Correlation between central corneal thickness, applanation tonometry, and direct intracameral IOP readings

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.