The Effect of Induced Intraocular Stray Light (Cataract Simulation) on Thresholds of Standard and Newer Perimetric Tests

Abstract

Purpose: : To investigate the effect of increases in intraocular stray light (ISL) on threshold measurements made by four modern forms of perimetry: Standard Automated Perimetry (SAP) using a HFA II (SITA 24-2), Frequency Doubling Perimetry (FDT) using a Zeiss Matrix (N-24-2), the Heidelberg Edge Perimeter (HEP; ASTA) and the Moorfields Motion Displacement Test (MDT; WEBS)

Methods: : Six healthy psychophysically experienced observers were recruited (mean age 26yrs [21yrs, 29yrs]), refractive correction [0 D,-4.25D]). Five white opacity filters (WOF), each scattering light by a different amount, were used to create incremental increases in ISL. Resultant ISL values were measured with each WOF and at baseline (no WOF) for each subject using a C-Quant Straylight Meter (Oculus, Wetzlar, Germany). An average 25 yr old has an ISL value of ~0.85dB, an increase of 40% in ISL to 1.2dB, is similar to that of a 70 yr old. Each WOFs created an increase in ISL between 10-150% from baseline, ranging from effects similar to normal aging to those of considerable cataract. Each subject underwent 6 test sessions over a 2 week period; each session consisted of the 4 perimetric tests using one of the five WOFs and baseline (both instrument and filter were randomised).

Results: : The reduction in sensitivity from baseline was normalised with respect to the spread of the respective normative values from each instrument (in some cases derived from in-house data) allowing comparison of standardised (z) scores. Initially both MDT and SAP measured thresholds were invariant; however with for both moderate to large increases in straylight (50-150%) SAP, FDT and HEP were highly significantly affected (p<0.001), while MDT remained unaffected.

Conclusions: : The Moorfields MDT measurement of threshold is robust to effects of additional stray light as compared to SAP, FDT and HEP

Keywords: visual fields • cataract • contrast sensitivity