21.35 arcsec (median 60 arcsec (TNO)) and 23.66 ± 5.07 arcsec (median 20 arcsec (Randot)). There was a significant correlation between FD2 and Randot in the cases but not in controls (p=0.005), however no correlation was found between TNO and FD2.
  
  
  CONCLUSIONS
  Distance stereoacuity is reduced in X(T) to a greater extent than the near stereoacuity and both improve after surgery. FD2 is useful for deciding timing of surgery and a stereoacuity worse than 20 arcsec is an indication for surgical intervention. A preoperative distance stereoacuity which is worse than 70 arcsec implies a poor prognosis for stereoacuity improvement after surgery.
authors.affiliation: Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, , New Delhi, India.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Singh
authors.forename: Pradeep
authors.initials: P
authors.lastname: Sharma
authors.forename: Digvijay
authors.initials: D
authors.lastname: Singh
authors.forename: Rohit
authors.initials: R
authors.lastname: Saxena
authors.forename: Anudeepa
authors.initials: A
authors.lastname: Sharma
authors.forename: Vimla
authors.initials: V
authors.lastname: Menon
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D003867:Depth Perception / Q000502:physiology*; D005099:Exotropia / Q000175:diagnosis* / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D014787:Vision Tests / Q000379:methods*; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult
keywords: Muscles