By Dr. Mark S. Siegel
Cataract surgery continues to evolve, with microincisional clear corneal incisions, femtosecond lasers, new imaging modalities, and improved lens implants. However, the published literature is having trouble keeping up with clinical practice. Despite the ongoing change, one concern remains constant: endophthalmitis (infection) prophylaxis. The use of perioperative povidone-iodine, a lid speculum, and drape with isolation of lids and lashes, and sterile preparation, is effective in limiting the incidence of endophthalmitis after cataract surgery.
The recent advent of “dropless” cataract surgery via transzonular ocular injections of TriMoxi or TriMoxiVanc, offers another option of infection prophylaxis. As some cataract surgeons consider adopting dropless cataract surgery it is important to balance the potential complications and risks involved with this technique.
These combinations of antibiotics and steroids are delivered to the anterior vitreous (jelly that fills the back of the eye) by injection through the zonules (tiny spider web-like ligaments that anchor the lens to the wall of the eye). This is intended to mitigate the need for post-operative topical drops. Drops can be costly, can irritate the surface of the eye, can be difficult for some patients to administer and can be burdensome to prescribers. Though post-operative drops are less than ideal, this new mode of dropless infection prophylaxis contains some inherent risks.
A clear concern is compounding errors. There have been reports of dilutional errors with intraocular antibiotics that have resulted in complications including macular swelling, retinal detachment, macular infarction, toxic anterior segment syndrome (severe inflammation) and a large outbreak of Fusarium endophthalmitis.
The pharmacokinetics of TriMoxi(+/-) Vanc is unclear when placed in the anterior vitreous. These antibiotics have the shortest half-life of current intravitreal antibiotics being used (1.7 hours). Vancomycin has a half-life of 25.1 hours. Routine topical antibiotics are able to produce concentrations inside the eye for a week post-operatively. While one European study showed decreased rates of endophthalmitis with injected antibiotics, all arms of the study used 6 days of topical postoperative antibiotics! The question remains: is the duration of coverage with injected antibiotics without topical antibiotics adequate?
Antibiotic resistance is another consideration when using TriMoxi. Emerging resistance has been identified. A recent review found resistance rates to moxifloxacin has increased from 21% in 1995 to 62% in 2014.
The use of prophylactic vancomycin in TriMoxiVanc during routine cataract surgery is controversial. The Centers for Disease Control issued guidelines in 1995 specifically discouraging the use of vancomycin in routine surgical prophylaxis because of increasing bacterial resistance. The risk of fueling the emerging resistance to vancomycin for an unproven practice is worrisome. Given that there are more than 3 million cataract surgeries performed in the United States each year, exposure of the ocular surface to low doses of vancomycin could result in an increase in vancomycin resistant bacteria.
Another unknown is the risk of steroid-induced ocular hypertension (elevated eye pressure) associated with TriMoxi(+/-) Vanc. It is well known that topical steroids can induce ocular hypertension, but drops are easily discontinued, whereas injected intraocular steroids are not. Currently there is a paucity of literature addressing transzonular triamcinolone (the steroid component in TriMoxi) and its associated ocular hypertension risk. Furthermore, the use of triamcinolone leaves patients with obscured vision and floaters for the first week or more. Patient complaints of foggy vision postoperatively have led some cataract surgeons to discontinue the product. Many randomized trials show that topical nonsteroidal anti-inflammatory drugs (NSAIDS) are superior to topical steroids in reducing post-operative macular swelling after cataract surgery. Thus, regardless of the intraocular steroid and antibiotic used, it is likely that a topical NSAID will need to be prescribed.
Technical and mechanical issues must be considered in addition to issues of bacterial resistance, compounding risks, steroid-induced elevated eye pressure, and post-operative foggy vision. In patients with lens zonular weakness (pseudoexfoliation), intraocular lens (IOL) decentration or dislocation may occur. The impact of this technique for premium IOL decentration could create significant visual disturbance. Since most patients using blood thinners do not discontinue this medication, there could be intraocular hemorrhage from inadvertent cannula contact with the iris ciliary muscle. Finally, very short eyes may not have the space to accommodate the injected volume of these antibiotic and steroid preparations.
Today’s cataract surgery is safer for the patient and shorter in duration than in decades past. Improvements in technology, techniques, and training have led to improved outcomes for our patients. Although the concept of dropless cataract surgery is clearly attractive, cataract surgeons should consider the serious issue of bacterial resistance and the unnecessary risk of the transzonular delivery of TriMoxi(+/-) Vanc. In an era of increasing cost-benefit analysis where physicians will be judged on outcomes and the allocation of limited healthcare resources, the value of dropless cataract surgery remains uncertain, risky and currently not the standard of care.