4247 Magnocellular visual deficit in dusplexia-evidence from motion specific visual evoked potentials

Pureose: In a lot of patients an objectivization of visual field defects is needed. The commonly used VEPs (pattern-reversal, pattern-onset/offset) are not helpful because of their considerable amplitude reduction outside the macula. In contrast the motion-onset VEPs that can be obtained beyond the central 40 " of the vtsual field without significant amplitude reduction (Kuba, M. and Kubova, 2.: Dot. Ophthalmol., EiO: 63-69, 1992) seem to be suitable for this purpose. Methods: VEPs to monocular motion stimulation on 21 " PC monitor (screen size of 4O " x30 ") were recorded from lateral occipital leads. High (95%) or low (10%) contrast patterns moved in random directions at a velocity of 5 or IO'ls for 200 ms with an 1.5 s interstimulus interval. Masking of the central part of visual field or one quadrant stimulation .st various peripheral locations were used to test the residual visual function. Results: No amplitude reduction of motion-onset VEPs and normal latency of the main negative ps!ak N,T~ was tound in control subjects when the central 40 " was masked whereas a prolonged, reduced or mtssing motion-onset response confimted visual field loss in patients. Conlusions: The motion-onset VEPs can serve as an objective diagnostic tool for a detection of large visual field changes. This examination enables also to discover a subclinical magnocellular system disfunction which can be a first sign of some diseases W-pose. Increasing anatomic evidence has suggested that large retinal ganglion cells (M-cells) are pmfemntially damaged in the early stages of primary open angle glaucoma (POAG), Wile the smaller ganglion cells (P-cells) are relatively spared. Aim of this study is to evaluate the visual function of patients with early POAG by means of the pattern electmtetinegram (PERG) and visual evoked potentials (VEPs) in mspcnse to sttmuli designed to favour either the M-or the P-stmam of the visual pathway (patterns of pure luminance contrast or pum chmmatic contrast. respec2ively) Melhods. Sutzjecls were 13 patients tih early POAG @ood visual acuity, moderate loss of peripheral sensitivity al Humphrey 302 test, rile or no disk cupping) and twelve qbmatched wntmfs. PERGs and MPs were recorded in response to either red-green equiluminant gmtinQs or yellowblack luminance gratinQe (0.3 deg. se% contrast). Both trmsiml and steady state responses to 8 range of temporal frequencies (Z-24 Hz) wem recorded. Resuk?. On average. PERGs and VEPs of patients with POAG, as compared to mntmls, r&wed si~niflcant losses for bdh kind of …