The Ophthalmic Retrobulbar Injection Simulator (ORIS): An Application of Virtual Reality to Medical Education Jonathan R. Merril, M.D., Neil F. Notaroberto, M.D., Daniel M. Laby, M.D., Andrew M. Rabinowitz, M.D., and Thomas E. Piemme, M.D. The Departments of Ophthalmology and Computer Medicine, George Washington University Medical Center
Retrobulbar injection is one of the most commonly utilized techniques in ophthalmic surgery. Although proven to be a relatively safe procedure, severe complications can occur with improper technique. The Ophthalmic Retrobulbar Injection Simulator (ORIS) offers ophthalmology residents an opportunity to learn and practice the technique of retrobulbar and peribulbar anesthesia prior to performing it on a patient. Introduction
Retrobulbar anesthesia serves two purposes in ophthalmic surgery. Not only is pain controlled by the injection of anesthetic agents, but ocular motility is paralyzed. Loss of voluntary motor ability insures against any ocular movement which may deform an open globe1. Retrobulbar injection blocks the ciliary ganglion and paralyzes the ocular muscles by diffusely infiltrating the posterior portion of the muscle cone. The orbital apex is vulnerable, however, because the optic nerve, and the central retinal artery and vein are so closely related that they will not yield to an advancing needle, and are susceptible to puncture. In addition to the risk of damaging nerve and vessel, other complications include globe rupture, apnea, respiratory arrest, retinopathy, grand mal seizure, transient retinal arty occlusion, and amaurosis2'3. These dangers can be reduced by using cannulas of an appropriate shape, length, and rigidity, and by using an appropriate guidance technique. ORIS was developed to aid in perfecting the guidance technique, permitting rehearsal of the procedure without hazard.
The preferred approach of retrobulbar injection is transcutaneous. The needle is inserted in the lower temporal quadrant, below the tarsus and above the orbital rim. Rotating the eye upward and nasally removes the inferior oblique muscle from the peribulbar tissue, which is then pierced more easily1. The cannula pierces, in order: lid, orbital septum, fascia, and fat. The technique involves a
0195-4210/92/$5.00 ©1993 AMIA, Inc.
relatively high superficial resistance. This may make it difficult to appreciate the lesser resistance offered by the deeper structures. Simulations and Virtual Reality
The concept of using tools to help teach medical procedures dates back thousands of years to the introduction in China of dolls which were used to instruct students about the structure of the body. Almost every available medium has been employed: physical models, cadavers, graphics, text, projected transparencies, motion pictures, and videotape are among familiar examples. More recently, the computer has come to be used as a leaming tool. Because the computer can manipulate information and change a presentation according to a combination of user input and stored information, it has been widely used to simulate clinical cases. Several studies have supported the credibility of these simulators which users report to accurately represent clinical encounters with patients.4'5'6 Popular applications include the RxDxTm series from the Massachusetts General Hospital and the Scientific American DiscoTestTm . As technology has become more sophisticated, clinical simulations have begun to use graphics, and sequences from videodiscs to illustrate different concepts and to add additional information or realism to a case.
Over the years computers have, on occasion, been used to simulate clinical procedures. One of the first of these, a simulation of cardiopulmonary resuscitation, was described by Abrahamson in the late 1960's 7. A mannequin was equipped with sensors that interfaced with a computer. There are few other good examples, however, because such simulators have often involved complex input devices and software. They have been technically difficult, and expensive. On the other hand, the recent development of cheaper input devices and faster machines has brought the
702
modelling of clinical procedures within reach. It is a domain termed, 'virtual reality.'
Goals of ORIS
Virtual reality represents a convergence of many different fields including human/machine interface design, event simulation, data visualization, and computer graphics. World War II era pilots remember the Link. The Link allowed pilots to sit in a mock-up airplane cockpit located on a moveable platform. Inside was the first flight simulator. The pilot climbed in, pushed the ignition button, grabbed the control stick, and felt the cockpit tilt and roll, even vibrate, in response to the pilot's actions8.
