Abstract
Purpose:
To explore and compare the choroidal thickness (CT) and the retinal nerve fiber layer thickness (RNFLT) measured by means of Swept-Source Optical Coherence Tomography (SS-OCT) in highly myopic and in healthy eyes.
Methods:
In this prospective, cross-sectional clinical study 26 highly myopic eyes (>6 D) without any macular diseases and 50 age-matched control eyes were imaged with the SS-OCT (Topcon Corporation, Tokyo, Japan). In all eyes a 12 mm wide scan was performed that allows a volumetric reconstruction of a 3d scan area of 12x9 mm including the posterior pole and over the vascular arcades (wide scan), obtaining a wide choroidal and RNFL map. The wide scan area was divided into 4 areas of study: the upper hemiwide scan (U), the inferior hemiwide scan (I), the macular area (M), and the peripapillary area (PP). Moreover the subfoveal CT was analysed. Visual acuity and axial length (AXL), and refractive error (RE) measurements were collected and the relationships between CT, RNFLT, AXL and RE were explored. Comparisons between groups were performed by Mann-Whitney U test and Chi-squared test as appropriate and relationships between variables were explored by linear regression analysis.
Results:
26 myopic eyes (13M/13F, mean age 50±6.78 years) and 50 control eyes (18M/32F, mean age 48.67±7.2 years) were included in the analysis. CT was thinner in highly myopic than in control eyes in the inferior hemiwide scan (162.14±49.86 µm versus 189.52±42.89 µm, p=0.0023), in the macular area (179.71±58.55 µm versus 211.73±44.82 µm, p=0.0044) and at the fovea (182.76±63.39 µm versus 226.24±53.65 µm, p=0.0027). RNFLT was thinner in highly myopic than in control eyes both in the superior and inferior hemiwide scan (46.58±35.10 µm versus 54.45±6.13 µm, p<0.0001 and 34.99±13.36 µm versus 53.11±5.63 µm p<0.0001 respectively) and in the peripapillary area (65.52±34.82 µm versus 95.55±10.85 µm, p=0.0006). A significant relationship was found between peripapillary CT, RNFLT and AXL (R2=0.25, p=0.0126 and R2=0.19, p=0.03 respectively) and refractive error (R2=0.31, p=0.004 and R2=0.18, p=0.03 respectively) as well as between macular RNFLT and AXL (R2=0.22, p=0.01).
Conclusions:
Both the RNFL and the choroidal thickness as measured by SS-OCT are significantly reduced in highly myopic eyes compared to emmetropic eyes.
Keywords: 452 choroid •
605 myopia •
552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)