Contact lens wearers must have at least one pair of back-up spectacles available, which can be tinted or untinted but must be suitable for the overall light conditions of the entire flight or duty shift.
Contact lenses have an optical advantage over glasses. The change of image size induced by higher prescription lenses is minimised.
Ring scotomas (area of visual field missed) caused by spectacle frame and lenses are eliminated as are any peripheral aberrations induced by a spectacle lens.
For Class 1 / 2 certification, UK implementing rules (MED.B.070) require that:
- If contact lenses are worn when exercising the privileges of the applicable licence(s), they shall be for distant vision, monofocal, non-tinted and well-tolerated.
- Applicants with a large refractive error shall use contact lenses or high-index spectacle lenses.
- Orthokeratological lenses shall not be used.
AMC1 MED.B.070 indicates that contact lenses should be worn by Class 1 applicants where:
- Hypermetropia (long sight) exceeds +5.00 dioptres.
- Anisometropia (difference in prescription between the 2 eyes) exceeds 3.00 dioptres.
A pilot wishing to use contact lenses for flying will need to ensure that the lenses can be comfortably worn on the ground before using them on the flight deck. As a guide, a minimum wearing time of 8 hours a day for 5 days a week consistently for at least one month should be achieved. It is important that the wearing times do not impact on visual acuity, comfort, or eye health.
It should be noted that there are some successful contact lens wearers who are not able to use their lenses in flight due to several factors, including lens dehydration and altered lens parameters.
For Class 3 certification, UK regulations (ATCO.MED.B.070) state:
- Contact lenses, when worn during the exercise of licensed privileges, shall be mono-focal, non-tinted and not orthokeratological.
- Monovision contact lenses shall not be used.
- Applicants with a large refractive error shall use contact lenses or high index spectacle lenses.
An air traffic controller (ATCO) will need to ensure that the lenses can be worn comfortably for the duration of their duty. It is important that the wearing times do not impact on the visual acuity, comfort, or eye health.
All contact lens materials (soft, gas permeable, or hard) are acceptable for certification provided they are well tolerated. Optimum distance correction must be achieved. The correction of astigmatism should always be considered for soft contact lens wearers (using toric lenses). Silicon hydrogels (a type of lens material used in some soft disposable contact lenses) should be considered for pilots due to their low water content and high oxygen transmission.
All contact lens wearers are expected to attend for regular check-ups as advised by their contact lens practitioners. All contact lenses must be for distance only correction. Therefore, for presbyopic pilots or ATCOs who regularly wears contact lenses, a VML limitation (for distance contact lenses and back-up multifocal spectacles) plus a VNL limitation (for reading glasses available for use over the contact lenses) may be required.
The following types of contact lens correction are not acceptable:
Monovision is where the dominant eye is fully corrected for distance and the non-dominant eye is corrected for near. The distance visual acuity in the ‘reading eye’ will often fall below the appropriate acuity standard. It can interfere with depth perception and does not ensure optimum distance vision.
Unlike spectacle lenses where the user can use eye movements to view through a different portion of the lens and consequently a different focal length, a contact lens will move with eye movement. This means that a different optical system must be applied to enable the viewing of more than one focal length simultaneously. There are several designs of multifocal contact lenses; however, they will tend to have a poorer optical quality and cause potential reduction in distance or near visual acuity and/or contrast sensitivity. Some designs are also problematic in bright light conditions. For these reasons, multifocal contact lenses are not acceptable for aviation use.
Cosmetic coloured lenses
Cosmetic coloured lenses have either a tint or an iris pattern to change the apparent colour of the user’s eyes. Coloured lenses are not compatible with aviation use. This is due to potential visual disturbances in lower light levels where the pupil widens beyond the central clear zone of the lens. Some lenses also have a high risk of inducing corneal hypoxia in flight due to poor oxygen transmissibility.
Orthokeratology (or Ortho K) lenses
Orthokeratology lenses are ‘reverse geometry’ lenses designed to remould the front corneal surface to reduce or control myopia progression. They are typically worn at night and removed during waking hours. Any change to the corneal shape (and hence improvement to unaided vision) tends to wear off during the day and wearers of these lenses are unable to achieve optimum vision throughout the day. For this reason, this type of lens is not acceptable for aviation use.
Lenses to alter colour perception
Lenses to alter colour perception are coloured lenses which filter specific wavelength bands and are occasionally worn by people with colour vision deficiencies to aid them in a particular area where they may confuse certain colours. The lenses do not correct a colour vision deficiency but merely move the colour confusion to a different area of the colour spectrum. They are not compatible with aviation use.