The goals of ORIS are three:
1. To improve the user's knowledge of the anatomic structures prior to performing the procedure.
2. To acquaint the user with the theory and technique of performing an invasive surgical procedure. 3. To improve the user's motor skills prior to performing the procedure.
Goal # 1. To improve the user's knowledge of the relevant anatomic structures prior to performing the procedure.
A pioneer in the introduction of virtual reality to medicine has been David Hon. Having perfected a CPR simulator, he went on to develop a gastrointestinal endoscopy simulator which used a custom built endoscope/position sensor device coupled to a 386 computer and laserdisc player. This system allows for the display of endoscopic pictures at 1/30th of a second to simulate the performance of the procedure7.
To educate the resident about the procedure, we used interactive software which displays images of the different structures present at different layers within the orbit. Each of these layers contains features which are important when conducting the procedure.
ORIS provides another example of a virtual environment simulator which allows the user to perform the retrobulbar injection procedure using real- time, computer-generated, three-dimensional graphics. Fast microcomputers such as Apple Computers Macintosh IIfx and Quadra series, as well as the Intel 80486 computer, equipped with digital video interactive (DVI) boards, make this possible. It is our purpose to discuss the goals of the simulator, the technical means by which the goals were achieved, and the issues surrounding the production of a simulator for teaching a particular invasive procedure.
To develop the software, we used the textbook, The Human Eye in Anatomical Transparencies1O. Sagital and coronal cross section images were scanned with a Hewlett Packard ScanJet IIcT 24 bit, 400 dpi flat bed color scanner using the HP DeskScanTm software which is supplied with the scanner. The images were then imported into an Aldus Corp. SuperCardT interface, and placed onto interactive cards which allow the user to select different anatomic planes. Each card permits the user to view the important structures with the use of a semitransparent pointer which appears on the structure along
proccourrm VI 1:.. 1:
V
Rnutomq. r. I simtootils --Y
IEWV P-OCEID'JRi
|degree
m
2215
d.qruu .,.
Figure 1. Oris incorporates Apple's QuickTime technology to allow the use of digital video sequences to instruct residents on the retrobulbar injection procedure. The student can control the video sequence using the controls found on the right side of the screen. 703
To help acquaint the user with the procedure, retrobulbar injection was filmed in the operating room and digitally converted for display on the computer monitor. Digital video sequences permit instantaneous access to any given frame in the movie, and allow for the inclusion of multiple sound trcks. Using Apple's QuickTnme® software, motion pictures with sound can be included within the educational program without the need for additional hardware. Seefigure I which depicts the computer screen layout for this portion of ORIS.
15
a
:
KqFrbSSt: UPS"_ Emw:2 FIiimto t _: d camel
E@
D OK_ _
_*@eB
Figure 2. The control panel from Apple Computers ConvertToMovie software which allows the developer to select different parameters in determining the compression of QuickTime movies. Compression method, desired depth of color, spatial and temporal resolution, and key and maximum
frame rates
are
all variables which determine
the amount of resulting compression. with textual information regarding the importance of the structure, and its relation to the procedure. Goal # 2. To acquaint the user with the theory and technique of performing an invasive surgical procedure. lft
megabyt sftwar
dC
To generate digital footage, the procedure was filmed at multiple angles using a super-VHS camcorder. The tape was then digitized using a TrueVision NuVistaT image capture board equipped with 12 megabytes of VMX video RAM, and a Macintosh Ucx computer with 8 megabytes of RAM. This pemits the digitization of 1.5 minutes of video. The images were stored as a PICS file format. This format consists of the series of still images (PICT) which are linked together to ultimately yield a motion sequence. The file was then edited on a Macintosh QuadraS computer with 20 megabytes of RAM using MacroMind Director 3.0 software, and resaved as a PICS file. Finally, the PICS file (6.5 megabytes) was converted to an Apple QuickTume® movie using the Convert To Movie"m software supplied by Apple Computer, and was compressed to a size of 4 megabytes using the animation compression routine provided with the Convert To Movie"m software (seefigure 2).
computer wish 8
of RAK
Runng ORIS interface (deWveed uing Aldus
rd), Trunfiie System'
rsi cknd
XCMDs,
QuickTmue X WaL-hough.
