Refraction

Question 1

Refraction in low vision

Answer 1

• importance of refraction
• retinoscopy
• autorefraction
• trial frame use
• subjective trial frame refraction
• practical tips

Question 2

Importance of refraction in low vision

Answer 2

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

Question 3

Retinoscopy without phoroptor in low vision

Answer 3

• 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

Question 4

Of neutrality found without lenses (using dynamic retinopscopy), that working distance represents the patients ____ near point

Answer 4

Myopic

Not further working distance taken out

Question 5

Autorefraction and low vis9ojn

Answer 5

Not used often
Can be really far off

Used in circumstances where trial frame cannot be performed or is unreliable

Question 6

Why not phoroptor in low vision

Answer 6

• 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

Question 7

Trial frame and trial lenses for low vision refraction

Answer 7

• 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

Question 8

Trial frame adjustment

Answer 8

1. Extend temples to max length
2. Place frame on patient
3. Shorten temples
4. Adjust around all three axes plus vertex distance and height. Lowering height when testing add at near
5. Hold frame securely when inserting plus vertex or removing lenses to improve comfort for the patient

Question 9

Subjective refraction with trial frame

Answer 9

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

Question 10

Initial sphere for trial frame

Answer 10

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

Question 11

Flippers for initial sphere

Answer 11

• 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?”

Question 12

Cylinder in the trial frame

Answer 12

• 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

Question 13

What does it mean when the patient says “the same” when doing cyl

Answer 13

The cyl power/axis is correct, OR

The patient isn’t sensitive to the lens you are using

Question 14

When the patient reports that both JCC options are the same,

Answer 14

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

Question 15

Final sphere trial frame

Answer 15

• 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

Question 16

Practical tips for trial fram refraction

Answer 16

• can get within 0.25D
• its ok to show them twice
• go slowly
• give them a break between OD and OS
• make sure not overminsued in non presbyope
• in nystagmus, occlude with high plus lens
• track time spend on refraction for billing purpose
• unwise to keep doing the same thing and expect different results
• base JND on entering VAs, dont need to repeat after ret
• dont always need to refract both eyes If significant VA reduction present