Under the ICAO SARPS there are no dioptre limits for certification. However high refractive correction result in aberrations. High refractive correction should thus be achieved by means of contact lenses or high refractive index lenses that include aberration control (i.e. aspheric lenses). The ICAO Medical Manual Ophthalmology Chapter gives comprehensive information about the types of visual aids available and their use in aviation.
Coloured lenses are not permitted.
Under the ICAO SARPS, when near and distance correction are both needed, the applicant is required to demonstrate that one pair of spectacles is sufficient to meet both distant and near vision requirements. This is to allow effective outside vision to be maintained together with the ability to read charts and instruments without changing spectacles. CAA has adopted this recommendation as a policy (see Presbyopia). If this requirement is not appropriate for some types of operations, i.e. helicopter long line work, CAA should be contacted for advice.
The combination of contact lenses and look-over spectacles is acceptable as this allows both distance and near vision without the need to remove or change spectacles.
Bifocal or Trifocal spectacles may be necessary to achieve the distance, intermediate and near vision standards with one pair of spectacles. Please refer to the ICAO medical manual for the various configuration options.
Progressive power lenses, also called varifocal lenses may be permitted following a period of adaptation on the ground. This usually takes days to about one month.
They have a narrow field of sharp vision and require precise head movements to orientate the visual axis as necessary. In addition they may create unwanted visual illusion in the periphery. Some people are unable to adapt to this type of visual aids.
The use of varifocal spectacles is more likely to be problematic in small aircraft or helicopters because of the seating closer to the ground and the greater use of peripheral vision during landing.
Once comfortable, applicants using progressive spectacles should be advised to initially fly dual with an instructor or check pilot while wearing their progressive spectacles to ensure good visual judgement.
ICAO SARPS require spare spectacles to be available when refractive correction is needed to achieve the vision standards. CAA policy now requires medical certificate holders to have spare spectacles readily available (see also sunglasses).
Contact lenses are permitted if well tolerated. Under ICAO SARPS contact lenses must be non-tinted and multifocal contact lenses are not permitted.
An applicant who is starting to wear contact lenses should demonstrate good tolerance after a period of adaptation. This is particularly important for long haul pilots who spend long hours in a very dry environment. Occasionally applicants present wearing multifocal lenses. An applicant who insists on using this type of lenses should be assessed as not meeting the vision standards.
Monovision contact lenses, aiming at giving satisfactory distance vision in one eye and satisfactory near vision in the other eye are not acceptable.
Monovision achieved by way of refractive surgery, by rendering on eye myopic, is an increasingly common practice used to achieve freedom of glasses. This is not acceptable.
Orthokeratology (Ortho-K) is the use of rigid gas-permeable contact lenses that reshape the cornea to reduce refractive errors, normally worn only during sleep, to improve vision through reshaping of the cornea. It is used as an alternative to refractive surgery or for those who prefer not to wear contact lenses while awake. The correction is not permanent and the visual acuity will regress while not wearing the Ortho-K lenses. There is no reasonable or reliable way to determine whether visual standards continue to be met for the entire period the lenses are removed. Those lenses require several weeks to adapt to and some users may experience initial difficulties such as ghosting, contrast problems and double vision. There may also be issues with corneal hypoxia.
The FAA requires applicants who use Ortho-K lenses to meet the applicable vision standard while wearing the Ortho-K lenses and to wear the Ortho-K lenses while piloting.
The NZ CAA generally has a more restrictive approach and MEs should specifically inquire about the use of Ortho-K lenses.
The use of orthokeratology lenses is not acceptable and should be considered as being of aeromedical significance. Applicants using such lenses should be considered under the flexibility process. It is unlikely that they will be issued a medical certificate unless they revert to other forms of acceptable refractive correction.
ICAO SARPS recommend the use of neutral grey tint to avoid altered perception of surroundings. The use of transition lenses is discouraged due to their sluggish light transmission change characteristics when moving into dim lighting conditions. They must not be used by night. If used by day, clear spare spectacles, allowing the vision standards to be met, should be also carried. Prescriptions sunglasses are acceptable as third pair of corrective lenses in addition to the main and spare corrective lenses which should both be clear lenses. The use of Polaroid lenses is not acceptable as further polarisation through the windscreen or instrument glass can lead to unexpected loss of outside or instruments vision.