Spectral content of the intraocular pressure pulse wave: glaucoma patients versus normal subjects

Many studies have found that the intraocular pressure (IOP) is lower in glaucomatous populations than in normal groups. An alternative method of analysis, commonly used in the investigation of arterial blood pressure, is to reduce the pulse waveform to its component Fourier parts. The purpose of this study, therefore, was to determine whether such a technique is applicable to the IOP pulse and to investigate whether it was superior at differentiating diseased from healthy eyes. Using a pneumatonometer, continuous 10-s IOP recordings were taken from 10 glaucoma patients and 10 normal subjects. The IOP recordings were then analysed using the fast Fourier transform (FFT) to determine their spectral components. In addition, standard IOP parameters (pulse amplitude, pulse volume, and pulsatile ocular blood flow) were measured to allow comparison with the waveform analysis technique. Analysis by FFT successfully determined the IOP pulse's higher spectral components up to the fourth harmonic. In addition, although standard measurements of the IOP pulse (such as pulse amplitude) were insignificant, the second ( P=0.034), third ( P=0.015) and fourth ( P=0.013) harmonics of the waveform successfully differentiated between the glaucoma and normal groups. Spectral analysis of the IOP pulse appears to be a promising technique in the investigation of ocular vascular disease.