The influence of axial length on confocal scanning laser ophthalmoscopy and spectral-domain optical coherence tomography size measurements: a pilot study

Abstract

To investigate the influence of axial length on SD-OCT and cSLO size measurements from the Heidelberg Spectralis. In this pilot study, eight emmetropic pseudophakic eyes with subretinal visual implant were selected. The axial length was measured in three short (<22.5 mm), three medium (22.51-25.50 mm) and two long (>25.52 mm) eyes. The known size of subretinal implant sensor field (2800 × 2800 μm) was measured on 15 images per eye with cSLO and SD-OCT. The mean axial length was 20.8 ± 0.8 mm in short eyes, 23.3 ± 0.4 mm in medium eyes, and 26.3 ± 0.5 mm in long eyes respectively. We found in short eyes, in medium eyes and in long eyes a mean value of sensor field size measurements from cSLO of 3327 ± 9 μm, 2800 ± 9 μm and 2589 ± 12 μm and from SD-OCT of 3328 ± 9 μm, 2800 ± 12 μm and 2585 ± 19 μm respectively. The size measurements decreased in SD-OCT and cSLO measurements with longer axial lengths significantly (p < 0.0001). The present findings demonstrate accuracy of the scaling in cSLO and SD-OCT measurements of the Heidelberg Spectralis for emmetropic medium eyes. The size measurements from SD-OCT to those from cSLO were approximately equal. Caution is recommended when comparing the measured values of short and long eyes with the normative database of the instrument. Further studies with larger sample sizes are needed to confirm findings.