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Binocular Refraction with the Vectographic Slide
PURPOSE To permit monocular refraction under binocular viewing conditions．Through the use of polarization，separate targets are shown simultaneously to the left and right eyes．The active involvement of the convergence system helps to stabilize accommodation．
INDICATIONS
Binocular refraction techniques are used as an alternative to the monocular subjective refraction with accompanying binocular balance．Due to the presence of binocularity during the refraction，this approach offers greater control of accommodation and a more accurate endpoint for the cylinder axis than a monocular subjective procedure．This method requires that a patient have binocular vision．
EQUIPMENT
·Phoropter with polarized filters．
·AO vectographic projector slide(see Figure 3-21)
SET-UP
·The patient should be comfortably positioned behind the phoropter．Take care to ensure that the phoropter and the patient are level．If there is misalignment, the effectiveness of the polarizing filters will decrease．
·Do not put the polarizing filters in place．
·Place the vectographic slide in the projector with the first line(20/200) projected．Without the polarizers, this will be seen by both eyes and is an appropriate fixation target for retinoscopy．
STEP-BY-STEP PROCEDURES
RETINOSCOPY
1．Perform retinoscopy using the routine technique．
2．Remove your working distance so your net retinoscopy finding is in the phoropter．
3．Put the polarizing filters in place．
4．Check the patient’s VAs in each eye．(The subchart numbers in the text refer to those illustrated in Figure 3-21．) Through the polarizers, the patient will see the first chart(#1)with his right eye and the second chart(#2)with his left eye．
5．Record your net retinoscopy and the patient’s visual acuities．
SUBJECTIVE REFRACTION
Clock Dial
This step in the refraction is optional．If the cylinder found with retinoscopy appears reasonably accurate or the acuity obtained with a spherical result is good(20/20 0r better)，the clock dial may be skipped．Proceed to step 13．
6．Remove the cylinder found with retinoscopy and fog the patient to 20/40 in each eye．
7．Expose the clock dial target(#3)．The right eye will see the right side of the target and the left eye will see the left．
8．Direct the patient’s attention to the right side of the clock dial．
9．Perform the clock dial test on the right eye．
10．Direct the patient’s attention to the left side of the clock dial．
11．Perform the clock dial test on the left eye．
Bi-ocular MPMVA
12．Change the target to chart #4．The letters on the right side are seen only by the right eye．The letters on the left are seen only by the left eye．
13．Direct the patient’s attention to the three lines on the right．
14．Perform an MPMVA test on the right eye．
15．Add one extra 0.25 D of minus in preparation for the Jackson Cross Cylinder test．
16．Direct the patient’s attention to the three lines on the left．
17．Repeat steps 14 and 15 for the left eye．
Jackson Cross Cylinder
18．Isolate the line one line above the patient’s best VA．If one of the three lines on chart #4 is not large enough, use the larger acuity charts(#1 and #2)，although this is likely to decrease the patient’s stimulus to fusion and accommodative stability．
19．Direct the patient’s attention to the letters on the right and modify the correcting cylinder axis and power for the right eye using the JCC test．
20．Redirect the patient’s attention to the letters on the left and modify the correcting cylinder axis and power for the left eye using the JCC test．
Bi-ocular MPMVA
21．Expose all three lines of chart #4．
22．Fog the patient binocularly with +0.75 D
23．Perform an MPMVA on the right eye．
24．Perform an MPMVA on the left eye．
Binocular MPMVA
25．Go to chart #6(four lines，20/30 to 20/15, seen binocularly)．
26．Fog the patient with +0.75 D spheres over both eyes and perform a binocular MPMVA to obtain the final sphere value．
RECORDING
·Specify the technique used for refraction．
·Record the patient’s final correction．
·Record the visual acuities for the right eye，the left eye，and both eyes.
EXAMPLE
·Binocular Refraction (Vectographic)
0D +4.00 sph 20/20
0S +3.50= -0.50×180 20/20
0U 20/15
EXPECTED FINDINGS
The refraction results for this technique are very similar to those obtained using a monocular subjective technique with a binocular balance．The spherical value may contain an additional +0.25 D．In patients with a cyclophoria, the cylinder axis may shift by as much as 5°．
Note：The vectographic slide comes with several other targets．These allow the examiner to eva luate a patient’s binocular function at distance．Included are checks for spression, the associated phoria with and without a central fusion stimulus, and stereopsis charts．It is also possible to screen for aniseikonia by comparing the two sides of chart #4． |
