A Simplified (Screening) Approach to Check the Calibration Status of the Goldmann Applanation Tonometer

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Abstract

Background:

To investigate whether a lower-end calibration error check alone can identify a Goldmann applanation tonometer (GAT) with acceptable calibration error as per Asia-Pacific Glaucoma Society (APGS) and World Glaucoma Association (WGA) guidelines.

Methods:

This was a multicentric prospective study in a tertiary eye-care institutional setting. Seventy-six slit-lamp–mounted Haag-Streit GATs (Model AT 900 C/M) were included in the study. All GATs were checked for calibration error at 0, 20, and 60 mm Hg testing levels as recommended by the manufacturer. The ability of 2 screening criteria (calibration error within ±1 or ±2 mm Hg, respectively, at the 0 mm Hg testing level without using the calibration error check weight bar) to identify a tonometer within acceptable calibration limits defined by APGS (calibration error within ±2, ±3, and ±4 mm Hg at 0, 20, and 60 mm Hg testing levels, respectively) and WGA (calibration error within ±1 mm Hg at all testing levels) was determined.

Main Outcome Measure:

The negative likelihood ratio of the screening criteria

Results:

Five (6.6%) and 42 (55%) GATs were outside of the APGS and the WGA calibration limits, respectively. Negative likelihood ratios of the first and the second screening criteria at the APGS definition of calibration error tolerance were 0.11 and 0.25, respectively, and at that of the WGA definition of calibration error tolerance were 0.38 and 0.90, respectively.

Conclusions:

The screening criteria of calibration error within ±1 mm Hg at the 0 mm Hg testing level seem to be clinically useful to detect GAT with an acceptable calibration error as per the APGS guideline.

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