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Download fileFunctional Loss in the Magnocellular and Parvocellular Pathways in Patients with Optic Neuritis
journal contribution
posted on 2012-06-25, 00:00 authored by Dingcai Cao, Andrew J. Zele, Joel Pokorny, David Y. Lee, Leonard V. Messner, Christopher Diehl, Susan KsiazekPurpose: To evaluate contrast threshold and contrast gain in patients with optic neuritis
under conditions designed to favor mediation by either the inferred Magnocellular (MC-)
or Parvocellular (PC-) pathway.
Methods: Achromatic and chromatic contrast discrimination was measured in 11
patients with unilateral or bilateral optic neuritis and 18 age-matched controls with
normal vision, using achromatic steady-pedestal and pulsed-pedestal paradigms to bias performance toward the MC- or PC- pathway respectively. Additionally, L-M chromatic discrimination at equiluminance was evaluated using the steady-pedestal paradigm. . A physiologically plausible model could describe the data with parameters accounting
for contrast gain and contrast sensitivity in the inferred MC- or PC- pathway. The fitted
parameters from the affected eye by optic neuritis were compared with those from the
normal eyes using Generalized Estimation Equation (GEE) models that can account for
within-subject correlations.
Results: Compared with normal eyes, the affected eyes had significantly higher
saturation parameters when measured with both the achromatic pulsed-pedestal
paradigm [GEE: β(se) = 0.35(0.06), p < 0.001] and the chromatic discrimination
paradigm [β(se) = 0.18(0.08), p = 0.015], suggesting contrast gain in the inferred PCpathway is reduced; the affected eyes also had reduced absolute sensitivity in the
inferred MC-pathway measured with the achromatic steady-pedestal paradigm [β(se) =
0.12 (0.04), p = 0.005].
Conclusion: Optic neuritis produced large sensitivity loss mediated by the MCpathway
and contrast gain losses in the inferred PC- pathway. A clinical framework is
presented for interpreting contrast sensitivity and gain loss to chromatic and achromatic stimuli in terms of retinal and post-retinogeniculate loci contributions to detection and discrimination.