Comparison of birefringence-related data between scanning laser polarimetry (GDx) and polarization sensitive optical coherence tomography (PS-OCT)

Abstract

 

Purpose

 

To compare the retardation of the retinal nerve fiber layer (RNFL) measured with the scanning laser polarimeter GDx-VCC and GDx-ECC (Carl Zeiss Meditec Inc.) with the retardation as measured with polarization sensitive optical coherence tomography (PS-OCT).

 

Methods

 

A sample of 8 healthy volunteers, 13 glaucoma suspects and 5 early glaucoma patients underwent complete ophthalmologic examination, including visual field testing, GDx-VCC and GDx-ECC and PS-OCT. Early glaucoma was defined as glaucomatous optic neuropathy with a visual field mean deviation (VF-MD) of -4 dB or better. The definition of glaucoma suspect was based on the suspect appearance of the optic disc while VF was normal. PS-OCT was measured with a system operating at 70kHz A-scan rate (scan angle 30°x30° or 40°x40°, scan pattern 1024x250 A-scans). We compared the average retardation of the superior and inferior sectors. The thickness values of the GDx were converted to degree of retardation for comparison using the published fixed conversion factor. When converting the data we furthermore took into account for the different wavelengths of the GDx and our PS-OCT.

 

Results

 

For the mean values (deg.) and standard deviations of the three different measurements please see the table. For GDx-ECC, GDx-VCC and PS-OCT we found statistically significant differences between the healthy and the suspect groups (p<0.05). There was also a small but statistically significant difference between the retardation found with the GDx and the PS-OCT, the latter giving slightly higher values (p<0.05).

 

Conclusions

 

The retardation values given by the GDx and the PS-OCT are comparable as are the differences between the groups.

 

 

Keywords: 610 nerve fiber layer • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 550 imaging/image analysis: clinical