Formation of free radicals during phacoemulsification

Identification of free radicals produced during phacoemulsification

PURPOSE

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

SETTING

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

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Effect of Healon5 and 4 other viscoelastic substances on intraocular pressure and endothelium after cataract surgery

PURPOSE

To compare the ophthalmic viscoelastic device (OVD) Healon5 (sodium hyaluronate 2.3%) with 4 other commonly used OVDs during phacoemulsification and intraocular lens implantation in terms of influence on intraocular pressure (IOP) postoperatively and endothelial cells preoperatively and postoperatively.

SETTING

Department of Ophthalmology, Ruprecht-Karls-University Heidelberg, Germany.

METHODS

This clinical randomized prospective study, in which patients and observer were masked, comprised 81 eyes. Seventy-four eyes (mean patient age 71.2 years +/- 7.8 [SD]) completed all preoperative and 5 postoperative examinations. The OVDs used were OcuCoat and Celoftal (hydroxypropyl methylcellulose 2.0%), Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%), Healon GV (sodium hyaluronate 1.4%), and Healon5 (sodium hyaluronate 2.3%). Intraocular pressure was measured by standard Goldmann applanation tonometry preoperatively and 4 to 6 and 24 hours and 7, 30, and 90 days postoperatively. Endothelial cell counts were done preoperatively and 90 days postoperatively using a Pro/Koester WFSCM contact endothelial microscope. Exclusion criteria were IOP greater than 21 mm Hg at the preoperative examination, age younger than 40 years, significant corneal pathology, and a history or presence of uveitis or pseudoexfoliation syndrome.

RESULTS

All groups had increased IOP 4 hours postoperatively. The Healon5 group had the highest mean pressure (24.9 mm Hg) followed by the Viscoat group (23.6 mm Hg). The mean IOP in the other OVD groups was less than 22.1 mm Hg. These differences were not significant. Twenty-four hours postoperatively and at all subsequent examinations, mean IOP was below 20 mm Hg. The Healon5 group had the lowest mean endothelial cell loss (6.2%), significantly lower than in the other groups (P < .02).

CONCLUSION

With all 5 OVDs, endothelial cell loss was found, with the lowest in the Healon5 group, and IOP was increased 4 to 6 hours postoperatively. After 24 hours, no significant increases in IOP were noted.

Daily tonometric curves after cataract surgery

AIM

To evaluate daily tonometric curves after cataract surgery in patients with cataract only and in patients with cataract and glaucoma.

METHODS

108 patients scheduled for cataract surgery were randomly allocated to two groups: 57 patients with cataract only (normal) and 51 with cataract and primary open angle glaucoma (POAG). All patients underwent extracapsular cataract extraction (ECCE) (manual technique with long wound), phacoemulsification (automated technique with short wound), or nucleus capture (manual technique with short wound). Intraocular pressure (IOP) was measured by Goldmann tonometry in all patients every 2 hours for 12 hours before the operation and at 1 and 6 months postoperatively.

RESULTS

79 patients completed the 6 month examination. ECCE resulted in greater reductions in IOP than the other procedures (ECCE: 27% and 36% in normal patients and those with POAG, respectively; nucleus capture: 20% and 31%, respectively; phacoemulsification: 19% and 22%, respectively). The fluctuations in IOP before and after surgery were not statistically significant.

CONCLUSION

Cataract surgery in normal patients reduces IOP but does not eliminate fluctuations which are directly proportional to the IOP value and result partly from circadian rhythms. This important finding might influence our approach to treatment of patients with glaucoma.

The resiliency of the corneal endothelium to refractive and intraocular surgery

PURPOSE

To describe stress factors (phenylephrine and contact lenses) from the corneal epithelium that can affect the corneal endothelium, and to describe the effects of refractive and intraocular surgery on the corneal endothelial structure and function.

METHODS

Significant clinical and experimental publications are reviewed and recent experiments conducted in the author's laboratory to describe the corneal endothelial stresses.

RESULTS

The corneal epithelium serves as a barrier to topical phenylephrine (2.5-10%). In a compromised epithelium, topical phenylephrine will cause drug-induced stromal edema and endothelial vacuolization. Contact lenses are capable of stimulating the epithelial arachidonic acid cascade to release 12(R)hydroxyeicosatetraenoic acid (12(R)HETE) and 8(R)hydroxy-hexadecatrienoic acid (8(R)HHDTrE) to cause endothelial Na+/K+ adenosine triphosphatase (ATPase)-inhibition and polymegethism. Specular microscopy of the corneal endothelial cells after refractive surgery (photorefractive keratectomy [PRK], laser in situ keratomileusis [LASIK], intrastromal rings [INTACs]) has shown that there is minimal effect. However, laser ablation of the stroma within 200 microm of the corneal endothelium will result in endothelial cell structural changes and the formation of the amorphous substance deposited onto Descemet's membrane. Phacoemulsification with a high flow of the irrigation solution can alter the endothelial surface glycoprotein layer. Lidocaine hydrochloride (1%) used as intracameral anesthesia readily diffuses through the corneal endothelium, resulting in stromal uptake and endothelial cell swelling. With phacoemulsification, however, the washout of lidocaine from the cornea (T1/2, 5 minutes) and iris (T1/2, 9 minutes) occurs quickly. Corneal endothelial wound healing after keratoplasty occurs in the following sequence: migration of endothelial cells, development of tight junctions, and the formation of Na+/K+ ATPase pump sites.

