Article Text

other Versions

Foveal contrast processing of increment and decrement targets is equivalently reduced in glaucoma.
  1. Geoff P Sampson (sampsong{at},
  2. David R Badcock (david{at},
  3. Mark J Walland (mwalland{at},
  4. Allison M McKendrick (allisonm{at}
  1. University of Melbourne, Australia
  2. University of Western Australia, Australia
  3. University of Melbourne, Australia
  4. University of Melbourne, Australia


    Background: Psychophysical measurement of the function of individual precortical visual pathways (magnocellular, parvocellular and koniocellular) has enabled development of sensitive tests for glaucoma, and has enhanced understanding of its pathophysiology. Such pathways can be further subdivided into their "On" and "Off" components, which have anatomical and physiological asymmetries. This study investigated whether On and Off subdivisions of the magnocellular (M) pathway are differentially affected by glaucoma.

    Methods: Twenty participants with glaucoma and twenty controls underwent two psychophysical procedures that have been shown to assess the M pathway (steady pedestal task) and it's On and Off subdivisions (pedestal-Δ-pedestal task) respectively. Luminance discrimination thresholds were measured foveally, using both increment and decrement stimuli.

    Results: The steady pedestal (undifferentiated M-pathway) task separated the glaucoma and control groups (p = 0.04) with equivalent outcomes for increment and decrement targets. The pedestal-Δ-pedestal task (isolated On and Off M-pathway subdivisions) also differentiated between groups (p = 0.025) but the outcome was not dependant on which subdivision was isolated.

    Conclusion: This study found that increment and decrement targets can be used with equal effectiveness for detecting contrast processing deficits in early glaucoma. Outcomes further suggested that glaucoma affects On and Off subdivisions of the M-pathway equivalently.

    Statistics from

    Request Permissions

    If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.