title: Quantifying nystagmus in infants and young children: relation between foveation and visual acuity deficit.
abstract: OBJECTIVE
  Nystagmus eye movement data from infants and young children are often not suitable for advanced quantitative analysis. A method was developed to capture useful information from noisy data and validate the technique by showing meaningful relationships with visual functioning.
  
  
  METHODS
  Horizontal eye movements from patients (age 5 months-8 years) with idiopathic infantile nystagmus syndrome (INS) were used to develop a quantitative outcome measure that allowed for head and body movement during the recording. The validity of this outcome was assessed by evaluating its relation to visual acuity deficit in 130 subjects, its relation to actual fixation as assessed under simultaneous fundus imaging, its correlation with the established expanded nystagmus acuity function (NAFX), and its test-retest variability.
  
  
  RESULTS
  The nystagmus optimal fixation function (NOFF) was defined as the logit transform of the fraction of data points meeting position and velocity criteria within a moving window. A decreasing exponential relationship was found between visual acuity deficit and the NOFF, yielding a 0.75 logMAR deficit for the poorest NOFF and diminishing deficits with improving foveation. As much as 96% of the points identified as foveation events fell within 0.25° of the actual target. Good correlation (r = 0.96) was found between NOFF and NAFX. Test-retest variability was 0.49 logit units.
  
  
  CONCLUSIONS
  The NOFF is a feasible method to quantify noisy nystagmus eye movement data. Its validation makes it a promising outcome measure for the progression and treatment of nystagmus during early childhood.
authors: Retina Foundation of the Southwest, 9900 N. Central Expressway, Suite 400, Dallas, TX 75231, USA. jfelius@retinafoundation.org
authors: Joost
authors: J
authors: Felius
authors: Valeria L N
authors: VL
authors: Fu
authors: Eileen E
authors: EE
authors: Birch
authors: Richard W
authors: RW
authors: Hertle
authors: Reed M
authors: RM
authors: Jost
authors: Vidhya
authors: V
authors: Subramanian
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D002648:Child; D002675:Child, Preschool; D003941:Diagnostic Techniques, Ophthalmological / Q000592:standards*; D018450:Disease Progression; D005240:Feasibility Studies; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D005584:Fovea Centralis / Q000503:physiopathology; D006801:Humans; D007223:Infant; D008297:Male; D008954:Models, Biological; D020417:Nystagmus, Congenital / Q000175:diagnosis* / Q000503:physiopathology*; D012720:Severity of Illness Index; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult