A sctoma centered on the fixation point with a sloping border is highly characteristic of ON, while an inferior altitudinal defect with a sharp border along the horizontal meridian, particularly in the nasal periphery, is highly characteristic of AION. To identify these diagnostic criteria, it can be necessary to examine full fields. With restriction of perimetry to 30 degrees a large central scotoma can be mistaken for a diffuse defect and the border in the nasal periphery can be missed.

Aims-To find out whether the size of the blind spot area, determined by static perimetry, depends on the surface topography of the optic disc and its surrounding area. Methods-Ten eyes were examined; all had a parapapillary atrophy adjacent to the temporal side of the disc. Microperimetry was performed under direct fundus control using a Rodenstock scanning laser ophthalmoscope. The horizontal meridian of the optic discs was examined in 0.5°s teps using five stimulus sizes (Goldmann I to V), each with 10 diVerent degrees of brightness. Optic disc topography was measured with the Heidelberg retina tomograph (HRT).Results-Stimuli with a high luminance level (Goldmann IV, 4 dB), presented on the horizontal meridian, were seen up to 0.75°centrally (that is, towards the optic disc centre) from the temporal edge of the parapapillary atrophy but up to 1.85°cen-trally from the nasal optic disc border (p<0.01). Horizontal HRT section profiles of the optic disc consistently showed prominent nasal disc borders contrasting with a shallow excavation within the temporal parapapillary atrophy. Conclusions-The size of scotomas depends on the surface topography of the tested area. The prominent nasal part of the optic disc appears less 'blind' than the shallow temporal part, probably because of more intensive light scattering by the prominent nasal part of the disc. These considerations should also apply to other scotomas. (Br J Ophthalmol 1997;81:355-359) It is known that a scotoma (for example, the blind spot) can decrease in size when the luminance level of the test stimuli increases. Von Helmholtz (quoted in Le Grand 1 ) was probably the first to describe the phenomenon of a diVuse flash, which is noticed by many individuals, when stimuli with a high luminance level are projected into the centre of the optic disc, even if the stimulus size is much smaller than the disc diameter. Fankhauser and Haeberlin, using a cupula perimeter, showed that this eVect was due to entoptic light scattering and not instrumental stray light. 2

Cyclocryocoagulation is considered an effective method to lower IOP and simplify drug therapy without having serious complications.

Blind spots of normal discs seem to be smaller than those of deeply excavated discs in eyes with early glaucoma, possibly because there is more light scattering by the normal disc surface towards the adjacent functioning retina.

In one third of all cases the needling is effective for more than 6 months. A complicated pressure lowering surgery does not necessarily diminish the effectiveness of a needling procedure. Re-needlings are as successful as the first one.