Trandiit Sysms' GoldBridc interface
ppe
M, and
Vi,tm_
device
_
Ultrsonic detecton forthmee dimen sial position sesing (modified from Matd PoweGlove"')
transmittr, ataced to needl ~~Position (modified frm Matel PNwerGleT9).
Figure 3. Schematic Diagram of the ORIS system demonstrating sensor,data acquistion device, model head, computer.
704
s*mmuhinnSflf
l
AN
o on
t JeIIm
Figure 4 . The interface for three-dimensional tracking of the surgical probe provides the user with real-time, threedimensional graphic display of the structures with which the surgical probe is in contact.
Sound was recorded using the built in microphone on the Macintosh Quadra, and incorporated into a resource file using Apple Computer's HyperCardI' Audio stack. After recording, files were digitally edited using the sound editing facilities of this program. After the audio tracks were completed, they were combined with the QuickTime movie using Apple® Computer's QuickTime development software.
Manipulation of the QuickTime file was accomplished using the QuickTime XCMDs (software written in C or Pascal which extends the capabilities of HyperCard or SuperCard), permitting the control of the digital sequences within an interface design using Aldus S uperCard. Goal # 3. To improve the user's skills prior to performing a procedure.
motor
This goal is the most difficult to accomplish. We had chosen the procedure of retrobulbar injection specifically because it permits a fairly straight forward technique for modeling a simulation.
First, we must consider the fact that the technique involves the use of a needle which is placed through structures of differing resistance. In order to track the position of the needle, we contemplated a variety of tools. A data glove was considered. It would track the position of the fingers, and transmit to the computer information about how the clinician was holding the instrument. This approach was thought to be unreasonable since the position of the instrument could change without any change in finger or hand position. The ideal placement of
the position sensor would have to reside on the instrument itself. After selection of the location of the position sensor, we needed to determine the best method of tracking the sensor. We considered systems which employed magnetic, ultrasonic, gyroscopic, infrared, and laser technologies. One of our goals in the ORIS project was to construct the most cost effective simulator possible without sacrificing educational benefits. To this end, we ultimately chose ultrasonic sensing from a modified Mattel PowerGlove'm which utilizes a sonar tracking system similar to that used in the Polaroid® Land camera. The output of the PowerGlove was connected to the Apple Desktop Bus (ADB) port of a Macintosh IIfx computer through an adaptor called the Gold Brick." (available from Transfinite Systems, Boston, MA). The GoldBrick provided conversion of the Nintendo formatted signals to Macintosh compatible ADB format. Transfinite Systems provided an operating system extension, allowing for software support for the three dimensional information. The GoldBrick software transmits x,y, and z coordinates of the sensor probe through the use of an XCMD imported into SuperCard (seefigure 3 for a schematic diagram). Due to the limitations of ultrasonic technology, accuracy of this tracking was limited to 1/4 of an inch.
Once the sensor had been constructed, a three dimensional model of the orbit was created using serial sagital CT scans. The geographic contour of each relevant anatomic structure was then traced from CT images. Tracing was accomplished with use of Paracomp/MacroMind's Swivel 3D Professional'rm program. A three dimensional reconstruction of the orbital structures was achieved using sequential contour maps. After these objects were
705
constructed, the file was saved as a DXF 3D file format (an interchange file format, allowing the import and export of three dimensional files between different applications). The file was imported into the Virtus Walkthroughm program which allows for real-time movement through three dimensional models. Figure 4 demonstrates the software interface for three-dimensional tracking of the surgical probe. The Virtus program utilizes the position sensor x,y, and z coordinate input and renders a motion view of the movement of the surgical probe through the model. When the x,y,and z coordinates are within a given structure, the Virtus program sends a message via AppleEventsT (an intra-application operating system feature in Apple Computer's System 7.x operating system) to the SuperCard interface program and hence, lets the user know when a structure has been entered. The program has a database which contains information regarding the possible complications which may occur when any of these structures is entered, and this information is promptly presented to the learner.
