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Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them

Received: 16 February 2021     Accepted: 11 March 2021     Published: 17 March 2021
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Abstract

Purpose: Ophthalmic prisms are routinely used to measure ocular deviation. However, large measurement errors could be induced when a prism is not accurately positioned at its calibration position. We report a simple way to minimize the errors. Methods: We measured powers of prisms and plastic prisms at their calibration position and at angles the prism was rotated away from the calibration position. Glass prisms that have power of 20, 25, 30, 40, 50, and 60 prism diopters (PD) and plastic prisms that has power of 20, 25, 30, 35, 40, 45, 50 PD were used. To minimize the errors, we developed a pair of prism frame so that the prism can always be positioned accurately. Results: We have demonstrated large errors induced by rotating glass prisms and plastic prism away from their calibration position. Larger errors were recorded with glass prisms than with plastic prisms. The measurement errors are significant even with a small angle rotation for a large power glass prism. For instance, a 10-degrees rotation of a 50PD glass prism produces an error of 30PD. However, measurements errors were minimized when the prism frame was used. Conclusion: It suggests that the glass ophthalmic prism should be abandoned and the use of ophthalmic prisms in strabismus measurement should be standardized with assistance of the prism frame.

Published in International Journal of Ophthalmology & Visual Science (Volume 6, Issue 1)
DOI 10.11648/j.ijovs.20210601.19
Page(s) 59-62
Creative Commons

This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.

Copyright

Copyright © The Author(s), 2021. Published by Science Publishing Group

Keywords

Ophthalmic Prisms, Strabismus, Ocular Deviation

References
[1] Thompson JT, Guyton DL. Ophthalmic Prisms. Measurement errors and how to minimize them. Ophthalmology. 90: 204-210 (1983).
[2] Thompson JT, Guyton DL. Ophthalmic Prisms. Deviant behavior at near. Ophthalmology. 92: 684-90 (1985).
[3] Kaye SB, Ansons AM, Green JR, Wylie J. The prism bar—Prentice and frontal positions. Eye 3: 404–408 (1989).
[4] Irsch K. Optical Issues in Measuring Strabismus. Middle East Afr J Ophthalmol. 22: 265-70 (2015).
[5] Yang D. et cl. Ophthalmic prisms: Optical measurement errors and a simple device to minimize the errors. AAPOS annual meeting, Vancouver, Canada, April 6-10, 2016.
[6] Von Noorden GK, Campos EC. Binocular Vision and Ocular Motility: Theory and management of strabismus. 6th ed by Mosby. Page 190.
[7] Freedman K, Ray C, Kirk D. Reevaluation of Current Prism Standards with Recommendations to Increase Accuracy in the Measurement of Strabismus. Am J Ophthalmol. 2019 Feb; 198: 130-135.
[8] Flüeler UR, Elhatton KM, Guyton DL. A combination of horizontal/vertical prism bar. Klin Monbl Augenheilkd. 1996 May; 2008 (5): 343-7.
[9] Kommerell G, Kromeier M. Prism correction in heterophoria. Ophthalmologe. 2002 Jan; 99 (1): 3-9.
[10] Cestari DM, Hunter DG. Learning strabismus surgery: a case-based approach. Page 230-233. By Wolter Kluwer.
Cite This Article
  • APA Style

    Ping Wang, Ya Pan, Jie Zhang, Dongsheng Yang. (2021). Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them. International Journal of Ophthalmology & Visual Science, 6(1), 59-62. https://doi.org/10.11648/j.ijovs.20210601.19

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    ACS Style

    Ping Wang; Ya Pan; Jie Zhang; Dongsheng Yang. Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them. Int. J. Ophthalmol. Vis. Sci. 2021, 6(1), 59-62. doi: 10.11648/j.ijovs.20210601.19

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    AMA Style

    Ping Wang, Ya Pan, Jie Zhang, Dongsheng Yang. Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them. Int J Ophthalmol Vis Sci. 2021;6(1):59-62. doi: 10.11648/j.ijovs.20210601.19

