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Use of the Trial Frame to Modify a Prescription
PURPOSE
To demonstrate a new prescription for the patient and to modify the subjective refraction findings for maximum patient comfort.
EQUIPMENT
·Trial lens set．
·Trial frame．
·Distance visual acuity chart．
·Near visual acuity chart．
·Reading material一newspaper, magazine，phone book, music.
SET-UP
·Place the trial frame on the patient．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．See the section on trial frame refraction in this chapter．
·If the patient has a previous pair of glasses and the change is spherical, the trial lenses can be held directly over the patient’s current glasses to demonstrate the change in prescription as shown in Figure 3-15．
STEP-BY-STEP PROCEDURE
1．Instruct the patient to look at the distance acuity chart if the new prescription is for distance or at the near point card if the new prescription is for near．Alternatively，the patient may look out a window rather than at the distance acuity chart or at reading material rather than at the near acuity chart．
2．Ask the patient if things look clear and if he feels comfortable looking through the new prescription．
3．If the patient reports that things are not clear or are not comfortable through the new prescription，adjust the prescription in one of the following ways until the patient reports clear and comfortable vision：
a．increase the minus sphere in 0.25 D steps．
b．increase the plus sphere in 0.25 D steps．
c．move the axis of the cylinder toward the axis in the patient’s previous prescription or toward 90° or 180°(see Figure 3-16)．
d．decrease the cylinder power in 0.25 D steps, making concurrent changes in the sphere to maintain the spherical equivalent of the prescription．
4．For prescriptions that are for near only，instruct the patient to move the reading material in until it blurs and out until it blurs to ensure that there is an adequate range for the patient’s needs．
5．For prescriptions that are for near only，instruct the patient to look through the prescription at distance and explain that it is normal for distance objects to look blurry through a near prescription．
RECORDING
·Record all of the prescriptions that were tested．
·Record the patient’s response to each of the trial framed prescriptions．
EXAMPLES
·TF
OD -4.75 sphere 20/20
OS -3.50= - 0.50×175 20/20 for distance and near；
patient comfortable at D and N．
·TF for near
1．0D +1.00=-1.00×10
0S +1.00=-1.00×165
2．0D +1.00 sph
0S +1.00 sph
3．OD +0.50 sph
OS +0.50 sph
Patient was 20/20 with each—most comfortable with +1.00 sph OU．
Range adequate for patient’s near needs．
·TF +2.00 0U for near；patient reports clear, comfortable vision for reading, but blurry at the computer screen．TF +1.75 0U and +1.50 OU for computer；patient most comfortable with +1.50 0U at CRT．
·TF +0.25 0U and +0.50 0U over patient’s current near glasses；patient prefers +0.50 0U． |
