Pilots and Air Traffic Controllers have to change their gaze frequently between objects at near, intermediate and far distances. With age, the ability of the eye to focus on near tasks decreases. This is known as presbyopia and the individual requires a prescription for near tasks. If a distance prescription is also required, some form of optical correction is needed which incorporates focus for both distance and near (and also intermediate) vision.
The following offers information for Pilots and Air Traffic Controllers in the following areas of optical correction:
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 less ideal, and are not recommended for helicopter pilots.
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 towards the bottom. These lenses will also have an area of intermediate focus in-between the distance and near portions. The other type of lens available with an intermediate prescription is a trifocal lens. These are usually similar in appearance to bifocals but with an extra segment on top of the near portion. Occasionally the intermediate portion is incorporated into the top of the lens, with the reading portion at the bottom of the lens and the distance area in the centre. This may be useful for viewing overhead panels.
Occasionally, a pilot may use a flip-up type frame. This would have a hinge at the top part of the glasses front with a second set of lenses that can be swung down in front of the eyes when required. Here, a bifocal distance/intermediate lens can be put into the main part of the frame with an intermediate prescription in the hinged portion. When lowered, the correction would change from distance/intermediate to intermediate/near.
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All IOLs must be monofocal.
Multifocal IOLs are not acceptable. These lenses are available however they function very differently to multifocal spectacle lenses which have distinct separate areas for different focal lengths. With multifocal spectacle lenses, the user can use eye movements to view through a different portion of the lens and consequently a different focal length. A multifocal IOL employs a type of simultaneous viewing where distance and near focus are presented and the subject uses the part of the lens which is least out of focus for the task. A poorer quality of image is received at the retina and although high contrast visual acuities may be unaffected, contrast sensitivity, particularly in mesopic conditions, is often affected.
There have been recent developments with ‘accommodating’ IOLs which, although they still sit in the capsular bag, are able to move slightly with ciliary muscle action. This enables some accommodation, but not enough to negate the need for reading glasses. The optics of these lenses should not affect visual acuity or contrast sensitivity and may be acceptable for certificatory use following aeromedical assessment.
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