Video otoscopy substitutes a miniature color video camera for the eye at the focal point of the rod (VOE) or macro- (VOM) lens. The television signal produced by the VO camera contains a luminance component (Y) with luminous intensity information, perceived as brightness, and a chrominance (C) component that transmits the two color parameters, hue and saturation, perceived as color and purity, respectively. Two different video signal formats are used in VO, composite and S-Video component. In the composite format, the luminance (Y) and chrominance (C) components are combined and transmitted in a single channel. The S-video component format separates and transmits (Y) and (C) on separate channels. Given equivalent VO optics, an S-VIDEO component system has a wider bandwidth which produces a higher horizontal resolution of vertical lines and superior color definition to that obtained with a composite video system.The camera amplifier / power supply typically contains variable controls for automatic, semi-automatic and manual white balance, automatic (light sensitivity) gain control and electronic shutter speed.
Both composite and S-Video component formats in the United States, Canada, Mexico and Japan conform to the NTSC (National Television System Committee) standard for TV signal generation used in the U.S. TV broadcasting industry. This standard specifies a screen image or frame consisting of 525 horizontal (raster) scan lines refreshed at ~60 image halves per second, ~1/30 second each for the odd and even scan lines. Of the 525 lines, 440 are active in the viewed image. VO systems used in other countries are manufactured to conform to the indigenous TV industry standards, typically PAL (Great Britain, Germany, Austria, Italy and Scandinavia) and SECAM (France, Soviet Countries).
The heart of the video camera is a tiny CCD (charge-coupled device) chip which converts optical images to video signals. More than 400,000 light sensitive picture elements or pixels are integrated on a 6.5 X 5 mm surface. Complementary color filters are placed on top of each pixel so that a color analysis of the subject can be made and the fundamental additive color signals of red, blue and green (RGB) can be interpreted by the color demodulation circuit.
For medical / surgical-grade applications, a 3CCD or 3 chip camera uses three separate CCD chips, one each for R, G and B, to produce a superior color resolution and output. A fourth camera output, S(ynch) synchronizes the signals. The figure below shows a JEDMED 3CCD color camera with high resolution optical video oto-endoscope and camera amplifier. The higher quality - and significantly more costly - electronic image processing provides a superior depth of field. The VOE includes surgical-grade optics with both zoom and focus controls on the C-mount adapter.
Single chip, DIGITAL video cameras with "firewire" connection have arrived in commercial markets with the promise of yet higher resolution. This technology has not yet been made available for clinical VO applications.
Roy F. Sullivan, Ph.D.