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Editors Selection IGR 14-2

Intraocular Pressure: Effect astigmatism on IOP

Comment by Fabian Lerner on:

25041 Effect of corneal astigmatism on intraocular pressure measurement using ocular response analyzer and Goldmann applanation tonometer, Hagishima M; Kamiya K; Fujimura F et al., Graefe's Archive for Clinical and Experimental Ophthalmology, 2010; 248: 257-262

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Hagishima et al. (140) evaluated the effect of corneal astigmatism, measured with an autokeratometer, on IOP measured both with an Ocular Response Analyzer (ORA) and a Goldmann applanation tonometer (GAT), in a group of healthy subjects. Individuals had low to moderate corneal astigmatism: 0.9 ± 0.5 D (R: 0-2.25 D). The two IOP measurements provided by the ORA were used: the corneal-compensated IOP (IOP_cc) which uses corneal viscosity and elasticity data, and the Goldmann-correlated IOP (IOP_G), derived from the inward and outward applanation data. No correlation was found between IOP_cc and astigmatism, or between IOP_G and astigmatism. A weak correlation was found between the amount of astigmatism and GAT-IOP. These results suggest that both IOPs measured with the ORA were less affected by low to moderate corneal astigmatism than GAT-IOP. High corneal astigmatism may generate substantial errors in GAT. Regular with the rule astigmatism over 4 D will result in underestimation of IOP, while the opposite will occur with against the rule astigmatism. A useful way to solve this is to take two readings, one with the prism oriented vertically and another with the prism horizontally, and average both. Hagishima et al. addressed the low-to-moderate astigmatism range, which is more common in the population. This information may be valuable for the practitioner when measuring IOP in individuals with corneal astigmatism. More studies are needed to elucidate the relationship between corneal astigmatism and IOP measurements with the different tonometers available.

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