tion of the orbital structures. We would like to thank Paul McGuire for his excellent technical support throughout the project.
Bibliography 1. Eisner, Georg. Ey Sur, Springer-Verlag, Berlin, 1990
2. Evans, T.J. Retrobulbar block: A Review for the Clinian. A A N A - Journal, 199 1; 59(2): 101 3. Peterson, W.C., Yanoff, M.. Why Retrobulbar Anesthesia? Trans. Am. Ophthalmology Society, 1990;88:136-40
4. DeDombaL F. A Computer Aided System for Learning ClinicalDiagnosis, Lancet ,1969; 1:145-148 5. Finchman, S., Grace, M., Taylor, W., Skakun, E. & Davis, F. Pediatric Candidates' Attitudes to Computerized Patient Management Probems in a Certifying Examination. J. Med. Educ. ,1976;10:404-407 6. Hoffer, E.P., Mathewson, H.O., Lougherey, A., Barnett, G.O. "Use of Computer Aided Instruction in Graduate Nursing Educaton: A Controlled Trial," Journal of E. Nursing, 1975; 1(2):27-29.
Discussion
ORIS is designed to permit hazard free, physically realistic, practice of an invasive procedure prior to patient contact. It is expected that ORIS will serve both to educate residents about the three dimensional anatomy of the orbit, and to help them perfect the procedure. Users must ultimately transfer skills from the simulation to the real situation. One would hope to find a decreased rate of complications as a result of the educational experience.
The more realistic the simulation, the more users feel that they are in the actual environment. Until recently cost has been an impediment to realism. One of the most significant features of ORIS is that it is constructed to provide the most realistic simulation possible using an off-the-shelf microcomputer, and state-of-the-art software that permits real-time three dimensional modeling from digital images. We believe the result is a cost effective, unique educational experience. A second, and perhaps even more important attribute, is that the simulation technique developed is readily extended to many other procedures such as thoracentesis, lumbar puncture, and needle biopsy of different organ systems. ORIS is currently in a prototype form. The prototype, will be tested to assess its efficacy in assisting residents to leam the procedure. Acknowledgenwnts The authors would like to acknowledge efforts which have greatly contributed to the success of the ORIS project. We would like to thank Karen Wolfall, M.D. and Jim Olson for their work on the three dimensional image reconstruc-
706
7. Denson, J.S., and Abrahamson, S., A Computer-controlled Patient Simulator, JAMA, 1969; 208: 504-508. 8. Rheingold, Howard. Vlrtual Reality Summit Books, New York, 1991
9. Hon, David. The Robotic Endoscopy Simulator, Project Description Manual- unpublished. 10. McHugh, Gladys. The Human Eye In Anatomical Transparencies. Baush & Lomb Press, New York, 1943
Trademark
Information:
Virtus WalkthroughTm is a registered trademark of Virtus Corporation SuperCardTm is a registered trademark of Aldus CorporationMacroMind Director.T is a registered trademark of MacroMind/Paracomp
Quadraltm, QuickTimeTm, HyperCard>m, AppleEventstm, Macintoshtm are registered
trademarks of Apple Computer Corporation GoldBrickTm is a registered trademark of Transfinite Systems Corporation DVITm is a registered trademark of Intel Corporation PowerGloveTm is a registered trademark of Mattel
Corporation
RxDxtm
is a registered trademark of Massachusetts General Hospital DiscoTestTm is a registered trademark of Scientific American NuVista.m is a registered trademark of TrueVision Inc ScanJet IIc- and HP DeskScantm software are registered trademarks of Hewlett Packard, Inc.
