Pilots and air traffic controllers (ATCOs) change their gaze frequently between objects at near, intermediate, and far distances.
The ability of the eyes to focus on near tasks decreases with age. This is known as presbyopia, which results in the individual requiring a prescription for near and intermediate tasks. Typically this becomes apparent in the mid-forties, although it may do so at an earlier age in hyperopes and later in myopes. The prescription required increases with age, usually stabilising in the late fifties.
The ideal presbyopic correction sometimes incorporates a distance prescription as well (even if the distance prescription is zero) so that one pair of spectacles covers all visual tasks. An intermediate zone for screen or instrument panel vision will usually also be required.
Possible forms of optical correction are:
- contact lenses
- refractive surgery
All types of correction (bifocal, progressive or trifocal) are acceptable, provided they are well tolerated.
Bifocals will offer distance and near correction with the near portion being a distinct segment within the lower part of the lens. There are different bifocal types:
- D- segment are the most prevalent and these are acceptable.
- Executive bifocals (where the reading portion covers the whole width of the lens) are not recommended for pilots as the lower half of the distance visual field is blurred by the reading segment, which is particularly important for helicopter pilots and with the use of night vision goggles.
Progressive lenses (or varifocals) change in prescription gradually from the distance part of the lens at the top to the near portion of the lens at the bottom. These lenses are the most common type of multifocal spectacle correction used and have an area of intermediate focus between the distance and near portions.
The most appropriate lens design should be chosen based on the actual position and distance of the instrument panel of the particular aircraft flown or the screen used in the case of ATCOs. Trifocal lenses are similar to bifocals but have a second distinct segment for intermediate as well as a near vision segment. It is also possible to include another intermediate portion at the very top of the lens for viewing overhead panels.