VISION CATEGORY AND ACUITY
Army.ca currently has over 20 threads regarding vision categories, refractions and minimum categories.
Usually, these take the form of "I have ____ vision. Can I still be a infanteer/pilot/diver"?
or "I have _____ vision, what is my category? Can I still be a _______"?
Here is a short guide to help you answer your own questions on vision categories without starting
another new thread.
If you currently wear prescribed eyewear, you will need to bring both your
glasses and a copy of
your most recent eyewear prescription to the testing.
An visual acuity test is a part of every recruiting medical. The result of this exam is expressed by
a vision category. The vision category is only one part of the medical category. It is expressed
as being V1, V2, V3, V4 or V5. The V stands for Vision. V1 is for good acuity, while a rating of
V5 would be very poor. To be enrolled, you must be V4 or above, as the V5 category does not
meet the common enrolment standard.
There is also a CV category for Colour Vision. If your interested in colour vision, try this forum:
http://forums.army.ca/forums/threads/37585.0.html
To see what each military occupation requires for vision (and other categories), check here:
http://www.forces.gc.ca/health-sante/pd/cfp-pfc-154/pdf/AN-Eapp1-eng.pdf
There are actually two acuity tests. A test for distance acuity that everyone must complete,
and a test for near vision that only Pilots, Tac Hel Obs and SAR techs must complete in addition
to distance testing.
The near vision testing for those three occupations is only conducted by ophthalmologists,
ophthalmic technicians, or optometrists. Near vision is determined using "TIMES ROMAN" type
and is assessed at reading distance (30-50 cm) and at 100 cm. The 100 cm distance is important
in the aircraft cockpit and similar environments and for users of CRT displays.
For further details on vision testing for air crew trades, see this document (March 2008):
http://forums.army.ca/forums/index.php?action=dlattach;topic=69305.0;attach=25147
The distance vision testing that everyone must take can be conducted at the CFRC or any
Medical Inspection Room. It can be done two ways. Using a projector that displays slides,
or using a standard eye chart on the wall.
The results of the distance acuity test will fit into one of these categories from the Medical
Standards Manual:
GRADE | BETTER EYE Uncorrected | OTHER EYE Uncorrected | BETTER EYE Corrected | OTHER EYE Corrected |
V1 | 6/6 | up to 6/9 | N/A | N/A |
V2 | up to 6/18 | up to 6/18 | | |
| | OR | 6/6 | 6/9 |
| up to 6/12 | up to 6/30 | | |
V3 | up to 6/60 | up to 6/60 | 6/6 | 6/9 |
V4 | Worse than 6/60 | Worse than 6/60 | 6/9 | 6/60 |
V5 | This grading is assigned to those whose visual acuity is worse than the V4 grading or when the refractive error exceeds plus or minus 7.00 dioptres (+/- 7.00 D) spherical equivalent in the better eye regardless of the uncorrected distant vision. |
NOTE 1: Those who do not meet the V1 standard of uncorrected visual acuity must have
a (current) refractive error measured.
NOTE 2: The spherical equivalent is equal to: (cylinder/2) + sphere.
NOTE 3: An ophthalmologist must examine (fundoscopy) those whose refractive error
exceeds plus or minus 7.00 dioptres (+/- 7.00 D) spherical equivalent in either
eye to rule out any complications.
Testing procedure from CFP-154:
3. The procedure for testing visual acuity is as follows:
a. vision for each eye is tested separately, with the other eye occluded (covered); and
b. candidates must not be allowed to squeeze their eyelids or to posture their head as an aid to vision.
4. The visual acuity for each eye is recorded as a fraction, using the number 6 as the numerator, and, for the
denominator, the number of the lowest (smallest letters) line on the chart which can be read without error.
Thus, if the lowest line which the subject can read bears the number 9, visual acuity for that eye is 6/9. The
grading of distant visual acuity is presented in Appendix 1.
