Retinal Anatomy and Electrode Array Position in Retinitis Pigmentosa Patients After Argus II Implantation: An International Study

Abstract

Purpose: To assess the retinal anatomy and array position in Argus II retinal prosthesis recipients.

Design: Prospective, noncomparative cohort study.

Methods: Setting: International multicenter study.

Patients: Argus II recipients enrolled in the Post-Market Surveillance Studies.

Procedures: Spectral-domain optical coherence tomography images collected for the Surveillance Studies (NCT01860092 and NCT01490827) were reviewed. Baseline and postoperative macular thickness, electrode-retina distance (gap), optic disc-array overlap, and preretinal membrane presence were recorded at 1, 3, 6, and 12 months.

Main outcome measures: Axial retinal thickness and axial gap along the array's long axis (a line between the tack and handle); maximal retinal thickness and maximal gap along a B-scan near the tack, midline, and handle.

Results: Thirty-three patients from 16 surgical sites in the United States and Germany were included. Mean axial retinal thickness increased from month 1 through month 12 at each location, but reached statistical significance only at the array midline (P = .007). The rate of maximal thickness increase was highest near the array midline (slope = 6.02, P = .004), compared to the tack (slope = 3.60, P < .001) or the handle (slope = 1.93, P = .368). The mean axial and maximal gaps decreased over the study period, and the mean maximal gap size decrease was significant at midline (P = .032). Optic disc-array overlap was seen in the minority of patients. Preretinal membranes were common before and after implantation.

Conclusions: Progressive macular thickening under the array was common and corresponded to decreased electrode-retina gap over time. By month 12, the array was completely apposed to the macula in approximately half of the eyes.

Copyright © 2018 Elsevier Inc. All rights reserved.

Figures

Figure 1.. Measurement of Argus II Optical Coherence Tomography Characteristics

Top: En face OCT view of Argus II retinal prosthesis implant (Second Sight Medical Products, Inc., Sylmar, CA) with B-scan near the tack (top left), midline (top middle), and the handle (top right). Middle: Illustration of the Argus II implant from the Surgeon’s manual labeled with the tack, midline, handle, and the array’s long axis (red line) shown. The red line represents the long axis of the array used to measure axial thickness and gap. Bottom: An OCT B-scan near the handle demonstrates how axial and maximal retinal thickness and electrode-retina gap were measured, and an example of an adherent preretinal hyperreflective membrane (asterisk *). The B-scan cuts through the array diagonally and thus the handle is not visible. The A-scan through the array’s long axis is shown as a red vertical line. The blue line represents the axial macular thickness measurement. The yellow line represents the axial electrode-retina gap. The purple line shows the maximal retinal thickness along the B-scan. The pink line shows the maximal electrode-retina gap along the B-scan. Measurements were taken using the Heidelberg software program.

Figure 2.. Axial Macular Thicknesses Along Array’s Long Axis by Location through Month 12 after Argus II Implantation.

Boxplots with Tukey’s quartiles are shown for the tack (left), midline (center), and handle (right) with the measured retinal thickness in micrometers along the array’s long axis during postoperative months 1, 3, 6, and 12. The median value is indicated by the horizontal line in the box encompassing data points in the 25th to the 75th quartiles. The median values remained fairly unchanged at the tack and the handle, however steadily increased at midline from month 1 through month 12. The X-axis represents months after surgery, the Y-axis represents thickness in microns.

Figure 3.. Maximal Macular Thicknesses Along the B-scan by Location through Month 12 after Argus II Implantation.

Boxplots with Tukey’s quartiles are shown for the tack (left), midline (center), and handle (right) with the maximum retinal thickness along the B-Scan measured in micrometers at postoperative months 1, 3, 6, and 12. The median value is indicated by the horizontal line in the box encompassing data points in the 25th to the 75th quartiles. The X-axis represents months after surgery, the Y-axis represents thickness in microns.

Figure 4.. Axial Electrode-Retina Gap Along Array’s Long Axis by Location through Month 12 after Argus II Implantation.

Boxplots with Tukey’s quartiles are shown for the tack (left), midline (center), and handle (right) with the electrode-retina distance (gap) measured in micrometers during postoperative months 1, 3, 6, and 12. The median value is indicated by the horizontal line in the box encompassing data points in the 25th to the 75th quartiles. Median gap was zero near the tack and the handle at all points, and steadily decreased at midline from month 1 through month 12. The X-axis represents months after surgery, the Y-axis represents thickness in microns.

Figure 5.. The Maximal Electrode-Retina Gap Along the B-scan by Location through Month 12 after Argus II Implantation.

Boxplots with Tukey’s quartiles are shown for the tack (left), midline (center), and handle (right) with the electrode-retina distance (gap) measured in micrometers during post-operative months 1, 3, 6, and 12. The median value is indicated by the horizontal line in the box encompassing data points in the 25th to the 75th quartiles. The median maximal gap was under 100 microns near the tack and the handle at month 1 and zero at most other time points. The median maximal gap at midline was 214 microns at month 1 and steadily decreased to 40 microns by month 12. The X-axis represents months after surgery, the Y-axis represents thickness in microns.

Figure 6.. Representative Optical Coherence Tomography (OCT) Scans at Baseline and After Argus II Retinal Prosthesis Implantation.

Top Left. Baseline OCT scan shows intraretinal cyst and completely adherent hyperreflective preretinal membrane (arrow). Top Center. Baseline OCT scan shows an example of a thick off-the-retina membrane (arrow) resembling either an epiretinal membrane or thick hyaloid. Top Right. Baseline OCT scan shows macular concavity in a patient with one of the largest electrode-retina gaps (359 microns maximal gap at midline at month 1). Middle Left. OCT scan shows low-lying off-the-retina membrane (arrow) commonly seen after Argus II implantation. Middle Center. OCT scan shows a peculiar hyperreflective layer (asterisk *) adherent to the posterior surface of the array separate from the retina, which may represent either fibrosis or inflammatory material. Thickened retina is seen below the hyperreflective layer. Middle Right. OCT scan at month 1 shows one of the largest maximal electrode-retina gaps (433 microns at midline) in the eye with a macular concavity shown in Top Right image. Bottom Left. OCT scan shows a “snowplow” effect of the array pressing against the retina (arrow) and causing adjacent thickening. Bottom Center. OCT example of boggy macular thickening under the array and hyperreflective layer (asterisk *) under the array. OCT quality is not sufficient to distinguish if cysts are present. Bottom Right. OCT example of the array completely apposed against the retina. No retinal thickening is seen in this scan. Mild “snowplow” effect is visible (arrow).