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

PURPOSE: To assess the rise in intraocular pressure following phacoemulsifi cation 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 eye s preoperatively, then underwent routine scleral section phacoemulsificatio n. They were randomly assigned to perpendicular (blow-off valve) and obliqu e (water-tight) peripheral corneal incision groups. Postoperative intraocul ar pressures were measured at 3, 6, 12 and 18 hours. Pressures from the uno perated eyes were used as controls. Aqueous release from the second instrum ent peripheral corneal incisions and frown scleral incision were assessed u sing the Seidel's test. both groups compared to the control eyes (mean 10.9 5+/-2.19mnHg, 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 p erpendicular incisions and 15% of the oblique incisions were Seidel's posit ive. The frown incision did not leak. CONCLUSION:This study documents the natural history of the rise in intraocu lar pressure following phacoemulsification peaking at 6 hours. Pharmacologi cal agents should be administered to cover this period. The perpendicular p eripheral corneal incision had a tendency to acr as a blow-off valve allowi ng release of aqueous when intraocular pressures were elevated in the first 18 hours following phacoemulsification. This phenomenon is likely to resul t in a reduction in rise of intraocular pressure compared to the oblique pe ripheral corneal incision group which tended to be water-tight.