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D. K. Mojumder, T. G. Wensel; Mydriatics Augment Light-Evoked Retinal Potentials by a Combination of -Adrenergic Agonism and Muscarinic Antagonism in the Murine Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2178.
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To determine the basis of the augmentation of ERG amplitudes after combined topical corneal application of commonly used mydriatics: atropine (muscarinic antagonist) and phenylephrine (-adrenergic agonist).
Pupillary area was sampled from C57BL/6 mice every 3 minutes for 2 hours after ketamine (77 mg/kg) and xylazine (7 mg/kg) anesthesia (K+X) and after topical application of either atropine or atropine + phenylephrine. Dark-adapted Ganzfeld ERG’s were recorded from similarly anesthetized mice in response to a 0.2 Hz brief flashes of -1.3 log sc td s and 0 log sc td s (max=462 nm) and after topical atropine, phenylephrine or a combination of both for ~ 130 min.
K+X anesthesia, alone, or in combination with atropine or atropine + phenylephrine caused similar extents of mydriasis. B-wave amplitudes after K+X anesthesia and after atropine or phenylephrine were similar with no significant growth over a ~33.3 min period of recording. B-wave amplitude grew to ~200% of the pre-drug anesthetized control b-wave only after a combination of topical atropine and phenylephrine, but its sensitivity remained comparable to that without topical mydriasis. 98% saturation of this growth took ~ 60 minutes. Topical application of both mydriatics augmented the amplitude of the photoreceptor-derived a-wave to ~208% of atropine alone or pre-drug control but without a change in sensitivity. There was also an augmentation of inner-retinal originating scotopic threshold responses compared to the pre-drug anesthetized control or topical application of atropine alone.
Topical mydriatics by co-operative -adrenergic agonism and muscarinic antagonism augment ERG amplitudes by mechanisms that are independent of pupillary dilation and involve direct effects on resting photoreceptor membrane potentials. The retinal effects of mydriatics can affect experimental and clinical study designs where they are used. To get consistent recording of ERG’s topical atropine + phenylephrine should be applied >1 hour before recording.
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