3D microscopy offers

Digital 3D microscopy

Two years of surgery using a digital 3D microscope convinces surgeon. Leigh Spielberg MD reports

After using a digital 3D microscopy system for two years, Peter Stalmans MD is convinced that the new technology confers several advantages compared to the traditional analogue setup.

Dr Stalmans, Leuven University Hospital, Belgium, discussed both the advantages and disadvantages of 3D system during a session of the 19th Annual EURETINA Congress in Paris. He discussed 3D microscopy in general and the ZEISS ARTEVO 800 system in particular.

A 3D digital operating microscope consists of a 3D camera system, a 3D monitor and 3D glasses. The camera is incorporated into what looks like a traditional operating microscope. The 3D monitor is positioned in front of the surgeon at approximately 1.2 metres’ distance. The 3D glasses are worn by the surgeon and instrumentation nurse, and confer the ability to see the screen’s image in three dimensions.

“A digital microscope allows us to operate with much less light. In 90% of vitrectomy cases, the surgery can be performed with 10% or less of the maximal endolight,” said Dr Stalmans, citing a study published in RETINA in 2017. “Besides the increased safety in terms of retinal light toxicity, the lower light requirement represents an advantage for 27G surgery, in which low illumination can be a limiting issue due to the decreased diameter of the light fibres. “

The low light requirement of the 3D digital microscopes confers other advantages as well. Because of the increased light sensitivity of the digital microscope, the microscope diaphragm size can be decreased. A smaller diaphragm size increases the depth of field. This eliminates the need to adjust the focus during anterior segment surgery and gives a better overview during posterior segment surgery, he noted.

An oft-cited advantage of so-called heads-up surgery is reduced surgeon fatigue and cervical spine injury.

“A study published by Eckardt et al in RETINA in 2016 demonstrated that 91.7% of surgeons preferred the ergonomics of the heads-up technique, and I agree,” said Dr Stalmans.

In an occupation in which 60% of ophthalmologists in the United States complain of back and neck pain due to surgery (ASRS PAT-survey), this could represent a major improvement on the current model. In heads-up surgery, the surgeon is not required to adopt and maintain a particular posture to see through the microscope.

“There are, however, things to bear in mind,” Dr Stalmans informed delegates. “The use of a 3D digital microscope will require you to rearrange the layout of your operating room.”

This is because the (large) 3D monitor needs to be placed approximately 1.2 metres from the surgeon. This distance is required to avoid so-called accommodation-convergence disparity. Ambiguity between accommodation and vergence cues is a well-known limitation in many stereoscopic display technologies and can lead to disorientation and nausea. “This positioning of the screen requires the instrumentation nurse to be facing in the same direction as the surgeon, which represents an adjustment for many operating rooms. Side-assisting on a 3D screen takes time to learn.”

Latency time used to be a limiting issue with digital microscopes, one which turned surgeons off to the idea of using it. The latency time could be up to 90 milliseconds, which was perceived as a lag between actual movement of the instruments and the movements’ appearance on the monitor.

“Newer microscopes’ latency time is less than 50 milliseconds, which is beyond the threshold of human

perception. You don’t notice it at all,” Dr Stalmans assured delegates.

He also noted that the visualisation itself is excellent, even when circumstances are less than ideal, such as in an air-filled eye. He admitted that 3D digital visualisation might never be universally adopted.

“Not everyone likes 3D imaging. Some surgeons may still prefer to work with traditional microscope oculars.”

This is something that the designers of ARTEVO 800 have anticipated, in case there might be disparity in preferences within a single vitreoretinal practice. The fact that some surgeons would like to use it and others would prefer to use the traditional oculars is not a problem.

“The ARTEVO 800 has a hybrid mode in which the surgeon can use the oculars and the nurse can continue to use the 3D screen, so that the operating room layout need not be altered for every surgeon,” continued Dr Stalmans. This is a distinct advantage over previous iterations of 3D digital microscopes, in which switching between 3D visualisation and ocular visualisation was time-consuming and could lead to mechanical failures.

“In hybrid mode, 70% of the available light is sent to the oculars and the remaining 30% is sent to the 3D screen,” explained Dr Stalmans. “The 70% equals the amount of light available through the previous generation of microscopes.” Dr Stalmans encouraged delegates to give the 3D digital microscope a try. Peter Stalmans: Peter.Stalmans@uz.kuleuven.ac.be