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ACCOMODATION AND VERGENCE (also covers vision therapy concepts)
- 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