ON THE RELAXED STATE OF ACCOMMODATION

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ON THE RELAXED STATE OF ACCOMMODATION
[Article by H. Schober:: "On the Relaxed State of Accommodation"; city of
publication unknown, Optik (Optics), German, Volume 11, No. 6, 1954, pp.
282-290]*
It was 98 years ago that H. von Helmholtz, in his basic work which
appeared in the first issue of Graefes Archiv fir OphthaZmoZogie (Graefe's
Archives of Ophthalmology), set down the concepts which, despite many at-
tacks upon them, are still accepted today. In his well-founded opinion, all
the processes leading to accommodation occur exclusively in the ciliary-
body/zonular-fibers/lens system, which operates as a mechanically elastic
unit. The lens of the eye, or its capsule, is an elastic body which will
revert to nearly spherical form if free of outside influences. This is pre-
vented, however, by the pull of the zonular fibers, which are firmly at-
tached to the outer edge of the capsule and cause an oblation of the lens.
The elastic pull of the zonular fibers is always present unless a contrac-
tion of the ciliary muscle changes this condition and thereby permits the
lens to assume a more highly curved form. The ciliary muscle therefore
acts as the only "living member" of the system; the other two members (zonu-
lar fiber and lens) are merely affected by the change in the physical rela-
tionships. Since in the doctrine of physiology contraction of a muscle is
normally the result of active effort and the release of the muscle is the
relaxed state, it is generally accepted on the basis of Helmholtz's precepts
that the adjustment of the eye to distant points [far point] (extended cili-
ary muscle, relaxed zonular fibers, flat lens) must represent the relaxed
state, while the accommodation of the eye to near points [near point] (con-
tracted ciliary muscles, convex lens) must represent the active state of
accommodation.
However, the conclusion from Helmholtz's observations just described
is not very compelling. It does not show the actual relationships, as will
*A report from the Tbc-Forschungsinstitut Borstel. Dedicated to
Professor Dr. Clemens Schaefer on the occasion of his seventy-fifth birthday.
Declass Review by NIMA/DOD
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be shown below. The actual relaxed state of accommodation must in all
probability be somewhere between the far point and the (withs
the eye adjusted to a distance of about one meter).
of extraordinary theoretical and practical significance. It is not to be
ignored either in physiologico-optical studies or in the construction of
optical instruments.
Anatomico-Neurological Indications of the Actual Relaxed State of Accommo-
dation
iliar muscle is a "smooth m
c e.his
the c y
n
Viewed anatomically,aopposed type of muscle (e.g. intestinal muscle, blood-vessel walls),
the cross-striated skeletal musculature, is not induced to contract by the
fibers of a given motor nerve. Its greater or lesser state of contraction
is brought about by a change in the balance between the contracting (para-
sympathetic) and the relaxing (sympathetic) fibers of the autonomous nerv-
ous system. For this reason, for the smooth muscles there is no real state
of rest, -- or, if there is one, it is at least not represented by the
state of maximal contraction or expansion. For a long time it has been be-
lieved that the ciliary muscle was an exception in this respect, because
only the contracting fibers of the parasympathetic oculomotor nerve were that
mus known, and it was bhaheihdcould beecontracted atclwie from all other
smooth muscles in
In the past few years, however, this precept has been set aside in
the field of innervation, particularly as a result of detailed histological
studies by Meesmann. The ciliary muscle actually consists of a very high-
ly developed system of fibers. The old division of the ciliary muscle into
fibers running meridionally (Brucke's muscles), radially (Ivanov's muscles),
and circularly (Miller's muscles) does not stand the test of precise criti-
cism; the musculature is a much more tightly woven system, which can only
be regarded as a unit. That orthosympathetic nerve fibers from the cervical
sympathetic nerve extend to the ciliary muscle as well as the parasympathet-
ic nerve fibers from the oculomotor nerve is of particular significance.
Contrary to previous conceptions, then, the ciliary muscle, like all other
smooth muscles, is controlled by both types of autonomous nerve fibers.
