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Convergence Controlled Refraction
PURPOSE To control the accommodative response by eliminating the convergence demand present in cases of high exophoria．Base in prism is used to neutralize the influence of the exo deviation．This technique may be performed alone or done in conjunction with the delayed refraction (Pierce-Borish test)．The Pierce-Borish test is described here．
INDICATIONS
This technique is useful for patients with suspected accommodative dysfunction secondary to a high exophoria．
EQUIPMENT
·Phoropter with nearpoint rod.
·Nearpoint cards．
·Distance acuity chart．
SET-UP
·This technique is performed following a complete routine refraction.
·Perform the phorometry tests with the NRA test last(see Chapter 4).
·Leave the plus from the NRA test in the phoropter．
STEP-BY-STEP PROCEDURE
1．Reduce the plus in the phoropter by -0.25 D to allow the patient to clear the near target．
2．Using the Risley prisms，gradually introduce base in prism binocularly until the patient again reports a blur．
3．Remove the nearpoint rod，leaving the plus and the base in prism in place．
4．Present a distance target consisting of an isolated line of letters equal to the patient’s best distance acuity level．
5．Direct the patient to view the target, letting him know it may be quite blurry．
6．Reduce the fog in both eyes simultaneously using 0.25 D steps until the letters are clear．
7．Confirm your endpoint with the duochrome test(optional)．
RECORDING
·Record the technique used：
a．Pierce-Borish Test
b．Delayed Ref．with BI Prism
·Record the correction obtained and the patient’s visual acuities．
EXAMPLE
·Refraction (Delayed with BI prism)
0D +2.50 sphere 20/20
0S +2.00 = -0.50×90 20/20 |
