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Show J. Clin. Neuro-ophthalmol. 4: 53-55, 1984. A Light-Emitting Diode Array Globe Protector Photostimulator* KENYON K. KRAMER, M.D., LTC, MC VINCENT A. PRZYBYLA, JR. FRANCIS G. LA PlANA, M.D., COL, MC Abstract Intraoperative visual-evoked potential recording has been a potentially useful procedure for monitoring the functional status of the visual pathways during certain neurosurgical procedures. Technical problems have limited its adoption. We report a light-emitting diode array globe protector photostimulator which enhances the stimulation component of the visual-evoked potential recording technique. Information about the function of the visual pathways during neurological manipulation is useful. The ability to continuously monitor optic nerve function during the performance of orbital surgery and neurosurgery near the anterior visual pathways might help permit the surgeon to avoid unnecessary damage to those structures. Feinsod et al.I reported using a scleral contact lens with a light-emitting diode embedded at the center to provide photostimulation for intraoperative visual- evoked potential stimulation. Goggles with a light-emitting diode array at the spectacle plane are commercially available (Nicolet Biomedical Instrumentation) and have been used with closed eyelids. In the first instance, however, questions ~ave been raised concerning the adequacy of the lIght reaching the retina if the lens should shift during surgery. In the second instance, the goggles themselves are objectionable as encroaching on the neurosurgical operative field. Enlarging upon the idea of the scleral contact lens, we have, ~herefore, developed a light-emitting diode array In a methylmethacrylate globe protector, which is inserted behind the eyelids. From the Ophthalmology Service (KKK, YAP, FGLP), Walter Reed Army Medical Center, Washington, D.C.; and the Division of Ophthalmology (KKK, FGLP), Uniformed Services University of the Health Sciences, Bethesda, Maryland. • The opinions or assertions contained herein are the private views of the authors and are not to be constroed as official or as reflecting the views of the Department of the Army or the Department of Defense. March 1984 Methods and Results Globe protectors 24 mm in diameter of polymethylmethacrylate made in the usual way by an ocularist (VAP) were modified by drilling 15 holes distributed evenly over the central 16 mm of the protector. Fifteen light-emitting diodes (HLMP6300, Hewlett Packard) were mounted in the holes with glue. The light-emitting diodes were parallel-wired and were connected to a fine flexible polyvinyl chloride insulated two conductor copper cables of 60 cm length (hearing aid leads). Methylmethacrylate was added to both surfaces by repeatedly applying liquid monomer-pOlymer mixture and allowing the assembly to dry until a suitable degree of smoothness on all surfaces was obtained (Fig. 1). The free ends of the cable from each of the two globe protectors were joined to a 4-conductor cable of 3-meter length, which terminated in a four-pin connector. The peak radiance of each diode was calculated to be 1.47 Watts/cm2 steradian for continuous peak power. Assuming a maximum frequency is used of 8 flashes/second and a pulse duration from the stimulator of no more than 5 mseconds, a peak radiance level of 0.06 Watts/cm2 steradian is obtained which is below the usual safety levels of 0.1 to 0.4 Watts/ cm2 steradian for continuous exposure to a large light source for periods of hours. This assembly was then used with a commercially available visual-evoked potential system (Nicolet Biomedical Instrumentation, CAI000) with which it is compatible. An awake subject (KK) had the globe protectors inserted after instillation of topical anesthesic drops. No dilating drops were used. During testing, blurred circles of red light were seen corresponding to the individual light-emitting diodes. Standard visual-evoked potential recording techniques for transient records (Fig. 2) were used to record the visual-evoked potential for approximately liz hour. After images were transient lasting less than 1 minute, and no effect on visual acuity was noted except that usually associated with topical anesthetic drops. Visual-evoked potential recordings were also made on an anesthetized cynomologous monkey. 53 Light-Emitting Diode Photostimulator Figure 1. Light-emitting diode array photostimulators and connector. 100 msec I 00 as Figure 2. Transient visual-evoked potential (right and left eye). Journal of Clinical Neuro-ophthalmology No adverse effects on the eye were noted after 3 hours of recording. We believe this device may be of use for intraoperative visual-evoked potential recordings in that the array light-emitting diodes should provide continued stimulation despite considerable random ocular movement. It is compatible with a commercially available evoked potential system. This device has been used clinically on two occasions. In the first instance, an internal carotid aneurysm near the ophthalmic artery was surgically treated with no reduction of baseline visual- evoked potential during the procedure. In the second case, a pituitary lesion was resected. Immediately after pressure on the visual pathway March 1984 Kramer, Przybyla, La Piana was reduced an increase in the visual-evoked potential was seen. Reference 1. Feinsod, M., Madey, J.M.J., and Susal, A.L.: A new photostimulator for continuous recording of the visual evoked potential. Electroenceph. C/in. Neurophy. 38: 641-642,1975. Write for reprints to: Kenyon K. Kramer, M.D., LTC, MC, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, Maryland 20814. 55 |