Retrobulbar injection is one of the most commonly utilized techniques in ophthalmic surgery. Although proven to be a relatively safe procedure, severe complications can occur with improper technique. The Ophthalmic Retrobulbar Injection Simulator (ORIS) offers ophthalmology residents an opportunity to learn and practice the technique of retrobulbar and peribulbar anesthesia prior to performing it on a patient. Introduction
Retrobulbar anesthesia serves two purposes in ophthalmic surgery. Not only is pain controlled by the injection of anesthetic agents, but ocular motility is paralyzed. Loss of voluntary motor ability insures against any ocular movement which may deform an open globe1. Retrobulbar injection blocks the ciliary ganglion and paralyzes the ocular muscles by diffusely infiltrating the posterior portion of the muscle cone. The orbital apex is vulnerable, however, because the optic nerve, and the central retinal artery and vein are so closely related that they will not yield to an advancing needle, and are susceptible to puncture. In addition to the risk of damaging nerve and vessel, other complications include globe rupture, apnea, respiratory arrest, retinopathy, grand mal seizure, transient retinal arty occlusion, and amaurosis2'3. These dangers can be reduced by using cannulas of an appropriate shape, length, and rigidity, and by using an appropriate guidance technique. ORIS was developed to aid in perfecting the guidance technique, permitting rehearsal of the procedure without hazard.
The preferred approach of retrobulbar injection is transcutaneous. The needle is inserted in the lower temporal quadrant, below the tarsus and above the orbital rim. Rotating the eye upward and nasally removes the inferior oblique muscle from the peribulbar tissue, which is then pierced more easily1. The cannula pierces, in order: lid, orbital septum, fascia, and fat. The technique involves a
0195-4210/92/$5.00 ©1993 AMIA, Inc.
relatively high superficial resistance. This may make it difficult to appreciate the lesser resistance offered by the deeper structures. Simulations and Virtual Reality
The concept of using tools to help teach medical procedures dates back thousands of years to the introduction in China of dolls which were used to instruct students about the structure of the body. Almost every available medium has been employed: physical models, cadavers, graphics, text, projected transparencies, motion pictures, and videotape are among familiar examples. More recently, the computer has come to be used as a leaming tool. Because the computer can manipulate information and change a presentation according to a combination of user input and stored information, it has been widely used to simulate clinical cases. Several studies have supported the credibility of these simulators which users report to accurately represent clinical encounters with patients.4'5'6 Popular applications include the RxDxTm series from the Massachusetts General Hospital and the Scientific American DiscoTestTm . As technology has become more sophisticated, clinical simulations have begun to use graphics, and sequences from videodiscs to illustrate different concepts and to add additional information or realism to a case.
Over the years computers have, on occasion, been used to simulate clinical procedures. One of the first of these, a simulation of cardiopulmonary resuscitation, was described by Abrahamson in the late 1960's 7. A mannequin was equipped with sensors that interfaced with a computer. There are few other good examples, however, because such simulators have often involved complex input devices and software. They have been technically difficult, and expensive. On the other hand, the recent development of cheaper input devices and faster machines has brought the
702
modelling of clinical procedures within reach. It is a domain termed, 'virtual reality.'
Goals of ORIS
Virtual reality represents a convergence of many different fields including human/machine interface design, event simulation, data visualization, and computer graphics. World War II era pilots remember the Link. The Link allowed pilots to sit in a mock-up airplane cockpit located on a moveable platform. Inside was the first flight simulator. The pilot climbed in, pushed the ignition button, grabbed the control stick, and felt the cockpit tilt and roll, even vibrate, in response to the pilot's actions8.
