Astigmatism

Astigmatism occurs when different refractive errors are present in different lens/eye meridians. Astigmatism requires cylindrical rather than spherical lenses for correction. The prescription typically includes the dioptre value correction and the cylindrical axis of the required lens. i.e. Dioptres of Cylinder DC: -1.5 x 75 [dioptres x degrees]. Astigmatism is most often combined with a spherical error, myopia or hypermetropia.

The equivalent spherical error is taken as the mathematical sum of any spherical refraction error plus half that of the cylindrical refraction error.

For instance an applicant with the following prescription:

DS -4.0 / DC -2.5 x 150 can be estimated to have a total error: -4.0 + (-2.5 x 1/2) = -5.25

One should be suspicious of keratoconus in applicants with worsening astigmatism. Keratoconus can be missed at the early stage, only to compromise a flying career later.

Thus an applicant with worsening astigmatism should be assessed for keratoconus. If present, the condition may progress and eventually render an applicant ineligible some years later, despite currently meeting the corrected visual acuity standards. In case of doubt a yearly optometrist or ophthalmologist report including corneal topography mapping should be obtained. The applicant should be well informed of the potential for future certification difficulties.

Information to be provided

A special eye report must or should be provided in the following circumstances:

• As required in the Timing of Routine Examinations GD [PDF 500 KB];
• On the first occasion that an applicant presents with progressive astigmatism (any previous reports by vision professionals must also be provided for comparison).
• At regular intervals subsequently if keratoconus is suspected;
• On the first occasion that an applicant presents with contact lenses;
• On the first occasion that an applicant presents with uncorrected distance visual acuity of 6/60 or worse in either eye;
• Every five years if an applicant has uncorrected distance visual acuity of 6/60 or worse, in accordance with ICAO recommendation;
• Every 2 years or as determined by the ME, if an applicant is young and the ME suspects that the refractive error has not yet stabilised. Alternatively, in this latter situation, the ME may elect to review the applicant and only refer if the standards are not met.

Disposition in case of astigmatism

An applicant with astigmatism who meets the uncorrected or corrected visual acuity standards may be considered as not having a condition that is of aeromedical significance.

An applicant with astigmatism, who only meets the visual acuity standards while using spectacles, may be considered as having a condition that is not of aeromedical significance if the certificate is endorsed with:

• Distance spectacles must be worn, or
• Distance spectacles must be worn, contact lenses permitted - if using contact lenses; or
• Spare spectacles must be readily available