When fitting Scleral lenses, it is important to be able to measure the anterior chamber depth in order to select your initial diagnostic trial lens. This can be done a number of ways – most commonly by using either a slit-lamp, topographer or OCT.

Smith technique is one such method of anterior chamber estimation using the slit-lamp, biomicroscope and graticule. It was first published in 1979, and has since become an efficient and accurate test that can be used in everyday clinical practice.

We recommend watching this video for an introduction to the technique and keep the step-by-step instructions (below) on hand the first few times you perform the procedure.

For more information on initial lens selection using our Scleral 5ZRS diagnostic trial kits, please see the user guides located in the EyeSpace Knowledge Base.

Step-by-step guide

  1. Lock the illumination at 60 degrees on the temporal side. Keep the eye piece straight ahead.
  2. Rotate the illumination to give a horizontal, small, thin, bright beam.
  3. With the patient looking at the microscope, focus on the anterior surface of the lens. There should be two beams visible, one in focus at the anterior lens surface, and one out of focus on the temporal edge of the cornea.
  4. Slowly increase the slit lamp length, keeping the focus on the anterior surface of the lens
  5. Stop once the inside edges of both the focussed and unfocussed beams meet.
  6. Read off the illumination graticule the width of the beam.
  7. Multiply this number by 1.4. This is the Anterior Chamber Depth. eg. Graticule reads 3.5. This gives 3.5 x 1.4 = 4.9 mm or 4900 microns.