The goals of ORIS are three:
1. To improve the user's knowledge of the anatomic structures prior to performing the procedure.
2. To acquaint the user with the theory and technique of performing an invasive surgical procedure. 3. To improve the user's motor skills prior to performing the procedure.
Goal # 1. To improve the user's knowledge of the relevant anatomic structures prior to performing the procedure.
A pioneer in the introduction of virtual reality to medicine has been David Hon. Having perfected a CPR simulator, he went on to develop a gastrointestinal endoscopy simulator which used a custom built endoscope/position sensor device coupled to a 386 computer and laserdisc player. This system allows for the display of endoscopic pictures at 1/30th of a second to simulate the performance of the procedure7.
To educate the resident about the procedure, we used interactive software which displays images of the different structures present at different layers within the orbit. Each of these layers contains features which are important when conducting the procedure.
ORIS provides another example of a virtual environment simulator which allows the user to perform the retrobulbar injection procedure using real- time, computer-generated, three-dimensional graphics. Fast microcomputers such as Apple Computers Macintosh IIfx and Quadra series, as well as the Intel 80486 computer, equipped with digital video interactive (DVI) boards, make this possible. It is our purpose to discuss the goals of the simulator, the technical means by which the goals were achieved, and the issues surrounding the production of a simulator for teaching a particular invasive procedure.
To develop the software, we used the textbook, The Human Eye in Anatomical Transparencies1O. Sagital and coronal cross section images were scanned with a Hewlett Packard ScanJet IIcT 24 bit, 400 dpi flat bed color scanner using the HP DeskScanTm software which is supplied with the scanner. The images were then imported into an Aldus Corp. SuperCardT interface, and placed onto interactive cards which allow the user to select different anatomic planes. Each card permits the user to view the important structures with the use of a semitransparent pointer which appears on the structure along
proccourrm VI 1:.. 1:
V
Rnutomq. r. I simtootils --Y
IEWV P-OCEID'JRi
|degree
m
2215
d.qruu .,.
Figure 1. Oris incorporates Apple's QuickTime technology to allow the use of digital video sequences to instruct residents on the retrobulbar injection procedure. The student can control the video sequence using the controls found on the right side of the screen. 703
To help acquaint the user with the procedure, retrobulbar injection was filmed in the operating room and digitally converted for display on the computer monitor. Digital video sequences permit instantaneous access to any given frame in the movie, and allow for the inclusion of multiple sound trcks. Using Apple's QuickTnme® software, motion pictures with sound can be included within the educational program without the need for additional hardware. Seefigure I which depicts the computer screen layout for this portion of ORIS.
15
a
:
KqFrbSSt: UPS"_ Emw:2 FIiimto t _: d camel
E@
D OK_ _
_*@eB
Figure 2. The control panel from Apple Computers ConvertToMovie software which allows the developer to select different parameters in determining the compression of QuickTime movies. Compression method, desired depth of color, spatial and temporal resolution, and key and maximum
frame rates
are
all variables which determine
the amount of resulting compression. with textual information regarding the importance of the structure, and its relation to the procedure. Goal # 2. To acquaint the user with the theory and technique of performing an invasive surgical procedure. lft
megabyt sftwar
dC
To generate digital footage, the procedure was filmed at multiple angles using a super-VHS camcorder. The tape was then digitized using a TrueVision NuVistaT image capture board equipped with 12 megabytes of VMX video RAM, and a Macintosh Ucx computer with 8 megabytes of RAM. This pemits the digitization of 1.5 minutes of video. The images were stored as a PICS file format. This format consists of the series of still images (PICT) which are linked together to ultimately yield a motion sequence. The file was then edited on a Macintosh QuadraS computer with 20 megabytes of RAM using MacroMind Director 3.0 software, and resaved as a PICS file. Finally, the PICS file (6.5 megabytes) was converted to an Apple QuickTume® movie using the Convert To Movie"m software supplied by Apple Computer, and was compressed to a size of 4 megabytes using the animation compression routine provided with the Convert To Movie"m software (seefigure 2).
computer wish 8
of RAK
Runng ORIS interface (deWveed uing Aldus
rd), Trunfiie System'
rsi cknd
XCMDs,
QuickTmue X WaL-hough.
