The aviation environment is visually complex and tri-dimensional. It includes poor visibility and contrast by day and night, extensive use of colours on maps, in instruments and at airports. The visual targets are small and moving. There is a plethora of small print information.
It is therefore evident that good visual performance is essential to flight safety. The ICAO SARPS and the CAR Part 67 vision standards reflect this necessity.
Approximately 50% of civilian pilots require refractive correction while flying, probably more in some Asian countries. Van B. Nkakagawara et al. (2002) studied the USA civilian aggregated data base of aviation incidents and accidents in which the use of an ophthalmic device was considered to have been a contributing factor. They found this to be the case in 45 out of 78216 events, or 0.06% of incidents and accidents. The distribution of the incidents causes were:
|Spectacles lost or broken||11|
|New or inappropriate refractive correction||12|
|Refractive correction not worn when should||4|
|Lack or misuse of sunglasses||10|
|Eyewear interfering with protective breathing equipment resulting in hypoxia or impaired vision||2|
|Contact lenses displace or dislodged||2|
While these numbers are indeed very small, it is probable that a large number of minor but potentially serious incidents have not been documented in this series.
This section of the CAA medical manual aims to assist Medical Examiners in the assessment of applicants with a functionally impaired visual system.
Examination techniques are described in the ICAO Medical Manual and:
As a reminder Visual acuity determination must be done with a 6 metres chart presented at 6 metres from the applicant (6 metres achieved at a distance of 3 metres with the use of mirror is acceptable).
A distance of 6 metres obtained via a mirror is acceptable. The 6 metre 'equivalent' charts, used at 4 metres are not acceptable.