A five degree-of-freedom remote center of motion device for stable volumetric OCT imaging of the retina

Abstract

Purpose : Handheld optical coherence tomography (HH-OCT) is gaining attention for retinal imaging of supine patients but is associated with some OCT probe stability challenges. Accurate 3-D images for lesion examination or quantitation requires maintaining a fixed position for prolonged periods of time. Measurement accuracy can deteriorate significantly with small physiologic tremors. This work presents a stabilizing statically balanced five degree-of-freedom (DoF) remote center of motion (RCM) device designed to hold a handheld OCT probe for high-fidelity and more accurate measurements.

Methods : A six-bar linkage RCM device was designed to carry a Bioptigen retinal OCT probe offering five DoF of image plane alignment. C-Mode OCT images were taken of two 1mm diameter steel balls fixed within a phantom eye at 0^o, 90^o, and 135^o from the vertical meridian comparing traditional handheld and RCM device approaches. An optical tracker recorded the probe's movements via attached markers during the imaging process. Acquired OCT ball images were analyzed with Imaris 9.9, Oxford Instruments.

Results : For each angular position, the average calculated volumetric error of the spheres with the handheld approach was 0.0870, 0.1212, and 0.1309mm³ and the average error using the RCM apparatus was 0.0580, 0.0965, and 0.709mm³, respectively. The handheld and RCM approaches had 29.6% and 5.6% failure rate of sphere imaging, respectively (imaging failure rates increased with larger peripheral angles). Positional variance of the OCT probe during trials showed an average maximum of 0.248 and 0.001mm with manual and RCM approaches, respectively. A Mann-Whitney rank sum test showed no significant difference between expected and measured volumes for all successful trial attempts (p≥0.11). A significant differences of the measured sphericity between approaches across all trials was found (p≤0.002) (Fig. 1).

Conclusions : A rigid mechanical RCM device demonstrated improved C-Mode OCT images of steel balls in a phantom eye by minimizing positional variance of an OCT probe. This work presents a device enabling fine OCT image control and improves image fidelity over handheld approaches, especially for peripheral imaging, and at lower costs than robotic systems.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

3D reconstructions of metal spheres positioned at 135^o from the eye’s vertical meridian using a) the handheld approach and b) the RCM device.