Abstract
Purpose :
Intraocular pressure (IOP) measurement is an important component of screening and management of ophthalmologic pathology, particularly glaucoma. The accuracy of IOP measurement is limited if there is significant corneal pathology, such as scarring, thinning, or edema. Scleral measurement has been proposed as an alternative method for IOP assessment in patients who cannot undergo corneal measurements, with studies showing mixed results depending on the method used. Our prospective cross-sectional study aims to evaluate whether there is correlation between scleral and corneal IOP measurements in healthy eyes, taken by three different contact tonometers.
Methods :
One central corneal reading and three inferotemporal scleral IOP readings were obtained by pneumatonometer, TonoPen, and iCare tonometer in one randomly selected eye of each subject. Subjects with history of ocular pathology that would interfere with accurate IOP measurement, including glaucoma, corneal disease, uveitis, or ocular surgery, were excluded. Pearson correlation coefficients were calculated to assess the correlation between IOP measurements taken from the cornea and sclera for each of the three tonometers separately.
Results :
Analysis was performed on a monocular dataset from 27 patients (age:16-61y). Average scleral IOP (sIOP) readings were consistently higher than corneal IOP (cIOP) readings, with mean difference between sIOP and cIOP measurements taken by pneumatonometer, TonoPen, and iCare being 9.47, 13.44, and 24.08 mmHg respectively. Difference between sIOP and cIOP correlated positively with age for pneumatonometry (r=0.514, p=0.01) and TonoPen (r=0.51, p=0.011), but not for iCare (r=0.02, p=0.92). sIOP correlated positively with cIOP when measured by pneumatonometry (r=0.61, p<0.01), but showed no relationship when measured by either iCare (r=0.08, p=0.72) or Tono-Pen (r=0.37, p=0.08). Regression analysis of pneumatonometry data yielded the equation: cIOP=(0.365 x sIOP) + 9.69.
Conclusions :
In healthy eyes, corneal and scleral IOP correlated significantly when measured by pneumatonometer, but not when using the TonoPen or iCare tonometers. Scleral pneumatonometry can be considered as an alternative in cases where corneal IOP measurements are impractical; conversely, scleral IOP measurements by TonoPen and iCare offer little clinical value.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.