Spatial and temporal visual filtering in patients with glaucoma and ocular hypertension

Abstract

Purpose: To investigate the spatial and temporal response characteristics in patients with glaucoma and ocular hypertension (OHT), in order to demonstrate the earliest specific measure of vision loss and to elucidate the precise mechanism of early glaucomatous damage. Methods: The Open Optical View System was used to assess changes in spatial and temporal vision in patients with clearly defined glaucoma (30 eyes), patients with OHT (30 eyes) and 30 eye-matched normal control eyes. The psychophysical methods applied were developed by Barber and Ruddock, who showed that the responses called ST1 and ST2 have similar characteristics to those found in the parvocellular and magnocellular pathway respectively. The measurement of spatial and temporal responses rests upon the measurement of a target that moves across a background, itself modulated spatially (gratings) and temporally (flicker). Results: The results reported, taken together with the current data on retinal ganglion cell function, reveal damage to both the parvocellular and magnocellular pathway in patients with glaucoma. In the OHT groups only marginal changes were found in the parvocellular response, but significant changes in the magnocellular response. In both OHT and glaucoma, the temporal processing shows greatest abnormalities at a small number of low flicker frequencies. Conclusion: We provide psychophysical evidence of the detectable ganglion cell damage in patients with OHT who remain normal on testing with automated perimetry. The psychophysical method chosen (which measures the function of specific sub-divisions of the visual pathway) may prove useful in screening for glaucomatous damage.