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Initial MPMVA(Maximum Plus to Maximum Visual Acuity)
PURPOSE
To determine the maximum plus (minimum minus) spherical power which provides the patient with his maximum visual acuity．The initial MPMVA begins with the net static retinoscopy findings in the phoropter．
1．Open the right eye and occlude the left eye．
2．Fog the eye to a visual acuity of 20/40 to 20/60．This will usually require the addition of about +1.00 sphere to (or the removal of -1.00 diopter sphere from) the net static retinoscopy finding or the clock chart finding．Check the patient’s VA through the fogging lenses to be sure he is fogged to the correct level．
3．Predict the final sphere by comparing the patient’s VA under fog to Egger’s chart．Remember that the patient should obtain approximately one additional line of VA for each 0.25 D of minus-sphere added (or each 0.25 diopter of plus-sphere that is removed)during the MPMVA．
4．Reduce the plus(add minus)0.25 D at a time, checking VA and encouraging the patient to read the next smaller line each time．
5．Keep in mind that each 0.25 D should allow the patient to read smaller letters．Having the chart look “better” to the patient is not sufficient justification to give him more minus．
Initial Duochrome (Bichrome, Red-Green Test)
PURPOSE
To determine the correcting spherical lens power．
The duochrome should be used as the endpoint procedure for the initial MPMVA．
6．Put the projector’s red-green filter over the chart of letters．
7．Direct the patient’s attention to the 20/25 line or to the letters one line above his best VA so far. For some patients it may be necessary to isolate this line of letters．
8．Tell the patient to look from the green side to the red side and back to the green side．Have him state which side has the sharper and clearer (not “better, ” darker or brighter ) letters or to state if the two sides are equally clear．Because this test works on the principle of chromatic aberration, it will work for color anomalous patients．For such individuals, it may be necessary to tell them to look at the left or right sides of the chart rather than at the green or red sides．
9．If the letter’s on the red side are clearer or if the letters on both sides are equally clear, introduce an additional 0.25 D of minus-spherical power. If the letter’s on the green side are clearer，take away 0.25 D of minus (or add another 0.25 D of plus sphere)．
10．Repeat steps 8 and 9 until you find the minimum amount of minus power (or maximum plus) at which the patient reports that the green side has the clearer letters．Then the patient is “one into the green．”
11．Remove the red-green filter and recheck the VA．
Note：Some patients are unresponsive to this test and seem to choose one side or the other， regardless of the lens powers in place．Be alert to this possibility and abandon the duochrome test in favor of some other endpoint to the MPMVA(see step 31)．
12．Consider the following：
a．Does the amount of minus added correlate with the amount of improvement in VA over the starting point with the patient fogged? The correct refraction will yield a close match between the actual and the predicted changes in lens power．
b．If the phoropter contains a tentative cylinder from static retinoscopy or some other test, proceed with the Jackson Cross Cylinder test (step 13)．Remember that a visual acuity of 20/20, or sharp, clear vision may not be possible at this point in the refraction，since the cylindrical part of the prescription has not yet been refined．
c．If the patient has clear VA of 20/20 or better with spherical lenses and if you are refracting the right eye，proceed to the monocular refraction of the left eye．If the patient has clear VA of 20/20 or better with spherical lenses and if you are refracting the left eye，proceed to the binocular balance．
d．If the static retinoscopy and other starting data do not indicate an astigmatism and the patient does not have clear 20/20 VA or better with a spherical correction, perform one or both of the side trips for astigmatism，the JCC Check Test or the Clock Chart，described later in this chapter, to search for a small, uncorrected astigmatism．These side trips may be called for if the static retinoscopy is unreliable for reasons such as opacities in the media or poor patient cooperation．
e．If the starting data and the side trips do not detect any astigmatism and the patient does not achieve 20/20 VA with spherical lenses, consider the possibility that the eye suffers from pathology or amblyopia．
The Jackson Cross Cylinder (JCC) Test
PURPOSE
To refine the axis and power of the cylindrical component of the correction after the initial monocular MPMVA has determined the tentative spherical correction．
PERFORM THE JCC AXIS CHECK
13．Isolate a line of letter’s one line above the best VA obtained so far in the monocular subjective refraction．
14．As shown in Figure 3-11，place the JCC lens before the eye such that its axes straddle at 45° angles the axis of the correcting cylinder in the phoropter．This is achieved by lining the handle of the JCC with the axis of the cylinder in the phoropter．
15．Instruct the patient that you will show him two views of the line of letters and will identify each view with a number．Tell him that both views may be blurry, but to tell you which view is sharper or less blurry．Further instruct him to try to ignore differences in the shapes of the letters when comparing the views．
16．Have the patient look at the letters and tell him, “This is view number one．”
17．After 2 to 5 seconds, flip the JCC and say, “This is view number two．Which view has the clearer letters?” If the views are equally blurry，the axis is set in the appropriate position．Go to step 21 to refine the cylinder power by the JCC．
18．If the views are not equally blurry or equally clear, move the axis of the phoropter cylinder by 15°toward the minus-cylinder axis (indicated by the red marks) that gave the clearer view．In Figure 3-11, if view number 1 provided the patient with clearer vision，the axis in the phoropter should be moved in a clockwise direction．If view number 2 provided the patient with clearer vision, the axis in the phoropter should be moved in a counterclockwise direction．
19．Shift the orientation of the JCC lens so that the handle remains aligned with the axis of the phoropter cylinder．In many phoropters，the JCC will rotate automatically along with the phoropter cylinder, so this step is unnecessary．
20．Repeat steps 14 through 19 as long as you have to keep adjusting the cylinder axis in the same direction (ie, clockwise or counterclockwise)．When the axis has to be moved in the opposite direction, repeat steps 14 through 19, but move the axis in 5° or 10° steps．Hone in on the correct axis by successively decreasing the step size．
