Minimizing Pupil Size Dependence in Flicker ERG Using Stiles-Crawford Compensation

This study determined the impact of the Stiles-Crawford effect (SCE) on electroretinograms (ERGs). Compensating for the SCE can improve the diagnostic reliability of ERGs by providing a stimulus minimally affected by pupil size.

Flicker ERGs were recorded from 10 healthy subjects at 3-minute intervals over 21 minutes after mydriasis. The RETeval system adjusted retinal illuminance in real time based on pupil size measurements, using a Troland stimulus and preset SCE compensation factors (ρdevice) of 0, 0.05, 0.085, and 0.12 mm-2.

Larger pupil areas led to prolonged implicit times with ρdevice = 0 and 0.05 mm-2, whereas ρdevice = 0.12 mm-2 reduced implicit time. Amplitudes were lower with ρdevice = 0 mm-2 but increased with ρdevice = 0.085 and 0.12 mm-2. The values that minimized pupil size dependence were ρdevice = 0.086 mm-2 for the implicit time of the fundamental component of the ERG and ρdevice = 0.05 mm-2 for all other measures. Variability in ERGs based on pupil size is predicted to be ≤7% of the associated 95% reference interval for Troland stimuli over the range of nonmydriatic pupil sizes, compared to ≤43% for luminance stimuli over the range of mydriatic pupil sizes.

Using Troland stimuli with ρdevice = 0.05 mm-2 for all cone-mediated ERGs would minimize the impact of pupil size, although the improvement would be modest for ERGs performed with Troland stimulation without SCE compensation on non-dilated subjects.

Applying the appropriate SCE coefficient (ρdevice) enables more reliable ERG measurements, improving diagnostic accuracy despite pupil size variations in clinical settings.