[A combination of horizontal/vertical prism bar]

Area of Science:

• Ophthalmology
• Optometry
• Vision Science

Background:

• Prism bar calibration and positioning lack standardization, leading to measurement inaccuracies.
• Improper use, such as holding prism bars back-to-back in front of one eye, results in erroneous measurements.
• Existing methods for combining horizontal and vertical prism bars are prone to error.

Purpose of the Study:

• To investigate calibration and positioning errors in prism bars from R. O. Gulden and Luneau.
• To evaluate the impact of improper prism bar positioning on measurement accuracy.
• To propose improved prism bar designs and usage guidelines.

Main Methods:

• An optical bench was utilized to assess calibration and positioning errors of Gulden and Luneau prism bars.
• Gulden was prompted to redesign its prism bars for improved alignment and sliding.
• New combination horizontal/vertical prism bars require calibration in the frontal plane and Prentice positions, respectively.

Main Results:

• Gulden's redesigned combination prism bar demonstrated minimal error (+/- 0.5 delta).
• Luneau's prism bars showed calibration close to the frontal plane (+/- 0.4 delta), with significant errors when positioned improperly.
• Improper positioning of Luneau's 25 delta and 40 delta segments resulted in substantial deviations (27.8 delta and 67.5 delta).
• Gulden's vertical prism bars (old and new) measured 23.2 delta in the frontal plane position.

Conclusions:

• Gulden's vertical prism bars, calibrated in the Prentice position, should be held with the flat surface toward the examiner.
• Luneau's prism bars require simultaneous use with one in front of each eye.
• Adherence to recommended orientations is essential for accurate primary and secondary deviation measurements.