Empty Field Myopia

Empty Field Myopia (EFM) — also called "empty sky myopia" or "sky myopia" — is an important physiological effect that severely impairs traffic scan in flight.

What is EFM?

Definition: when the human eye has no clear focus point in the visual environment (e.g. cloudless blue sky, uniform cloud deck, dense fog), it does not focus to infinity but to a "resting point" about 1–2 m in front of the eye.

Consequence: distant objects (especially small, low-contrast ones such as an oncoming aircraft) are out of focus on the retina — the pilot detects a converging traffic only late or not at all.

Cause — eye accommodation

The eye focuses on different distances by accommodation (lens adjustment via the ciliary muscle):

Near point: lens strongly curved, ciliary muscle tense.
Far point: lens flattened, ciliary muscle relaxed.

But when no focus stimulus exists in the image (no lines, structures, textures), the eye relaxes into an "accommodation rest position" — at 1–2 m, not at infinity.

This effect was scientifically established in 1970s aviation research and is standard knowledge in modern pilot training.

When does EFM occur?

Typical situations:

1. Cloudless blue sky:

No contrast, no structures.
Pilot fixates on "nothing" — oncoming traffic missed.

2. Uniform cloud deck:

Stratus deck below the aircraft without structure.
Most difficult conditions for traffic scan.

3. Fog / haze over water:

Almost no visual reference.
Very high EFM risk, plus spatial disorientation.

4. Polar light / snowfield / desert:

Few structures, no depth perception.

Effects

Reduced detection range:

In unstructured visibility a pilot detects an oncoming aircraft only from < 1 NM — at a closure rate of 300 kt (two VFR aircraft head-on) only < 12 seconds remain to react.

Increased collision risk:

Mid-air collisions often occur in good visibility but "empty" environments.
Statistics: about 75% of mid-air collisions happen in VMC.

Counter-measures

1. Active scanning

Scan technique (see Visual scan) — periodically focusing on concrete objects forces accommodation to infinity:

Focus on the wing tip (1–2 s), then back to the field of view.
Wing/cockpit structures as anchor points.
Horizon structures (clouds, terrain, sun) deliberately looked at.

2. Deliberately seek visual stimuli

Clouds in the background — even single cumulus helps.
Terrain structures below (fields, woods, rivers).
Other aircraft (contrails, other traffic) act as anchors.

3. Regular eye movement

Move the eyes every 5–10 seconds — prevents staring.
Pause between outside views and instruments matters.

4. On IMC entry

If EFM conditions appear (nothing more visible): transition to instrument flying — a VFR pilot without IR must turn back or descend to visible conditions.

5. Sunglasses and polariser

Reduce glare, but do not eliminate EFM.

6. Use traffic information

ATC / FIS / TIS / ADS-B actively used.
Transponder Mode S / ADS-B enables TIS display in EFB.

Night Myopia:

At night without light stimuli the eye focuses at ~1–2 m instead of infinity.
Consequence: stars appear blurred; approach lights are perceived blurred.

Instrument Myopia:

A pilot who has stared at instruments long focuses to 0.5–1 m.
On looking out: brief accommodation delay.

Dark Focus:

Accommodation rest position in complete darkness — usually 1 m, with individual variation.