A 44 channel suprachoroidal retinal prosthesis: inter-observer reliability measuring electrode to retina distance

Abstract

Purpose : The electrode to retina (ER) distance may be an important factor in determining the efficacy and stability of a retinal prosthesis. The aim of this study is to determine the inter-observer reliability of measuring ER distance between 3 observers.

Methods : Single section optical coherence tomography (OCT) line scans with infrared (IR) light source were acquired using a Heidelberg Spectralis® OCT from one participant with advanced retinitis pigmentosa, implanted with a 44 channel suprachoroidal retinal prosthesis (NCT03406416). The IR image was used to orientate the single section line scan either horizontally or vertically through the retina and electrode array. Images were captured, between April and July 2018 and retrospectively screened to meet inclusion criteria: image quality greater than 20, high speed or high resolution with a minimum automatic real time (ART) of 2. The ER distances were measured in microns (µm) from centre of electrode to the inner boundary of the retinal pigment epithelium, utilising the mark-up tools within the Heyex software. A total of 129 ER distance measurements, encompassing 37 different electrode positions, from 38 IR images across 8 time-points were measured by each trained observer. Statistical analyses were conducted using Stata/SE version 15.1 (StataCorp, College Station, Tx).

Results : ER distance measurements ranged from 208 to 509 µm across electrode positions and observers. The mean ER distance for the three observers were 369.7 ± 59.6 µm, 371.9 ± 59.7 µm, and 376.4 ± 60.1 µm. There was excellent agreement between observers in measuring ER (Pearson’s ρ≥0.98 for each pairwise comparison). The mean difference in ER distance between observers ranged from 2.2 to 6.8 µm with limits of agreement ranging from 35.5 to 42.4 µm in width. The intraclass correlation (ICC) showed almost perfect agreement between observers: 0.98 (95% CI 0.97-0.99) for absolute agreement and 0.98 (95% CI 0.98-0.99) for consistency.

Conclusions : Our method of measuring ER distances is highly reliable between observers. This is important because when acquiring a large volume of scans, measuring images is a time-consuming, manual process, requiring multiple trained personnel. Having a reliable procedure of measuring ER distance gives confidence in interpreting clinical trial results relating to the safety and efficacy of retinal prostheses.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.