title: Sympathetic inhibition of accommodation after sustained nearwork in subjects with myopia and emmetropia.
abstract: OBJECTIVE
  The purposes of the present study were to assess the effect of a sympathetic inhibitory pharmacologic agent, timolol maleate, on the magnitude of nearwork-induced transient myopia (NITM) and its decay in different refractive groups for an extended near task duration and to determine the proportion of the young adult population manifesting effective sympathetic access under naturalistic closed-loop viewing conditions.
  
  
  METHODS
  Ten subjects with emmetropia and 10 with myopia were tested. They read binocularly for 1 hour at a distance of 35 to 40 cm. NITM was calculated as the difference in distance refractive state after task as compared with before task immediately after reading. All subjects received timolol maleate to block the sympathetic nervous system and betaxolol as a control agent in independent test sessions separated by at least 3 days. Forty minutes after drug instillation, the NITM measurement procedure was repeated.
  
  
  RESULTS
  Initial NITM magnitude was larger in subjects with myopia than in subjects with emmetropia before and after timolol instillation. Furthermore, NITM magnitude in subjects with sympathetic access was increased after timolol instillation. In contrast, with the control agent betaxolol, there was no increase. NITM decay duration to baseline was increased after timolol instillation in the subjects with myopia only. Only 15% of the subjects (n = 3 subjects with myopia) demonstrated effective and significant access to sympathetic facility.
  
  
  CONCLUSIONS
  Subjects with myopia demonstrated an increase in decay duration with timolol, thus suggesting impaired sympathetic inhibition of accommodation. This may be a precursor for myopia progression in some persons.
authors.affiliation: State University of New York, State College of Optometry, New York, New York 10036, USA. bvasudevan@sunyopt.edu
authors.forename: Balamurali
authors.initials: B
authors.lastname: Vasudevan
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Ciuffreda
authors.forename: Bernard
authors.initials: B
authors.lastname: Gilmartin
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D015784:Betaxolol / Q000494:pharmacology; D002924:Ciliary Body / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D009130:Muscle, Smooth / Q000294:innervation*; D009216:Myopia / Q000503:physiopathology*; D011932:Reading; D013564:Sympathetic Nervous System / Q000187:drug effects*; D013999:Timolol / Q000494:pharmacology
chemical_list: D000319:Adrenergic beta-Antagonists; D013999:Timolol; D015784:Betaxolol