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Editors Selection IGR 9-4

Intraocular Pressure: DCT + thick cornea = risk

Comment by James Brandt on:

47620 The Effect of Thin, Thick, and Normal Corneas on Goldmann Intraocular Pressure Measurements and Correction Formulae in Individual Eyes, Park SJK; Ang GS; Nicholas S et al., Ophthalmology, 2011;

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After the Ocular Hypertension Treatment Study (OHTS) demonstrated that central corneal thickness (CCT) is an important predictive factor for the development of glaucoma, ophthalmologists embraced pachymetry as an important diagnostic tool in the management of patients with glaucoma and ocular hypertension. However, how CCT should actually be used in day-to-day management of individual patients remains unclear. Some have chosen to use CCT as just one component of global risk assessment, whereas others have chosen to use one of the many published 'correction' nomograms to adjust IOP estimates acquired by Goldmann applanation tonometry (GAT). While GAT is the most widely-used tonometry technique worldwide, its measurements are affected by CCT and other corneal parameters. The Pascal Dynamic Contour Tonometer (DCT) is probably the most 'cornea-independent' and accurate tonometer in our armamentarium, and its readings most closely represent 'true' IOP as determined by direct intracameral measurement.

Park et al. (1800) retrospectively explored a database of tonometry measurements among almost 300 patients, in whom GAT, DCT and Ocular Response Analyzer (ORA) measurements had been obtained. They asked the question 'if DCT is the new reference standard (i.e., closest to "true" IOP), do the various "correction" nomograms actually improve the accuracy of GAT?'

The authors found that adjusting GAT estimates using CCT-based formulae actually resulted in worse agreement between GAT and DCT. This finding was especially true in eyes with increased CCT.

These data strongly suggest that clinicians should not use so-called correction nomograms in individual patients

Park et al.'s data strongly suggest that clinicians should not use so-called correction nomograms in individual patients. The fact that the agreement between GAT and DCT is worst among eyes with thick corneas should make us particularly careful about considering an ocular hypertensive with thick CCTs to be low risk without fully assessing the optic nerve and visual field.

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