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B. Link, A. G. Jünemann, J. Kremers; L/M Cone Ratio in Glaucoma Patients Assessed by Electroretinography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):527.
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At 12 Hz L- and M-cone isolating stimuli may reflect postreceptoral mechanisms belonging to the parvocellular pathway (see abstract by JK). In glaucoma mainly the retinal ganglion cells are damaged, the outer retina is left intact. Our hypothesis is that an L/M-cone stimulating ERG can give valuable information regarding the pathophysiology and diagnosis of this common disease.
16 eyes of 16 open-angle glaucoma patients (visual acuity 0.9 ± 0.2; glaucomatous visual field defect (Octopus G1) MD [dB]: 8.7 ± 5.4, CLV [dB²]: 82.2 ± 36.5; glaucomatous cupping of the optic disc) and 17 eyes of 17 healthy control subjects (visual acuity 1.0 ± 0.1; normal visual field; normal optic disc) were examined. Colour vision deficiencies were excluded: the anomalous quotient as determined with Nagel anomaloscope (Rayleigh equation) was 1.1 ± 0.1 (glaucoma) and 1.0 ± 0.2 (control). ERG recordings were performed using DTL-electrodes. 12 Hz and 30 Hz square-wave modulations were applied which stimulated the L- and M-cones; the rod contrast was always 0%. The L/M ratio and phase-difference were calculated and compared (T-test).
The ratio of the L- and M-cone response was 1.056 ± 0.39 in the control group and 0.935 ± 0.26 in the glaucoma group at 12 Hz and 3.995 ± 2.12 (control) and 3.084 ± 1.29 (glaucoma) at 30 Hz. The phase difference between L- and M-cones was 175.6° ± 21.9° (control) and 160.9° ± 17.1° (glaucoma) at 12 Hz and 96.9° ± 59.8° (control) and 130.5° ± 52.3° (glaucoma) at 30 Hz. There was a statistically significant difference (p < 0.05) between control group and glaucoma patients in the phase difference between L- and M-cones at 12 Hz.
Glaucoma mainly involves postreceptoral mechanisms. This is in agreement with changes in the ERGs that are driven by the parvocellular pathway. Our data suggest that glaucoma does not only affect the magnocellular pathway.
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