November 26, 2013 | POSTED BY | Clinical Pearls
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Trial LensesObtaining a good and accurate refraction in a low vision patient is extremely important because this is the starting point for prescribing many devices.  Every practitioner’s refraction techniques vary, but typically involve utilizing a trial frame and loose lenses (yes, you need to brush up on free space/no phoropter refraction).

Here’s a tip on how to bracket & start your refraction- use Just Noticeable Difference (JND):

  • JND is the reciprocal of visual acuity (VA)
  • Use JND of best tentative VA
    • Example: VA of 20/200, JND = 2.00 -> use +/-1.00 flipper
    • Example: VA of 20/50, JND = 0.50 -> use +/-0.25 flipper
    • Example: VA of 20/125, JND = 1.25 -> use+/-0.75 flipper (instead of +/-0.50 because patient may NOT notice the 1.00 difference)

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