Identification of free radicals produced during phacoemulsification

To detect, identify, and quantitate free radicals produced during conditions similar to phacoemulsification cataract surgery.

Research laboratory at the Biotechnology Center, Utah State University, Logan, Utah, USA.

All experiments were performed using a Series Ten Thousand phacoemulsifier (Alcon Laboratories) modified to make a 10 mL continuous circulation loop (to increase sensitivity). The irrigating solution was passed through a 3 mL chamber in line with the circulation loop, and electron spin resonance spin trapping methods were used to detect, identify, and quantitate free radical production during phacoemulsification. As an additional indication of hydroxyl radical production, the hydroxylation of salicylate and thiocyanate was detected by high-performance liquid chromatography and spectrophotometry, respectively.

The hydroxyl radical was formed when phacoemulsification was performed in the presence of solutions containing spin trap in double deionized water or balanced salt solution (BSS). Hydroxyl radical production was linear with respect to phacoemulsification time. Production of the hydroxyl radical was not observed when phacoemulsification was performed with anaerobic solutions, indicating a requirement for oxygen in radical production. The concentration of trapped hydroxyl radical was reduced in the presence of balanced salt solution with bicarbonate, dextrose, and glutathione (BSS Plus). Upon phacoemulsification, both salicylate and thiocyanate underwent hydroxylation when included in the irrigating solution, confirming the generation of the hydroxyl radical. Additional tests discounted the formation of superoxide or hydrogen peroxide during phacoemulsification.

Hydroxyl radical was produced by phacoemulsification in the presence of aerobic solutions. Hydroxyl radical production was dependent on the presence of molecular oxygen and was not generated as a result of the homolytic cleavage of water. The amount of hydroxyl radical detected was directly proportional to phacoemulsification time and was reduced in the presence of BSS Plus. Other reactive oxygen species such as superoxide, hydrogen peroxide, and ozone were not detected during phacoemulsification under these conditions.