Influence of axial length on thickness measurements using spectral-domain optical coherence tomography

Invest Ophthalmol Vis Sci. 2014 Oct 8;55(11):7494-8. doi: 10.1167/iovs.14-14043.


Purpose: The purpose of this study was to assess the influence of axial length on spectral-domain optical coherence tomography (SD-OCT) thickness measurements in patients with subretinal visual implants.

Methods: Data from eight emmetropic pseudophakic eyes of eight patients with subretinal visual implants were analyzed retrospectively. These patients participated in the monocentric part of a multicenter trial. 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. Using Heidelberg Spectralis, the known thickness of a subretinal implant microchip (70 μm) was measured on 15 images per eye with SD-OCT, using the software calipers.

Results: 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. We found in short eyes, in medium eyes, and in long eyes a mean value of microchip thickness measurements from SD-OCT of 82.9 ± 1.4 μm, 70.5 ± 1.3 μm, and 64.2 ± 1.3 μm, respectively. The thickness measurements decreased in SD-OCT measurements with longer axial lengths significantly (P < 0.0001).

Conclusions: Axial length influences SD-OCT thickness measurements. Our findings demonstrate accuracy of the scaling in SD-OCT thickness measurements in emmetropic medium eyes. Caution is recommended when comparing the measured values of short and long eyes with the normative database of the instrument. There is a need for larger sample-size studies to confirm our results. ( number, NCT01024803.).

Keywords: Heidelberg Spectralis; axial length; in vivo measurement; spectral-domain optical coherence tomography (SD-OCT); subretinal visual implant.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Axial Length, Eye*
  • Blindness / pathology*
  • Blindness / physiopathology
  • Blindness / surgery
  • Female
  • Follow-Up Studies
  • Humans
  • Male
  • Middle Aged
  • Retrospective Studies
  • Tomography, Optical Coherence / methods*
  • Visual Acuity*
  • Visual Prosthesis*

Associated data