- Email: [email protected]
Phototoxicity
Phototoxicity The Eclipse Filter DAVID J. McINTYRE, MD, FACS
Abstract: In conjunction with ultraviolet filtration and to further minimize the risk of phototoxic retinal damage during anterior segment surgery, the operation microscope has been modified to eliminate on demand all light entering the eye by eclipsing the pupil when the red reflex is not required . Retinal light exposure may be reduced as much as 75%. [Key words: eclipse filter, microscope, phototoxicity.] Ophthalmology 92:364-365, 1985
Concurrent with the development of more sophisticated and prolonged diagnostic and surgical procedures utilizing more intense illumination to enhance observation and recording, researchers have explored the question of retinal phototoxicity. It has now been clearly established that permanent retinal damage can result from our sophisticated instruments and procedures. I We are particularly concerned that our patients be protected from potential damage during microsurgical procedures on the anterior segment. 2
POTENTIALLY USEFUL PROTECTIVE MEASURES FILTRATION
Retinal susceptibility to phototoxic effects is greatest at the blue-violet end of the spectrum. 3 Consequently, filtration to cut off below 400 to 450 nm may be added to the microscope illumination system. (Note: the ultraviolet absorption characteristics of glass cause glass fiber bundles to provide very effective ultraviolet absorption automatically, perhaps making further filtration unnecessary on fiberoptic equipped microscopes.) OBLIQUE ILLUMINATION
Oblique rather than coaxial illumination will place the intense image of the illuminating beam in the far periphery of the retina, thus protecting the posterior pole. However, the commonly available oblique illumination attachments are somewhat inconvenient, cause vignetting of photo/video images and increase the "length" of the microscope body. From the Mcintyre Eye Clinic, Bellevue, Washington. Presented at the Eighty·eighth Annual Meeting of the American Academy of Ophthalmology, Chicago, Illinois, October 3D-November 3, 1983. Reprint requests to David J. Mcintyre, MD, Mcintyre Eye Clinic, 1920 116th Avenue, NE, Bellevue, WA 98004.
364
DEFOCUSING
Defocusing the illumination beam on the retina by insertion of an air bubble in the anterior chamber will increase the size and thus decrease the intensity of the illumination beam as it falls on the retina. However, the amount of defocusing varies greatly with the size of the bubble and no data currently exists to help us predict the usefulness of this technique. CORNEAL COVERS
Obstructing light transmission on the corneal surface is one immediately obvious protective measure. The obstruction can be provided by materials ranging from a patch of Gel-Foam® to an opaque soft contact lens. The surgeon may be inconvenienced if such a patch is in place during surgery, and we must note that one case of retinal phototoxicity has thus far been reported in a patient who was stated to have Gel-Foam® over the cornea during his operation. 4 THE ECLIPSE
We have devised a fifth approach to minimize retinal exposure to the microscope light beam. A movable opaque disk has been placed in the appropriate plane of the illumination system of the microscope to project a sharply focused black spot of 11 mm diameter. In the Zeiss Op Mi-6 (Carl Zeiss, Inc., Thornwood, NY) (Fig 1) with ordinary incandescent illumination, the intensity of light in the umbra of the eclipse is 26-foot candles, while the intensity in the surrounding annular light beam is 2000-foot candles. Consequently, when the pupil is eclipsed by its position within the dark area, the retinal light exposure is decreased to near zero. USE OF THE ECLIPSE FILTER
Following routine prep and drape and precise positioning of the patient for surgery, the surgeon brings the microscope into position and makes his final visual examination.
MciNTYRE •
ILLUMINATOR HOUSING
MICROSCOPE BODY
t I
~
THE ECLIPSE FILTER
ECLIPSE FILTER
~~~~
Fig 2. Eclipse is moved in and out of position by a small lever on the side of the illumination system of the modified Zeiss microscope.
UMBRA OF ECLIPSE
Fig 1. Diagram of the OpMi VI with eclipse filter shows the position of the eclipse filter producing a black spot in the microscope beam.
The eclipse filter is then brought down from "above" into the microscope field until it's "lower" edge is at the center of the field as seen by the surgeon (Fig 2). Using the X/Y control, the surgeon then "raises" the pupil into the eclipse when the red reflex is not needed or "lowers" it into the illuminated area when the reflex is required (Fig 3). FUNCTIONAL EFFECT OF THE ECLIPSE FILTER
The eclipse filter is a convenient, simple modification of the operation microscope. It is used without interference with the surgical field, sutures or assistant. Use as described places the superior limbus in the center of the microscopic field when the pupil is eclipsed, the optimum position for making and closing the usual anterior segment incision. In our practice, with an average overall operating time of 27 to 28 minutes for extracapsular cataract extraction with lens implantation, the red reflex is required for only 6 to 7 minutes. With the eclipse filter, we are able to avoid some 21 minutes of unnecessary retinal exposure to the intense and potentially harmful illumination beam of the operation microscope.
REFERENCES 1. Mainster MA, Ham WT Jr, Delori FC. Potential retinal hazards; instrument and environmental light sources. Ophthalmology 1983;
90:927-32.
Fig 3. Eclipse filter just above center in the surgeon's view of the microscope field. Pupil is then moved in and out of the eclipse area (see Figure 2) with the X/V control.
2. McDonald HR, INine AR. Light-induced maculopathy from the operating microscope in the extracapsular cataract extraction and intraocular lens implantation. Ophthalmology 1983; 90:945-51. 3. Ham WT Jr, Mueller HA, Ruffolo JJ Jr, Guerry D III. The nature of retinal radiation damage: dependence on wavelength, power level and exposure time. Vision Res 1980; 20: 11 05-11. 4. Soldrey EE, Ho ST. Poster presentation. American Academy of Ophthalmology, 1983.
