Can you reduce oxidative stress during phaco?

May 1, 2009

Assessing whether certain surgical methods can minimize exposing the eye to oxidation during phacoemulsification/

Key Points

Our laboratory previously identified the hydroxyl radical as one by-product of phacoemulsification2 The hydroxyl radical is a potent oxidant that reacts with the first organic molecule that it encounters. In order to study this potentially damaging species, we developed a method to quantitate the production of the hydroxyl radical during phacoemulsification. This quantitation allows us to compare factors that might influence hydroxyl radical generation and/or subsequent hydroxyl radical reaction with biomolecules. The goal was to learn if particular surgical methods could provide additional protection for the eye from exposure to hydroxyl radicals.

Radical generation

Using a laboratory test cell and the Infiniti Vision System (Alcon Laboratories), we studied the effects of different modalities, tips, and irrigation solutions on hydroxyl radical concentration sampled from the aspirate during the application of phacoemulsification ultrasonic energy. The concentration of hydroxyl was quantified using a well-established deoxyribose method.3 The hydroxyl radical reacts with deoxyribose to form malondialdeyde (MDA). Malondialdehyde then reacts with thiobarbituric acid (when acid and heat are added) to produce a bright pink colour that can be quantitated spectrophotometrically. For our experiment, the deoxyribose was added to the irrigation solution and samples were taken from a port in the collection bag during phacoemulsification; these samples then were assayed for MDA.

Longitudinal ultrasound v. torsional mode

Best protection

In conclusion, oxidative stress on the eye during phacoemulsification may be minimized by using modalities and tips that produce fewer free radicals, and irrigation solutions which can compete for reaction with the hydroxyl radical. With BSS as the irrigation solution, using the torsional modality with either the 0.9 mm Kelman Mini-Flared tip or the OZil-12 tip reduced MDA production by approximately 50%. Using irrigation solutions that contained organic molecules also decreased the concentration of MDA. Using torsional mode, appropriate tips, and irrigation solutions with organic content can potentially reduce a surgeon's concerns about exposing the eye to oxidation by the hydroxyl radical during phacoemulsification.

References

1. A. Holst, et al, Curr Eye Res, 1993; 12:359-365.

2. M.D.Cameron, et al, J Cataract Refract Surg, 2001; 27:463-470.

3. K.H. Cheeseman, et al, Biochem J, 1988; 252:649-653.