5. When uncorrected vision is below acceptable standards, the possibility of correction to normal shall be
tested with the candidate's own spectacles. If correction to acceptable standards is not possible by these
means, the candidate shall be referred for the opinion of a qualified ophthalmologist.
Some Explanation
Acuity is represented as a fraction, with the distance at which you are standing being the numerator (top part of fraction).
Not all eye charts are the same. Standard Snellen charts have you stand a distance of 20 feet back and express the fraction
as 20/x. Metric charts (like the CF charts) have you stand a distance of 6 meters back. (6.09 meters is actually
20 feet) and express the fraction as 6/x. Note that there are charts that specify a test distance of only 4 meters (4/x).
Likewise there are Snellen charts that specify a testing distance of 10 feet. Examiners should be familiar with the
chart they are using.
The bottom number of the fraction represents the distance that the average eye can see the letters on a certain line
of the eye chart. For example, the line marked 6/30 should be visable to the average eye at a distance of 30 meters.
Here is how the fractions equate:
METRIC | SNELLEN |
6/3 | 20/10 |
6/4.5 | 20/15 |
6/6 | 20/20 |
6/7.5 | 20/25 |
6/9 | 20/30 |
6/12 | 20/40 |
6/15 | 20/50 |
6/30 | 20/100 |
6/60 | 20/200 |
REFRACTION vs. CATEGORY
Occasionally a thread pops up with someone asking something similar to "I have a -1.25 refraction,
what vision category will I have"?
Answer: We can't really tell you with any great accuracy. The two things are only loosely related. This is why we
ask for a refraction along with your acuity. The reverse is also true. We can't take your acuity score
and accurately predict your refraction.
The refraction is only useful regarding correction of the lens. It does not tell us enough about your
visual acuity. for example, you might need a -xx.x lens correction, but numerous other eye problems
(opaqueness, retina) can have a big bearing on your acuity.
You
might be able to use the chart below as a rough guide. Be warned it works best for myopia
(nearsightedness) because hyperopic (farsighted) people can focus and compensate for a certain
amount of their prescription.
Fraction | Estimated Prescription |
6/3 | N/A |
6/4.5 | N/A |
6/6 | N/A to -0.25 |
6/9 | -0.50 |
6/12 | -0.75 |
6/15 | -1.00 to -1.25 |
6/30 | -1.75 to -2.00 |
6/60 | -2.00 to -2.50 |
TERMS:
Accommodation - Process where the eye increases optical power to maintain a clear focus on an object
Astigmatism - The cornea or the lens of the eye is not perfectly spherical.
Axis - The direction of a Cylinder correction in a refraction. Expressed in degrees from 1 to 180.
Cornea - The transparent front part of the eye that covers the iris, pupil, and anterior chamber
Cycloplegia (Cycloplegic) - Paralysis of the ciliary muscle in the eye, affecting the ability to focus.
Cylinder - The secondary correction of the lens in a refraction. See Axis above.
Diopter - A unit of measurement of the optical power of a lense.
dv - Distance Vision
Hyperopia (Hyperopic) - farsighted. Usually a convex lense with a positive diopter.
Myopia (Myopic) - nearsighted. Usuallly a concave lense with a negative diopter.
nv - Near Vision
OD (oculus dexter) - the right eye
OS (oculus sinister) - the left eye
OU - both eyes
PL or Plano - No refractive error
Refractive Error (Refraction) usually expressed in Diopters
Retina - Back of the eye containing the photoreceptor cells (rods and cones) which convert light into nervous signals.
Sphere - The spherical error in a refraction. The Main part of a lens correction. Expressed in + or - diopters.
Visual acuity - The ability to see and discriminate a certain size target at a specified distance.
SUGGESTED READING:
http://www.yorku.ca/eye/toc.htm
Please PM me with errors or corrections.
<edit: Updated to reflect standard changes effective 24 June 2005>