It is a good practice, and a requirement for most NDT programs, that personnel working in thermal NDT to take an annual vision acuity exam and color perception testing shall be conducted at least every five years.  At a minimum this should include a Jaeger Eye Test, to see if you can see small detail, as well as a color perception test such as the widely accepted Ishihara Color Deficiency.

Know that both the National Aerospace Standard NAS 410 Rev. 5 and the American Society of Non-destructive Testing ASNT-TC-1A-2021 have vision testing requirements as part of their certification compliance process. These requirements address visual acuity and color deficiency. Unfortunately, they do not reference the same eye charts, but they do allow flexibility by utilizing the phrase “or equivalent”. The Responsible Level 3 will establish the protocol to be used.

ASNT-TC-1A and CP189 references Jaeger J1 (or equivalent) and NAS 410 Rev. 5 references Snellen 20/25 (or equivalent) be administered as part of a certification program.

According to the Field Guide to Visual and Ophthalmic Optics (SPIE Press Book):

A table comparing Jaeger values and their equivalent Snellen distance acuities along with point/font sizes for Time New Roman is shown below:

From this table we can conclude that the Jaeger J1 is the equivalent of the Snellen 20/25 and vice versa. Now that infrared thermography is no longer considered an emerging method in NAS 410 Rev. 5, programs utilizing ASNT certification guidelines may utilize Jaeger J1 test for near vision acuity and be in compliance.

The Near Vision requirement options are:

• 20/25 (Snellen) at 16” ± 1”, in at least one eye natural or corrected.
• Jaeger No.1 @ not less than12” minimum, in at least one eye natural or corrected.
• • Tumbling E in accordance with ISO 18490

Color perception requirements are in place for both ASNT and NAS certification programs. An examination should be given to validate personnel are capable of adequately distinguishing and differentiating contrast and colors in the method or process utilized. Pseudo-Isochromatic Plate or Ishihara Eye Charts are acceptable examinations for this.

Color perception issues tend to be more common among males than females, however; most people who are deemed “color blind” are actually more “color deficient”. If you have a deficiency, this does not necessarily mean you have to give up thermal NDT. What it does is help you better understand what color palette to use when testing and analyzing (grayscale vs. monochromatic vs. high contrast) and it re-enforces the need for you to exercise due care when interpreting color thermal images.