Rarebit test principles- use stimuli of minimal subtense (ideally smaller than receptive fields),

- at high & fixed contrast,

- check once only for the presence of function (no thresholding),

- in ever-new, non-overlapping locations;

- calculate hit rate

- briefly exposed (to negate sweep gains);

Model of receptive field matrix with 10% ”holes”.

Model of receptive field matrix with 10% ”holes”. A macro stimulus can activate several good fields. Micro stimuli (”rare bits”) in ever new positions should on average activate 9 fields out of 10.

Key rarebit parameters:

Dot size: 0.5 x MAR** Minimum Angle of Resolution

Contrast: high & fixed

Main result parameter Hit Rate =

Sum of responses Sum of presentations

Expected normal hit rate 100% (except at blindspot and in angioscotoma)

Case of mild optic neuritis

HRP (High-pass Resolution Perimetry)

RBP (Rarebit Perimetry)

VA = 0.8 = 20/25