Abstract
Purpose: Intraocular pressure (IOP) is important in the diagnosis and management of glaucoma and remains the most significant, and only modifiable, risk factor for the development and/or progression of glaucoma. Investigators have used different techniques for IOP measurement including: Non-contact (PT100), indentation (a resurgence in Schoitz tonometry ST) and the Gold standard, Goldman applanation (GAT) tonometers. These techniques are affected by changes in head and body position and differ between individuals. To date, no study has investigated the repeatability of such postural change on IOP using different devices. This study determined the effects of change in head/neck and body posture on IOP measured with three devices.
Methods: Tonometric measurements of 84 healthy subjects (mean age 21.9 ± 2.0 yrs; range, 19 to 29 years) was taken on two visits. PT100 was used to assess IOP, in a randomized fashion, in three head/body positions (HBPs), followed by GAT and ST, with a 15-minute wait period between measurements of GAT and ST. Outcome measures were IOP, limits of repeatability (LoR) and limits of agreement (LoA). The IOPs were separated into ‘high’ and ‘low’ subgroups to further assess agreement.
Results: IOP measured in 3 HBPs were similar. The PT100 returned IOP measurements that were comparable to GAT IOP in both sessions with 74% and 86% of its measurements within ±3mmHg of the GAT IOP, in sessions 1 and 2, respectively. The ST IOPs were higher than the GAT measured IOPs in sessions one (p < 0.05) and two (p < 0.001) with 60% and 44% of its measurements within ±3mmHg of the GAT IOP in sessions 1 and 2, respectively. The LoR within and between sessions were best with the PT100 and worst with the ST. The ST IOP was in agreement with the GAT IOP only in subjects with IOP above 18 mmHg.
Conclusions: Postural changes had no influence on the measured IOP with all three devices. The PT100 noncontact tonometer measured IOP was valid, repeatable and comparable with the gold standard (GAT IOP), but the validities and repeatabilities of the ST (indentation) measured IOPs were poor. The ST measured IOP better approximates the GAT IOP only in the higher range of IOPs and should not be used for IOP measurement in clinical practice.