Central corneal thickness and measured IOP: a clinical study

We have attempted to document that the pachometer used in primary eye care practices will show the same corneal thickness relationship with measured intraocular pressure (mIOP) as the research studies. A second purpose of the study is to determine what role, if any, corneal thickness has on the increase in mIOP with age.

Sonogage Corneo-Gage Plus ultrasound central corneal thickness (CCT) measurements were taken on 101 white ocular hypertensive (OHT) patients with mIOP at or above 21 mmHg, as measured by Goldmann tonometry, and compared with age-matched controls with mIOP of 16 mmHg or less. To evaluate the impact of CCT on mIOP with age, a subset of patients was selected from the subjects and controls who had had a Goldmann tonometry reading recorded more than 10 years before the collection of the study data.

The mean age of the (OHT) patients was 65.3 years +/- 12.3. The average CCT of the OHT patients was 595 pm +/- 36 microm, and for the control patients the average CCT was 554 microm +/- 34 microm. This difference was statistically significant (P < 0.0001). Evaluation of the age subset revealed that patients with thick corneas showed a 1.22 mmHg increase in mIOP per decade, whereas the patients with thin corneas showed a 0.69 mmHg decrease in mIOP per decade. This difference was statistically significant (P = 0.0001). This study demonstrates the same relationship between corneal thickness and mIOP in clinical practice as has been reported from research settings. This finding suggests that knowledge of corneal thickness is necessary to adjust the mIOP to better monitor and evaluate patients for glaucoma risk in the primary eye care practice. Of more significance is the finding that mIOP increases in the thick cornea patients over time. This suggests an age-related change in corneal resistance to applanation that impacts on mIOP measurements. More study is needed pertaining to the role of CCT on mIOP.