Trandiit Sysms' GoldBridc interface
ppe
M, and
Vi,tm_
device
_
Ultrsonic detecton forthmee dimen sial position sesing (modified from Matd PoweGlove"')
transmittr, ataced to needl ~~Position (modified frm Matel PNwerGleT9).
Figure 3. Schematic Diagram of the ORIS system demonstrating sensor,data acquistion device, model head, computer.
704
s*mmuhinnSflf
l
AN
o on
t JeIIm
Figure 4 . The interface for three-dimensional tracking of the surgical probe provides the user with real-time, threedimensional graphic display of the structures with which the surgical probe is in contact.
Sound was recorded using the built in microphone on the Macintosh Quadra, and incorporated into a resource file using Apple Computer's HyperCardI' Audio stack. After recording, files were digitally edited using the sound editing facilities of this program. After the audio tracks were completed, they were combined with the QuickTime movie using Apple® Computer's QuickTime development software.
Manipulation of the QuickTime file was accomplished using the QuickTime XCMDs (software written in C or Pascal which extends the capabilities of HyperCard or SuperCard), permitting the control of the digital sequences within an interface design using Aldus S uperCard. Goal # 3. To improve the user's skills prior to performing a procedure.
motor
This goal is the most difficult to accomplish. We had chosen the procedure of retrobulbar injection specifically because it permits a fairly straight forward technique for modeling a simulation.
First, we must consider the fact that the technique involves the use of a needle which is placed through structures of differing resistance. In order to track the position of the needle, we contemplated a variety of tools. A data glove was considered. It would track the position of the fingers, and transmit to the computer information about how the clinician was holding the instrument. This approach was thought to be unreasonable since the position of the instrument could change without any change in finger or hand position. The ideal placement of
the position sensor would have to reside on the instrument itself. After selection of the location of the position sensor, we needed to determine the best method of tracking the sensor. We considered systems which employed magnetic, ultrasonic, gyroscopic, infrared, and laser technologies. One of our goals in the ORIS project was to construct the most cost effective simulator possible without sacrificing educational benefits. To this end, we ultimately chose ultrasonic sensing from a modified Mattel PowerGlove'm which utilizes a sonar tracking system similar to that used in the Polaroid® Land camera. The output of the PowerGlove was connected to the Apple Desktop Bus (ADB) port of a Macintosh IIfx computer through an adaptor called the Gold Brick." (available from Transfinite Systems, Boston, MA). The GoldBrick provided conversion of the Nintendo formatted signals to Macintosh compatible ADB format. Transfinite Systems provided an operating system extension, allowing for software support for the three dimensional information. The GoldBrick software transmits x,y, and z coordinates of the sensor probe through the use of an XCMD imported into SuperCard (seefigure 3 for a schematic diagram). Due to the limitations of ultrasonic technology, accuracy of this tracking was limited to 1/4 of an inch.
Once the sensor had been constructed, a three dimensional model of the orbit was created using serial sagital CT scans. The geographic contour of each relevant anatomic structure was then traced from CT images. Tracing was accomplished with use of Paracomp/MacroMind's Swivel 3D Professional'rm program. A three dimensional reconstruction of the orbital structures was achieved using sequential contour maps. After these objects were
705
constructed, the file was saved as a DXF 3D file format (an interchange file format, allowing the import and export of three dimensional files between different applications). The file was imported into the Virtus Walkthroughm program which allows for real-time movement through three dimensional models. Figure 4 demonstrates the software interface for three-dimensional tracking of the surgical probe. The Virtus program utilizes the position sensor x,y, and z coordinate input and renders a motion view of the movement of the surgical probe through the model. When the x,y,and z coordinates are within a given structure, the Virtus program sends a message via AppleEventsT (an intra-application operating system feature in Apple Computer's System 7.x operating system) to the SuperCard interface program and hence, lets the user know when a structure has been entered. The program has a database which contains information regarding the possible complications which may occur when any of these structures is entered, and this information is promptly presented to the learner.
tion of the orbital structures. We would like to thank Paul McGuire for his excellent technical support throughout the project.
