Human visual hardware is a result of a billion years of evolution
within the earths atmosphere where light is scattered by
molecules of air, moisture, particular matter etc. However as we
ascend into our atmosphere with  decrease density, light
distribution is changed resulting in our visual hardware
receiving visual data in different format.

Some Aspects to Consider:

1. Visual acuity is the degree to which the details and contours
of objects are perceived. Visual acuity is usually defined in
terms of minimum separable.Large variety of factors influence
this complex phenomenon which includes :

# Optical factors- state of the image forming mechanisms of
the eye.
# Retinal factors such as the state of the cones.
# Stimulus factors such as illumination, brightness of the
stimulus, contrast between the stimulus and background,
length of time exposed to the stimulus.

* Minimum separable: shortest distance by which two lines can be
separated and still be perceived as two lines.

“During the day, the earth has a predominantly bluish cast…..
I could detect individual houses and streets in the low humidity
and cloudless areas such as the Himalaya mountain area….
I saw a steam locomotive by seeing the smoke first…..
I also saw the wake of a boat on a large river in the Burma-India
area… and a bright orange light from the British oil refinery
to the south of the city (Perth,Australia.)”

The above observation was made by Gordon Cooper in Faith 7 [1963]
and which generated much skepticism in the light of the thesis by
Muckler and Narvan “Visual Surveillance and Reconnaissance from
space vehicles” in which they determined that a visual angle of
ten minutes was the operational minimum, and that the minimum
resolvable object length [M.R.O.L] at an altitude of 113 miles
would be 1730 ft. This limitation of acuity was revised the next
year to 0.5 seconds of arc for an extended contrasting line and
15 seconds of arc for minimum separation of two points sharply
contrasting with the background.

Orbiting at 237 miles in the skylab it was possible to see the
entire east coast [Canada to Florida Keys] and resolve details of
a 500 feet long bridge based on inference. Of Interest is the
fact that even though the mechanical eye [camera systems] can
resolve objects greater than fifty times better than the human
eye, without the human ability to infer, interpretation of the
data is meaningless.

Conclusion: Visual acuity in space exceeds that of earth norm
when objects with linear extension such as roads, airfields, wake
of ships etc.

Stereoscopic vision: the perception of two images as one by means
of fusing the impressions on both retinas. In space one has to
deal with a poverty of reference points.  For hardware evolved in
a reference oriented paradigm, this possess a grave problem.
Once out of the space craft and gazing outward, the eye can only
fix on the stars [without even a twinkle] which for all practical
purpose is at infinity ie. without stereoscopic vision “Empty
field myopia” prevails.

Empty Field Myopia is a condition in which the eyes, having
nothing in the visual field upon which to focus, focus
automatically at about 9 feet.  An astronaut/cosmonaut
experiencing empty field myopia focusing at 9 ft would be unable
see objects at a range close as 100 ft. If another spacecraft,
satellite, meteorite or L.E.M entered his field of vision,
he would not be able to determine the size nor the distance.

Solution:

Man does not face any hostile environment in his birthday suit,
the clothing industry and need for walk in closet say it all.  In
space we will wear our exoskeleton just as we wear winter jackets
in winter and we will wear our helmets with visors to maintain
our internal environment, filter out all those nasty rads etc.
Since Empty Field Myopia is secondary to loss of reference points
why not just  build them into the visor itself giving the eye
points of reference– create a virtual reality ??? This line of
speculation leads to amazing concepts……

PERCEPTION OF COLORS.

Studies done by the Russian cosmonauts on effects on perception
of colors in space suggests a reduction in the perception of
brightness of all colors. The greatest degradation seem to affect
purple, azure, & green.

LIGHT FLASHES.

Not the so-called fireflies noted in orbital flights by
astronauts [shown graphically in the movie right stuff] but
lights as faint spots / flashes seen after dark adaptation in the
cabin of the Apollo missions. Generally described as
white/colorless and classified as three types.

# Described as “spots” / “starlike” 66 % of the time. Appearing
in both eyes simultaneously or one eye at a time.

# Described as “streaks” 25 % of the time.

# Described as “lightning discharge seen behind clouds” 9 % of
the times.

It was of interest that the very same astronauts who reported
them in the Apollo flights failed to see them in previous Gemini
flights. After the Apollo flights this phenomena was noted by the
crew of all three Skylab missions especially when they crossed
the South Atlantic Anomaly.

W.Zachary Osborne, Ph.D., Lawrence Pinsky, Ph.D., at University
of Houston & J.Vernon Bailey at Lyndon B. Johnson Space Center
conducted an investigation on this phenomena and concluded that
they were due to heavy cosmic radiation penetrating thru the
craft and impinging on the retina to cause this phenomena of
flashes.  The fact that this was noted only after the eyes were
darkadapted points to retinal interaction than optic nerve per
se.