CONCLUSIONS

Corneal endothelial resiliency is due to the increased peripheral endothelial cell number for migration, the ability of endothelial cells to form tight junctions to maintain the endothelial barrier, the increase in endothelial Na+/K+ ATPase pump sites under stress, and the ability of the corneal endothelial cells to shift their metabolism of glucose to the hexose monophosphate shunt for the production of nicotinamide adenine dinucleotide phosphate (NADPH) and membrane repair. All of these factors are important, along with the aqueous humor sodium concentration, which establishes the osmotic gradient for corneal deturgescence and transparency.

Ultrasonic transmission in viscoelastic substances

PURPOSE

To study the propagation of ultrasonic shock waves in viscoelastic agents and the resulting corneal load.

SETTING

University Siegen, Institute for Mechanics and Control Engineering, Siegen, Germany.

METHODS

The anterior chamber of a manufactured artificial eye was constructed according to anatomic dimensions. Three openings were drilled--for the phaco tip, for the exchange of a viscoelastic agent or water, and for the shock-wave sensor. The sensor was fixed to the area corresponding to the corneal apex. The sensor signal was analyzed using a direct oscilloscope that measured the amplitude reaching the corneal apex. Shock-wave propagation in several viscoelastic agents was compared with that in balanced salt solution.

RESULTS

In hydroxypropyl methylcellulose, the shock wave was amplified or influenced slightly. In hyaluronic-acid preparations, acoustic dampening occurred.

CONCLUSION

Removal of hyaluronic-acid derivatives prior to phacoemulsification is not necessary.

Corneal endothelial changes after divide and conquer versus chip and flip phacoemulsification

PURPOSE

To evaluate changes in central corneal endothelial cells and corneal thickness after divide and conquer phacoemulsification and chip and flip phacoemulsification.

SETTING

Houston Eye Clinic, Houston, Texas, USA.

METHODS

Forty-four eyes were randomly assigned to one of two groups to have divide and conquer (D/C Group) or chip and flip (C/F Group) phacoemulsification with implantation of a posterior chamber, foldable, silicone intraocular lens performed by one surgeon. Of these, 41 eyes of 37 patients (22 D/C Group, 19 C/F Group) met the inclusion criteria. All surgeries were uneventful. A complete eye examination including specular microscopy and pachymetry was performed preoperatively and 1 week and 1 and 3 months postoperatively.

RESULTS

There were no significant between-group differences in any of the following means: sex; age; time at 70% phaco power; total phacoemulsification time. No correlation was found between ultrasound time and increased corneal thickness except for a significant increase in percentage of hexagonal cells in the C/F Group at 1 month. The only statistically significant between-group differences were greater endothelial cell loss in the C/F Group at 1 month and the percentage change in hexagonal cells at 1 week (1.1% increase, D/C Group; 10.7% decrease, C/F Group).

CONCLUSION

The divide and conquer technique led to less endothelial loss and hexagonal cell change than the chip and flip technique, although at 3 months the differences were not significant.

Inflammatory response after endocapsular phacoemulsification or conventional extracapsular lens extraction in the rabbit eye

PURPOSE

We compared the inflammatory response after phacoemulsification and conventional extracapsular lens extraction in New Zealand albino rabbits.

METHODS

One eye was selected at random and phacoemulsification was performed. Extracapsular lens extraction was done in the fellow eye. In both eyes a polymethylmetacrylate intraocular lens was implanted into the capsular bag and the wound was sutured with a 9-0 polypropylene continuous suture. The levels of prostaglandin E2 in aqueous humour and wet mass of the iris-ciliary bodies were measured at day 1. The number of white blood cells and protein levels in the aqueous humour were measured at day 1, 3, 7, 14 and 30. Corneal thickness was estimated with pachymetry.

RESULTS

Prostaglandin E2 levels and wet masses of iris-ciliary bodies were significantly higher after extracapsular lens extraction, which also induced significantly higher white blood cells counts at day 1 and 3 and higher protein levels at day 7. Extracapsular lens extraction caused more corneal edema at day 3, 7 and 14.

CONCLUSION

The results suggest that phacoemulsification induced less surgical trauma with less breakdown of the blood-aqueous barrier.

Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation

PURPOSE

To evaluate transient increases in intraocular pressure (IOP) after use of high-viscosity viscoelastic agents in cataract surgery.

SETTING

Military Hospital, Ulm, Germany.

