I first read about the Medical Review Board’s (MRB) recommendation to change the Field of Vision (FOV) from the current standard of 70 degrees monocular to 120 degrees horizontal binocular field of vision (FOV) in the Commercial Driver Medical Examiner (CDME), a quarterly publication from the American College of Occupational and Environmnental Medicine (ACOEM). Furthermore it was recommended by the MRB that drivers with any visual defects that may affect their visual fields stemming from diabetes, to age related macular degeneration, cataracts, glaucoma, and retinits pigmentosa be referred for formal vision evaluation by an ophthalmologist or optometrist.
The report was based on a presentation to the MRB on October 19, 2012 by Dr. Michelle Tregear of Manila consulting. I will try to summarize some of the essentials of the presentation.
- Prevalence: Visual impairment defined as 20/40 or worse, is one of 10 most prevalent disabilities in the U.S. affecting approximately 3.5-5 million people, with 1 million of those legally blind (defined as a vision of 20/200 or worst).
- Causes: Age related (cataracts) most prevalent, other leading causes include diabetic retinopathy, glaucoma, and age related macular degeneration; It was noted in their report that truck drivers have an increasing median age.
- Normal human FOV: Stated as 180 degrees binocular (both eyes) and 160 degrees monocular (each eye).
- History and a possible historical blunder: It appears that originally in the year 1952 the FOV was set to 140 degrees binocular by the Agency and later changed to 70 degrees in the horizontal median for monocular vision in 1970. Where’s the blunder? Well, it is now thought that the 70 degrees monocular vision standard of today was probably an incorrect restatement of the one in 1952 of 140 degrees binocular. Remember, normal binocular vision is 180 degrees, and normal monocular vision is 160 degrees. So where did the 70 degrees monocular of today come from? Apparently in error (they just divided the 140 binocular in half).
- In 1993 the Federal Highway Administration (FHA) commissioned the Bionetics Commision (Ketron Division) who did not recommend any change to the visual standard but did recommend the FOV recommended in 1970 be stated as 120 degrees monocular.
- In comparing the FOV requirement of the FMCSA with other DOT agencies and other countries Dr. Tregear reported the following differences: The U.S. Coast Guard requires at least 100 degrees of FOV in each eye. Countries such as Canada, New Zealand and Australia all used a binocular vision standard. ( In the horizontal median there is a required 150 degrees in Canada and 140 degrees in both New Zealand and Australia). There was also a requirement of 20 degrees above and below fixation which we will not get into now (thankfully).
- In 1998 an expert panel again reviewed the Ketron study and supported the 120 degrees in the horizontal field of each eye. The expert panel also recommended that those who failed the requirement due to medical conditions be seen by an ophthalmologist or optometrist ( as mentioned earlier).
- However, in 2008 the Expert Panel stated that the current standard of 70 degrees in each eye may be adequate.
- Finally Dr. Tregear evaluated the composition of individual drivers who were granted a vision exemption and found out that: 53 % of them had a FOV in the better eye equal to or greater than 120 degrees. The majority of the drivers had a FOV less than 120 degrees but greater than 110 degrees and 96 % had a field of vision of at least 100 degrees or greater in the better eye.
- Some experts think that we should return to a binocular FOV requirement. It’s used by other countries such as Australia, New Zealand and Canada as we have seen. A benefit for us is that it would first of all correct the apparent mistake of 70 degrees in each eye that we have in our current standard. More importantly, others argue that it is more practical because people drive with both eyes, and that a binocular vision standard would also be helpful in determing how one eye compensates for another in real driving and perhaps better assess drivers with visual deficiencies.
To be continued….
1. USDOT FMCSA Meeting Summary. Field of Vision Updated Evidence Report. Presenting FMCSA Contractors: Michelle Tregear Ph.D Manila Contracting, Stephen Tregear D. Phil Manila Contracting. October 19, 2012
2. Commercial Driver Medical Examiner. Spring 2013. Natalie Hartenbaum M.D., Edidor in Chief. Amercian College of Occupational And Environmental Medicine.