Bibliography 1. Eisner, Georg. Ey Sur, Springer-Verlag, Berlin, 1990
2. Evans, T.J. Retrobulbar block: A Review for the Clinian. A A N A - Journal, 199 1; 59(2): 101 3. Peterson, W.C., Yanoff, M.. Why Retrobulbar Anesthesia? Trans. Am. Ophthalmology Society, 1990;88:136-40
4. DeDombaL F. A Computer Aided System for Learning ClinicalDiagnosis, Lancet ,1969; 1:145-148 5. Finchman, S., Grace, M., Taylor, W., Skakun, E. & Davis, F. Pediatric Candidates' Attitudes to Computerized Patient Management Probems in a Certifying Examination. J. Med. Educ. ,1976;10:404-407 6. Hoffer, E.P., Mathewson, H.O., Lougherey, A., Barnett, G.O. "Use of Computer Aided Instruction in Graduate Nursing Educaton: A Controlled Trial," Journal of E. Nursing, 1975; 1(2):27-29.
Discussion
ORIS is designed to permit hazard free, physically realistic, practice of an invasive procedure prior to patient contact. It is expected that ORIS will serve both to educate residents about the three dimensional anatomy of the orbit, and to help them perfect the procedure. Users must ultimately transfer skills from the simulation to the real situation. One would hope to find a decreased rate of complications as a result of the educational experience.
The more realistic the simulation, the more users feel that they are in the actual environment. Until recently cost has been an impediment to realism. One of the most significant features of ORIS is that it is constructed to provide the most realistic simulation possible using an off-the-shelf microcomputer, and state-of-the-art software that permits real-time three dimensional modeling from digital images. We believe the result is a cost effective, unique educational experience. A second, and perhaps even more important attribute, is that the simulation technique developed is readily extended to many other procedures such as thoracentesis, lumbar puncture, and needle biopsy of different organ systems. ORIS is currently in a prototype form. The prototype, will be tested to assess its efficacy in assisting residents to leam the procedure. Acknowledgenwnts The authors would like to acknowledge efforts which have greatly contributed to the success of the ORIS project. We would like to thank Karen Wolfall, M.D. and Jim Olson for their work on the three dimensional image reconstruc-
706
7. Denson, J.S., and Abrahamson, S., A Computer-controlled Patient Simulator, JAMA, 1969; 208: 504-508. 8. Rheingold, Howard. Vlrtual Reality Summit Books, New York, 1991
9. Hon, David. The Robotic Endoscopy Simulator, Project Description Manual- unpublished. 10. McHugh, Gladys. The Human Eye In Anatomical Transparencies. Baush & Lomb Press, New York, 1943
Trademark
Information:
Virtus WalkthroughTm is a registered trademark of Virtus Corporation SuperCardTm is a registered trademark of Aldus CorporationMacroMind Director.T is a registered trademark of MacroMind/Paracomp
Quadraltm, QuickTimeTm, HyperCard>m, AppleEventstm, Macintoshtm are registered
trademarks of Apple Computer Corporation GoldBrickTm is a registered trademark of Transfinite Systems Corporation DVITm is a registered trademark of Intel Corporation PowerGloveTm is a registered trademark of Mattel
Corporation
RxDxtm
is a registered trademark of Massachusetts General Hospital DiscoTestTm is a registered trademark of Scientific American NuVista.m is a registered trademark of TrueVision Inc ScanJet IIc- and HP DeskScantm software are registered trademarks of Hewlett Packard, Inc.
