Clinical science Department of Ophthalmology, Medical University of Vienna, Austria Correspondence to Clemens Vass, Department of Ophthalmology and Optometry, Medical University of Vienna, General Hospital, W¨ahringer G¨urtel 18-20, A-1090 Vienna, Austria; clemens.vass@ meduniwien.ac.at Accepted 3 July 2010 Published Online First 30 August 2010 This paper is freely available online under the BMJ Journals unlocked scheme, see http:// bjo.bmj.com/site/about/ unlocked.xhtml 680 Position of retinal blood vessels correlates with retinal nerve ﬁbre layer thickness proﬁles as measured with GDx VCC and ECC Hemma Resch, Barbara Brela, Christa Resch-Wolfslehner, Clemens Vass 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 mm/8). Using this slope, the difference in RNFL thickness for the interquartile range of the superior angle was 13 mm. 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.1e4 In healthy eyes, the peripapillary RNFL thickness modulation pattern around the optic disc, also referred to as a temporalesuperiore nasaleinferioretemporal (TSNIT) graph, was shown to follow a double-hump pattern, with thicker RNFL superiorly and inferiorly and thinner RNFL temporally and nasally.5 Considerable inter- individual variability in RNFL thickness values among normal subjects as measured with optical coherence tomography (OCT),6 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).2e4 7 8 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 appear- ance 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.9 10 Statistical analyses concerning the impact of retinal blood vessel position on the total circum- papillary TSNIT proﬁle of RNFL have not yet been published. Understanding the sources of the inter- subject variability is central to the understanding and improvement of RNFL thickness measure- ments as a test for glaucomatous damage. It was the aim of the present study to examine the inﬂu- ence 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). SUBJECTS AND METHODS Subjects The study protocol was approved by the Ethics Committee of the Medical University of Vienna and followed the guidelines of Good Clinical Prac- tice and the Declaration of Helsinki. A total of 83 subjects of both sexes aged between 19 and 71 years (mean 27.27 years, 6 9.5) were included. Inclusion and exclusion criteria Inclusion criteria were normal ophthalmic ﬁndings, especially normal appearance of the optic disc, normal visual ﬁelds and intraocular pressure (IOP), and lack of signiﬁcant retinal disorder. An abnormal visual ﬁeld was deﬁned as a glaucoma hemiﬁeld test outside normal limits and/or a corrected pattern standard deviation with p <0.05.11 A normal IOP was deﬁned as #21 mm Hg. Any of the following excluded a subject from participation in the trial: evidence of any eye disease except refractive error, history of ocular trauma or intraocular surgery within the last 6 months, ocular inﬂammation or infection within the last 3 months, astigmatism more than +2.0 dioptres and ametropia of more than 65.0 dioptres. Experimental paradigm Initially a prestudy screening was carried out, where the medical and ocular history was taken. A complete ophthalmological examination was performed, including fundoscopy, visual acuity, Br J Ophthalmol 2011;95:680e684. doi:10.1136/bjo.2009.170068