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11.4.17 Symptoms of presbyopia develop gradually and in the early stages an individual may only have
difficulty when tired or in low light levels or when print quality is poor. A pilot with early presbyopia may have no
trouble reading maps and charts in bright daylight but will have difficulty doing so as the light fails. Pilots should
therefore be provided with reading spectacles as soon as they become presbyopic rather than waiting until they
have difficulty reading small print in bright illumination.
11.4.18 The medical examiner should be aware that Annex 1 requires a flight crew member to have a spare set
of suitable correcting spectacles readily available during the exercise of the privileges of the licence or rating
applied for or held. Also when only near correction is required, a second pair of near-correction spectacles shall
be kept available for immediate use.
Trifocals type 1
Bifocals
Trifocals type 2
Intermediate
Distance
Near
III-11-28 Manual of Civil Aviation Medicine
Contact lenses
11.4.19 While the usual reason for wearing contact lenses is cosmetic, there are important visual
advantages compared with spectacles. These include improved field of vision and abolition or marked
reduction of the aberrations mentioned above. For applicants with large refractive errors, contact lenses
generally provide better visual function than spectacles.
11.4.20 The modern soft (hydrophilic) contact lenses and the gas-permeable hard contact lenses can be
satisfactorily worn by many persons with spherical and astigmatic refractive errors. The old
polymethylmethacrylate (PMMA), non-gas-permeable hard contacts with their associated spectacle blur
problems have almost disappeared. Bifocal contact lenses are available but their success rate is much lower
than for ordinary single vision contacts and they are not acceptable for flight crew.
11.4.21 Even the best fitting contact lens is a foreign body in the eye and interferes somewhat with the
normal physiology of the cornea. Wearing contact lenses is associated with slight but definite risks which
include abrasion of the cornea, allergic reaction to the contact lens solutions, development of corneal
neovascularization, conjunctivitis, corneal ulceration and eye infections.
11.4.22 Nevertheless, after establishing that an applicant has been properly fitted with contact lenses and
that he can handle them and wear them comfortably for a period of time sufficient for the required flying duties,
such an applicant may be allowed to use the contact lenses instead of spectacles.
11.4.23 The availability of high index materials allows individuals with large refractive errors to be fitted with
spectacles which cause less distortion and less interference with the peripheral visual field than is the case with
conventional spectacle lenses. Even so, there are applicants with high refractive errors such that the required
spectacles would have unacceptable aberrations and/or cause visual field limitations. In such cases, the
successful use of contact lenses may be a requirement, i.e. the applicant may fly wearing contact lenses but
not wearing spectacles. In such a situation the applicant should have a spare set of contact lenses available
whenever exercising the privileges of the licence. In addition to a spare set of contact lenses, applicants who
meet the requirements with contact lenses but not with spectacles must have available a set of spectacles
(preferably with high refractive index lenses) for use in an emergency situation when it may be impossible to
insert the spare contact lenses.
11.4.24 Applicants who are successful contact lens wearers need not have their uncorrected visual acuity
measured on a regular basis provided the recent history of the contact lens prescription is known. Stability of
the contact lens prescription would indicate no significant change in the uncorrected distance visual acuity.
11.4.25 Monofit or monovision is a method of dealing with presbyopia in an individual who uses contact
lenses for distance and does not wish to use reading spectacles while wearing the contact lenses. The method
uses contact lens correction of the dominant eye for distance vision and of the non-dominant eye for near. This
technique is not acceptable for flight crew because of the reduced distance visual acuity in the non-dominant
eye.
11.4.26 In certain situations air traffic controllers may use contact lenses while working at their display
screens and need a set of spectacles to correct their distance vision while wearing the contact lenses.
11.4.27 The low relative humidity in aircraft can affect soft contact lenses so that wearing time may be
reduced. In some situations the use of non-preserved artificial tears may be desirable if the flight is prolonged.
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Manual of Civil Aviation Medicine 2(48)
