Microperimetric indices in patients with AMD derived using a new spatial interpolation technique

Title Microperimetric indices in patients with AMD derived using a new spatial interpolation technique
Author, Co-Author Helen Baggaley, Andrew Astle, Jonathan Denniss
Topic Low Vision
Program Number
Ballroom A-B

Purpose: We recently demonstrated a spatial interpolation method that enables comparison of microperimetry data to normative data despite non-foveal fixation (Denniss & Astle, ARVO 2016). The method also enables calculation of conventional perimetric indices such as Total Deviation (TD), Pattern Deviation (PD), Mean Deviation (MD) and Pattern Standard Deviation (PSD). Here we demonstrate this technique and report microperimetric characteristics of patients with age-related macular degeneration (AMD), tested at their monocular preferred retinal locus (PRL). 

Methods: Data from 96 eyes of 96 patients with AMD were included. Patients (median age 79 years, range 57-97) were tested using the 4-2 Expert strategy of the MAIA-2 microperimeter (CenterVue, Padova, Italy) with the test grid (37 locations, 5° radius) centred on the monocular PRL as determined by the instrument. For each patient, age-corrected sensitivity at each location was compared to the corresponding point (resolution 0.1°) on the previously described normative surface, and indices equivalent to those of the Humphrey Field Analyzer (Carl Zeiss Meditec, Jena, Germany) (TD, PD, MD, PSD) were computed. 

Results: Measured monocular PRL location (and therefore test grid centre) varied by 14° horizontally and 11° vertically.  Median MD was -11.3dB (Interquartile range (IQR) -16.8 to -6.0dB). Median PSD was 6.5dB (IQR 4.0 to 8.4dB). Across all patients median 35 (IQR 28-37) locations fell below the TD 5% probability level, and median 22 (IQR 18-26) locations fell below the PD 5% probability level. 

Conclusions Patients with AMD fixate with disparate retinal locations, making comparison to conventional, fixed-location normative data impossible. Comparison to normative data and calculation of conventional perimetric indices is enabled by our previously demonstrated spatial interpolation technique. Patients with AMD demonstrated significant and varied perimetric loss around their chosen monocular PRL.

Affiliation of Co-Authors University of Nottingham, University of Nottingham