Slit-Lamp OCT Scans of Implants and Metal Spheres in the Subconjunctival Space of Rabbits

Abstract

 

Purpose:

 

To establish whether Slit Lamp Optical Coherence Tomography (SL-OCT) can 1) image a subconjunctival drug delivery implant in rabbits and 2) accurately measure various sized metal spheres in the subconjunctival space.

 

Methods:

 

Subconjunctival imaging of an implant was performed with the SL-OCT (Heidelberg Engineering, Germany) in conscious rabbits. Following terminal anaesthesia, three subconjunctival spheres (small, medium, large) were placed and imaged. Two observers took 5 independent scans of the spheres using SL-OCT. Images were then analysed by the 2 observers independently at a later date. At a 3rd session one observer re-analysed the scans independent to the previous measurements.The diameter of the spheres was measured using the scale provided by the SL-OCT and constructing a spherical overlay using ImageJ. Actual physical diameters of the spheres were measured with a digital micrometer (Mitutoyo 0-25mm, accuracy 0.001 mm). Bland-Altman analysis was used to calculate limits of agreement (LOA).

 

Results:

 

It was possible to visualize the subconjunctival implants in a conscious rabbit but it was not possible to corroborate the actual size due to technical difficulties in extracting the tablet. For spherical spheres the range of the LOA are shown in Table 1.

 

Conclusions:

 

There was moderate inter- and intra-observer agreement of measurements of spheres, however the LOA was greater than 5% compared to the micrometer measurements. Although the use of SL-OCT for accurate measurements of subconjunctival spheres is still preliminary, the potential for using this method for imaging and measuring subconjunctival implants warrants further study.  

 

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: non-clinical • image processing