New pressure-to-cornea index in glaucoma created

A new pressure-to-cornea index (PCI) has been created in an attempt to integrate intraocular pressure (IOP) and central corneal thickness (CCT) into a unified risk factor, according to a report published in the October issue of the British Journal of Ophthalmology.

Milko Iliev from the University of Bern, Switzerland and colleagues from Ophthalmologists Association Thun, Switzerland and Yale University School of Medicine, New Haven, USA defined PCI as the ration between untreated IOP and CCT3 in mm (ultrasound pachymetry).

PCI was then investigated in 220 normal controls, 53 subjects with normal-tension glaucoma (NTG), 76 with ocular hypertension (OHT) and 89 with primary open-angle glaucoma (POAG). The ability of PCI to discriminate between glaucoma and non-glaucoma was compared with that of three other formulae for correcting IOP for CCT. Receiver operating characteristic curves (ROC) were then built.

The mean PCI value in the control group was 92.0, 129.1 in the NTG group, 134.0 in the OHT group and 173.6 in the POAG group. PCI demonstrated a larger area under the ROC and significantly higher sensitivity at fixed 80% and 90% specificities than any of the other formulae. Optimum PCI cut-off value was 133.8.

The authors believe that PCI may reflect individual susceptibility to a given IOP level and, therefore, represents a glaucoma risk factor.