Abstract and Introduction
Abstract
Aim To evaluate the correlation of the retinal blood vessel position and the retinal nerve fibre layer (RNFL) thickness profile.
Methods RNFL thickness of 81 healthy subjects was measured using scanning laser polarimetry (SLP). To quantify the retinal blood vessel position, the angle (superior and inferior) between a horizontal line and a line from the optic disc centre to the intersection of the most temporal major retinal blood vessel and the outer margin of the measurement ellipse was measured on the SLP printout.
Results A negative correlation was found between both the superior and inferior angle and the superotemporal and inferotemporal RNFL thickness, and a positive correlation between both angles and the superonasal and inferonasal RFNL thickness. The steepest slope of the regression line was located in the superotemporal and inferotemporal regions (−0.7 to −1.0 μm/°). Using this slope, the difference in RNFL thickness for the interquartile range of the superior angle was 13 μm.
Conclusion RNFL thickness profiles correlate with the location of the main temporal superior and inferior blood vessels. The application of a normative database, taking into account the position of major blood vessels, might improve the diagnostic power of RNFL measurement.
Introduction
The GDx (Carl Zeiss Meditec, Dublin, Califonia, USA) is a scanning laser polarimeter that assesses retinal nerve fibre layer (RNFL) thickness in the peripapillary retina and discriminates well between normal subjects and patients with glaucoma.
In healthy eyes, the peripapillary RNFL thickness modulation pattern around the optic disc, also referred to as a temporal–superior–nasal–inferior–temporal (TSNIT) graph, was shown to follow a double-hump pattern, with thicker RNFL superiorly and inferiorly and thinner RNFL temporally and nasally. Considerable interindividual variability in RNFL thickness values among normal subjects as measured with optical coherence tomography (OCT), and some overlap in thickness values between normal subjects and patients with glaucoma have been reported in several studies conducted by scanning laser polarimetry (SLP).
Various diseases, most notably glaucoma, result in the death of retinal ganglion cells (RGCs) and the degeneration of their axons. The loss of RGC axons in turn leads to a thinning of the RNFL. One method for assessing pathological RNFL appearance is by comparing the RNFL with normative values, derived from healthy subjects. These normative values will be more specific when normal physiological differences are taken into account.
Only recently, Hood et al have demonstrated qualitatively that the local maxima in the RNFL profile of OCT and GDx are associated with blood vessels.
Statistical analyses concerning the impact of retinal blood vessel position on the total circumpapillary TSNIT profile of RNFL have not yet been published. Understanding the sources of the intersubject variability is central to the understanding and improvement of RNFL thickness measurements as a test for glaucomatous damage. It was the aim of the present study to examine the influence of the retinal blood vessel position on the RNFL thickness profile around the optic disc as measured with GDx VCC (variable corneal compensation) and ECC (enhanced corneal compensation).