Stimulation of adrenergic β‐receptors enhances mydriasis in a porcine eye model

Abstract

Abstract.Purpose: To compare the mydriatic effect of intracamerally injected isoprenaline plus phenylephrine to phenylephrine alone and to epinephrine in a porcine eye model, aiming to eventually find the best combination of adrenergic substances for surgical mydriasis in humans.Methods: In this study, we used 89 intact eyes from newly slaughtered pigs, pretreated with 2.0 mg of intracameral acetylcholine. After waiting 60 seconds for miosis to develop, 0.15 ml 0.3% isoprenaline and 0.15 ml 3.0% phenylephrine were injected sequentially with a 90‐second interval in 21 eyes. In another 22 eyes, the same substances were given in the reverse order. In 20 eyes, 0.15 ml of 0.025% epinephrine was injected, and as a negative control 0.15 ml of balanced salt solution was injected in 26 eyes. The pupils were filmed during the treatments, and the mean pupil diameters were measured every 15 seconds from the video recordings.Results: Phenylephrine injected after isoprenaline had a larger mydriatic effect than epinephrine (p < 0.01). Without isoprenaline pretreatment, the mydriatic effect of phenylephrine was significantly smaller than that of epinephrine (p < 0.05). Isoprenaline also exhibited a small mydriatic effect of its own.Conclusions: The β‐receptor stimulator isoprenaline enhances the mydriatic effect of intracameral phenylephrine, indicating a role for the β‐receptor in the mydriatic response. Mydriasis mediated by β‐receptors may explain why nonspecific adrenergic stimulators such as epinine and epinephrine can have larger mydriatic effects than the specific α1‐receptor stimulator phenylephrine.

Intracameral Mydriatics in Cataract Surgery

“…The study of Myers and Shugar indicates that epinephrine may be a more potent mydriatic agent than phenylephrine when injected intracamerally (Myers and Shugar 2009), and indeed, epinephrine has a larger affinity for the -receptor than phenylephrine (Mishima 1982). Accordingly, we have shown in a porcine eye model that the -receptor stimulator isoprenaline fortifies mydriasis from intracameral phenylephrine (Janbaz, Lundberg et al 2011), which further suggests a role for the -receptor in the mydriatic response. Mydriasis mediated by -receptors may explain why non-specific adrenergic stimulators such as epinephrine can have larger mydriatic effects than the specific   -receptor stimulator phenylephrine.…”

“…The -receptor stimulator isoprenaline enhances the mydriatic effect of intracameral phenylephrine, indicating a role for the -receptor in the mydriatic response. Mydriasis mediated by -receptors may explain why non-specific adrenergic stimulators such as epinine and epinephrine can have larger mydriatic effects than the specific   -receptor stimulator phenylephrine (Janbaz, Lundberg et al 2011). …”

Phenylephrine 5% added to Tropicamide 0.5% eye drops does not influence retinal oxygen saturation values or retinal vessel diameter in glaucoma patients

“…Conclusion: The addition of topical phenylephrine 5% after tropicamide 0.5% improved the proportion of high-quality retinal oximetry images without influencing the retinal oxygen saturation values or the retinal vessel diameter in patients with glaucoma. specific alpha adrenergic agonists can mediate dilation, also the nonspecific beta receptor agonists can enhance the mydriatic effect of intracameral phenylephrine in a porcine eye model (Janbaz et al 2011).…”

“…The parasympathetic regulation dominates over the sympathetic effect in control of the pupil (Trinavarat & Pituksung 2009). Not only specific alpha adrenergic agonists can mediate dilation, also the nonspecific beta receptor agonists can enhance the mydriatic effect of intracameral phenylephrine in a porcine eye model (Janbaz et al. 2011).…”