For a few years, we have worked together with the practice variance surveys to tease out differences in the way we work and to discuss issues that arise. I hope that we have learnt some lessons and reflected on what we do.
We know that cataract surgery is one of the most commonly carried out operations in the world. It is inherently safe and outcomes are generally good. The use of Luer lock syringes is standard practice however, despite that ocular harm is still occurring. This is a result of the cannula shooting off the end of the syringe into the eye, damaging ocular structures and resulting in visual loss or even blindness in what should be a routine procedure. When injecting, we generate significant hydraulic force as we push a large volume of liquid through a fine lumen. If the cannula is not properly and firmly attached to the syringe it can fly off with significant force and speed resulting in damage. This has been reported extensively in the literature and has been the subject of two recent safety alerts by the Royal College of Ophthalmologists in England. It has also been the subject of a United Kingdom and Ireland Society of Cataract and Refractive Surgeon (UKISCRS)’s alert.
It can occur for three possible reasons:
- Not tightening the cannula into the Luer lock syringe,
- A fault in the manufacture of the syringe, or
- Mis threading of the cannula into the Luer lock mechanism.
Unfortunately, it is likely that the first reason is the culprit in most circumstances and it is due to human error. The consequences can be blinding and it is completely avoidable and indefensible. It usually occurs in a routine procedure and takes patients from a visual outcome of 6/6 to potential no light perception (NPL) or even loss of the eye.
Cannula detachment is a well-recognised, unaddressed safety issue which can result in blindness or even loss of the eye [1-12]. Estimates of incidence vary at between 0.009–0.07% [1,2].
A recent survey facilitated by the Eye News readership and the UKISCRS found that this happens quite frequently [3]:
- 84% of respondents had experienced dislocation of the cannula during an intraocular procedure.
- 78.04% of respondents had seen episodes of harm due to this complication.
- 50.37% of respondents indicated that the last time a cannula dislocation occurred there was ocular damage.
- 16.08% indicated that they had never had a cannula dislocation.
- 22.95% indicated that a cannula dislocation occurred on average once per year; in 38.43% it occurred on average twice per year; 15.66% responded that it occurred three times per year; while 6.92% stated that it occurred four or more times per year.
- 86.90% felt that better cannula design or a safety device was required to prevent further occurrences.
- 45.76% suggested that checking each time to ensure the cannula was tight was necessitated.
- 25.46% and 23.80% of respondents suggested better scrub practitioner training and surgical practice respectively were needed.
If we assume circa 2000 eye surgeons in the UK [13], then 22.95% experience a cannula dislocation once per year, meaning 459 dislocations per year in the UK. If we further extrapolate from the rest of the data where surgeons experience it more than once, then in total there are at least 4256 dislocations per year in the UK alone. In approximately 50% of cases harm occurred, meaning a staggering 2128 episodes of ocular harm occurring each year due to this avoidable phenomenon. In the vast majority, the harm will be minimal and potentially not even documented in the clinical record. For example, a small iris or angle bleed may settle rapidly and not cause any morbidity however the harm can be severe and there is a ‘Russian roulette’ of avoidable harm clearly occurring daily in our work.
Several issues ago, I asked the Eye News readership who was to blame [4]:
Almost half of you laid the blame at the foot of the surgeon and indeed there is a ‘captain of the ship’ argument that it is the surgeon who is in overall control of the procedure. The scrub practitioner does no harm to the patient themselves even if they do not screw the cannula on properly, but it is the surgeon putting that cannula into the eye that causes the problem and the harm. We have a duty of care to ensure that all the equipment we use is safe and fit for purpose. It seems from the data presented that we are not fulfilling that obligation and indeed more than 80% of cataract surgeons responding felt that a safety device was needed.
A paper published in Eye entitled ‘Iatrogenic cannula-associated ocular injuries during anterior segment surgery: time to re-think luer-lock design?’ [8] 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.”
This is not financially feasible as it would be costly, and every syringe size would need to be catered for. This issue has been highlighted by a paper as far back as 2012 in the Canadian Journal of Ophthalmology [9].
They found that:
“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%).”
For 13 years, there has been no solution available and from a medico-legal perspective, it is indefensible. I still have one case every two months or so of this exact occurrence resulting in visual loss, which is heart-breaking as a solution needs to be enacted. As shown in the Canadian Journal of Ophthalmology paper, this most commonly occurs during stromal hydration, which is likely at the end of an otherwise uncomplicated procedure taking a patient from a perfect outcome to potential blindness in an instant.
Some viscoelastic suppliers have adopted a screw cap that goes over the cannula and screws to the body of the syringe. While this is a welcome acknowledgement to the issue, it is not feasible for all the other cannulas used during the procedure and indeed, as shown above, the viscoelastic is not the main culprit but instead stromal hydration from a Luer lock syringe of volume ranging between 2–5ml.