Therefore no other behavior is to be expected of it than that observed in
the other smooth muscles. Just as is the case with the other smooth muscles,
definitely the
it should have
state of full
The only difference remaining between it and the other smooth mus-
cles that is often encountered is thus the possibilityf voluntarily in-
fluencing the state of contraction. But this very possibility h as
been very problematical. The stimulus for accommodation is inseparable from
the stimulus for convergence. Any convergence impulse deriving from an ob-
ject in sight carries with it an accommodation impulse. The voluntary
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control of convergence, however, presents no problems from the viewpoint
of physiology, since the movement of the eye is controlled by striated
muscles of the same type as the skeletal musculature, and can therefore
be affected by an act of will. To stimulate convergence it is sufficient
to imagine a point within the field of vision and wish to fix on that
point. At the same time, because of the unconscious connection between
convergence and accommodation, accommodation also occurs.
Meesmann's anatomical findings are confirmed by several clinical
observations. In the inactivation of the cervical sympathetic nerve (Horn-
er's syndrome), besides the contraction of the pupil there are difficul-
ties in adjustment of the eye for distance. The contrary case is to be
found in hyperactivity of the orthosympathetic nerve (as in certain forms
of Basedow's disease), where difficulties in near-point accommodation occur
simultaneously with dilation of the pupil. It can thus be seen that the
far-point accommodation as well as the near-point accommodation is stimu-
lated by the autonomous nervous system, the former being brought about by
a preponderance of the orthosympathetic and the latter by a preponderance
of the parasympathetic element.
The observations of the pharmacological effects of certain nerve
poisons also point in the same direction. Thus the parasympathetic stimu-
lants or orthosympathetic depressants (such as pilocarpine andthe ergot de-
rivatives) normally lead to difficulties in far-point accommodation, while
poisons that either suppress the parasympathetic nerves or stimulate the
orthosympathetic ones (such as atropine or cocaine) have an adverse effect
on the near-point accommodation. If the autonomous nervous system is
largely cut off by certain drugs (as by an overdose of sulfonamides), it is
not rare that the state of accommodation becomes fixed at a distance of
about 0.5 meter. The eye then behaves like that of a full presbyopic who
is at the same time afflicted with myopia to about 2 diopters.
Physiologico-Optical Studies of the Relaxed State of Accommodation
A. Adjustment of Optical Instruments
The observation is often made that in the adjustment of optical
instruments, if free movement of the ocular is permitted myopic values
are often favored. Especially young and inexperienced observers shift the
oculars to values one or more diopters less than the refraction state
measured for their unaided eyes. This condition also causes the difference
in the position of the maximum in the statistical distribution of the
state of refraction if the study is made first with the unaided eye and
then by means of the position of adjustment of a telescope.
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AMF
On observations with the unassisted eye the comprehensive works
of Steiger3 and Betsch4 state that the frequency maximum of the refraction
state is approximately +0.5 diopter. In the case of optical adjustment
of telescopes, however, during the last war the author's observations of
a large number of seamen agreed quite well with the relevant experiences
of optical firms in that the maximum frequency lay not at + 0.5 diopters
but rather at about - 1.0.5 Thus between observations dealing with the
unassisted eye and those dealing with the adjustments of optical instru-
ments there is a gap of about 1.5 diopters. This differential can be_ex-
plained without difficulty if we consider that the maximum frequency for
vision profiles is normally determined by using an eye chart at a distance
of from 6 to 7 meters, thus automatically requiring the eye to adjust for
distance, while with telescopic observations changes in accomodation can
largely be compensated for by moving the optics. Thus the observations
with the unassisted eye pre-determine a certain state of accommodation from
the beginning, while the adjustment of optical instruments permits
choice of the most suitable position of accommodation. If, however,tthis
does not coincide with what is to be expected from the anatomical and
clinical observations.- the far point, or maximal extension of the cili-
ary muscle - that menns_ that the far point does not represent the relaxed
state of aceommodation. The telescopic studies agree precisely
clinical experience to the effect that the relaxed statteof--ac-lotion
is to be-found between the far point and the near point. The honor of being
the first t'o recognize this condition and its significance must be accorded
to Kuhl.. 6_
Diopters
Far Point
Near Point
Relaxed State of Ac-
commodation
Figure-I-., Dependence of the Position of Far and Near Points
on Age according to Donders'and the Probable Relaxed State of
Accommodation from the Dioptrometer
In the past few years the accuracy of the assertions just made
has been confirmed, particularly by Lau7 and Mu.tze8 with the dioptro-
meters they-developed. In these instruments, virtual strip whose position in the room can be changed by the movement of two uparal-
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lel grates. If clear-sighted observers are permitted to adjust the stri
picture for greatest clarity, we find that this does not occur t,t the p
near point or far point, but rather at solve s e
(See Figure 1.) The younger the observer, theeasier bhewcan accommodate
and tthe closer the
ande therefore, refor point of highest clarity of the stri
approaches. Lau writes _of this: P als
trials
it is expected that the eye accornmo.datesrtOo ahe given venis distance the e in first studies
with this instrument. The adjusted value corresponds to an accommodation
of the eye where the forces of the ciliary muscle and the lens tension
equate' This equation is primarily dependant on the elasticity of the
lens, and therefore changes with increasing age."
