CFII - Trial Frame Refraction

What is the purpose of trial frame refraction?

To determine refractive state when a phoropter is unavailable or contraindicated.

When is trial frame refraction useful?

When a phoropter is not the optimal method.

What can trial frame refraction be used to do with phoropter results?

Confirm and refine phoropter-based refraction results.

What types of patients benefit from trial frame refraction?

Low vision, high refractive error (including aphakia), accommodative instability, deafness, and ambulatory restrictions.

What prior skill should the examiner have before performing trial frame refraction?

Familiarity with routine distance subjective refraction using a phoropter.

What materials are required for trial frame refraction?

VA chart, trial frame, retinoscope, retinoscopy rack, trial lens set, and handheld JCC.

What JCC powers are available?

±0.25 D, ±0.50 D, ±1.00 D.

What JCC should be used for 20/25 or better acuity?

±0.25 D.

What JCC should be used for worse than 20/30 acuity?

Higher-powered JCC.

What front adjustments are available on a trial frame?

Height, vertex, PD (monocular), lens clips, cylinder rotation, and cylinder lock.

What side adjustments are available on a trial frame?

Temple tilt, temple length, and vertex scale.

What four alignment steps must be performed before each trial frame refraction?

Temple length, temple tilt, PD alignment, and vertex distance.

How is temple length adjusted?

Increase length, place behind ears, and tighten gently.

What is the purpose of leveling the trial frame?

To make lenses parallel to the face.

How is PD alignment achieved?

Center optical center on the pupil using cross hair lens.

How is vertex distance adjusted?

Using the center knob.

What is the standard vertex distance in trial frame refraction?

10–13 mm.

Why is proper trial frame fit critical?

It directly impacts accuracy of the final refraction.

Where should the patient’s eyes be positioned in the trial frame?

Centered in the lens apertures.

What is the order of lens placement in the trial frame?

Back clip: base sphere; front clip back: balance sphere; front clip middle: cylinder; front clip front: reading/fogging/test lens.

How many lens wells does a trial frame have?

Four.

How should lenses be inserted into the trial frame?

Rotate clips toward the nose and insert from the top.

What should be done before placing lenses in the frame?

Lift the frame off the nose to reduce pressure.

What is the recommended base lens sphere range?

Between 1 DS and 3 DS.

Why should sphere power be split between clips?

To reduce distortion.

How should a 3.00 D sphere be distributed?

1 D in back and 2 D in front balance clip.

How should a 6.00 D sphere be distributed?

3 D in back and 3 D in front balance clip.

What are starting points for trial frame refraction?

Habitual correction or retinoscopy results.

What should be done if using habitual correction?

Place it into the trial frame.

What is done when using retinoscopy racks?

Perform retinoscopy first, then fit trial frame.

What is used to fog during retinoscopy starting point?

+1.50 to +2.00 lenses.

What technique is used to neutralize meridians?

Lens bar technique.

What is used to represent refractive error after retinoscopy?

Power cross.

Where is sphere placed in the trial frame?

Posterior lens well.

Where is cylinder placed in the trial frame?

Anterior lens wells.

How is one eye occluded in trial frame refraction?

Using a black or frosted occluder.

When is a frosted occluder preferred?

Pediatric patients, esotropia, and nystagmus.

What is the first step in monocular refraction?

Perform MPMVA on the right eye.

What starting condition is used for MPMVA?

Slight over-minus of −0.25 D.

What is used for bracketing during MPMVA?

Handheld lenses or lens rack.

What is done after bracketing sphere?

Update sphere in the trial frame.

What is ret blur check?

Using plus lenses to confirm 20/40 fog before reducing to best vision.

What is used to occlude the fellow eye during monocular testing?

Blank lens.

What line should be used for cylinder refinement?

About 2 lines above BCVA (around 20/40).

What tool is used for cylinder refinement?

Handheld JCC.

What is the sequence for cylinder refinement when cylinder >0.50 D?

Check axis first.

What is the sequence when cylinder ≤0.50 D?

Check power first.

What is done if no cylinder is initially present?

Perform cylinder check.

What guideline is used for JCC selection?

Just noticeable difference (JND).

What color represents minus axis on JCC?

Red.

What color represents plus axis on JCC?

Black.

What should be ignored on the JCC?

White dots.

What do white dots represent?

Correspondence to phoropter axis wheel.

What does the red line represent on JCC?

Cylinder power.

What is the rule for axis adjustment with JCC?

“Chase the red line.”

How is axis refinement performed?

Flip JCC 45° from correcting axis and rotate cylinder toward red dots.

How is power refinement performed?

Align JCC axes with correcting axis and adjust cylinder power.

How is spherical equivalent maintained during cylinder changes?

Adjust sphere accordingly.

What is the efficient adjustment rule for cylinder power?

Change cylinder by 2× JCC power.

What is an example of JCC adjustment?

±0.25 JCC corresponds to 0.50 D change.

What does it mean if patient prefers minus during JCC?

Add −0.50 D cylinder.

What does it mean if patient prefers plus during JCC?

Reduce minus cylinder by 0.25 D.

How is cylinder checked if none is present?

Insert −0.50 D at axis 180° and test multiple meridians.

What happens if cylinder is rejected in all meridians?

No cylinder is needed.

What happens if cylinder is accepted in any meridian?

Proceed with axis and power refinement.

What is the final step after cylinder refinement?

Perform second MPMVA.

What should be recorded after monocular refraction?

Monocular subjective refraction and visual acuity.

What is done after completing right eye refraction?

Repeat steps for left eye.

When is binocular balance performed?

When both eyes have equal VA.

What are methods for binocular balance?

Prism dissociation or modified Humphriss method.

What is the first step of modified Humphriss method?

Fog one eye with +1.00 D.

What line is used during binocular balance?

1–2 lines above best VA.

What lenses are shown during balancing?

+0.25 D vs −0.25 D.

What is done if patient prefers +0.25 or equal?

Add +0.25 D and repeat.

What indicates completion of balancing for one eye?

When −0.25 D is preferred.

What is done after balancing one eye?

Switch eyes and repeat.

What must be recorded after trial frame refraction?

Technique used, final correction, and VA for each eye and both eyes.

What is an example of recorded trial frame refraction?

OD: −3.00 −0.50 × 135 20/20−1; OS: −2.75 −0.50 × 045 20/20.

What is the most important step during trial frame refraction?

Clean each lens before use.

Why must lenses be cleaned before use?

They accumulate film that affects clarity.

How can trial frames be used clinically beyond refraction?

Demonstrate final prescription to patients.

How can trial lenses be used without full setup?

Hold lenses over habitual correction.

When is trial frame especially useful clinically?

Large prescription changes or rechecks.

What can trial frames help demonstrate?

Prism effects.

What should students bring to lab for trial frame practice?

Trial frame, retinoscope, retinoscopy rack, trial lens set, lens flipper, handheld JCC.

What is an advantage of the Jannelli clip?

Leveling bubble and use of base curve of habitual Rx.

What is a disadvantage of the Jannelli clip?

No axis lock and cannot compare new axis vs old.