ON THE PRECISION OF POLYAK MEASURING SCALES IN MAKLAKOV TONOMETRY

PURPOSE: To determine the precision of selected samples of Polyak measuring scales used in Maklakov tonometry.

METHODS: Twenty two samples of different models of Polyak measuring scales for Maklakov tonometers were assessed. So called “tonometric” intraocular pressure (IOP) scales were appraised. The ideal size of the imprint for each grade of the scale was calculated using the ImbertFick law formula. These calculations were considered a “golden standard” for the purpose of this study. The scales were scanned and saved as JPG-files with resolution 300 or 600 DPI. The following parameters were measured for each sample: the diameter of imprints which can fit in between “16” and “17”, “25” and “26”, “35” and “36”, and “54” and “56” mm Hg, representing low, borderline, high and very high IOP. Measurements were then compared to the “golden standard”, and the conclusions were made regarding the precision of each sample of tonometric measuring scale. Results were compared to three additional IOP measuring scales: 2 models of Nesterov–Egorov measuring scale and 1 model of Nesterov–Vurgaft–Vagin measuring scale.

RESULTS: Twenty two Polyak measuring scales were evaluated according to the precision of “16”, “25”, “35” and “54” mm Hg marks. Three scales were determined as accurate. The study revealed six measuring scales critically underestimating the IOP level (up to 5-16 mm Hg of underestimation).

CONCLUSION: The study revealed critical heterogeneity of Polyak measuring scales for Maklakov tonometry. Measurement results may differ significantly with different scale models, proving unsatisfactory correlation between various modern scales. The most accurate and the least accurate scales were determined. Implications of such measurement errors were discussed. Poor correlation of “true” IOP measuring scales was also demonstrated.

glaucoma, intraocular pressure, Maklakov tonometry, applanation tonometry, Polyak measuring scale, screening

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