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Amplitude of Accommodation: Minus Lens to Blur
PURPOSE To measure the amplitude of accommodation by using minus lenses to increase the stimulus to accommodation.
INDICATIONS
This test is done when other tests, such as the push- amplitude, suggest that a nonpresbyopic patient has reduced amplitude of accommodation.
EQUIPMENT
·Phoropter.
·Near point card.
·Near point rod.
·Illumination source.
SET-UP
·The phoropter contains the patient’s best distance correction from the most recent refraction.
·Place the near point card at 40 cm on the near point rod under bright illumination.
·Remember that the test is done monocularly only.
STEP-BY-STEP PROCEDURE
1. With the patient seated behind the phoropter, occlude his left eye.
2. Instruct the patient to look at a row of letters one or two lines larger than his best near visual acuity. For most nonpresbyopes, 20/30 letters are appropriate.
3. Add minus lenses -0.25 D at a time, allowing 5 to 10 seconds for the patient to clear the letters. Continue to add lenses until the patient reports that he can no longer clear the target and keep it clear. The first sustained blur marks the endpoint of this test.
4. The amount of minus added to the patient’s prescription plus 2.50 D (the accommodative demand for a near point card at 40 cm) is the total amplitude of accommodation.
5. Repeat steps 2 through 4 on the left eye with the right eye occluded.
RECORDING
·Record the amplitude of accommodation in diopters for each eye separately.
·Record the method of testing used.
EXAMPLES
·Amp OD 7 D OS 7 D (minus lens method)
·Amp OD 3.5 D OS 3.5 D (minus lens method)
EXPECTED FINDINGS
The amplitude of accommodation as measured by the minus lens to blur method is approximately 2.0 D less than that measured by the push- method (see Donders' Table). |
