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Vision - 49 CFR 391.41(b)(10)

Snellen Distant Acuity Test

The Snellen chart is widely used for measuring central
visual acuity.

  • The Snellen wall chart should be 20 feet away
    from the driver.
    • Measure distance.
    • Mark testing location.
  • The chart should be illuminated with white light.
  • The driver may wear corrective lenses during
    the examination.
  • When the driver is reading larger lines easily,
    the medical examiner may ask the driver to skip
    to smaller lines.

Snellen chart is illustrative only and not suitable for vision testing.

Visual acuity test results

The Snellen eye test results use 20 feet as the norm, represented by the numerator in the Snellen test result. The number of the last line of type the driver read accurately is recorded as the denominator in the Snellen test result.

The minimum qualification requirement is distant visual acuity of at least 20/40 in each eye and distant binocular acuity of at least 20/40.

If a test other than the Snellen is used to test visual acuity, the test results should be recorded in Snellen-equivalent values.

Types of Snellen charts

There are versions of the Snellen chart that compensate for
failure to read letters because of limited English reading skill,
not because of poor eyesight. One example is the "Snellen
Eye Chart - Illiterate" that requires the individual to indicate
the orientation of the letter "E" on the chart.

Snellen chart is illustrative only and not suitable for vision testing.

Protocol for Screening the Visual Field

The driver must have at least 70° in the horizontal meridian for each eye. Some form of confrontational testing that tests vision of selected horizontal points is generally used in the clinical setting.

A "Protocol for Screening the Visual Field Using a Confrontation Method" is found in Appendix E of the Visual Requirements and Commercial Drivers report.

Right eye examination

  1. Stand or sit approximately two feet in front of the driver so that your eyes are at about the same level as the eyes of the driver.
  2. Instruct the driver to use the palm of the left hand to cover the left eye.
  3. Ask the driver to fixate on your left eye.
  4. Extend your arms forward and position your hands halfway between yourself and the driver. Position your right hand one foot to the right of the straight-ahead axis and six inches above the horizontal plane. Position your left hand one-and-a-half feet to the left of the straight-ahead axis and six inches above the horizontal plane.
  5. Ask the driver to confirm when a moving finger is detected. Repeat the procedure with your hands positioned six inches below the horizontal meridian.

 

Left eye examination

Repeat the procedure for the left eye (steps 2 through 5), making sure the driver fixates on your right eye and the hand placement is appropriately reversed.

When test results are inconclusive, obtain specialist evaluation for precise measurement of peripheral vision.

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