Obtaining 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)