I began practicing 25 G vitrectomy surgery some years ago but I have since abandoned the technique because I did not feel confident with it. My decision was based on a number of factors, but largely because I believe the design of the instruments is flawed.

A flaw in instrument design

Naturally, in present times, our natural inclination as surgeons is to opt for the minimally invasive option wherever possible. As such, the introduction of 25 G instruments did spark interest and intrigue amongst the retina community. However, the slimmer design of these instruments has, in my opinion, left us exposed to an increased risk of complications and decreased surgical control.

First and foremost, the overly flexible nature of the instruments is unacceptable. As ophthalmologists, we must be able to maintain strict control over our tools, with the instrument mirroring our hand movement. The increased flexibility of 25 G instruments, in comparison to 20 G and 23 G instrumentation, reduces my ability to control the bulbus and, ultimately, makes me feel uneasy and unsafe. Although I have been able to perform 25 G surgery successfully, I realized very early on that less experienced surgeons would encounter difficulties with it. Thus, in teaching facilities such as ours, it is hard to justify the implementation of a surgical technique or tool that is only suitable for experienced surgeons.

Complications cause for concern

In fact, some studies have linked 25 G surgery with a series of complications. For example, a review of the records of 565 eyes that underwent the minimally invasive procedure found surgery was associated with an increased incidence of retinal detachment, endophthalmitis and hypotony, when compared with 20 G surgery.¹ A significant increase in retinal detachment^2,3 and tear rates⁴ have also been reported elsewhere. Meanwhile, further evidence of the failure of a 25 G wound to self-seal has been presented, where more than 20% of eyes required sclerotomy suture placement or suffered hypotony.⁴

Most recently, a Microsurgical Safety Task Force of US surgeons disseminated guidelines to reduce the rate of complications associated with 25 G vitrectomy, particularly endophthalmitis.⁵ In a presentation made during this year's congress of the AAO, Dr Richard Kaiser of the Retina Service, Wills Eye Institute, US, and taskforce member, claimed that the risk of infection is in fact 12.4 times greater with the 25 G procedure when compared with 20 G surgery. The list of suggestions included advice on wound construction, ocular preparation, and the use of air-fluid exchange.

Although further substantive research is required to prove these claims, it creates further cause for concern.

I believe that the ophthalmic community is also exercising caution; as far as I am aware, the rate of uptake of microincision vitrectomy surgery is much slower than industry had expected. Concerns relating to instrument flexibility, fluidics, control, and the certain risk of hypotony coupled with the theoretical higher risk of endophthalmitis, have each contributed to this reluctance.

Are the newer generation instruments no better?

I am aware that industry has made major improvements to 25 G instrument fluidics by altering the duty cycle. The newer generation of instruments are also less flexible than earlier models. However, I still believe there are some fundamental problems with 25 G instrument design. Although experienced surgeons may not be exposed to the problems with these new instruments, I believe that the less experienced surgeon would encounter difficulties. For example, the reduced control with these instruments, in comparison to 20 G and 23 G instruments, make manoeuvres in the periphery more difficult. In addition, the narrow diameter of the instruments means a physical barrier to flow and thus fluidics still exists. Even by optimizing the duty cycle and by making the blade as fast as possible, there are still important factors that are directly correlated to the size of the device. These factors cannot be modified. Hence, I would advise that every novice 25 G surgeon starts with easy cases and exercises great caution.

I have to say that, conversely, I have been very impressed by 23 G instruments. Since introducing them into my practice, I have not looked back. Now, I perform 23 G surgery in over 90% of my vitrectomy cases. As well as being stiffer, and thus affording greater surgical control, 23 G instruments are associated with significantly improved fluidics in comparison to 25 G instruments. Although I have personally witnessed few differences in overall outcomes between 23 G and 25 G surgery, these different attributes are very important.