Empty field myopia occurs when the eyes have nothing specific to focus on in the visual field, causing them to focus automatically at a distance of a few meters. Without visual stimulation, the eyes' lenses shift to a resting state of mild near-sightedness. This condition is a risk for pilots flying in open airspace with featureless skies, haze, glare, snow, or over large bodies of water, as distant aircraft or terrain become difficult to see until very close. Pilots can counter empty field myopia by frequently focusing on distant horizons or wingtips to stimulate the eyes' long distance focus.

1. Empty space myopia (Empty field myopia ) - a condition in which the
eyes, having nothing specific within the available visual field upon which to
focus, focus automatically at a range of the order of a few meters ahead.
Detection of objects outside this restricted field of view is delayed and if an
object of interest does enter the restricted field of vision, the determination
of its size or range would be problematic.
The normal function of the eye lens is to physically focus light from
the object on the retina. To do this, the eye must be stimulated by an
image. Empty field myopia manifests itself when the human eye is in a
passive state of focal point adjustment, i.e. when there is no image
(stimulus) for the eye to focus on, for example, when the eye is either in

2. complete darkness, or looking at a bright empty field. If the eye lacks this
stimulation, the lens is shifting to a resting state.
Resting State of Accommodation of the Human Eye
In this condition, the eye is usually focused at an intermediate point (about
80 cm on average, although there are large variations up to few meters),
thus the healthy human eye becomes myopic.
Adaptation of the eye - automatically reverses when whatever is being accommodated is
removed

3. Beyond the visual threshold the image of distant aircraft, whether seen in
silhouette as a dark speck or relatively bright dot may thus be spread over
a larger region of the retina and become an insufficient stimulus for the eye
to focus on. Human factors studies show that a dot very close to the
threshold size in an otherwise empty field could suddenly disappear
because it was an insufficient stimulus to prevent the adjustment of the eye
to assume its resting state.
RISK SCENARIOS
The higher risk probability is distributed among general aviation flights
conducted outside controlled airspace (in airspace classes, E, F and G
where the Visual Flight Rules (VFR) flights are not subject to ATC
clearances), or any flights in such airspace and conditions with
predominant see and avoid rules and where the ATC assistance to
avoid loss of separation (LOS) is limited.
The list below consists of several identified conditions when the eyes often
tend to turn back to their natural resting state:
 in Visual Meteorological Conditions (VMC), when the sky is
featureless and visibility is 10 km. or more;
 in very dark night with no stimuli outside the cockpit to focus on;
 in hazy conditions when the optical properties of the atmosphere alter
the appearance of aircraft and terrain;
 in bright light and glare when the flight is conducted in very sunny
conditions over a cloud layer or the flight course is in the direction of
the sun;
 flying over snow covered or desert surfaces with predominantly
featureless ground characteristics and over large bodies of water; the
risk factor is especially high for low level inspection flights and military
low flying assignments;

4. All of the above scenarios are associated not only with LOS but also
with controlled flight into terrain (CFIT) risks. In these scenarios the visual
detection of traffic and terrain could be hindered by empty field myopia and
the healthy human eye can effectively become near-sighted. The danger
might not become apparent until it is too late for evasive actions.
The hazard of mid air collision contributed by empty field myopia is
compounded by the fact that the frontal area of the aircraft profile is small
and an aircraft viewed directly from the front, especially flying a head-on
collision course, shows little relative movement. This makes detecting the
other aircraft by the pilot very difficult.
Relativity of distance and time to impact
In addition an aircraft that has a high degree of contrast against the
background will be easier to spot, while spotting one with low contrast at
the same distance may be hard and sometimes next to impossible.

5. DEFENCES
To counter the weakened ability of the eye to maintain a distant focus,
good practices are to:
 Focus frequently on distant visible objects, e.g. on outlines of terrain at
or near the horizon; this helps to stimulate the eyes to establish long-
distance focal points;
 Stimulate the eyes by focusing at own aircraft wing tips;
 Consider flying above a haze/smoke layer if possible;
 It may be preferable when scanning the sky for other aircraft to use
peripheral vision to detect movement. Peripheral vision responds
better in terms of detection of weak stimuli associated with slight
movement than the central vision.