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Correlation between central corneal thickness, applanation tonometry, and direct intracameral IOP readings
1Department of Ophthalmology, Albert-Ludwigs- University Freiburg, Germany. feltgen@aug.ukl.uni-freiburg.de
Background:
Several authors reported incorrect high intraocular pressure (IOP) values in eyes with a thick cornea using applanation tonometry. This hypothesis was checked by comparing applanation tonometry with direct intracameral manometry.
Methods:
73 patients, scheduled for intraocular surgery, were enrolled. Immediately before surgery, the following were registered: (i) central corneal thickness (CCT), (ii) applanatory IOP (Perkins/Tonopen), and (iii) intracameral IOP.
Results:
The difference between applanatory and intraocular measurements was completely independent of CCT (y= -3.43 + 3.8x; where y is the difference between applanatory and intracamerally measured IOP (mm Hg) and x is CCT (mm); r(2) = 0.002; p = 0.72).
Conclusions:
There is no systematic error of applanation tonometry with increasing CCT. Therefore it is inadequate to recalculate IOP based on regression formula of applanatory IOP versus CCT.