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Atlas of colposcopy – principles and practice

Description of a colposcope

  

A colposcope is a binocular microscope to examine the cervix and other parts of the lower genital tract under magnified stereoscopic vision with good illumination. A standard colposcope has essentially three parts::
  • the head, which contains the optics
  • the light source
  • the body.
The head of the colposcope comprises:
  • two eyepieces, which may be adjusted to the colposcopist’s eye position and may be focused independently by turning the dioptre ring (the dioptre ring should be adjusted initially to align the “0” mark on it with the indicator if the vision of the operator is normal with or without glasses)
  • a green filter, which takes away the background redness, so that the blood vessels appear black in contrast with a green background and the fine vessel patterns may be more easily appreciated
  • a magnification changer, to change the magnification (may vary from 6× to 40×) in steps or in a smooth, continuous fashion (zooming)
  • a focus adjustment knob, which allows fine focusing on the object.
Note: The focal length of most colposcopes is 30 cm, which signifies that for best focusing and convenience of use, the lens at the front of the head should be at a distance of 30 cm from the object (the cervix).





The light source is fixed to the body and comprises:
  • lamps, which can be halogen bulbs or light-emitting diode (LED) lamps
  • a fibre-optic light cable, to carry light to the optics fitted to the colposcope head
  • an illumination adjustment knob, to change the intensity of light (and also to turn off the light)
  • a fan to cool the bulbs (if halogen bulbs are used).
Note: The colposcope should not be switched off from the main electricity supply immediately after use. The light should be turned off or dimmed when the procedure is over. This will allow the fan to cool the bulbs. The machine should be switched off after about 3–5 minutes, depending on the duration of use.




The body of the colposcope is either portable or non-portable. The portable type has a single vertical stand with height adjustment facilities, fixed to a base with wheels. The non-portable type has a weighted stand with an adjustable arm, which allows the colposcope head to be manoeuvred according to the operator’s comfort.




Many types of colposcopes have the option of having a camera attachment. The camera is attached to the optics using a beam splitter through a special port at the side of the colposcope head. This allows simultaneous visualization of the image focused through the colposcope on a television monitor or a computer screen.




A video colposcope is a variant of the colposcope that does not have a binocular lens system. Video colposcopes have a video camera with LED lamps at the front of the optics, mounted on a height-adjustable stand. A control panel at the back of the head is used for changing the magnification, turning the green filter on and off, and capturing the image. Video colposcopes can autofocus the image if kept at a distance of 25–30 cm from the object. A good-quality monitor (or LED television screen) is necessary to see and interpret the two-dimensional images. Video colposcopes have the advantage of recording and storing the still or video images for future reference.


























  
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