A Thickening of the Macular Papillary Retinal Nerve Fiber Layer in Patients With AZOOR

Abstract

Purpose: : RNFL thickening occurs in patients with RP [1-3], but because of the uncertain time of disease onset it is hard to distinguish between short-term mechanical factors (e.g. neuronal swelling) and long-term remodeling (gliosis and neural plasticity). Here we measure the retinal nerve fiber layer (RNFL) thickness in patients with acute zonal occult outer retinopathy (AZOOR), a disease with an abrupt onset affecting the receptors.

Methods: : A frequency domain optical coherence tomography (fdOCT; Spectralis, Heidelberg) horizontal line scan of the midline was obtained from the more affected eye of 13 patients with AZOOR and onsets from 3 months to 13 years before testing (mean 4.4 yrs; median 2.2 yrs). Raw images were exported and the thicknesses of the RNFL and receptor layer (REC+: from Bruch's Membrane to inner nuclear layer) measured by 2 authors with a computer-aided, manual segmentation procedure.[1] The BCVA of the eyes with AZOOR ranged from 20/20 to 20/80. For all individuals, the thicknesses of the macular papillary RNFL and REC+ were averaged from the center of the fovea to 3 mm (10.4°) into the nasal retina, the portion of the midline scan with a distinct RNFL.

Results: : For the AZOOR patients, the mean±SE of the thickness of the REC+ layer was 126±8.3um, significantly thinner than controls (183±4.9um; p<0.0001,t-test). The mean±SE of the thickness of the RNFL for the AZOOR patients was 43±3.9um, significantly thicker than the means of the controls (27±0.7um; p<0.002). The mean RNFL thickness (39 um) of the 5 AZOOR patients with time to onset ≤ 12 months was similar to the thickness (36 um) for the 5 with the longest times since onset. Neither RNFL thickness (r²=0.05) nor REC+ thickness (r²=0.03) were correlated with time since onset of AZOOR.

Conclusions: : AZOOR patients show a thickening of the macular papillary RNFL that is not correlated with time from onset. The degree of RNFL thickening is comparable to that seen in patients with RP and with comparable receptor thinning.[1,3] This raises the possibility that short-term mechanical factors may play a role in both AZOOR and RP RNFL thickening. 1. Hood et al (2008) IOVS; 2. Wallia & Fishman (2008) IOVS; 3. Hood et al (2009) ARVO.

Keywords: autoimmune disease • retina • nerve fiber layer