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Dynamic Retinoscopy: Bell Retinoscopy
PURPOSE To measure the linear magnitude of the accommodative lag using a mobile target and a retinoscope. This procedure allows the examiner to directly view the patient’s response to changes in the stimulus to accommodation. This technique is useful in the diagnosis of binocular anomalies and for predicting the efficacy of some forms of therapy.
EQUIPMENT
·Retinoscope.
·Bell retinoscopy target. Current practice suggests that either a reflectant chrome or clear Lucite sphere be used. The actual target is not the sphere but rather the reflected or transmitted image in the sphere.
·Yardstick.
SET-UP
·The test is performed under normal room illumination.
·The patient should wear his habitual or induced near correction.
·The test is performed under binocular viewing conditions.
·The patient holds one end of the yardstick against his cheek while the examiner sets the other end over either his shoulder or his ear.
·The examiner should be positioned at eye level and at a distance where the retinoscope is 20 in (50 cm) from the patient (see Figure 4-17).
STEP-BY-STEP PROCEDURE
1. Position the target against your forehead directly above the retinoscope.
2. Ask the patient to look at the image in the sphere and to keep it clear.
3. Observe the initial retinoscopic reflex in the right eye using a vertical streak. Typically, with motion is observed indicating an accommodative lag. It may be useful to screen for astigmatic error by rotating the streak.
4. If with motion is seen as expected, begin to move the sphere toward the patient, while you remain stationary.
Note: If against motion is seen at the outset, the examiner may use +0.50 probe lenses. If the patient has a need for plus at near, the addition of these lenses may stimulate a relaxation of the accommodation creating a shift to with motion.
5. Continue moving the target toward the patient until the motion changes from with to against motion. Look at the yard stick and mentally note this distance.
6. Continue moving the target toward the patient for an additional two to three inches and then reverse direction, moving the sphere away from the patient and toward you.
7. Continue to monitor the retinoscopic reflex and note the distance at which the reflex changes from against to with motion.
8. Repeat steps 3 through 7 for the left eye.
RECORDING
·Record the technique used.
·For each eye record the distance at which the initial with motion changed to against motion and when the against then returned to with motion.
·If the retinoscopic reflex was initially against, record this and the patient's response to the probe lenses.
EXAMPLES
·Bell Retinoscopy: OD 15"/17"
OS 14"/17"
·Bell Retinoscopy: Against motion/no change with +0.50
EXPECTED FINDINGS
Normal findings for Bell Retinoscopy are 17 to 14 inches for the change to against motion and 15 to 18 inches for the reverse shift to with motion. |
