Novel electrophysiological instrument for rapid and objective assessment of magnocellular deficits associated with glaucoma.
OBJECTIVE
To introduce a rapid and objective electrophysiological technique that can assess visual function in the magnocellular pathway, which is thought to be affected in early-stage glaucoma.


METHODS
Low-contrast bright or dark isolated-checks were luminance-modulated against a static background at 10 Hz in order to drive preferentially the magnocellular ON or OFF pathway. Visual evoked potentials were recorded during 1-s epochs of stimulation and responses at the stimulus frequency were measured. Artifact rejection features ensured that eight valid runs were obtained per eye. Signal-to-noise ratios (SNR) were derived based on a multivariate statistic. In order to demonstrate its functionality, a small group of patients with glaucoma (N = 18, Snellen acuity of 20/30 or better) and control observers (N = 16) were tested. A participant failed the test if either eye yielded an SNR < or = 1. Receiver-operating-characteristic curve analysis was used to estimate the accuracy of group classification.


RESULTS
The instrument was found to elicit reliable responses from control observers. For the 15% bright condition, all control observers yielded significant isolated-check VEPs (icVEPs), whereas the majority of patients failed to do so, indicating significant losses in central visual function. This condition produced the highest classification accuracy (94%), followed by the 10% dark condition (91%).


CONCLUSIONS
Both ON and OFF divisions of the magnocellular pathway can be assessed rapidly through the application of the icVEP technique. This measure of central visual function may be of value in the detection of glaucomatous deficits and may complement tests of peripheral function.
Zemon
Vance
V
Ferkauf Graduate School of Psychology, Yeshiva University, Albert Einstein College of Medicine Campus, 1300 Morris Park Ave, Bronx, NY, 10461, USA. vepman@aol.com
Tsai
James C
JC
Forbes
Max
M
Al-Aswad
Lama A
LA
Chen
Chi-Ming
CM
Gordon
James
J
Greenstein
Vivienne C
VC
Hu
George
G
Strugstad
Evy C
EC
Dhrami-Gavazi
Elona
E
Jindra
Lawrence F
LF
D000328:Adult; D000368:Aged; D003623:Dark Adaptation; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D005074:Evoked Potentials, Visual; D015812:Glaucoma, Angle-Closure / Q000175:diagnosis*; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008875:Middle Aged; D010775:Photic Stimulation; D012164:Retinal Diseases / Q000175:diagnosis*; D012165:Retinal Ganglion Cells / Q000473:pathology*