Phenylephrine and pilocarpine in the treatment of post-operative irido-corneal adhesion

Abstract

SUMMARYFollowing cataract surgery, entrapment of the iris within the surgical wound is often managed by intensive use of miotics. As the radial fibres stretch, only a small amount of traction is exerted upon the entrapped iris. Applica tion of a combination of phenylephrine and pilocarpine drops causes simultaneous contraction of the pupil sphincter and the radial muscle fibres. This study investigated the relative magnitude of forces induced in the iris periphery by pilocarpine and phenylephrine and the effectiveness of adding g. phenylephrine 10% to g. pilocarpine 4% drops in the treatment of post operative irido-comeal adhesions. The investigation was divided into two parts. First, the forces induced in the iris periphery upon exposure to pilocarpine and phenylephrine were measured in 6 cadaver irises. The mean force was 27.5 ± 5.7 X 10-3 N for pilocarpine and 23.3 ± 4.0 X 10-3 N for phenylephrine. The combina tion of the two drugs produced a force of 54.2 ± 6.6 X 10-3 N (p<0.05). In the second part of the study intensive pilocarpine 4% drops were administered to 17 patients who had iris-wound entrapment on the first post-operative day. Patients with persistent adhesion were commenced on intensive g. phenylephrine 10%and assessed after 90 minutes. Of the 17 patients, 6responded to pilocarpine drops alone; in a further 7 the irido-comeal adhesion was released only by the addition of phenylephrine drops, and in 4 patients drops were ineffective in relieving the adhesion. This study indicates that addition of phenylephrine 10% to pilocarpine 4% drops enhances the effectiveness of pharmacological treatment of post-operative irido-comeal adhesion.Adherence of the iris to the internal opening of the corneal wound or its incarceration within the surgical section is a not uncommon complication of cataract surgery. If untreated, the adhesions may result in METHODS AND SUBJECTS Laboratory InvestigationsThe iris and anterior uveal tissue of 6 donor eyes were isolated and stored in Krebs solution at 4 °C for a maximum period of 48 hours. A fine suture (10/0 nylon) was passed through the iris periphery at a location corresponding to the site of iris prolapse.The iris tissue was placed in an organ bath containing Krebs solution at 37°C, gassed with 95% oxygen and 5% carbon dioxide in order to maintain the oxygenation and the acid/base balance with a pH of 7.2 (Fig. 1)

Numerical stress analysis of the iris tissue induced by pupil expansion: Comparison of commercial devices

“…Sixth, we proposed an iris model that combined knowledge and biomechanical properties from various literature. Although our FE models produced forces that were in agreement with the literature (18.6–41.2 mN in our FE, up to 54.2 ± 6.6 mN for active muscle contraction) [ 54 ], there could still be errors from combining literature data that were obtained under different experimental conditions. For instance, the Ogden model [ 41 ] was derived from rabbit data, which was similar but not identical in representing the human iris [ 47 , 58 , 59 ].…”

“…Heys and Barocas extrapolated bovine data and estimated the human iris modulus to be 6.2 kPa, based on anatomical measurement differences between human and bovine irides [ 50 , 53 ]. Tabandeh et al conducted pharmacological treatment on donor cadaver eyes with pilocarpine and phenylephrine to induce sphincter and dilator muscle constriction [ 54 ]. The reported mean forces were 27.5 ± 5.7 mN and 23.3 ± 4.0 mN respectively, and 54.2 ± 6.6 mN when both drugs were combined.…”

An inverse method to determine the mechanical properties of the iris in vivo

“…Indentation tests [6,7] were used to determine the mechanical properties on the local regions of the iris. Besides, relative contraction forces of cadaver irides [8] were quantified due to drug stimulation. The mechanical properties of the iris sphincter and dilator muscles were measured by the isometric contraction experiment and the isotonic quick release experiment [9].…”