Refining Decisions for Identifying Primary Care Patients Who Require A Work-Up for Glaucoma: Intraocular Pressure Changes with Central Corneal Thickness

Abstract

Purpose: The factors associated with the increased risk of glaucoma include intraocular pressure (IoP), central corneal thickness (CCT), vertical cup-to-disc ratio, visual field index, age, and diabetes mellitus. We have investigated the relation of IoP with CCT in normal, healthy pre-presbyopic persons.
 Methods: A total population of 698 normal patients (1396 eyes), aged 4 to 40 years, were evaluated in two separate clinics, one in Houston, Texas, USA and the second in oakville, ontario, Canada. IoP was measured using a noncontact tonometry (nCT 20 Topcon). In Houston, CCT was determined by using the Pentacam (occulus Pentacam – Belinea) and an optical pachymetry that utilized optical low-coherence reflectometry (oLCR) technology, and in oakville, a Hagg-Streit slit lamp–mounted pachymeter was used.
 Results: of the total number of eyes tested, 1226 eyes had IoP of 21 millimetres of mercury (mm Hg) or lower and 134 eyes had IoP greater than 21 mm Hg. For the normal IoP group (n = 1226 eyes), the overall IoP mean was 15.63 +/– 2.87 mm Hg; the overall CCT mean was 550.21 +/– 39.64 micrometres (µm). In the normal IoP group, for every 10 µm change in CCT, IoP changed a statistically significant amount of 2.49 mm Hg (p <0.05 to <0.001), except for the 10 nm CCT bins above and below the 550 µm mean.
 Conclusions: Although many investigators have described a positive correlation between IoP and CCT, this relationship has not been demonstrated in normal, healthy pre-presbyopic persons. There is a significant change of IoP with CCT (2.49 mm Hg IoP change per 100 µm of CCT). These normative data allow primary eye care clinicians to accurately determine normal and abnormal IoP and refine the index of suspicion for identifying patients who need to be worked up for glaucoma.