Purpose:
To describe variability in corneal thickness in relation to region of thickness measurement and to determine whether a difference exists in central corneal thickness (CCT) between normal and ocular hypertensive (OHT) patient populations.
Methods:
Corneal thickness was measured in 111 OHT patients, 64 patients with primary open–angle glaucoma, and 252 normal subjects, using an ultrasonic pachymeter (model DGH 550). CCT was measured by aligning the pachymeter probe with the center of the pupil. Corneal thickness 3mm superior (SCT), inferior (ICT), lateral (LCT), and medial (MCT) to center were also measured. A Friedman ANOVA & Kendall’s Concordance test was performed to determine whether significant differences exist in thickness of different regions of the cornea. A Wilcoxon Matched Pairs Test was also performed to determine whether a difference in CCT exists between OHT and normal patients.
Results:
Statistically significant differences in thickness were found among different regions of the cornea in both eyes (p<.001) amongst all patient populations. Mean SCT was greatest (594.7 +/– 39.5 um), followed by TCT (578.9 +/– 38.2 um), NCT (570.3 +/– 34.5 um), ICT (565.3 +/– 34.9 um), and CCT (555.9 +/– 34.4 um) in the normal population. A statistically significant difference in central corneal thickness was found in both right and left eyes between the normal and OHT populations (p = .001). Table 1. Distribution of Thickness Measurements in Relation to Region of Cornea
Conclusions:
Currently, pachymetry, in adjunct with tonometry, is used to estimate intraocular pressure (IOP). It may be more useful to measure not only CCT, but also SCT, ICT, LCT and MCT, as these regions have a significantly different thickness than the center. This study confirms differences in central corneal thickness between OHT and normal populations. Corneal thickness significantly increases with placement of the probe superior or horizontal to "center". This anatomic alteration may account for variability of CCT measurement. Also, variability of IOP reading will occur if placement of the applanation prism deviates from "center".
Keywords: anterior segment • intraocular pressure