CASA told me that I must not have polarised sunglasses but gave me no other requirements
CASA does have a recommendation for sunnies - DAME handbook sect 2.1.13 below. Mine are prescription and to the CASA suggested ND 15 tint. Excellent.
Glare is often a cause of significant discomfort when flying above cloud or when flying into
the sun. Sunglasses may be required in such circumstances.
There are two basic factors to consider when selecting sunglasses, namely the frame and
the lenses.
Any spectacle frame reduces the field of vision. Narrow frames that carry large lenses are
desirable. The most critical problem with frames arises from the presence of wide sidearms
which significantly impair the peripheral visual field.
Sunglass lenses should protect the eyes from glare while not adversely affecting the visual
cues necessary for safe flight. Accordingly, lenses should not be too dark, and should
transmit at least 15% of incident light. The tint used should be "neutral density" (N.D.),
that is, a greyish tint that does not distort colour perception or adversely affect red signal
detection and recognition. The recommended tint is N.D.15.
Lenses of polycarbonate are preferred because of their impact-resistance and ability to
absorb ultra-violet and infrared rays. However, these lenses can scratch readily and any
scratched spectacles should be discarded.
To ensure that sunglasses provide adequate protection from solar radiation that may
damage the eyes, only those sunglasses that conform to the current Australian Standard
should be worn.
Sunglasses that conform to the current Australian Standard also meet acceptable
standards for lens quality, frame strength and lens retention.
For aviation use, those sunglasses marked "Specific Purpose Sunglasses" are
recommended, provided their frames are appropriate. The lenses of these sunglasses
have been specifically designed for use in conditions of intense glare, such as in flight
above cloud. At high altitude, atmospheric absorption of ultra-violet radiation is reduced.
Polarising sunglasses should not be used when flying. The polarising filter interacts with
the cockpit transparency to produce a distorted and degraded visual field that poses a
threat to air safety.
The pilot who already wears prescription spectacles for flying can choose from a number
of options for glare protection. Prescription sunglasses with N.D.15 lenses can be
obtained, or N.D.15 clip-on or flip-up sunglasses may be worn over prescription
spectacles.
Pilots who require correction of their near vision only and who wear "look-overs" are
advised to obtain bifocals and a plano upper segment. Clip-on or flip-up sunglasses can
then be worn. However, the dangers of flip-ups previously mentioned should be recalled.
2.1-14
Graduated lens tint is another option. This provides glare protection for distant vision
outside the aircraft, while near vision inside the aircraft is not impeded by the tint. It is
usually considered that the use of a single tinted segment in bifocal glasses should be
avoided as the visual effect of a "false horizon" may be disturbing and dangerous.