NOTES, CASES AND INSTRUMENTS

AUTOMATIC DIAPHRAGM CONTROL FOR TELEVISION

CAMERA USED IN MICROSURGERY

J E A N - M A R I E P A R E L , ING., ETS-G Miami, Florida

ROBERT M A C H E M E R , M.D.

Durham, North Carolina AND

RONALD LASHLEY, B.S., AND ISURU N O S E , B.S.

Miami, Florida

In ophthalmology where operations are frequently done with the aid of a micro­scope, the surgical procedures are tele­vised via a television camera.1 In many instances this television system is con­nected to a videorecorder for teaching purposes.

We chose a high quality television cam­era (Hitachi) that is coupled directly to the operating microscope via a 30/70 beam splitter and a 74- or 107-mm elbow-shaped Zeiss diaphragm. We found that the light intensity reaching the television tube varied enormously during surgery and the diaphragm had to be manually adjusted repeatedly. The television cam­era's own automatic light level control was almost always saturated, rendering the television pictures and video tapes over- or underexposed and thus useless.

From the Bascom Palmer Eye Institute, Universi­ty of Miami School of Medicine, Miami, Florida (Messrs. Parel, Lashley, and Nose), and Duke Uni­versity Eye Center (Dr. Machemer), Durham, North Carolina. This study was supported in part by Public Health Service Research Grant No. EY-00841 and Research to Prevent Blindness Inc., New York (Dr. Machemer).

Reprint requests to Robert Machemer, M.D., Duke University Eye Center, P.O. Box 3802, Durham, NC 27710.

To solve this problem we modified the television camera to accept an automatic diaphragm control. The commercially available Zeiss automatic diaphragm con­trol, originally designed for use with a 16-mm Beaulieu movie camera, was used. The modified television camera (Fig. 1)

Fig. 1 (Parel and associates). Modified color tele­vision camera is connected to and thus controls the Zeiss automatic diaphragm.

939

940 AMERICAN JOURNAL OF OPHTHALMOLOGY NOVEMBER, 1979

Fig. 2 (Parel and associates). Electronic schema of circuits needed for the Hitachi HV-9017U television camera to permit diaphragm control. C,= 1 u.F, D = diodes -1N4001, C,= 10 (J.F, P = 10 turns 50 K ohms trimpotentionieter, R = 68 K ohms, R,= 1 K ohm; S = Amphenol four-pin socket mounted onto camera bodv.

R, C ,

VIDEO [ j -D - f t "OH

a OS < O

u

< at ui X <

- Vdc

GROUN

+ Vdc

ffi

"ffi

I

1

LM320/-5

NEG REG

LM340/+5

POS REG

^ C 6

Fig. 3 (Parel and associates). Electronic schema for any other television cameras (black and white or color). All component values are as explained in Figure 2, but P= 10 turns 100 Kohms, C:iA= 1000 JJLF/25V, C.-,.,J= 1 H.F/25V. These differences are caused by the difference in power voltages available. These voltages have to be reduced to a level acceptable to the automatic diaphragm.

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.