Comparison of Ocular Pulse Amplitude in Glaucoma and Normal Subjects

Abstract

 

Purpose:

 

Fundus pulse amplitude (FPA) is the variation between the cornea and the retina distance. FPA is believed to play an important role in the development of glaucoma. It is closely related to the ocular blood flow, and arises due to imbalance between the pulsatile inflow of ocular blood during systole and steady outflow during diastole. Up to now, measurement of the FPA has been challenging, as it is of the order of only a few microns. Recently, we used Fourier-domain optical coherence tomography (FD-OCT) to demonstrate FPA measurement in normal human subjects with accuracy of approximately 1 μm. We used this technique to measure the FPA in glaucoma subjects and compared the results with those of age matched normal subjects.

 

Methods:

 

In this study, 10 healthy normal and 12 glaucoma subjects were recruited. Using a custom made FD-OCT device, we measured simultaneously at 30 Hz, the axial position of the cornea at the apex and the retina at three different locations, (i) at the peripapillary retina nasal side, (ii) peripapillary retina temporal side and (iii) the optic disc. In order to obtain the FPA for the three different locations of the retina, the position of the cornea was subtracted from the respective position of the retina. The measured FPA values were analyzed using paired t-test model, and a p-value of less than 0.05 was considered to be significantly different.

 

Results:

 

The measured FPA in glaucoma and normal subjects is shown in the attached figure as box plots. For the normal subjects, the mean ± standard deviation of the root-mean-square values of the FPA was found to be 8.3±2.3 μm, 7.7±2.0 μm and 6.4±2.5 μm, at the optic disc, the nasal side and the temporal side, respectively. In glaucoma patients the corresponding values were 12.2±9.2 μm, 12.2±5.0 μm and 9.2±4.5 μm. The mean FPA values found for the glaucoma patients were higher than the normal subjects and this difference reached statistical significance on the nasal side with a p-value of 0.01.

 

Conclusions:

 

These results suggest that the FPA in the glaucoma patients is higher than in normal subjects. Given the small size of the sample cohort a larger clinical study would be helpful to validate these findings. Nevertheless, the developed FD-OCT system provides the ability to study the role of pulsatile ocular dynamics in various ocular pathologies.  

 

Keywords: eye movements: recording techniques • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • blood supply