Autorefractor and Autolensometer


This page is part of the Ophthalmic Assistant Basic Training Course.
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  The autorefractor is an instrument that approximates the refractive error of the eye.  It measures the length of the eye and the shape of the cornea and then approximates what the glasses prescription should be.  Some instruments also provide corneal curvature readings (K readings).  The doctor or the technician uses this information as a starting place for refractometry, the process which results in a final glasses prescription.

  Most autorefractors are easy to operate. The patient is aligned in a headrest.  The operator views an image of the cornea on the screen.  There are reflections (mires) that must be focused on the cornea for proper alignment.  Once alignment is achieved, a button is pushed to capture the measurement.

  The autolensometer is an instrument that measures the prescription of a pair of glasses. Pictured here is a Zeiss - Humphrey autolensometer.  These instruments are very similar in operation from brand to brand, and it does not take long the learn the procedure.  The procedure for this instrument is outlined below, so that you can become familiar with the steps involved.
  The glasses are positioned against a stage (A), with the bottoms of the eyewires touching the stage at all times (this insures that the axis reading is correct).  The bridge of the glasses is places against the nose rest (B).  The lens is aligned with reading port of the instrument (C).  The blue button is pushed when taking / storing a reading (D).
  The instrument has a setting for reading single vision and lined bifocals and trifocals.  The lens must be moved against the stage in a manner that brings the cross in alignment with the cross hair of the screen.
  Once alignment is achieved, the cross becomes fatter to let you know that the lens is in proper alignment to read.  At this point you will push the blue button to store the reading.  If there is a bifocal, the lens is positioned so that the bifocal is over the reading port.  The blue button is pushed again and the instrument computes the reading add of the glasses.  The glasses are then re-positioned to read the other lens.  Most autolensometers can automatically sense which lens is being read.
  If the lens being read is a progressive add lens (PAL), the instrument must be set up for this (software selection).  Once the lens is initially positioned, the instrument will give you instructions on the screen about how to achieve alignment.  The instructions in this example are guiding you to move toward the top of the lens.
  The screen gives you feedback when alignment is achieved.  You will then press the button to store the reading.
  After storing the distance reading, the screen will give you guidance about proper alignment for reading the add section of the lens.  The instructions pictured tells you to move the reading port toward the bottom of the lens.
  Once proper alignment is achieved in the reading portion of the lens, the screen tells you to store the reading.
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