b. Night Myopia
It is known that the human eye becomes.myopic with decreasing il-
lumination, and that this is more marked the
cerned. Night myopia is caused in part b younger the person con-
y by the.dilation of the pupil and the'changein the?visualecolor,oandained
part by the change in accomodation.9 The effect of accomodation predom-
inates over all other influences in this phenomenon 19 and can be shown
in the behavior of the Purkinje-Samson mirror images in the eye.J1 Ac-
cording to the works of Otero., Duran, and Palaciosl2
range decreases with decreasing adaptation light densite accommodation
tion light densities less than 0.02 (full moon illumination) the young
eye no longer has any capacity for accomodation (Figure 2). For the e clear-
sighted the accomodation is then set at -2 diopters. accep-
ting this position as the relaxed state of accommodationeis d ap of pealing be-
cause due to the limited accuity of vision and the limited number of light
stimulii in the field of sight there should be no'causes for active ac-
commodation. The value for the relaxed state of accommodation derived
from night myopia also agrees well with the value derived from the pre-
viously described studies.
Density of Illumination in the Field of Vision
Figure 2. Range of Accommodation as a Function of the Light Den-
sity in the Field of Vision
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c. Negative Accommodation
If the adjustment of the eye to the far point does not coincide
with the relaxed state of accommodation, and is instead representative
of an active process of accommodation, systematic studies must bring-
to light some evidence for the existence of negative accommodation of
this type. This has, in fact, occurred. It has long been known that
hyperopic
persons show a specific rest accommodation. By using certain
aids, such as the simultaneous use of parasympathetic depressant and
orthosympathetic stimulant drugs, eg. atropine and cocaine, a far sharp-
er "relaxation of accommodation" can be reached than can be attaindd. by
using only one such drug. It is also known that such persona often ob-
ject to a full-correction
lens of this type, saying that they can see better
with weaker glasses. On the other,hand, through systematic training of
the sympathetic system, many near-sighted people can:, attain an improvement
in their refraction correction without a corresponding correcting lens ,._
Y . LeGrand13 was able to show a short while ago that such training pis al
so possible with the clear-sighted and far-sighted. If they are encour-
aged to look into the distance "with wide open pupils and wide open eyes"
a far greater positive correction will be noted than they would otherwise
be capable of. Morgan14 found that the eye. of a cat can be brought from
its refraction position of -0.5 diopters to +4 diopters in the direction
of far-sight through the stimulation of its orthosympathetic cervical gang-
lia. Cutting the parasympathetic fibers similarly causes a change in the
refraction index from =0.5 to +3.5 diopters. If later the orthosympathetic
cervical ganglia are also destroyed, the state of refraction then returns
to the normal value of -0.5. According to Fincham1S, the negative accom-
modation can also be supported by corresponding. simultaneous lessening
of the convergence tension. The state of refraction of most humans is
moved into the hyperopic values when they are encouraged to look through
diverging prisms.
d. The Dependence of Clarity of Vision on Distance
Aubert and Forster16 have already shown that for certain people
the measurements of clarity of vision at different distances do not lead
to the same results. In general, vision is sharper for near objects than
for distant ones. Bouma17 determined some years ago that the optimal
distance ,for sharpness of vision is about 2 to 3 m. (See Figure 3.) At
both shorter and greater distances to the object of vision, the sharpness
is noticeably decreased.