Furthermore, the screw cap solution has potentially inherent safety issues in itself. It is well established that you should not resheath a needle or a cannula and that is what the screw cap encourages.
The ‘aseptic non-touch technique’ (ANTT) is a widely used international healthcare method / standard that prevents infection during clinical procedures by ensuring that key aseptic sites and key parts are protected. It clearly states that the key parts – and the tip of the cannula which is introduced into the eye is clearly one of them – should not be touched even with a gloved hand. Touch carries the risk of a ‘cannula-stick’ injury but also the risk of endophthalmitis and toxic anterior segment syndrome due to contamination. As shown in the following figure, passing the cap over the cannula brings the cannula tip into proximity of the users fingers.
Figure 1.
Furthermore, the delicate cannula tip risks damage if it hits the hard inner surface of the cap. We know that if metallic intraocular devices have any sharp or rough edges, which may be only visible under high magnification, then there is a risk of causing a posterior capsule rupture [14]. As someone who uses the tip of the viscoelastic cannula to remove any residual plaque on the posterior capsule this concerns me. Clearly any link is speculative, however we need to try and avoid even theoretical risks to our patients.
The use of the screw cap is a step forwards and in the absence of other safety methods its use is encouraged, however, there has to be a better solution which can be applied to all the syringes we use, particularly for the stromal hydration step which the viscoelastic is not involved in. We know that:
- Patients are coming to avoidable harm.
- There is strong evidence that the problem is occurring regularly with patients coming to varying degrees of harm including blindness.
- Current safety protocols are ineffective and the screw cap solution some viscoelastic providers are currently providing introduce some risk in themselves.
- Furthermore, the screw cap solution only addresses the viscoelastic cannula and that is not the major cause of harm.
We are currently using syringes and cannulas with a known risk and we need a solution which is cheap, easy to apply to all our syringes, fast to apply, and effective. We and our hospitals have a duty of care to minimise that risk. It is important for viscoelastic manufacturers and phaco pack providers to engage in safety work to try and remedy the situation. Already, solicitors are asking the question as to whether the providers of these syringes should carry some liability when they fail. In the interim, it is vital that surgeons are aware of this complication and do everything they can to minimise the risk, including checking the cannula is tight each time you use it.
In line with the wishes of 80% of respondents to the Journal of Cataract and Refractive Surgeons, I am currently trying to work with production partners to devise a safety device that solves the problem and protects patients from this eminently avoidable harm.
References
1. Ting DS, Vaideanu-Collins D, Ellerton C. Cannula-associated ocular injuries during cataract surgery: the North East England Study. Eye 2016;30:764–5.
2. 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;125:889–92.
3. Alwitry A. Prevalence of Cannula Dislocation During Cataract Surgery: Survey. J Cataract Refract Surg 2025. [Epub ahead of print]
4. Alwitry A. The results of the last survey. Eye News 2021;28(2):40–1.
5. Ting DSJ, Dees C, Ellerton C. Cannula-associated ocular injuries during cataract surgery: a preventable intraoperative complication? Middle East Afr J Ophthalmol 2017;24:54–6.
6. Kahawita S, Cugati S, Casson R. Cyclodialysis cleft with late hypotony maculopathy after inadvertent cannula detachment during cataract surgery. J Cataract Refract Surg 2015;41:1107–8.
7. Prenner JL, Tolentino MJ, Maguire AM. Traumatic retinal break from viscoelastic cannula during cataract surgery. Arch Ophthalmol 2003;121:128–9.
8. 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 2019;33:341–2.
9. Pandey P, Kirkby G. Cannula detachment during cataract surgery: results of a survey. Can J Ophthalmol 2012;47(3):280-3.
10. 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;125:889–92.
11. Dinakaran S, Kayarkar VV. Intraoperative ocular damage caused by a cannula. J Cataract Refract Surg 1999;25:720–1.
12. Yadav S, Tandon R, Singh R, Pujari A. Viscoelastic cannula acting as a wrecker and saviour during cataract surgery. BMJ Case Rep 2019;12(8):e231778.
13. Maubon L, Nderitu P, O’Brart DPS. Returning to cataract surgery after a hiatus: a UK survey report. Eye 2022;36:1761–6.
14. Hart JC Jr, Tanner M, Rooney DM. Electron microscopy of silicone irrigation/aspiration tips involved in posterior capsule rupture. J Cataract Refract Surg 2018;44(12):1517–20.
Declaration of competing interests: The author is actively working with production partners to try to develop a safety device which will resolve the issue of cannula dislocation.
