Trial Framing

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Trial Framing

• Dr. Diana Shechtman

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Why Use a Trial Frame?

• REFRACTION
• Nursing home/hospital
• Ambulatory restrictions
• No phoropter
• Low vision patients
• Eccentric viewing (EV)
• Large head tilts (torticollis)
• or strabismus
• Aphakes high prescriptions
• Children

• TRIAL FRAMING
• New prescription
• Large change in prescriptions
• Prescribing prism
• Prescription checks

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When else can a trial frame be helpful?

• Performing test w/ Best-corrected Rx outside the
  phoropter
• cover test
• MEM
• vergence tests
• Measuring vertex distance
• Important for Rx gt/ /- 4.00 DS CL
• Important for Rx gt/ /- 6.00 DS Spectacles

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The Trial Frame (look at lab notes)
Adjustable temple
(bridge) height adjustment
Nose pad adjustment
PD
Cyl axis
Cyl lock
Front lens well
Pantoscopic tilt
Back lens well
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Parts of the Trial Frame

• Adjustable temple
• Tightens to evenly distribute weight of frame
• increase comfort
• Length 98-135mm
• Can minimize vertex distance (VD)

• Vertex distance (VD) rulers marking
• 0 15 mm
• located on the side of the frame
• each marking 1 mm

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Parts of the Trial Frame

• Nose pad adjustment (nose pad angle)
• located outward on the bridge
• moves the nose piece (pad) in out
• may helps adjust vertex distance

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Clinical Pearl

• Distometer
• designed to measure distance b/t cornea and
  spectacles back surface
• vertex distance
• A change in vertex distance results in a change
  in the effective power of the lens.

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Parts of the trial frame

• (bridge) height knob
• Upward pointing knob at bridge
• Vertically position to center with pts visual
  axis
• Moves nose pads up/down

Pantoscopic tilt adjustment knob (temple
angle) position on the temple tilts the frame
downward slightly, to level the frame

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Parts of the Trial Frame

• 1. Back lens well
• secret stand alone holder behind frame
• closest to patient
• place the largest sph here
• decreasing VD

2. Front lens wells 3 wells located in front of
the eye Low power lenses should go in front
wells cylinder should be place in the last well,
closest to pts eye help w/ axis adjustment
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Parts of a Trial Frame

• 1. Cylinder axis adjustment knob
• Located on temporal side of well
• 2. Axis lock screw
• Below axis adjustment knob
• Prevents axis from shifting while adjusting the
  frame or when pt is
• moving around

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Procedure for fitting the trial frame correctly

• Extend the temples slip over the patients ears

• Gently tighten temples so the frame snug against
  ears

• Nose pad should fit over nasal bone
• Adjust bridge height, centering it with the pts
  visual axis

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Procedure for Fitting the trial frame

• Adjust appropriate vertex distance
• Use the pantoscopic tilt knobs to level the frame
  
• and ensure proper tilt (inspected from the side)
• angles the lens with respect to vertical plane

• Adjust the pupillary distances (PD), centering
• the pts eyes horizontally

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Why Trial Framing?

• TRIAL FRAMING
• New prescription
• Large change in prescriptions (Rxs)
• Prescribing prism
• Prescription checks

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TRIAL FRAMING

• Be sure the patient feels comfortable with the
  prescription
• Pt should walk around
• look at edge of door frames or floor tiles
• look out at a distance
• look at reading material

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Why Trial Frame Refraction?

