[...The Effect of Light Upon the Eyes

Although the eyes were made to react to the light, a very general fear
of the effect of this element upon the organs of vision is entertained
both by the medical profession and by the laity. Extraordinary
precautions are taken in our homes, offices and schools to temper the
light, whether natural or artificial, and to insure that it shall not
shine directly into the eyes; smoked and amber glasses, eye-shades,
broad-brimmed hats and parasols are commonly used to protect the
organs of vision from what is considered an excess of light; and when
actual disease is present, it is no uncommon thing for patients to be
kept for weeks. months and years in dark rooms, or with bandages over
their eyes.

The evidence on which this universal fear of the light has been based
is of the slightest. In the voluminous literature of the subject one
finds such a lack of information that, in 1910, Dr. J. Herbert Parsons
of the Royal Ophthalmic Hospital of London, addressing a meeting of
the Ophthalmological Section of the American Medical Association, felt
justified in saying that ophthalmologists, if they were honest with
themselves, "must confess to a lamentable ignorance of the conditions
which render bright light injurious to the eyes." [1]. Since then,
Verhoeff and Bell have reported [2] an exhaustive series of
experiments carried on at the Pathological Laboratory of the
Massachusetts Charitable Eye and Ear Infirmary, which indicate that
the danger of injury to the eye from light radiation as such has been
"very greatly exaggerated." That brilliant sources of light sometimes
produce unpleasant temporary symptoms cannot, of course, be denied;
but as regards definite pathological effects, or permanent impairment
of vision from exposure to light alone, Drs. Verhoeff and Bell were
unable to find, either clinically or experimentally, anything of a
positive nature.

The results of these experiments are in complete accord with my own
observations as to the effect of strong light upon the eyes. In my
experience such light has never been permanently injurious. Persons
with normal sight have been able to look at the sun for an indefinite
length of time, even an hour or longer, without any discomfort or loss
of vision. Immediately afterward they were able to read the Snellen
test card with improved vision, their sight having become better than
what is ordinarily considered normal. Some persons with normal sight
do suffer discomfort and loss of vision when they look at the sun, but
in such cases the retinoscope always indicates an error of refraction,
showing that this condition is due, not to the light, but to strain.
In exceptional cases persons with defective sight have been able to
look at the sun, or have thought that they have looked at it, without
discomfort and without loss of vision; but, as a rule, the strain in
such eyes is enormously increased and the vision decidedly lowered by
sun-gazing, as manifested by inability to read the Snellen test card.
Blind areas (scotomata) may develop in various parts of the field--two
or three or more. The sun, instead of appearing perfectly white, may
appear to be slate-colored, yellow, red, blue, or even totally black.
After looking away from the sun, patches of color of various kinds and
sizes may be seen, continuing a variable length of time, from a few
seconds to a few minutes, hours, or even months. In fact, one patient
was troubled in this way for a year or more after looking at the sun
for a few seconds. Even total blindness lasting a few hours has been
produced. Organic changes may also be produced. Inflammation, redness
of the conjunctiva, cloudiness of the lens and of the aqueous and
viterous humours, congestion and cloudiness of the retina, optic nerve
and choroid, have all resulted from sun-gazing. These effects,
however, are always temporary. The scotomata, the strange colors, even
the total blindness, as explained in the preceding chapter, are only
mental illusions. No matter how much the sight may have been impaired
by sungazing, or how long the impairment may have lasted, a return to
normal has always occurred; while prompt relief of all the symptoms
mentioned has always followed the relief of eyestrain, showing that
the conditions are the result, not of the light, but of the strain.
Some persons who have believed their eyes to have been permanently
injured by the sun have been promptly cured by central fixation,
indicating that their blindness had been simply functional.

By persistence in looking at the sun, a person with normal sight soon
becomes able to do so without any loss of vision, but persons with
imperfect sight usually find it impossible to accustom themselves to
such a strong light until their vision has been improved by other
means. One has to be very careful in recommending sun-gazing to
persons with imperfect sight; because, although no permanent harm can
result from it, great temporary discomfort may be produced, with no
permanent benefit. In some rare cases, however, complete cures have
been effected by this means alone.

