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Trial Frame Refraction
PURPOSE
To determine the refractive state of the eye when a phoropter is unavailable or contraindicated. The trial frame is also used to confirm and modify phoropter-based refraction results．
INDICATIONS
This method of refraction is particularly useful with patients having high refractive errors (including aphakes)，low vision，accommodative instability，or ambulatory restrictions．
Note：The technique described here is a modification of a phoropter-based refraction．It is critical to point out that substeps of the procedure may be applied or eliminated depending on the patient and the refractive error．The substep sequence may also be modified to enhance the efficiency of the trial frame refraction．Prior to reading this section, the examiner should be thoroughly familiar with routine distance subjective refraction with the phoropter．
EQUIPMENT
·Trial frame．
·Retinoscopy rack．
·Trial lens kit．
·Hand-held Jackson Cross Cylinder(JCC)：Hand-held JCCs come in a variety of powers．The power used will depend on the patient’s acuity level．For patient’s with normal acuity, a ±O.25 D JCC is recommended．
SET-UP
·Have the patient remove any corrective lenses．
·Place the trial frame on the patient．Be certain to adjust the trial frame so that it sits comfortably on the patient’s face and the patient’s eyes are centered relative to the lens wells of the frame．This requires adjustment of the following(see Figure 3-18)：
a．the temple length to minimize vertex distance．
b．the frame height via the nose pad adjustment．
c．the pantoscopic tilt and leveling of the frame．
d．the interpillary distance．
·Fixation target：20/400 E projected through a red-green filter．An illustration of the trial frame on the patient is shown in Figure 3-19．
STEP-BY-STEP PROCEDURE
RETINOSCOPY
1．Tell the patient to look at the large E，or another large, nonaccommodative target．
2．The retinoscope should be held at the examiner’s customary working distance．
3．Using the retinoscopy rack neutralize the patient’s right eye：
a．locate the two major meridians．
b．determine the power required to obtain neutrality in each meridian．
4．Calculate and place the gross retinoscopy finding for the right eye into the trial frame．The lenses should be placed in trial frame with the sphere in the lens cell closest to the patient (behind the facade of the trial frame), and the cylinder in the next closest cell(located in the front of the trial frame)(see Figure 3-20)．Adjust the cylinder to the appropriate axis．The lens cell closest to the patient approximates the vertex distance of a spectacle correction．
5．Perform retinoscopy on the left eye repeating steps 3 and 4．
6．With your gross retinoscopy finding for the left eye in the trial frame，recheck the right eye for neutrality．
7．Change the lenses in the trial frame so your net retinoscopy findings are in place．
8．Take monocular VAs and record the net retinoscopy findings in minus cylinder form．
MONOCULAR SUBJECTIVE REFRACTION
9．Occlude the patient’s left eye．
10．Perform an initial MPMVA on the right eye leaving the patient over minused by 0.25 D or one into the green．This may be done by using hand-held lenses(several in one hand，eg．+0.25, +0.50，+0.75), or a lens rack．Modify the sphere in the trial frame to reflect the results of the MPMVA．
11．Perform the JCC test using a hand-held JCC．To increase manual control, a long handled JCC is recommended．
12．Refine the cylinder axis by flipping the JCC in front of the trial frame with the axis of the cross cylinders 45°away from the correcting cylinder axis．This is generally the case when the handle of the JCC is aligned with the correcting cylinder axis．Rotate the lens cell of the trial frame to change the cylinder axis.
13．Refine the cylinder power using the JCC．Adjust the power of the cylinder in the trial frame．Unnecessary lens changes may be avoided by changing the cylinder power in the trial frame by an amount equal to twice the power of the JCC．For example，if a ±0.25 D JCC is being used, and the patient prefers minus，add -0.50 D to the correcting cylinder．If on the next comparison the patient prefers minus you will have saved a step．Similarly, if the patient prefers plus, you can extrapolate that the endpoint is 0.25 D less minus．
14．Perform an MPMVA using loose lenses or a lens rack and make the final adjustment to the spherical component of the patient’s correction．
15．Record your monocular subjective results and the VA for the right eye．
16．Occlude the right eye and repeat steps 10 through 15 for the left eye．
BINOCULAR BALANCE
Perform this step only if each eye achieved the same VA following the monocular subjective refraction．As with a phoropter-based refraction，the binocular balance may be done via prism-dissociation using the loose prisms included in the trial lens kit．The technique described here, the alternate occlusion method, is preferred for a trial frame refraction．Although it is not quite as precise as the prism-dissociation method, it is less cumbersome．
17．Make sure neither eye is occluded and both eyes can see the VA chart．
18．Direct the patient’s attention to a single line of letters, one line above the patient’s best VA．If you are using a projector and VA slide, isolate the line．
19．Cover the patient’s left eye and then move the occluder to the right eye．
20．Ask the patient through which eye the target appears clearer．
21．Add +0.25 D to the better seeing eye．
22．Repeat steps 19 through 21 until the two eyes are equally clear or a reversal occurs．If a reversal occurs, select the dioptral values for which the clarity of the images in the two eyes is closest.
23．Perform a binocular MPMVA using loose lenses in each hand．
24．Measure and record the VA for the right eye，the left eye, and both eyes．
RECORDING
·Record the technique used．
·Record the final correction for the left eye and the right eye．
·Record the VA for the left eye，the right eye, and both eyes．
EXAMPLE
·Trial Frame Refraction
Static 0D -3.O0 = -0.50×135 20/20-1
0S -2.75 = -0.50×45 20/20
Subj OD -2.75 = -0.50×130 20/20
OS -2.25 = -0.50×50 20/20
0U 20/20
Note：Recommendations for performing efficient trial frame refractions：
·Avoid changing the lenses in the cells of the trial frame．This may be accomplished by holding lenses in front of the trial frame, rather than placing lenses in the lens cells．Learn to insert and remove lenses smoothly to promote patient comfort．
·If the patient has reduced acuity, be sure to use lens increments and JCC powers that allow the patient to make comparative judgments．For example，if a patient can only see 20/40 try using a ±0.50 D JCC instead of a ±0.25 D or±0.37 D JCC． |
