News

Mock cataract surgery

The Straits Times (11 April 2013)

Now, there is a surgical simulator which allows novice surgeons to practise the different steps of cataract surgery without putting patients at risk. Joan Chew reports

Dr Yong Shao Onn, a consultant at National Healthcare Group Eye Institute at Tan Tock Seng Hospital, looks on as his colleague, Dr Nicola Gan, a registrar, demonstrates the use of the Eyesi ophthalmic surgical simulator. ST PHOTO: ALPHONSUS CHERN

Just as trainee pilots practise flying in flight simulators, ophthalmology residents at Tan Tock Seng Hospital (TTSH) now hone their skill in performing cataract surgery with a surgical simulator.

Experienced ophthalmologists who have tried the $260,000 Eyesi ophthalmic surgical simulator say the mock surgery is as real as it can get.

Students can gain confidence and competence that will make surgery safer for patients, without putting any of them in harm's way during training.

The novice surgeon inserts mock instruments through openings in a mechanical eye suspended within a human head model.

Every twitch of his hands is detected via optical tracking and transmitted to a computer that creates a virtual three-dimensional image of the instruments moving on the eye, which he sees through a microscope. A flat-panel monitor projects this same view to others observing the training.

His feet controls two foot pedals - one to adjust the microscope and the other to control the phacoemulsification machine. This machine allows the infusion of fluid into the eye, provides ultrasound energy to break up the cataract into small pieces and then sucks them up with a probe.

LIMITATIONS OF PRACTISING

Cataracts are the top cause of blindness here, with about 65 per cent of those blind in both eyes suffering from the condition.

More than a third of people aged 40 and above have cataracts, a study here found.

Half the 10,000 to 12,000 cases of eye surgery done at TTSH each year are for cataracts.

A cataract is the clouding of the eye's natural lens, which is mostly made up of water and protein. It occurs when some of the protein clumps together with age.

To correct this, a doctor may recommend phacoemulsification cataract surgery, in which an ultrasonic device is used to break up and then remove a cataract from the eye through an incision no longer than 3mm.

This is replaced with a clear intraocular lens implant which restores vision.

Traditionally, ophthalmology residents practise cataract surgery on eyes of pigs - or in the case of Muslim surgeons, goats - in a wet laboratory. But such animal eyes do not fully replicate the demands of surgery on human eyes.

Dr Wong Hon Tym, medical director and senior consultant at National Healthcare Group (NHG) Eye Institute at TTSH, said dead eye tissue turns foggy rapidly, as blood supply is needed to maintain the clarity of the cornea, which the surgeon looks through to access the lens behind it.

Therefore, the medical resident has to race against time to practise on the animal eye while it is still clear. This is not an issue when practising surgery on the simulator.

Training on the eyes of young animals which do not have cataracts is also inadequate, said Dr Yong Shao Onn, a consultant at NHG Eye Institute at TTSH.

The lens is so soft that even before the ultrasonic energy is delivered through the phacoemulsification probe (an ultrasonic hand piece), the entire lens may already be sucked out.

Another drawback of working on animal eyes is that the lens capsule - a thin membrane which wraps around the lens - is much tougher than a human's. It is so tough that when a phacoemulsification probe is accidentally placed next to the animal lens capsule, it sometimes remains intact and does not break, giving ophthalmology residents "a false sense of security", said Dr Yong.

If the same were to happen to a human eye, it could lead to a tear in the posterior capsule, which would then allow the gel at the back of the eye to flow to the front of the eye.

MORE THAN A THIRD OF PEOPLE AGED 40 AND ABOVE HAVE CATARACTS

This would result in the retina, which is attached to the gel, being pulled out of place.

If not handled well, this complication could lead to blindness, Dr Yong warned.

The simulator will trigger this cascade of events just like in a real human cataract operation.

It also allows surgeons to practise handling other complications such as when the supporting structures of the lens are broken, said Dr Yong.

Though the simulator does not provide tactile feedback, this is not a concern since surgeons doing microsurgery rely more on visual feedback, he said.

In fact, Dr Nicola Gan, a registrar at the NHG Eye Institute at TTSH, said that doing "surgery" on the simulator feels more similar to doing so on a human eye than an animal eye.

The simulator was added to the residency programme at TTSH last July, but it has not replaced training using actual surgical instruments on animal eyes.

This is because the simulator cannot train surgeons in two steps of the surgery: creating the incision in the cornea and implanting the artificial lens.

DIFFERENT DIFFICULTY LEVELS

The simulator breaks down cataract surgery into 13 training courses of increasing difficulty. To advance through a course, trainees must meet a required performance level on each task.

Both Dr Wong and Dr Yong said that capsulorhexis is among the most difficult steps in cataract surgery. This involves making a continuous circular incision in the front of the lens capsule to access the cataract within it.

With the simulator, a novice surgeon holds a red-tipped instrument - representing the forceps during surgery - to pull a dot along a straight line in the front of the eye.

He then progresses to pulling the dot along a circular line and, eventually, does it with no line to aid him.

Associate Professor Chee Soon Phaik, the head of cataract service at Singapore National Eye Centre, said the simulator would be especially useful for beginners who need training in this technique.

In a study published in 2009 in international journal Graefe's Archive For Clinical And Experimental Ophthalmology, 63 novice surgeons were randomly assigned to receive either training on the simulator or no training. They performed capsulorhexis three times on an animal eye in a wet lab before and after that.

Compared with those without training, those who had virtual reality training performed the procedure more consistently, faster and with less collateral tissue damage. They also made incisions that were of better shape, size and centring.

In a review of 592 cataract

operations published in the Journal Of Cataract And Refractive Surgery in 2011, third-year ophthalmology residents who had used the simulator during training performed such operations more rapidly and with fewer complications.

The authors concluded: "Although simulation did not precisely mirror the actual operation, we believe that the psychomotor coordination acquired through simulator use is the most important factor in improving surgical skill."

The SNEC and National University Hospital are considering buying the simulator, said Mr Jason Jong, the director of Mandarin Opto-Medic, which distributes the machine here.

The machine, manufactured by German-based VRMagic, is being used in Moorfields Eye Hospital in Britain and Aravind Hospital in India, he added.

With different software that can be purchased at an additional $140,000, the simulator can also be used to provide training for vitreoretinal surgery, that is, treating problems of the retina, macula and vitreous fluid.

joanchew@sph.com.sg


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Source: The Straits Times © Singapore Press Holdings Limited. Reproduced with permission.