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.
Highlights
Ophthalmic prisms are routinely used to measure ocular deviations and to determine the amount of correction in strabismus surgeries
The measured data are listed in table 1 for glass prism and in table 2 for plastic prisms
A 50 prism diopters (PD) glass prism has a measured power of 80PD when it is anti-clockwise rotated by 10 degrees, see details in table 1
Summary
Ophthalmic prisms are routinely used to measure ocular deviations and to determine the amount of correction in strabismus surgeries. Inaccurate measurement of ocular deviation could lead to over-correction or under-correction of strabismus. Measurement deviation errors can be induced when a prism is not held at a calibrated position. This problem was pointed out long time ago and all authors focused on theoretical calculation [1,2,3]. Authors in a recent review paper summarized the issues related to this problem [4]. There has been no efficient solution to the problem
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: International Journal of Ophthalmology & Visual Science
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.