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ACCOMODATION AND VERGENCE

  • A simple definition of the AC/A ratio
  • AC/A defined = a change in vergence during accommodation
  • Example = AC/A of 4/1 means for every 1.00D in accommodation, you will converge 4 prism diopters
  • You can remember low and high AC/A in relation to excess or insufficiency (e.g. convergence insufficiency, etc.)
  • Insufficiency always has a low AC/A e.g. CI, DI (think "insufficient = low")
  • Excess always has a high AC/A e.g. CE, DE (think "excess = high")
  • High and low AC/A also has an importance in treatment of vergence dysfunction
  • High AC/A = Excess (CE, DE) = lenses are Effective in treatment
  • Normal AC/A = (Basic Eso, Basic Exo) sometimes effective
  • Low AC/A = Insufficiency (CI, DI) = lenses are Ineffective in treatment
  • A quick way to remember that plus lenses induces exo
  • The plus sign (+) looks like an rotated X
  • Remember, plus lenses relaxes accommodation, which results in decreased convergence (increased divergence)
  • How to figure out what prism stimulates what type of vergence
  • Mnemonic = "BIM BOP" - keep in mind of that general "rule" that the apex points towards where the eyes will move
  • BI stimulates Negative Fusional Vergence
  • Negative implies Minus in "BIM"
  • The apexes point temporally, causing divergence
  • BO stimulates Positive Fusional Vergence
  • Positive implies Plus in "BOP"
  • The apexes point nasally, causing convergence
  • How to know what type of demand to use during vergence therapy
  • Mnemonic = "BOCIDE-X, BIDICE-E" (prevent confusion by remembering BOCIDE as a "poison" and BIDICE as "two dice")
  • Use BO prism demand for training CI, DE, and Exo patients
  • Use BI prism demand for training DI, CE, and Eso patients

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