Blind spot size depends on the optic disc topography: a study using SLO controlled scotometry and the Heidelberg retina tomograph

Abstract

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

Scotoma mapping by semi‐automated kinetic perimetry: the effects of stimulus properties and the speed of subjects' responses

“…Although the physiological blind spot has been examined extensively with automated static perimetry (Safran et al 1993), manual kinetic perimetry (Armaly 1969) and also with scanning laser ophthalmoscope (SLO) microperimetry, using both automated static and manual kinetic testing (Meyer et al 1997; Glück et al 1999), to our knowledge, the blind spot has not previously been studied with automated kinetic perimetry. The majority of prior studies have used the blind spot as a well defined model of a small scotoma (Aulhorn et al 1987).…”

“…The majority of prior studies have used the blind spot as a well defined model of a small scotoma (Aulhorn et al 1987). Studies have been performed to determine rates of detection of the physiological blind spot by automated static perimetry using different strategies (Gramer et al 1979; Funkhouser et al 1988; Safran et al 1993); the influence of stray light and optic disc topography on the detection and size of the blind spot have been studied (Fankhauser & Haeberlin 1980; Meyer et al 1997); and the effect of varying stimulus qualities on the differential luminance thresholds at the border of the blind spot have been carefully documented (Bek & Lund‐Andersen 1989; Glück et al 1999).…”

“…When using static perimetry to detect small scotomas, a significant challenge is encountered in the trade‐off between limited resolution on one hand (Jonas et al 1991), or excessively long examination time on the other (Meyer et al 1997). Both problems can be in play, despite the use of adaptive strategies.…”

“…Additionally, the size of the blind spot has gained special interest in the last few years with reference to glaucoma (Meyer et al 1998), influences of the optic disc topography (Meyer et al 1997) and acute idiopathic blind spot enlargement syndrome (Fletcher et al 1988).…”

Effects of contralateral extremity manipulation on brain function

“…The use of computerized static perimetry to measure the cerebral effects of spinal manipulation has increased our understanding of the nervous system (5) . The size of the right blind spot is different from the size of the left blind spot such that the prominent nasal part of the optic disc appears less ' blind ' than the shallow temporal part (6) . Changes in the size of a mapped blind spot after any type of treatment (manipulation, acupuncture, etc.)…”