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  Familiarity with the controls is critical to performing a slit lamp examination.

  
  
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  When positioning the patient for the exam, make sure that their forehead is touching the forehead brace and encourage them to keep it there.

  
  
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  When using a slit lamp to remove a corneal foreign body, first guide the removal device (eg, 25-gauge needle) to the eye under direct vision, then switch to the magnified view.

  
  
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  To prevent puncturing the cornea, keep the removal device tangential to the globe at all times.

The slit lamp is used to evaluate the anterior eye including the lids, lashes, conjunctiva, cornea, visible sclera, anterior chamber, iris, and lens for signs of trauma, hemorrhage, inflammation, or foreign bodies.

The patient must be cooperative and capable of sitting upright for the duration of the examination.

In addition to a slit lamp, the examiner will need 2 chairs or stools, preferably of about equal height. Fluorescein allows visualization of corneal injury. Other supplies may include anesthetic drops and a needle or ophthalmic burr (for foreign body removal), cotton-tipped applicators (for lid eversion), and saline (to flush the eyes or lids).

Ideally, one should be familiar with use of the slit lamp before examining a patient. The slit lamp is a microscope in which focus is achieved by moving the lenses instead of the object being examined. The power of the microscope typically ranges from 10–25× (or higher) and is adjusted by a dial on the housing just in front of the eyepieces. The plane of focus is changed by using the joystick to move the microscope toward or away from the patient. The joystick also moves the microscope left or right. Twisting the joystick raises or lowers the microscope. If the microscope does not move when the joystick is moved, you may need to loosen the locking screw on the microscope base.

The light source is mounted on a swing arm that allows it to move independently from the microscope. Knowing how to adjust the multiple controls of the light source is critical to performing an exam. The power switch activates the lamp. Many slit lamps also have a rheostat (dimmer), usually near the power switch or on the base of the microscope. A selector switch near the base of the bulb housing allows the examiner to change from white to cobalt blue light (other options, including green, are usually available). Just below this is a dial to adjust the height of the light beam. Near the base of the microscope arm is another dial to adjust the width of the slit. The location of these controls may vary from lamp to lamp. Figure 74-1 demonstrates their position on one model.