In one of these cases the sensitiveness of the patient. even to
ordinary daylight, was so great that an eminent specialist had felt
justified in putting a black bandage over one eye and covering the
other with a smoked glass so dark as to be nearly opaque. She was kept
in this condition of almost total blindness for two years without any
improvement. Other treatment extending over some months also failed to
produce satisfactory results. She was then advised to look directly at
the sun. The immediate result was total blindness, which lasted
several hours; but next day the vision was not only restored to its
former condition, but was improved. The sun-gazing was repeated, and
each time the blindness lasted for a shorter period. At the end of a
week the patient was able to look directly at the sun without
discomfort, and her vision, which had been 20/200 without glasses and
20/70 with them, had improved to 20/10, twice the accepted standard
for normal vision.

Like the sun, a strong electric light may also lower the vision
temporarily, but never does any permanent harm. In those exceptional
cases in which the patient can become accustomed to the light, it is
beneficial. After looking at a strong electric light some patients
have been able to read the Snellen test card better.

It is not light but darkness that is dangerous to the eye. Prolonged
exclusion from the light always lowers the vision, and may produce
serious inflammatory conditions. Among young children living in
tenements this is a somewhat frequent cause of ulcers upon the cornea,
which ultimately destroy the sight. The children, finding their eyes
sensitive to light, bury them in the pillows and thus shut out the
light entirely. The universal fear of reading or doing fine work in a
dim light is, however, unfounded. So long as the light is sufficient
so that one can see without discomfort, this practice is not only
harmless, but may be beneficial.

Sudden contrasts of light are supposed to be particularly harmful to
the eye. The theory on which this idea is based is summed up as
follows by Fletcher B. Dresslar, specialist in school-hygiene and
sanitation of the United States Bureau of Education:

"The muscles of the iris are automatic in their movements, but rather
slow. Sudden strong light and weak illumination are painful and
likewise harmful to the retina. For example, if the eye adjusted to a
dim light is suddenly turned toward a brilliantly lighted object, the
retina will receive too much light, and will be shocked before the
muscles controlling the iris can react to shut out the superabundance
of light. If contrasts are not strong, but are frequently made, that
is, if the eye is called upon to function where frequent adjustments
in this way are necessary, the muscles controlling the iris become
fatigued, respond more slowly and less perfectly. As a result,
eyestrain in the ciliary muscles is produced and the retina is
overstimulated. This is one cause of headaches and tired eyes." [3]

There is no evidence whatever to support these statements. Sudden
fluctuations of light undoubtedly cause discomfort to many persons,
but far from being injurious, I have found them, in all cases
observed, to be actually beneficial. The pupil of the normal eye, when
it has normal sight, does not change appreciably under the influence
of changes of illumination, and persons with normal vision are not
inconvenienced by such changes. I have seen a patient look directly at
the sun after coming from an imperfectly lighted room, and then,
returning to the room, immediately pick up a newspaper and read it.
When the eye has imperfect sight, the pupil usually contracts in the
light and expands in the dark, but it has been observed to contract to
the size of a pinhole in the dark. Whether the contraction takes place
under the influence of light or of darkness, the cause is the same,
namely, strain. Persons with imperfect sight suffer great
inconvenience, resulting in lowered vision, from changes in the
intensity of the light; but the lowered vision is always temporary,
and if the eye is persistently exposed to these conditions, the sight
is benefited. Such practices as reading alternately in a bright and a
dim light, or going from a dark room to a well-lighted one, and vice
versa, are to be recommended. Even such rapid and violent fluctuations
of light as those involved in the production of the moving picture
are, in the long run, beneficial to all eyes. I always advise patients
under treatment for the cure of defective vision to go to the movies
frequently and practice central fixation. They soon become accustomed
to the flickering light, and afterward other lights and reflections
cause less annoyance.

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[1] Jour. Am. Med. Assn., Dec. 10, 1910, p. 2028
[2] Proc. Am. Acad. Arts and Sciences, July, 1916, vol. 51, No. 13
[3] School Hygiene, Brief Course Series in Education, edited by Paul
Monroe, Ph.D., 1916, pp. 235-236...]

- Dr. W. H. Bates, November 1919