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D.A. Valenti; Retinal Inhibition Secondary to Methotrexate: Identified With Frequency Doubling Technology . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4480.
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Acetyl cholinesterase has been found to be active in the retinal ganglion cell layer including amacrine cells and the magnocellular pathway. Acetyl cholinesterase in the retinal amacrine cells has been found to be inhibited by methotrexate in an animal model. This single case study investigated retinal inhibition induced by methotrexate in a clinical setting.
This project used Frequency Doubling Technology (FDT). The FDT measures low spatial frequencies and tests the central 20 degrees of the visual field. It is similar to a traditional visual field in that individuals respond when they see a target. The instrument is thought to isolate a subset of retinal ganglion cells in the magnocellular pathway by use of low spatial frequency sinusoidal gratings (<1 cycle/degree) that undergo a high temporal frequency counter–phase flicker at 15 Hz or greater. Additional relevant tests included; conventional visual fields, optic nerve assessment with direct and indirect ophthalmoscopy, optical coherence tomography, full field electroretinogram, focal electroretinogram, 100 hue color testing, dark adaptation function and customized macular functional assessment.
Two tests showed significant functional deficits in non macular function; the FDT and the off macula component of focal electroretinogram. The dark adaptation test showed reductions relative to an age matched population, but the reductions were not substantial. Dark squares are areas of greatest loss, white areas are normal. Circular area is the macula and black dot is the optic nerve.
Methotrexate may inhibit visual functions that are not traditionally measured in a clinical setting. Inhibition of amacrine cell function has implications for visual perceptions that are important in activities of daily living such as contrast and motion detection. This should be further investigated and taking into consideration if methotrexate is clinically indicated.
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