The eye is the pilot's most important information source — VFR flying rests on continuous visual perception.
Structure (simplified model)
| Structure | Function |
|---|---|
| Cornea | Front transparent layer, ~⅔ of refraction |
| Lens | Behind iris, fine focus by accommodation (ring muscle) |
| Iris + pupil | Regulates light intake (pupil 2–8 mm) |
| Retina | Light-sensitive layer — converts light to nerve signals |
| Optic nerve | Carries signals to the brain |
| Blind spot | Optic nerve exit — no receptors |
Receptors in the retina
| Type | Number | Function |
|---|---|---|
| Cones | ~ 7 million | Central vision, colour, day vision, detail resolution. Concentrated in the fovea centralis |
| Rods | ~ 120 million | Peripheral vision, dusk and night vision, motion detection. None in the fovea |
Consequences for the pilot
Day: central vision works — detail and colour in the sharp area.
Night: central vision is blind in low light (no rods in fovea). Solution: off-centre vision — see faint lights by looking ~10–15° to the side of the object. Peripheral rods detect the light.
Blind spot — collision risk
The blind spot of each eye is not compensated by the other when the eyes are still. For VFR traffic scanning: scan deliberately (see §5.2), so traffic doesn't sit unseen in one eye's blind spot.
Accommodation and age
With increasing age (from ~40 yrs) the lens loses elasticity (presbyopia) — near vision for charts/avionics becomes difficult. Often solved in the cockpit with reading glasses or progressive lenses.
Parallax error
Parallax = perceived shift of an object against background when the observer looks from a different angle.
In the cockpit: reading display instruments (analogue altimeter, ASI, etc.) depends on the viewing angle — looking obliquely at an instrument (e.g. from the right seat at a central instrument) reads a different value than looking head-on.
| Situation | Effect |
|---|---|
| Observer on the right, instrument central | Needle appears shifted right → lower value read than actual |
| Observer on the left, instrument central | Needle appears shifted left → higher value |
Consequence:
- In instructor-student setup: both seats can read the same instrument differently.
- Pilot position consistent (head position).
- When in doubt: for critical values look straight at it or use digital readout.
Pilot sunglasses
The right sunglasses are a safety topic in the cockpit:
| Property | Recommendation | Reason |
|---|---|---|
| Polarisation | NOT polarised | Polarised glasses cancel reflections on LCDs, glass cockpits, GPS screens, and Plexiglas windshields — important displays become invisible |
| Light transmission | 15–30 % (day), clear (night) | Good glare reduction without dimming critical displays |
| Colour fidelity | Neutral tint (grey, green) | Original colours preserved — important for traffic lights, weather, indicator colours |
| Text legibility | All instrument numbers / text clearly readable | If the lens kills the text → unsuitable |
| UV protection | 100 % UV-A + UV-B | At altitude (more UV) too — long-term cataract protection |
| Frame | Slim frame, no blocking temple | Don't restrict peripheral vision (traffic scanning) |
Test new glasses: read all cockpit displays through them pre-flight. If a display becomes unreadable → use a different pair.