The ongoing harm of cannula dislodgement

All intraocular surgery must be carried out utilising Luer Lock syringes with the specific aim of avoiding cannula dislocation during surgery. While injecting volumes of fluid through the narrow lumen of cannulae, significant hydraulic force is generated. If the cannula is misthreaded or insufficiently tightened, it can fly off into the eye with significant force, causing harm, blindness and even the loss of an eye in what would have otherwise been a routine cataract operation.

From a medicolegal perspective, it is indefensible, and blame for its occurrence could easily be laid at the feet of the surgeon, the scrub practitioner and the hospital itself.

Cannula dislodgement has been a known risk for over a decade

As far back as 2012, the issue was raised in a Canadian Journal of Ophthalmology article.¹ As Pandey and Kirkby reported, “Despite the use of Luer locks, 60 cases of cannula detachment were reported; 196 respondents experienced this complication, and the most common cause of cannula detachment was stromal hydration (50%). Hydrodissection and viscoelastic were experienced by 18% and 17%, respectively. No severe damage resulted in most cases (76 cases), but some serious complications were reported: retinal damage (9%) and vitreous loss (17%).”¹

In another article, Wilde et al² reviewed the issue of Luer Lock usage in this context. The authors suggested, “Simple statements that Luer locks never fail will not avoid future harm if human performance shortfalls cannot be eliminated from every possible step. The safest way to do this is at the manufacturing stage by moulding one-piece cannula-syringe devices, where syringe and cannula hub are moulded together, eliminating the possibility of detachment by force or inadequate tightening.”

Although a reasonable suggestion, this is not financially feasible as it would be costly, and manufacturers would need to cater to every syringe size.

Some viscoelastic suppliers have adopted a screw cap that goes over the cannula and screws to the body of the syringe. This secures the cannula to the syringe, preventing forceful dislodgement; however, it only addresses one of potentially five or six cannulae used during the procedure. There is also evidence that the stromal hydration step, with saline and not viscoelastic, is the highest risk manoeuvre.

Furthermore, the screw cap solution potentially has inherent safety issues. It is well established that you should not resheath a needle or cannula, and the screw cap encourages just that practice.

The aseptic non-touch technique is a widely used international health care standard that prevents infection during clinical procedures by ensuring that key aseptic sites and key parts are protected. The cannula tip is a key part, and it should not be touched even with a gloved hand. Touching the tip of the cannula (Figure 1) should be avoided, as it could theoretically increase the risk of infection or toxic anterior segment syndrome due to contamination.

Additionally, there is a theoretical potential risk of damage to the cannula tip by passing it through the plastic orifice in the cap (Figure 2). Any sharp edges on the cannula tip could result in posterior capsule rupture if it comes into contact during injection.

These risks are exceedingly small and theoretical as opposed to the real risk of cannula ejection. Therefore, until a better solution is developed, the use of the screw cap should be encouraged. However, it should be noted that if all viscoelastic providers adopted this method, with each cap weighing 2 g and approximately 24 million cataract procedures performed globally per year, it would result in an additional 48 metric tons of plastic waste per year, an obstacle to promoting sustainability in ophthalmic surgery.

Survey illustrates scope of cannula risk

This problem has been starkly highlighted by the responses to an anonymous survey sent to members of the United Kingdom and Ireland Society of Cataract and Refractive Surgeons, the European Society of Cataract and Refractive Surgeons and the readership of Eye News. The survey was designed to determine whether surgeons had experienced dislocation of a cannula during cataract surgery and whether any ocular damage had been sustained.³

According to the results, 84% of respondents had experienced dislocation of the cannula during an intraocular procedure. Further, 78.04% of respondents reported experiencing episodes of harm due to this complication, and 50.37% of respondents indicated that the last time a cannula dislocation occurred, ocular damage occured. In contrast, only 16.08% indicated that they had never had a cannula dislocation. Regarding frequency, 22.95% of respondents indicated that a cannula dislocation occurred in their hands on average once per year, 38.43% reported that it occurred on average twice per year, 15.66% responded that it occurred three times per year and, significantly, only 6.92% stated that it occurred four or more times per year. Notably, 86.90% felt that better cannula design or a safety device was required to prevent further occurrences. Respondents provided other ideas to mitigate risk, with 45.76% suggesting that checking each time to ensure the cannula was tight was necessary, while 25.46% and 23.80% of respondents suggested a need for better scrub practitioner training and surgical practice, respectively.

Assuming 40,000 ophthalmologists in Europe,⁴ and extrapolating from the data, if 22.95% of these surgeons experience a cannula dislocation once per year, then it occurs 9,180 times per year. If we include the numbers for those who experience it even more frequently, this results in an estimated 69,788 instances per year. Further, if clinicians acknowledge that harm is observed in 50% of cases, then avoidable ocular harm occurs in almost 35,000 cases per year across Europe alone. Other data sources estimate the incidence to vary between 0.009% and 0.07%.^5,6 In the vast majority of patients, the harm will be minimal and potentially not even documented in the clinical record, but in some cases, it can and will be blinding.

We are running the gauntlet of avoidable harm, and this has been occurring for decades without an effective solution being developed. A solution must be cheap, easy to apply to all our syringes, fast to apply, effective and environmentally conscious.

The onus must be placed on viscoelastic providers and surgical pack providers to develop a solution, working in conjunction with the ophthalmic community.

In the interim, it is vital that surgeons are aware of this complication and take every possible measure to minimise the risk, including checking the cannula is tight each time they use it.

References

1. Pandey P, Kirkby G. Cannula detachment during cataract surgery: results of a survey. Can J Ophthalmol. 2012;47(3):280-283. doi:10.1016/j.jcjo.2012.03.022

2. Wilde C, Ross AR, Orr G, Dua H. Iatrogenic cannula-associated ocular injuries during anterior segment surgery: time to re-think Luer-lock design? Eye (Lond). 2019;33(2):341-342. doi:10.1038/s41433-018-0250-9

3. Alwitry A. Prevalence of cannula dislocation during cataract surgery: a survey. J Cataract Refract Surg. 2025;51(11):1034-1036. doi:10.1097/j.jcrs.0000000000001724

4. Maubon L, Nderitu P, O'Brart DPS. Returning to cataract surgery after a hiatus: a UK survey report. Eye (Lond). 2022;36(9):1761-1766. doi:10.1038/s41433-021-01717-5

5. Rumelt S, Kassif Y, Koropov M, et al. The spectrum of iatrogenic intraocular injuries caused by inadvertent cannula release during anterior segment surgery. Arch Ophthalmol. 2007;125(7):889-892. doi:10.1001/archopht.125.7.889

6. Ting DSJ, Dees C, Ellerton C. Cannula-associated ocular injuries during cataract surgery: a preventable intraoperative complication? Middle East Afr J Ophthalmol. 2017;24(1):54-56. doi:10.4103/meajo.MEAJO_208_15

Amar Alwitry, BMedSci, BM, MRCS (Surgery), MRCSEd (Ophth), MRCOphth, FRCOphth, MMedLaw, PgD | E: [email protected]

Alwitry is a Consultant Ophthalmologist in the UK. He is a CQC Speciality Advisor and a GMC Expert. He is one of the foremost ophthalmic medicolegal experts in the UK.

Financial declaration: Alwitry is actively working with production partners to try to develop a safety device which will resolve the issue of cannula dislocation.