One embodiment of the invention provides a method for performing a supra-threshold test of sensitivity across a visual field of a subject. The method includes presenting a stimulus at each location of a set of locations spread across the visual field and obtaining for each stimulus a result indicating whether or not the stimulus was seen by the subject. The method further includes determining for each location whether or not to re-present a stimulus at that location, wherein for a given location, the determining involves combining results obtained from multiple locations. These multiple locations are defined by a cluster associated with the given location, with the cluster being determined based on the paths of optic nerve fibre bundles across the visual field.