title: Multifocal electroretinography changes in patients on ethambutol therapy.
abstract: OBJECTIVE
  To evaluate the multifocal electroretinography (mfERG) changes in patients on ethambutol therapy.
  
  
  METHODS
  A cross-sectional observational study of 17 visually asymptomatic patients receiving antituberculosis therapy with ethambutol. Patients underwent complete ophthalmic examination and mfERG recordings. The first-order mfERG N1 and P1 response amplitudes and implicit times of six concentric rings were analysed and compared with 17 normal age-similar controls. Correlation analyses were performed between the patients' mfERG parameters with parameters of ethambutol usage (daily dose of ethambutol per body weight, duration of ethambutol therapy, cumulative dose of ethambutol, and cumulative dose of ethambutol per body weight).
  
  
  RESULTS
  The mean duration of ethambutol therapy was 3.6 months (range: 2-9 months) and the mean daily dose per body weight was 13.2 mg/kg/day. Analysis of response amplitude measures showed no significant difference in the mfERG N1 and P1 response amplitudes between the ethambutol and control groups at all ring eccentricities (P>0.05). For implicit times, there were significant delays in the mfERG P1 implicit times of rings 4-6 in the ethambutol group compared with controls (P=0.012 to P=0.041). Correlation analyses showed no significant correlation between the mfERG and ethambutol parameters (P>0.05).
  
  
  CONCLUSIONS
  The mfERG findings suggested that visually asymptomatic patients receiving ethambutol therapy might have localized mild electrophysiological changes involving the peripheral macula. These changes might be related to localized alteration of metabolism or physiological changes associated with ethambutol therapy.
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Hong Kong, People's Republic of China. tyylai@cuhk.edu.hk
authors.forename: T Y Y
authors.initials: TY
authors.lastname: Lai
authors.forename: J W S
authors.initials: JW
authors.lastname: Ngai
authors.forename: R Y K
authors.initials: RY
authors.lastname: Lai
authors.forename: D S C
authors.initials: DS
authors.lastname: Lam
mesh_terms: D000328:Adult; D000995:Antitubercular Agents / Q000008:administration & dosage / Q000009:adverse effects*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D004305:Dose-Response Relationship, Drug; D004596:Electroretinography / Q000187:drug effects; D004977:Ethambutol / Q000008:administration & dosage / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000187:drug effects* / Q000503:physiopathology; D012164:Retinal Diseases / Q000139:chemically induced* / Q000503:physiopathology
chemical_list: D000995:Antitubercular Agents; D004977:Ethambutol