• REFRACTION
• Nursing home/hospital
• Children
• Ambulatory restrictions
• Large head tilts/strab
• Aphakes/high Rx
• Low vision patients

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Trial Frame Refractions Finding the Best Sphere

• Starting point
• Current spectacle Rx
• not highly recommended since its
• not always right!!
• Retinoscopy
• behind the phoropter
• dont forget WD
• using loose lenses
• using a lens rack
• Use entering VAs to guess-estimate a sphere

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Guess-estimating the Prescription
VA Sph
20/25 0.25 20/30 0.50 20/60 1.00
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Trial Frame Refractions Finding the Best Sphere

• Inset lenses with care
• Place highest sphere in back lens well
• occlude (or fog) the OD, while working on OS and
  vs.
• Take VAs

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Trial Frame Refractions Finding the Best Sphere

• Monocular subjective
• Determine JND (just noticeable difference)
• Important for low vision examination
• enough of a lens change for the patient to
  discriminate
• changes in blur
• JND the smallest amount of power change
  necessary
• to differentiate variation in blur at 20ft

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Trial Frame Refractions Finding the Best Sphere

• Monocular subjective
• Hold two lenses of the same JND power (opposite
  sign) ask which is clearer
• Increase the Sph lens power by the amount to
  the JND lens of choice
• Continue until you get reversal and then refine
  the sphere by bracketing until
• both choices equal
• neither choice produces better VA

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Example

• After retinoscopy you end up w/ a net result of
  2.00sph w/ VA 20/100
• JND
• Patient chooses 0.50

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Trial Frame Refractions Finding the Best Sphere

• Continue monocular subjective
• choosing correct JND lens with VA improvement
• Try to also push () at distance
• Thus, needing less () at near
• If pt sees NO difference b/t current Rx 1.00
  over it
• Then, add 1.00 over current lens (for distance
  refraction)
• Lets start refining CYL, using a hand-held JCC

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Hand-held JCC

• Come in different powers
• Come with different markings
• Dots or lines
• Red vs. white/green/black
• The red markings represent the minus cylinder
• Major meridian markings are 90 degrees apart
• These will always straddle the handle

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Hand-held JCC

• The handle attached midway b/t the two axes
• Permits rapid turns b/t () (-) axes of crossed
  cylinders by flipping the lens
• Axis can be moved w/o reversing power by
  rotating the handle clockwise or counterclockwise
  

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Trial Frame Refractions Determining the
Cylinder Axis

• Straddle
• Rotate JCC handle so the handle is aligning the
  TF cyl axis (correcting cyl axis)
• thus, the lines straddle 45 on either side of the
  TF axis
• Flip the JCC handle, and chase the red
• Rotate the TF cylinder axis toward the red line
  on the preferred side
• Realign the JCC as above and continue to refine
  the axis by bracketing

TF axis
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Example
CHOICE 2
CHOICE 1
Pt chooses 1
TF axis
TF axis
Move TF axis 5 degrees by following red
TF axis
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Example
Realign the JCC continue to refine the axis
TF axis
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Trial Frame Refractions Determining the
Cylinder Power

• Align
• Rotate the JCC handle so LINE markings align with
  the TF cylinder axis (correcting cyl axis)
• Begin flipping the JCC
• add minus cyl power to TF rx if pt chooses red
  lines
• remove minus cyl power from TF Rx if pt chooses
  green
• Continue refining power and bracket

TF axis
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Example
CHOICE 1
CHOICE 2
Pt chooses 2
TF axis
TF axis
Add cyl power
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Trial Frame Refractions Determining the Cyl Power

• Dont forget to maintain the spherical equivalent
• if you change the cylinder by 0.50, adjust the
  sphere by 0.25

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Trial Frame Refractions Fishing for Cylinder

• Dont forget to FISH
• when there is no cylinder, initially present
• Continue
• Re-check monocular subjective
• Bi-ocular balance
• if possible
• Binocular balance

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Other useful instruments

• Frame clips
• Over Refraction
• Allows for trial frame refraction or test a
  prescription change with the patients own
  glasses
• Secure and stable mounting
• Correct pantoscopic tilt, VD base curve
• May need to use lensometer for sphero-cylinder
  over-refraction

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Reference

• Nowakowskis Primary Low Vision care. Appleton
  Lange 1994 refraction chapter