VOL. 88, NO. 5 NOTES, CASES, INSTRUMENTS 941

provides the necessary control signal and the proper power to operate the automatic diaphragm within its full range. Once the sensitivity of the system is set, it responds reliably to changes in illumination and adjusts itself even during changes in mag­nification.

Proper calibration of the circuit added to the television camera (Figs. 2 and 3) is obtained by tuning a potentiometer that is within the camera body, while observing the television monitor screen for an ade­quately exposed picture. Maximum illu­mination of a bright object using the lowest magnification should be used at the time of calibration. The system is tested by increasing the magnification and reducing light intensity. This should open the diaphragm. Because the auto­mated diaphragm itself was not modified, it can also be used with the Beaulieu 16-mm movie camera as originally in­tended.

We are presently using a Hitachi HB-9017U television camera. The circuit needed for this camera is shown in Fig­ure 2. Similar good results were obtained earlier with the Magnavox 400 and 500 cameras, although a slightly different electronic circuit was used. Any black and white or color television camera can be modified to fit the automatic dia­phragm (Fig. 3).

SUMMARY

We developed an automated diaphragm control to achieve constant good exposure during televised microsurgery by using a commercially available diaphragm con­trol for a movie camera and modifying slightly the television camera.

R E F E R E N C E

1. Machemer, R., and Parel, J.-M.: An improved mierosurgieal ceiling-mounted unit and an automat­ed television. Am. J. Ophthalmol. 85:205, 1978.

RADIAL BUCKLING OF POSTERIOR RETINAL TEARS

J O H N D. S C O T T , F. R. C. S. Cambridge, England

AND W A L T E R H. STERN, M.D.

San Francisco, California

Posterior retinal holes are associated with myopia, branch vein occlusion, and proliferative diabetic retinopathy.1,2

Since the advent of vitrectomy and tech­niques for dissection of epiretinal mem­branes, iatrogenic posterior retinal holes have become increasingly important.3,4 In iatrogenic breaks associated with dissec­tion of epiretinal membranes, it is possi­ble to repair the posterior breaks by using an internal tamponade of sulfur hexa-fluoride gas-air mixture combined with either cryotherapy, diathermy, or photo-coagulation. However, in certain cases where tangential retinal traction persists as the result of epiretinal membrane for­mation, and cannot be adequately re­lieved, it is necessary to provide a posteri­or scleral buckle in combination with internal gas tamponade to seal these breaks effectively. We have devised a method for safely and easily placing the mattress sutures to secure a posterior radi­al buckle.

The placement of a posterior radial buckle is often hampered because of dif­ficulty in visualizing the needle as well as maintaining the correct depth of the nee­dle in the sclera. Tying the sutures poste­riorly can be facilitated by passing the needle in the anteroposterior direction opposite the curvature of the globe when the needle is posterior to the equator.

From the Department of Ophthalmology, Adden-brooke's Hospital, Cambridge University, Cam­bridge, England, (Mr. Scott); and the Department of Ophthalmology, University of California, San Fran­cisco, and the Veterans Administration Medical Center, San Francisco (Dr. Stern).

Reprint requests to Walter H. Stern, M.D., 400 Parnassus Ave., San Francisco, CA 94143.

942 AMERICAN JOURNAL OF OPHTHALMOLOGY NOVEMBER, 1979

Tying the posterior ends of the sutures anteriorly avoids the problem of tying sutures posteriorly. This procedure is made easier in vitrectomized eyes with a pars plana infusion line in which intraoc­ular pressure can be decreased to achieve greater visualization of the posterior scle-ra.

A single arm 4-0 or 5-0 Dacron suture on a spatula needle is used. Two scleral bites are made in the anteroposterior di­rection (Figure). Since the mattress suture is being placed posterior to the equator, the curve of the needle is opposite the curve of the globe, thus reducing the chances of the needle penetrating the globe. After the second scleral bite, the needle is removed, and the two posterior ends of the suture are brought forward and tied together. An appropriately sized Lincoff silicone sponge is now slipped beneath the posterior loop of the mattress suture and the anterior ends of the suture are tied snugly over the top of the silicone sponge.

Figure (Scott and Stern). A single arm suture is passed in the anteroposterior direction (a,b). After the second scleral bite, the needle is removed (c), and the posterior ends of the suture are brought anteriorly and tied together (d). A silicone sponge is slipped beneath the posterior loop of the mattress suture, and the anterior ends of the suture tied snugly over the top of the silicone sponge (e,f).

SUMMARY

We devised a method for safely placing mattress sutures for radial scleral buck­ling of posterior retinal holes. The ability to pass the needle in the anteroposterior direction, as well as the ability to tie the posterior ends of the mattress suture an­teriorly where they are easily accessible, makes this method of placing the mattress suture safe and effective for posterior ra­dial buckles.

REFERENCES 1. Joondeph, H. C , and Goldberg, M. F.: Rheg-

matogenous retinal detachment after tributary reti­nal vein occlusion. Am. J. Ophthalmol. 80:253, 1975.

2. McMeel, J. W.: Discussion of treatment and techniques of photocoagulation. In Goldberg, M. F., and Fine, S. L. (eds.): Symposium on the Treatment of Diabetic Retinopathy, bulletin 1890. Public Health Service, 1969, pp. 623-653.

3. Machemer, R.: A new concept for vitreous surgery. 2. Surgical techniques and complications. Am. J. Ophthalmol. 74:1022, 1972.

4. Machemer, R., and Laqua, H.: A logical ap­proach to the treatment of massive periretinal prolif­eration. Trans. Am. Acad. Ophthalmol. Otolaryngol. 85:584, 1978.

5. Michels, R. G.: Vitrectomy for the complica­tions of diabetic retinopathy. Arch. Ophthalmol. 96:237, 1978.

A NEW TYPE OF CORNEAL ELECTRODE

FOR ELECTRORETINOGRAPHY

P. G I L B E R T N I E L S E N , M.D.

Odense, Denmark

The contact lens-type of corneal elec­trodes most commonly used for electrore-tinograms can be cumbersome in clinical applications, and they often cause the patient discomfort. To reduce these dis­advantages I designed a new type of cor-

From the Department of Ophthalmology, Univer­sity Hospital, DK-5000 Odense C, Denmark.

Reprint requests to P. Gilbert Nielsen, M.D., Department of Ophthalmology, University Hospi­tal, DK-5000 Odense C, Denmark.