title: Hierarchical linear modeling of visual acuity change over time: rate of functional recovery after macular hole surgery.
abstract: OBJECTIVE
  To examine acuity recovery rate after Macular Hole (MH) surgery, using Hierarchical Linear Modeling (HLM) with linear and curvilinear regression analysis.
  
  
  METHODS
  Preoperative MH diameter (OCT) and acuity (ETDRS) were recorded in 20 eyes. Acuities were tested during follow-up (6 to 23 months), with three to eight measurements per eye. The resulting 95 acuities were analyzed using HLM. Variability at the level of the person was explained by change over time, using a natural logarithm conversion. Across patients, MH diameter was used to predict slopes and intercepts at the level of the individual.
  
  
  RESULTS
  MH diameter was able to account for significant amounts of variability in preoperative acuity (intercept) and significantly influenced rate of functional recovery (slope). A nonlinear approach to the data accounted for the largest amount of variance.
  
  
  CONCLUSIONS
  Participants with larger MHs recovered relatively more acuity sooner while eyes with smaller MHs had better absolute acuity outcome. HLM provides important insight into the recovery process after MH surgery and is more flexible with follow-up data. In the context of MH treatment, most recuperation occurred during the initial 6 months.
authors.affiliation: Department of Neurology and Neurosurgery-Neuroscience, McGill University, Montreal, Quebec, Canada. walterwittich@sympatico.ca
authors.forename: Walter
authors.initials: W
authors.lastname: Wittich
authors.forename: Olga
authors.initials: O
authors.lastname: Overbury
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kapusta
authors.forename: Donald H
authors.initials: DH
authors.lastname: Watanabe
mesh_terms: D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016014:Linear Models; D008297:Male; D011184:Postoperative Period; D020127:Recovery of Function; D012044:Regression Analysis; D012167:Retinal Perforations / Q000503:physiopathology* / Q000601:surgery*; D013997:Time Factors; D014792:Visual Acuity