Worksheet 12: Prentice rule, cancelling and compounding, ANSI standards for prism.

EFFECTS OF PRISM.

  1. Briefly describe the difference between wanted and unwanted prism.


  2. Briefly describe the visual effects of looking through a lens with base down prism. Assume that there are equal amounts of base down prism in each lens, so the eyes are not forced to diverge.


  3. If the refractionist requests base up prism for a myope, in what direction will the optical center of the lens be with respect to the wearer's pupil?

    4. up.
    down.
    in.
    out.

  4. The person shown here has

    5. OD esotropia.
    OD exotropia.
    OD hypertropia.
    OD hypotropia.
    OS hypertropia.

  5. The person shown here has

    6. OD esotropia.
    OD exotropia.
    OD hypertropia.
    OD hypotropia.
    OS hypertropia.

  6. The person shown here has

    7. OD esotropia.
    OD exotropia.
    OD hypertropia.
    OD hypotropia.
    OS hypertropia.

  7. The person shown here has

    8. OD esotropia.
    OD exotropia.
    OD hypertropia.
    OD hypotropia.
    OS hypertropia.
  8. What is the difference between an esotropia and an esophoria?


  9. Describe strabismus. Include: A) causes B) visual effects C) ways to correct.

  10. Describe the difference between relieving prism and adverse prism. Where would the base be for the person shown here for each type of prism?


  11. Describe diplopia. Include: A) causes B) visual effects C) ways to correct.


    12. CREATING PRISM.

  12. If a person is looking through a +6.50 lens at a point that is 4 mm above the optical center of the lens, what prism is the person experiencing?

    13. base
  13. If the optical centers are moved in to much on the lenses, where are the wearer's pupils with respect to the optical centers of the lenses when the eyes are in primary position? [Primary position is defined as looking straight ahead.]

    14. up.
    down.
    in.
    out.

  14. If the glasses lenses are each decentered out 3 mm too much and the prescription is -2.50 sph OU, what prism is the wearer experiencing with the eyes in primary position?

    15. OD base
    OS base

    The combination is cancelling compounding
    Total base

    Does this pair of glasses meet the ANSI standard for horizontal prism?
    yes. no. unknown.

    What visual effect will the wearer experience?


  15. The Rx says

    16. OD +4.00 -2.00 x 065
    OS +5.00
    What prismatic effect is the wearer experiencing when looking down through the lower half of the lenses, 7 mm below the optical centers?
    OD base
    OS base

    The combination is cancelling compounding
    Total vertical imbalance.

    Does this pair of glasses meet the ANSI standard for vertical prism?
    yes. no. unknown.

    What visual effect will the wearer experience?


  16. The Rx says

    17. OD -4.00 -2.00 x 025 pd 58
    OS -5.00 -1.00 x 125
    The glasses were made with a distance between optical centers of 56.
    OD base
    OS base

    The combination is cancelling compounding
    Total base

    Does this pair of glasses meet the ANSI standard for horizontal prism?
    yes. no. unknown.

    What visual effect will the wearer experience?


  17. How much prism is induced when looking through a point 3 mm closer to the nose than the optical center for the Rx -8.00 -4.00 x 135?

    18. base
  18. The Rx says

    19. OD +3.12 -1.62 x 056 3.5BU
    How much and in what direction will the optical center be moved to get the prescribed prism?
    mm (round to one decimal place) (in/out/up/down)

  19. The Rx says

    20. OD -1.50 +1.50 x 110 5 BU
    OS -2.00 +0.50 x 005 2 BI
    What will you order? (Split the prism evenly between the two lenses.)
    OD
    OS



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    Textbooks:
    Brooks & Borish, Systems for Ophthalmic Dispensing, 2nd Ed, Butterworth-Heinemann, 1996
    Stoner, Optical Formulas Tutorial, Butterworth-Heinemann, 1997

    Copyright 1998 - 2001, Ellen Stoner, MALS, ABOM, NCLC
    Registered students may print one copy for study purposes.