Cyclopentolate with phenylephrine

To achieve greater pupillary dilation and overcome the constrictor effect of cholinergic stimulation, particularly on exposure to bright illumination, both phenylephrine and hydroxyamphetamine can be used in conjunction with a cholinergic antagonist, such as tropicamide or cyclopentolate. Additionally, phenylephrine 1% combined with a low concentration of 0.2% cyclopentolate (Cyclomydril) is recommended for neonates for funduscopic examinations. 

To facilitate the application of mydriatics in neonates and infants, a single-instillation solution may be prepared by combining 3.75 ml cyclopentolate 2% with 7.5 ml tropicamide 1% and 3.75 ml phenylephrine 10%.The final solution contains 0.5% cyclopentolate, 0.5% tropicamide, and 2.5% phenylephrine.This combination produces no major side effects and provides an effective pupillary dilation. Alternatively, equal amounts of 1% tropicamide and 2.5% phenylephrine may be mixed together to yield a single combination solution with final concentrations of 0.5% tropicamide and 1.25% phenylephrine. This too should produce adequate pupillary dilation with no major side effects. Again, these solutions can also be applied as a spray. Cyclopentolate, tropicamide, and phenylephrine administered in microdrops (mean drop volume, 5.6 micro liters, as opposed to commercially available standard drops) have the same efficacy with a decreased risk for systemic side effects. 

New Zealand white rabbits (2-2.5 Kg) were anesthetized with an intravenously administered 3% sodium pentobarbital (30 mg/Kg of body weight). Both eyes of each rabbit were dilated with 1% cyclopentolate and 10% phenylephrine. Using a 28-gauge needle on a 1.0 ml syringe, 0.2 ml of aqueous humor was removed bilateraly. The vitreous of the left eye was injected with 0.2 ml of whole blood from the ear vein at the pars plana in the supperior temporal quadrant. The right eye received 0.2 ml of sterile normal saline. We monitored intraocular pressures by Shiotz tonometry immediately after each injection. 

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