Application Process for Medical Certification - Examination Equipment and Techniques
Item 50. Distant Vision
- Snellen 20-foot eye chart may be used as follows:
- The Snellen chart should be illuminated by a 100-watt incandescent lamp placed 4 feet in front of and slightly above the chart.
- The chart or screen should be placed 20 feet from the applicant's eyes and the 20/20 line should be placed 5 feet 4 inches above the floor.
- A metal, opaque plastic, or cardboard occluder should be used to cover the eye not being examined.
- The examining room should be darkened with the exception of the illuminated chart or screen.
- If the applicant wears corrective lenses, the uncorrected acuity should be determined first, then corrected acuity. If the applicant wears contact lenses, see the recommendations in Chapter 3, Items 31-34, Eye, Section II, #5.
- Common errors:
- Failure to shield the applicant's eyes from extraneous light.
- Permitting the applicant to view the chart with both eyes.
- Failure to observe the applicant's face to detect squinting.
- Incorrect sizing of projected chart letters for a 20-foot distance.
- Failure to focus the projector sharply.
- Failure to obtain the corrected acuity when the applicant wears glasses.
- Failure to note and to require the removal of contact lenses.
- Acceptable Substitutes for Distant Vision Testing: any commercial available visual acuities and heterphoria testing devices.
- Directions furnished by the manufacturer or distributor should be followed when using substitute devices for the above testing.
There are specific approved substitute testers for color vision, which may not include some commercially available vision testing machines. For an approved list,
see Item 52. Color Vision.
- Each eye will be tested separately, and both eyes together.