Static Perimetry-OCT Topographical Overlay Findings in the RUSH2A Study

Ellipsoid zone (EZ) loss on optical coherence tomography (OCT) correlates with diminished sensitivity on static perimetry (SP). We explore a topographical overlay analysis in USH2A-related retinitis pigmentosa (RP) to develop novel endpoints of structural and functional change.

Subjects (N = 105) had SP (3× baseline; once annually for 4 years) and annual OCT. B-scans were segmented to outline the EZ. Overlays used visual field modeling and analysis (VFMA) software to superimpose the hill of vision (HOV) onto the en face infrared (IR) fundus image with EZ contours segmented from OCT volume scans. EZ border and three ribbons straddling the EZ border were ray cast onto the HOV. The HOV volume, HOV slope, mean sensitivity (MS), and peak sensitivity were measured. Mixed effect models were used to estimate change rates.

Significant decrease over 4 years was found in all measures within the EZ, except slope and peak sensitivity. MS decreased for all ribbons, with outer ribbons showing greater progression than inner ribbons. Inner ribbons had larger decreases in volume and slope than outer ribbons.

SP-OCT overlay analysis showed faster loss of sensitivity outside the EZ margin. The widest ribbon outside the EZ showed greatest progression, suggesting more rapid vision loss occurring distal to the EZ margin. Slope progressed most within the widest inner ribbon, which could mean that slope change is a precursor to EZ loss.

This research explores novel endpoints and concepts to characterize the disease progression in USH2A-related RP using imaging and functional overlay techniques.