Refraction Flashcards
Refraction in low vision
- importance of refraction
- retinoscopy
- autorefraction
- trial frame use
- subjective trial frame refraction
- practical tips
Importance of refraction in low vision
Wilmer eye institute study
- 100 consecutive low vision patients
- amount of dioptric change
- 1 D change-23%
- 2D change-10%
- 3D-6%
Amount of VA improvement
- 1/2 line-30%
- 1 line-20%
- 2 lines- 10%
- 3 lines- 5%
Speaks to the role of optometry in low vision care
Retinoscopy without phoroptor in low vision
- do outside phgotoper bc may have EF
- ret bars over glasses, but must use conversions and janelli clips
- ok for presbypes, a-hakes, and pseudo-hakes to look directly at ret
- may need to reduce working distance (radical ret)
- try to sure a method which does not require writing down optical cross-pretend your retinoscopy bar is a phoroptor
- go as far down the ret bar as you can to make sure they dont just have a huge refractive error
Of neutrality found without lenses (using dynamic retinopscopy), that working distance represents the patients ____ near point
Myopic
Not further working distance taken out
Autorefraction and low vis9ojn
Not used often
Can be really far off
Used in circumstances where trial frame cannot be performed or is unreliable
Why not phoroptor in low vision
- phoroptor dont accommodate eccentric viewing well
- doesnt account for posture, true axis?
- hard to make big lens changes smoothly
- built in JCC usually lower powered than required
Trial frame and trial lenses for low vision refraction
- hold lenses by the handles, watch for fingerprints, smudges
- spheres only in back cell unless two are needed
- place handle of cylindrical lens against tab on rotating front cell of trial frame
- never use two spheres when one will do
Ex. Distance sphere=+1.75, add=+2.50, place +4.25 in back well
Trial frame adjustment
- Extend temples to max length
- Place frame on patient
- Shorten temples
- Adjust around all three axes plus vertex distance and height. Lowering height when testing add at near
- Hold frame securely when inserting plus vertex or removing lenses to improve comfort for the patient
Subjective refraction with trial frame
Target selection
- sphere-about 2 lines above threshold to start, use 1 line above threshold for final sphere
- cylinder-round optotype (ex, O, C) about 2 lines above threshold
Encourage habitual use of eccentric viewing
Initial sphere for trial frame
Initial sphere is a quick, approximate check to ensure sphere is close enough to do JCC
-show big changes as patient fixates two lines above threshjold
-JND-snellen denominator/100
—typically this is based on entering distance VA
—this is approximate (and perhaps a little overestimation)
—if the patient isn’t responding to your JND, increase it
Flippers for initial sphere
- use of flippers can be very helpful. Best not to flip, but to just move to comparison lens without flipping
- pay attention to qualitative aspect of repsosne
- select phrasing to match patients cognitive abiltiy
- “better with or without the lens”
- “does the lens make it clearer or blurrier”
- consider “better with first lense or second lens?”
Cylinder in the trial frame
- use +/- 0.50 JCC up to about 20/80 or 20/100 and +/-1.200 for VA worse than 20/100. May change as you go, increase JCC power if repsosnes not consistent
- make larger changes in power and axis
- may use two handed technique for JCC. 1 hand holds close to lens, 1 hand twists handle
- probe for cylinder with a cylinder power about=JCC used
- check initial power (quick, appx), then axis, then final power
What does it mean when the patient says “the same” when doing cyl
The cyl power/axis is correct, OR
The patient isn’t sensitive to the lens you are using
When the patient reports that both JCC options are the same,
Chang the power/axis
- if the patient brings you back toward original power/axis, then your original power/axis was appropriate
- if the Patient says “the same” again, then you need to increased the power of your JCC
- it is best to bracket the axis
Final sphere trial frame
- typically, we use slightly smaller optotypes than initial sphere as the target
- recommend bracketing, especially with presbyopes. Remember, young patients may not notice much of a difference with jumps in minus. Reduce bias compared with single lens
- what is our end point for normally sight? What is out end point for visually impaired?
- confirming what the Rx is proving what the Rx is not