365
Abstract: In conjunction with ultraviolet filtration and to further minimize the risk of phototoxic retinal damage during anterior segment surgery, the operation microscope has been modified to eliminate on demand all light entering the eye by eclipsing the pupil when the red reflex is not required . Retinal light exposure may be reduced as much as 75%. [Key words: eclipse filter, microscope, phototoxicity.] Ophthalmology 92:364-365, 1985
Concurrent with the development of more sophisticated and prolonged diagnostic and surgical procedures utilizing more intense illumination to enhance observation and recording, researchers have explored the question of retinal phototoxicity. It has now been clearly established that permanent retinal damage can result from our sophisticated instruments and procedures. I We are particularly concerned that our patients be protected from potential damage during microsurgical procedures on the anterior segment. 2
POTENTIALLY USEFUL PROTECTIVE MEASURES FILTRATION
Retinal susceptibility to phototoxic effects is greatest at the blue-violet end of the spectrum. 3 Consequently, filtration to cut off below 400 to 450 nm may be added to the microscope illumination system. (Note: the ultraviolet absorption characteristics of glass cause glass fiber bundles to provide very effective ultraviolet absorption automatically, perhaps making further filtration unnecessary on fiberoptic equipped microscopes.) OBLIQUE ILLUMINATION
Oblique rather than coaxial illumination will place the intense image of the illuminating beam in the far periphery of the retina, thus protecting the posterior pole. However, the commonly available oblique illumination attachments are somewhat inconvenient, cause vignetting of photo/video images and increase the "length" of the microscope body. From the Mcintyre Eye Clinic, Bellevue, Washington. Presented at the Eighty·eighth Annual Meeting of the American Academy of Ophthalmology, Chicago, Illinois, October 3D-November 3, 1983. Reprint requests to David J. Mcintyre, MD, Mcintyre Eye Clinic, 1920 116th Avenue, NE, Bellevue, WA 98004.
364
DEFOCUSING
Defocusing the illumination beam on the retina by insertion of an air bubble in the anterior chamber will increase the size and thus decrease the intensity of the illumination beam as it falls on the retina. However, the amount of defocusing varies greatly with the size of the bubble and no data currently exists to help us predict the usefulness of this technique. CORNEAL COVERS
Obstructing light transmission on the corneal surface is one immediately obvious protective measure. The obstruction can be provided by materials ranging from a patch of Gel-Foam® to an opaque soft contact lens. The surgeon may be inconvenienced if such a patch is in place during surgery, and we must note that one case of retinal phototoxicity has thus far been reported in a patient who was stated to have Gel-Foam® over the cornea during his operation. 4 THE ECLIPSE
We have devised a fifth approach to minimize retinal exposure to the microscope light beam. A movable opaque disk has been placed in the appropriate plane of the illumination system of the microscope to project a sharply focused black spot of 11 mm diameter. In the Zeiss Op Mi-6 (Carl Zeiss, Inc., Thornwood, NY) (Fig 1) with ordinary incandescent illumination, the intensity of light in the umbra of the eclipse is 26-foot candles, while the intensity in the surrounding annular light beam is 2000-foot candles. Consequently, when the pupil is eclipsed by its position within the dark area, the retinal light exposure is decreased to near zero. USE OF THE ECLIPSE FILTER
Following routine prep and drape and precise positioning of the patient for surgery, the surgeon brings the microscope into position and makes his final visual examination.
MciNTYRE •
ILLUMINATOR HOUSING
MICROSCOPE BODY
t I
~
THE ECLIPSE FILTER
ECLIPSE FILTER
~~~~
Fig 2. Eclipse is moved in and out of position by a small lever on the side of the illumination system of the modified Zeiss microscope.
UMBRA OF ECLIPSE
Fig 1. Diagram of the OpMi VI with eclipse filter shows the position of the eclipse filter producing a black spot in the microscope beam.
The eclipse filter is then brought down from "above" into the microscope field until it's "lower" edge is at the center of the field as seen by the surgeon (Fig 2). Using the X/Y control, the surgeon then "raises" the pupil into the eclipse when the red reflex is not needed or "lowers" it into the illuminated area when the reflex is required (Fig 3). FUNCTIONAL EFFECT OF THE ECLIPSE FILTER
The eclipse filter is a convenient, simple modification of the operation microscope. It is used without interference with the surgical field, sutures or assistant. Use as described places the superior limbus in the center of the microscopic field when the pupil is eclipsed, the optimum position for making and closing the usual anterior segment incision. In our practice, with an average overall operating time of 27 to 28 minutes for extracapsular cataract extraction with lens implantation, the red reflex is required for only 6 to 7 minutes. With the eclipse filter, we are able to avoid some 21 minutes of unnecessary retinal exposure to the intense and potentially harmful illumination beam of the operation microscope.
REFERENCES 1. Mainster MA, Ham WT Jr, Delori FC. Potential retinal hazards; instrument and environmental light sources. Ophthalmology 1983;
90:927-32.
Fig 3. Eclipse filter just above center in the surgeon's view of the microscope field. Pupil is then moved in and out of the eclipse area (see Figure 2) with the X/V control.
2. McDonald HR, INine AR. Light-induced maculopathy from the operating microscope in the extracapsular cataract extraction and intraocular lens implantation. Ophthalmology 1983; 90:945-51. 3. Ham WT Jr, Mueller HA, Ruffolo JJ Jr, Guerry D III. The nature of retinal radiation damage: dependence on wavelength, power level and exposure time. Vision Res 1980; 20: 11 05-11. 4. Soldrey EE, Ho ST. Poster presentation. American Academy of Ophthalmology, 1983.
365