Abstract
Purpose. To investigate misalignments (MAs) on retinal nerve fiber layer thickness (RNFLT) measurements obtained with Cirrus© SD-OCT. Methods. This was a retrospective, observational, cross-sectional study. Twenty-seven healthy and 29 glaucomatous eyes of 56 individuals with one normal exam and another showing MA were included. MAs were defined as an improper alignment of vertical vessels in the en face image. MAs were classified in complete MA (CMA) and partial MA (PMA), according to their site: 1 (superior, outside the measurement ring (MR)), 2 (superior, within MR), 3 (inferior, within MR), and 4 (inferior, outside MR). We compared RNFLT measurements of aligned versus misaligned exams in all 4 sectors, in the superior area (sectors 1 + 2), inferior area (sectors 3 + 4), and within the measurement ring (sectors 2 + 3). Results. RNFLT measurements at 12 clock-hour of eyes with MAs in the superior area (sectors 1 + 2) were significantly lower than those obtained in the same eyes without MAs (P = 0.043). No significant difference was found in other areas (sectors 1 + 2 + 3 + 4, sectors 3 + 4, and sectors 2 + 3). Conclusion. SD-OCT scans with superior MAs may present lower superior RNFLT measurements compared to aligned exams.
Highlights
Glaucoma is a progressive optic neuropathy characterized by death of retinal ganglion cells (RGC) and degeneration of the retinal nerve fiber layer (RNFL), resulting in a distinct appearance of the optic nerve head (ONH) and concomitant visual field (VF) loss [1]
In this study we found that the presence of complete MA (CMA) or partial MA (PMA) on superior sectors of the Cirrus standard deviation (SD)-optical coherence tomography (OCT) scan was associated with lower retinal nerve fiber layer thickness (RNFLT) in the 12 clock-hour (P = 0.043)
It is important to emphasize that the differences we observed can not be explained by differences in mean signal strength between eyes with and without MAs (Tables 2–5), which could potentially interfere with RNFLT measurements [14]
Summary
Glaucoma is a progressive optic neuropathy characterized by death of retinal ganglion cells (RGC) and degeneration of the retinal nerve fiber layer (RNFL), resulting in a distinct appearance of the optic nerve head (ONH) and concomitant visual field (VF) loss [1]. In the early stages of the disease, structural changes may precede VF defects. Some studies have shown that as many as half of RGC can be lost before a VF defect is detected by standard automated perimetry (SAP) [2, 3]. Detecting structural changes in the neuroretinal rim and RNFL is important for early glaucoma detection. Several techniques have been introduced over the past years aiming at detecting morphologic glaucomatous abnormalities earlier than functional tests [4]. The Cirrus (Carl Zeiss Meditec Inc., Dublin, CA) spectral domain
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