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  • @article{10.11648/j.ijovs.20210601.19,
      author = {Ping Wang and Ya Pan and Jie Zhang and Dongsheng Yang},
      title = {Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them},
      journal = {International Journal of Ophthalmology & Visual Science},
      volume = {6},
      number = {1},
      pages = {59-62},
      doi = {10.11648/j.ijovs.20210601.19},
      url = {https://doi.org/10.11648/j.ijovs.20210601.19},
      eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ijovs.20210601.19},
      abstract = {Purpose: Ophthalmic prisms are routinely used to measure ocular deviation. However, large measurement errors could be induced when a prism is not accurately positioned at its calibration position. We report a simple way to minimize the errors. Methods: We measured powers of prisms and plastic prisms at their calibration position and at angles the prism was rotated away from the calibration position. Glass prisms that have power of 20, 25, 30, 40, 50, and 60 prism diopters (PD) and plastic prisms that has power of 20, 25, 30, 35, 40, 45, 50 PD were used. To minimize the errors, we developed a pair of prism frame so that the prism can always be positioned accurately. Results: We have demonstrated large errors induced by rotating glass prisms and plastic prism away from their calibration position. Larger errors were recorded with glass prisms than with plastic prisms. The measurement errors are significant even with a small angle rotation for a large power glass prism. For instance, a 10-degrees rotation of a 50PD glass prism produces an error of 30PD. However, measurements errors were minimized when the prism frame was used. Conclusion: It suggests that the glass ophthalmic prism should be abandoned and the use of ophthalmic prisms in strabismus measurement should be standardized with assistance of the prism frame.},
     year = {2021}
    }
    

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  • TY  - JOUR
    T1  - Measurement Errors Induced by Inaccurate Positioning of Ophthalmic Prisms and a Simple Way to Minimize Them
    AU  - Ping Wang
    AU  - Ya Pan
    AU  - Jie Zhang
    AU  - Dongsheng Yang
    Y1  - 2021/03/17
    PY  - 2021
    N1  - https://doi.org/10.11648/j.ijovs.20210601.19
    DO  - 10.11648/j.ijovs.20210601.19
    T2  - International Journal of Ophthalmology & Visual Science
    JF  - International Journal of Ophthalmology & Visual Science
    JO  - International Journal of Ophthalmology & Visual Science
    SP  - 59
    EP  - 62
    PB  - Science Publishing Group
    SN  - 2637-3858
    UR  - https://doi.org/10.11648/j.ijovs.20210601.19
    AB  - Purpose: Ophthalmic prisms are routinely used to measure ocular deviation. However, large measurement errors could be induced when a prism is not accurately positioned at its calibration position. We report a simple way to minimize the errors. Methods: We measured powers of prisms and plastic prisms at their calibration position and at angles the prism was rotated away from the calibration position. Glass prisms that have power of 20, 25, 30, 40, 50, and 60 prism diopters (PD) and plastic prisms that has power of 20, 25, 30, 35, 40, 45, 50 PD were used. To minimize the errors, we developed a pair of prism frame so that the prism can always be positioned accurately. Results: We have demonstrated large errors induced by rotating glass prisms and plastic prism away from their calibration position. Larger errors were recorded with glass prisms than with plastic prisms. The measurement errors are significant even with a small angle rotation for a large power glass prism. For instance, a 10-degrees rotation of a 50PD glass prism produces an error of 30PD. However, measurements errors were minimized when the prism frame was used. Conclusion: It suggests that the glass ophthalmic prism should be abandoned and the use of ophthalmic prisms in strabismus measurement should be standardized with assistance of the prism frame.
    VL  - 6
    IS  - 1
    ER  - 

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Author Information
  • Department of Strabismus and Paediatric Ophthalmology, Shandong Liangkang Eye Hospital, Children’s Eye Disease and Ocular Motor Institute of Purui, Bright Eye Hospital Group, Jinan, P. R. China

  • Department of Strabismus and Paediatric Ophthalmology, Shandong Liangkang Eye Hospital, Children’s Eye Disease and Ocular Motor Institute of Purui, Bright Eye Hospital Group, Jinan, P. R. China

  • Department of Strabismus and Paediatric Ophthalmology, Shandong Liangkang Eye Hospital, Children’s Eye Disease and Ocular Motor Institute of Purui, Bright Eye Hospital Group, Jinan, P. R. China

  • Department of Strabismus and Paediatric Ophthalmology, Shandong Liangkang Eye Hospital, Children’s Eye Disease and Ocular Motor Institute of Purui, Bright Eye Hospital Group, Jinan, P. R. China

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