By: Michael R. Politzer, O.D., F.A.A.O., F.C.O.V.D.
The refraction component of a low vision examination is critically important but often challenging. The process is can be frustrating and the results questionable due to the level of acuity of the patient and their lack of discerning a “just noticeable” difference in the targets as they are presented.
The following has proven to be a successful and accurate method of determining the sphere, cylinder and cylinder axis for low vision patients. It is easy for the doctor to administer and is virtually stress and fatigue free for the patient.
- Do standard or radical retinoscopy using a phoropter, lens rack or loose trial lenses.
From the retinoscopy findings, place the spherical lens component of the right eye in the rear lens well of a trial lens frame and occlude the left eye.
Refine the spherical power for best-visual acuity by bracketing plus and minus lens powers, starting with +/- 3.00.
Reduce the bracketing lens powers appropriately for best visual acuity. EG. VA 20/400 TO 20/200 use +/- 2.00 VA <20/200 use +/- 1.00 and >20/50 use +/- 0.50. Continue until there is no improvement in visual acuity with the application of either plus or minus lenses.
From the retinoscopy findings, place the cylindrical lens component of the right eye in the front lens well of the trial lens frame.
Refine the cylindrical power for best-visual acuity by bracketing a +/- 1.00 Jackson Cross-Cylinder. If best-visual acuity is > 20/50 use a +/- 0.50 Jackson Cross-Cylinder. Continue until there is no improvement in visual acuity with the application of either plus or minus cylinder lenses.
Note: be sure to adjust the spherical power as the cylinder changes to maintain the same spherical equivalent power.
Place a full diameter 2.2X telescope in front of the cylinder lens in the furthest front lens well.
Check the cylinder axis by having the patient rotate clock wise and counter-clockwise the front lens wells until the position of best-visual acuity is reached.
Repeat steps four, five and six if necessary and record best visual acuity right eye.
Repeat steps two through ten and record best acuity left eye.
Remove the patch and record best-visual acuity both eyes.