Purpose In order to achieve an improved mydriasis in human eyes during cataract surgery, the effect of intracameral phenylephrine was compared to the combination of isoprenaline plus phenylephrine, to epinephrine alone and to a negative control, in a porcine eye model.
Methods A total of eighty-nine eyes from newly slaughtered pigs were acquired and randomly split into four groups. In order to gain miosis all eyes received 2.0 mg of acetylcholine intracamerally, and after 60 seconds the eyes were injected with 0.15 ml 0.3% isoprenaline and 0.15 ml 3.0% phenylephrine sequentially with a 90-second interval (n=21), the same substances in the reverse order (n=22), 0.15 ml of 0.025% epinephrine (n=20), or 0.15 ml of saline solution (n=26). The diameter of the pupils were measured every 15 seconds, and compared using Student’s t-test.
Results Phenylephrine injected after isoprenaline had a significantly (p<0.01) larger mydriatic effect than epinephrine. The mydriatic effect of phenylephrine, however, was significantly (p<0.05) smaller than that or epinephrine without the isoprenaline pretreatment. Isoprenaline also exhibited a small mydriatic effect of its own.
Conclusion This study shows that the β-receptor has a role in the dilation of the pupil, here demonstrated with the β-receptor stimulator isoprenaline which augments the mydriatic effect of intracamerally injected phenylephrine. The superior mydriatic effects of a nonspecific adrenergic stimulator such as epinephrine in compare to the specific α1-receptor stimulator phenylephrine may be explained by this β-receptor mediated mydriasis.