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Ophthalmic surgery is an example of a micro-surgical procedure where medical simulation can play an
important role. It involves a number of complex procedures that require a high level of training, and
excellent dextrous skills. The most frequent and difficult procedures are: cataract surgery, glaucoma
surgery, corneal surgery, vitro-retinal surgery and eye muscle surgery. Due to the small size of the eye,
instrument motion must be well controlled and the margin for error is very small. Although these reasons
are excellent motivations for developing training systems, little work has been done in this area (Neumann
et al., 1998) (Santerre et al., 2006) (Barea et al., 2007). One commercial product exists, the eye surgery
simulator EYESi, from the company VRmagic.
Neumann et al. (Neumann et al., 1998) described a vitrectomy simulator based on vectorial spring-mass
model, i.e. a modified spring-mass model in which forces not only depend on the variation of length of
the springs, but also on the variation of angle between spring directions. In the prototype developed by
Neumann, user interactions are driven by actual surgical instruments connected to position tracking
sensors, allowing tissue manipulation including cutting. No force feedback device is used, which is
understandable since limited haptic feedback exists in the real procedure. The simulator developed by
Meseure et al. (Meseure et al., 1995) targets retinal laser photocoagulation. Designed in close
collaboration with ophthalmologists, it includes a large library of cases, to offer an ideal training setup. An
actual slit-lamp is supplied with sensors measuring all the degrees of freedom of the system. The images
are calculated by a computer and are displayed on a miniature screen placed inside the binocular. A user
interface is provided through a Computer Assisted Training software, which allows users to manage
pigmentation and pathology data base, to follow the students skill level and to prepare critical operations.
Further developments by the same team (Santerre et al., 2006) aimed at cataract surgery. The eye lens
was modeled as a linear elastic material using a finite element approach and a spring-mass model was
used to describe the lens capsule. The contact with the lens is simulated by a collision sphere, which
provides the interaction between the surgical instruments and the virtual environment. The surgical
instruments viewed on the screen are controlled by a stylus with six degrees of freedom. The resulting
simulation allows basic training for phacoemulsification in real-time with rather realistic visual feedback.
A cataract is an opacity or cloudiness in the natural lens of the eye. It represents an important cause of
visual impairment and, if not treated, can lead to blindness. It is actually the leading cause of blindness
worldwide, and its development is related to aging, sunlight exposure, smoking, poor nutrition, eye
trauma, and certain medications. The best treatment for this pathology remains surgery. Cataract surgery
has made important advances over the past twenty years, and in 2005, more than 5 million people in the
United States and in Europe underwent cataract surgery. Most cataract surgeries are performed using
microscopic size incisions, advanced ultrasonic equipment to fragment cataracts into tiny fragments, and
foldable intraocular lenses to minimize the size of the incision. All these advances benefit the patient, but
increase training requirements for eye surgeons.
At the end of 2007, we started the development of a new training system for cataract surgery. The main
objectives of this simulation are to reproduce with great accuracy the three main steps of cataract
surgery: 1) capsulorhexis 2) phacoemulsification and 3) implantation of an intraocular lens.
Although a first proof of concept had been developed at INRIA by the Alcove team in 2005 and 2006, several limitations in the technical choices required a new development. We chose to develop this new simulation using the SOFA framework, both to have a more flexible choice of technical solutions, and also to test the prototyping capabilities in SOFA. The anatomical model of the eye, created by P. Neumann from CIMIT, was quickly integrated and the main focus went to the choice of appropriate deformable models for the lens and lens capsule. An important effort also went into the development of topological changes corresponding to the capsulorhexis and phacoemulsification.
- N. Santerre, F. Blondel, F. Racoussot, G. Laverdure, S. Karpf, P. Dubois, J-F. Rouland. "A teaching medical simulator: phacoemulsification in virtual reality". J Fr Ophtalmol; 30 (6):621-626, 2007. (PDF)
- P. Dubois, J.-F. Rouland, P. Meseure, S. Karpf, C. Chaillou. "Simulator for laser photocoagulation in ophthalmology". IEEE Trans Biomed Eng.;42(7):688-693, 1995. (PDF)
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VIDEO: simulation of phacoemulsification during cataract surgery. Movie in AVI DIVX format. |
Most serious retinal eye problems that require surgery are caused by problems with the vitreous, the
transparent gel-like substance which fills the center cavity of the eye. The vitreous
is attached to the retina, the thin layer of tissue lining the back of the eye. The retina has two parts: the
peripheral retina and the macula. The macula allows to see very fine detail while the peripheral retina
gives us our side vision. The vitreous is most strongly attached to the retina at the sides of the eye. It is
also attached to the optic nerve, the macula and the large retinal blood vessels.
Vitrectomy is a form of eye surgery that treats disorders of the retina and vitreous. The vitreous is
removed during vitrectomy and is usually replaced with balanced salt solution. A vitrectomy is required for
a variety of conditions. In particular, it is done to remove scar tissue that grow on the vitreous or the
surface of the retina and pulls on the retina, which causes a retinal detachment. Another pathology
requiring this type of procedure is diabetic traction retinopathy, which is characterized by bleeding and
scar tissue forming in the eye of a diabetic patient. Vitrectomy can also be required in case of
complications following cataract surgery. In a vitrectomy, microsurgical instruments are placed into the
eye through three tiny incisions in the sclera (the white part of the eye). A variety of instruments may be
used to remove the vitreous gel and any scar tissue that maybe be growing on the surface of the retina. A
laser probe can be inserted into the eye so that laser therapy can be performed during the surgery.
We have developed a prototype of a simulation of vitrectomy surgery using the SOFA framework where the
objective of the simulation is to remove scar tissue that grows on the surface of the retina and pulls on
the retina, causing a retinal detachment. This simulation uses a detailed anatomical model of the eye, a
soft tissue model for the scar tissue and the retina, and a generic haptic interface (Phantom Omni). The
scar tissue exerts a tensile force on the retina, thus causing a retinal detachment and consequently vision
problems. The basic principle of the surgical procedure, which we replicated in the simulation, consists in
making small incisions into the wall of the eye to allow the introduction of instruments into the vitreous
cavity. It is followed by the incision and removal of the scar tissue using microscopic scissors, scalpels,
and forceps.
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VIDEO: simulation of vitrectomy. Movie in AVI DIVX format. |