Using the second instrument peripheral corneal incision in phacoemulsification as a blow-off valve

PURPOSE: To assess the rise in intraocular pressure following phacoemulsification and whether it can be modified by the architecture of the peripheral corneal incision for the second instrument.

SETTING: Frimley Park Hospital, Frimley, United Kingdom.

METHOD: Forty-two patients had intraocular pressures measured from both eyes preoperatively, then underwent routine scleral section phacoemulsification. They were randomly assigned to perpendicular (blow-off valve) and oblique (water-tight) peripheral corneal incision groups. Postoperative intraocular pressures were measured at 3, 6, 12 and 18 hours. Pressures from the unoperated eyes were used as controls. Aqueous release from the second instrument peripheral corneal incisions and frown scleral incision were assessed using the Seidel's test.

RESULTS: There was a rise in intraocular pressure in both groups compared to the control eyes (mean 10.95+/-2.19 mmHg, P<0.00005) at 6 hours. The difference between the groups was significant at 12 hours (mean difference 3.35 mmHg, P<0.05); 63.6% of the perpendicular incisions and 15% of the oblique incisions were Seidel's positive. The frown incision did not leak.

CONCLUSION: This study documents the natural history of the rise in intraocular pressure following phacoemulsification peaking at 6 hours. Pharmacological agents should be administered to cover this period. The perpendicular peripheral corneal incision had a tendency to act as a blow-off valve allowing release of aqueous when intraocular pressures were elevated in the first 18 hours following phacoemulsification. This phenomenon is likely to result in a reduction in rise of intraocular pressure compared to the oblique peripheral corneal incision group which tended to be water-tight.