Note：The greater the cylinder power，the greater the need for precision in the axis．For cylinder powers greater than 5.0 diopters, the axis should be specified to the single degree．For cylinder powers less than 2.0 diopters, the axis should be specified to the nearest 5°．For cylinder powers between 2.0 and 5.0 D, exercise professional judgment．
21．End the JCC axis check when either of the following two conditions are met：
a．Both views look the same to the patient．
b．The patient’s responses move the axis back and forth within a narrow range．In this event，select an axis in the middle of the range．
PERFORM THE JCC POWER CHECK
22．Place the JCC lens so that one axis is aligned with and the other axis is perpendicular to the axis of the correcting cylinder in the phoropter，as shown in Figure 3-12．
23．The instructions are the same as in steps 15，16，and 17．It is often necessary to repeat them, however．
24．Present the two views to the patient by flipping the JCC lens．If the patient prefers the view with the RED dots (minus-cylinder axis) aligned with the cylinder axis in the phoropter，view number one in Figure 3-12，increase the power of the minus-cylinder in the phoropter by -0.25 D．If the patient prefers the view with the WHITE dots (plus-cylinder axis) aligned with the cylinder axis in the phoropter，view number two in Figure 3-12, reduce the power of the minus-cylinder in the phoropter by -0.25 D．
25．Throughout the JCC power check，maintain the spherical equivalent of the MPMVA starting point．For each increase in minus-cylinder of -0.50 D that the patient accepts，add +0.25 D to the sphere or take away -0.25 D．For each decrease in minus-cyl inder of -0.50 D，add -0.25 D to the sphere．
26．End the JCC power check when either of the following two conditions are met：
a．Both views look the same to the patient．
b．The patient’s responses call for changes within a narrow range of powers．In this event, select the power that is closer to that found in his habitual prescription．If an habitual prescription is not available, select the less minus cylinder power．
Note：For some patients，making the choice of which view is clearer is very difficult．Borish describes a variation on the JCC technique in which the whole VA chart，from the 20/50 to the 20/15 letters, rather than an isolated line of letters，is displayed．The patient is asked to report which view allows him to read farther down the chart．By having the patient try to read the chart，the examiner can exercise his professional judgment as to the view that provides the sharper retinal image．
Upon reaching the conclusion of the JCC test for both axis and power, perform the second monocular MPMVA．
Second Monocular MPMVA
PURPOSE To determine the maximum plus-spherical power which provides the patient with his maximum visual acuity．
Note：During the second monocular MPMVA and the remainder of the distance refraction, the cylinder in the phoropter at the end of step 26 is not changed．
27．Fog the patient to a visual acuity of 20/40 to 20/60．This will usually require the addition of about +1.00 to, or the removal of -1.00 from, the spherical lens in the phoropter．Check the patient’s VA through the fogging lenses to be sure he is fogged to the correct level．
28．Predict the final sphere by comparing the patient’s VA under fog to Egger’s chart．Remember that the patient should obtain approximately one additional line of VA for each 0.25 D of minus-sphere added or each 0.25 diopter of plus-sphere removed．
29．Reduce the plus (add minus ) 0.25 D at a time, checking VA and encouraging the patient to read the next smaller line each time．
30．Keep in mind that each 0.25 D should allow the patient to read smaller letters．The patient reporting that the chart looks “better” is not sufficient justification to give him more minus．
31．Reach an appropriate stopping point．To decide when to stop the second monocular MPMVA，choose one of the following endpoints．The order of presentation here does not imply order of preference．
a. The DUOCHROME endpoint
(1) Put the projector’s red-green filter over the chart of letters．
(2) Direct the patient’s attention to the line of letters one line above his best VA so far．For some patients it may be necessary to isolate this line．
(3) Tell the patient to look from the green side to the red side and back to the green side．Have him state which side has the sharper, clearer (not “better” or darker or brighter) letters or to state if the two sides are equally clear．
(4) If the letters on the red side are clearer or if the letters on the two sides appear equal, introduce an additional 0.25 D of minus-spherical power over the eye being tested. If the letters on the green side are clearer，take away 0.25 D of minus (or add another 0.25 D of plus sphere)．
(5) Repeat steps 3 and 4 above until the patient is one into the green，the minimum amount of minus power at which the patient reports that the green side has the clearer letters．As an alternative，use a red-green balance, the point at which both sides appear equally clear，rather than one into the green，as the endpoint．
(6) Remove the red-green filter and recheck the VA．
Note：Some patients always seem to choose one side or the other, regardless of the lens powers in place．Be alert to the possibility that your patient is unresponsive to this test and abandon the duochrome test in favor of one of the other endpoints described here．
b．The smaller/darker endpoint
(1) Introduce one more 0.25 D of minus (or remove 0.25 D of plus)．
(2) Ask the patient whether the change makes the letters clearer or just smaller，darker，or “better．”
(3) If the change makes the letters subjectively clearer to the patient，accept the change and repeat steps (1) and (2) above．If the change makes the letters smaller，darker, or “better，”do not accept the change and take away the 0.25 D added in step (1)．
c．The 20/20 endpoint
If the patient has subjectively clear 20/20 vision, and if the lenses in the phoropter at step 28 match the prescription that was predicted from the starting information，the second monocular MPMVA may be stopped．The amount of minus added (plus taken away) should correlate with the amount of improvement in VA over the starting point with the patient fogged (step 27)．The correct refraction must yield a close match between the actual and the predicted changes in lens power．
32．Record the sphere power，cylinder power，cylinder axis in the phoropter，and the VA achieved through these lenses．
33．Repeat steps 2 to 32 with the right eye occluded and the left eye open． |
