|
Humphriss Immediate Contrast Method
PURPOSE To allow for a subjective refraction under conditions which maintain peripheral fusion while testing foveal vision monocularly．This is accomplished by placing a fogging lens over the nontested eye to induce spression of its central retina．Nonfoveal zones remain binocularly active and stabilize accommodation.
Note：This is generally considered a method of refinement，with retinoscopy or monocular subjective findings used as a starting point．The method described below uses retinoscopy as the starting point and assumes the visual acuity in each eye through the net static to be 20/20．
EQUIPMENT
·Distance acuity chart．
·Phoropter or trial frame．
SET-UP
·Perform retinoscopy．For the Humphriss technique to be successful, the retinoscopy findings must be reasonably accurate，within 0.50 D of neutrality．
·Place your net retinoscopy findings in the phoropter．Neither eye should be occluded．
·Display the distance visual acuity chart with the 20/15 to 20/50 lines exposed．
STEP-BY-STEP PROCEDURE
1．Place a +0.75 D fogging lens over the net retinoscopy finding of the left eye．The patient’s visual acuity in the fogged eye should be either 20/30 0r 20/40．This is checked quickly by briefly occluding the right eye and asking the patient to read the lowest line of letters he can．
2．Take The patient’s acuity for the right eye through the net retinoscopy finding．Both eyes are open from this point on．
3．Fog the patient’s right eye by adding +0.75 D of sphere and perform an MPMVA．
4．Isolate the 20/30 line．
5．Place an additional +0.25 D sphere over the right eye, then quickly replace this with a -0.25 D sphere．Ask the patient which lens makes the line of letters appear clearer．This is done most effectively by using loose lenses．
a．If the patient reports that the -0.25 D sphere is clearer, add -0.25 D to the correction and continue step 5 until the two views appear equal．
b．If the +0.25 is preferred, add a +0.25 to the correction and continue step 5．If on the next comparison the patient prefers the -0.25, add the -0.25 and proceed to step 6．
c．If the two views appear equal．leave the correction as is and proceed to step 6．
6．Perform a cylinder axis check and power check using the JCC test．
7．Place +0.75 D fog in front of the right eye and proceed to refract the left eye．
8．Place an additional +0.25 D sphere over the left eye, quickly replace this with a -0.25 D sphere and ask the patient which lens makes the line of letters appear clearer．This is done most effectively by using loose lenses．
a．If the patient reports that the -0.25 D sphere is clearer, add -0.25 D to the correction and continue step 8 until the two views appear equal．
b．If the +0.25 is preferred, add a +0.25 to the correction and continue step 8．If on the next comparison the patient prefers the -0.25, add -0.25 and proceed to step 9．
c．If the two views appear equal，leave the correction as is and proceed to step 9．
9．Perform a cylinder axis check and power check using the JCC test．
10．Remove the +0.75 D fogging lenses from both the patient’s right and left eye．
11．Take the patient’s VA for the right eye，the left eye，and both eyes．
RECORDING
·Specify the type of refraction performed．
·Record the patient’s final correction and visual acuities．
EXAMPLE
·Binocular Refraction/Humphriss Immediate Contrast Method
OD -3.50 = -1.00×45 20/20+
OS -2.75 = -1.25×l35 20/20+
OU 20/15
EXPECTED FINDINGS
·Due to the binocular conditions under which the refraction occurs, there may be some additional plus acceptance and a small change in the cylinder axis to compensate for a cyclophoria． |
