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Abstract #5973 Published in IGR 2-2
Influence of corneal thickness on applanation intraocular pressure
Damji KF; Munger RJournal of Glaucoma 2000; 9: 205-207
The authors' approach to determining 'true' IOP depends on the status of the cornea. The central corneal thickness (CCT) does not influence IOP to a clinically significant degree in most patients with healthy unoperated corneas. The correction factor in this situation would likely be within measurement error for applanation IOP. However, CCT can be important when interpreting measured applanation IOP in patients with OHT or NTG who have corneas that appear normal. In these cases, the correction factor for IOP is likely to be 2.5-3.5 mmHg per 50 μm deviation in CCT from 545 μm. Measurement of CCT in people with OHT and in those with NTG may help guide the setting of target (measured) IOP and influence the decision to initiate or change treatment. In patients who have undergone myopic refractive surgery, there appears to be a high degree of variability in postoperative IOP. In the authors' opinion, correcting for changes in CCT alone is insufficient to predict postoperative change in IOP. They therefore suggest that the difference between preoperative IOP and six months IOP (when the cornea should be stable) could be used as a correction factor. They also suggest that the patient carries a card indicating what type of surgery has been performed, what the preoperative IOP was, and the degree of myopia. The authors emphasize the importance of careful stereoscopic examination of the optic disc and that interpretation of visual function tests in order to make a definitive diagnosis of glaucoma or to judge progression will become increasingly important in patients who have or may have a discrepancy between measured and 'true' IOP.
Dr. K.F. Damji, University of Ottawa Eye Institute, Ottawa, Canada
Classification:
2.2 Cornea (Part of: 2 Anatomical structures in glaucoma)
6.1 Intraocular pressure measurement; factors affecting IOP (Part of: 6 Clinical examination methods)