METHODS

In a prospective, randomized study, we evaluated IOP following cataract surgery using two different viscoelastic substances (Healon, Healon GV). The viscosity of Healon GV is 10 times higher than that of Healon because of higher concentration and molecular weight. Patients having identical phacoemulsification procedures (sutureless clear corneal tunnel incision with foldable silicone lens implantation) (N = 60) and identical viscoelastic removal were assigned to groups of 15 based on viscoelastic used and removal time (20 or 40 seconds). Intraocular pressure was measured preoperatively and at 6, 24, 36, and 48 hours and 1 month postoperatively.

RESULTS

The highest mean IOP elevations in both viscoelastic groups were obtained at 24 hours postoperatively (2.9 mm Hg +/- 4.3 [SD] with Healon and 3.3 +/- 6.3 mm Hg with Healon GV). There were no statistically significant differences between the two viscoelastics and the two removal times during the entire follow-up period (unpaired t-test), but standard deviations were higher in the Healon GV groups at 6 and 24 hours. Two patients in the Healon groups and three in the Healon GV groups required medical treatment for IOP within the first 24 postoperative hours; however, all five patients had an IOP lower than 22 mm Hg on the second postoperative day.

CONCLUSIONS

Based on postoperative IOP, both viscoelastics can be equally well removed from the anterior chamber. Incidence of high IOP using high-viscosity hyaluronic acid is minimized by the described removal technique.

Protective efficacy of sodium hyaluronate on the corneal endothelium against the damage induced by sonication

The protective efficacy of sodium hyaluronate (Na-HA) on the corneal endothelium against the damage induced by sonication was investigated using enucleated rabbit eyes and Na-HA fluorescence labeled with 5-aminofluorescein (FA-HA). The anterior chamber was reformed by injecting a 1% solution of FA-HA, and then sonication, irrigation and aspiration were performed in the anterior chamber using a phaco-needle attached to phacoemulsification and aspiration (PEA) equipment. The protective efficacy was evaluated by the area of damaged corneal endothelium. When the anterior chamber was reformed by the solution of FA-HA with a molecular weight of 2010 x 10(3) (FA-HA (2010 x 10(3) group), most of the FA-HA was eliminated within 20 seconds after starting the irrigation and aspiration, and the area of damaged endothelium was the same with the case when the FA-HA was not pre-injected (Control group). On the other hand, when the anterior chamber was reformed by the solution of FA-HA with a molecular weight of 1130 x 10(3) (FA-HA (1130 x 10(3) group), the FA-HA was gradually eliminated after mixing with an irrigating solution, and the area of damaged endothelium was significantly smaller than those of the Control and FA-HA (2010 x 10(3)) groups. These results suggest that the corneal endothelial damage induced by PEA can be avoided by pre-injecting a viscoelastic material which can remain in the anterior chamber during PEA.

Phaco-emulsification causes the formation of cavitation bubbles

There have been reports of complications arising from damage to non-lenticular ocular tissue during the increasingly popular procedure of cataract extraction with phaco-emulsification. One cause of this damage might be the formation of cavitation bubbles. Such bubbles are known to produce free radicals and shock waves. This paper demonstrates directly the formation of cavitation bubbles at the tip of the phaco-probe. It also shows the importance of a smooth probe profile in reducing bubble formation. Recommendations are made for probe and tip design and for the use of minimum power during the surgical procedure of phaco-emulsification.

Hyaluronic acid. A review of its pharmacology and use as a surgical aid in ophthalmology, and its therapeutic potential in joint disease and wound healing

Hyaluronic acid is a naturally occurring polysaccharide with distinct physicochemical properties which underlie its application as a viscoelastic tool in ophthalmological surgery. In cataract surgery the role of hyaluronic acid in facilitating procedures and protecting the corneal endothelium is well established. Some benefit has also been gained with the use of hyaluronic acid in penetrating keratoplasty, trabeculectomy, retinal reattachment and trauma surgery, although its efficacy in these indications is less well-defined in the published literature. In addition to its lubricating and cushioning properties, demonstration of some in vitro anti-inflammatory activity and a possible disease-modifying effect for hyaluronic acid in animals has prompted its investigation as a treatment in osteoarthritis and, to a much lesser extent, in rheumatoid arthritis. Hyaluronic acid 20 mg, as weekly intra-articular injections for 3 to 7 weeks, improved knee pain and joint motion in patients with osteoarthritis. Although this occurred to a greater degree than with placebo in most comparisons, the effects of hyaluronic acid was similar to those of placebo in the largest trial. In the few available comparisons with other agents, hyaluronic acid appeared equivalent to methylprednisolone 40 mg (for 3 weeks) and to a single injection of triamcinolone 40 mg. Hyaluronic acid was distinguished from other therapies by providing a sustained effect after treatment discontinuation. Together with its very good tolerability profile, these properties justify further study of hyaluronic acid in patients with osteoarthritis. Some limited evidence of improvement in patients with rheumatoid arthritis, and a possible healing effect of hyaluronic acid on tympanic membrane perforations, represent additional areas of interest for future investigation. In summary, hyaluronic acid is a well-established adjunct to cataract surgery and may prove to be a promising option in the treatment of patients with osteoarthritis. Its very good tolerability provides further impetus for examination of its potential role in an extended scope of arthritic and ophthalmological indications, and in wound healing.