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Figure 3: Clarity of Vision as a Function of Distance from the
Object
[Boumal
e. The significance of the Individual Portions of Objective Space for
Sight
The normal methods of determining sight give a false picture of
the actual significance of the individual portions of objective space in
vision. Normally objects lying in the area from 0.5 to 2 meters from the,
eye are of greater importance than those nearer and further, since they
must be noted and dealt with specifically in movement and in subconscious
actions. The necessity of;best vision in the distance is only present in
certain tasks. From this it can be seen-that even reletively near-sighted
people up to - about -2 d) are not disturbed by their handicap in
leading normal lives. They notice their nearsightedness mostly in the
movies, when they must accommodate to the distant screen, or when they
are engaged in certain occupations, as in sailing or driving an automobile,
etc. Objects lying within1 meter of the eye are solely important for
occupational reason, or in reading writing, etc.
The observations of Helmholz on the form of the true horopter18
agree
rather well with the significance described above for the individ-
ual portions of objective space in vision. He found that the true horop-
ter consists of a steep cone whose base is formed of a Vieth.-Muller circle
contained by the horizontal plane of the eye of the observer and whose
point lies on the ground at a distance of about one meter. He sees a very
practical arrangement in;thisa since the evaluation of the relief, that
is, the unevenness of the footing, is greatly simplified by this.
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modation lies precisely between the far-point and the near-point of the
individual observer. This is significant for various reasons.
If the far-point of the eye is taken as the norm in visual acuity
studies as is generally done, it should be noted that here we are alreadjr
dealing with a certain degree of negative accommodation effort. There
is always the possibility that, due to"inauspicious circumstances this
effort is artificially increased and thereby the state of refraction may
be falsly evaluated. Therefore, the old rule of refraction "the strongest
positive and the weakest negative correction" is only relative and has no
absolute significance. There is always the danger that due to a number
of inauspicious circumstances - that is, those that encourage negative
accommodation - the positive correction will be too strong. In optical
instruments with freely adjustable optics, it should be noted that adjust-
ment for the true relaxed state of accommodation is much easier here than
with the unassisted eye methods, and therefore that limited negative ad-
justments from the zero adjustment.-or the positive adjustment are to be
preferred.
Summary
The-previous view that the far-point adjustment of the eye,"corre-
sponds. to e relaxed state of accommodation no longer agrees with the
findings of anatomy,-histology, and optometry. The ciliary muscle consists
of smooth muscle fibers which are controlled by both parasympathetic and
orthosympathetic nerves. The adjustment of accommodation can only be con-
trolled voluntarily through the connection with the convergence stimuli
The differences between the'ocular adjustments of optical instruments and
the values of refraction measured for unassisted eyes, the studies using
dioptrometers, the findings in night myopia, and the existence of a neg~
ative accommodation, the position of maximum visual acuity, and the form
of the horopter all speak in favor of the hypothesis that the actual re-
laxed state of accommodation does not correspond with the adjustment of
the eye to distance, but rather is to be sought in the middle between the
far-point and the near-point.
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Practical Significance of the Relaxed State of Accommodation.
According to the anatomico-histological and physiologico-optical
considerations just described, the relaxed state of accommodation does not
coincide with the far-point adjustment. It is attained, rather, by the
adjustment of the eye for objective points that lie between the near-point
and the far-point, as can be seen from the table.
Probableiaxed Position of Accommodation Derived from Various Methods
Method of Study Probable Relaxed Position of Accommodation
in meters in diopters
Histology of the None None, at most
Ciliary Body
the average
between near-point
and far-point
Difference be- Approx. 0.67 Approx. 1.5
tween adjustment
of optical in-
struments and
refraction de-
terminationYof
the unassisted
eye
Dioptrometer
Between near-
Average of near-
point and far-
point and far-
point
point
Night Myopia
A
pprox. 0.5
Approx. 2
Maximum clarity
Approx. 2
Approx. 0.5
of vision
Horopter
Approx. 1
Approx. 1
If we consider that the accommodation capacities of the individual
observer; show an extreme dependence on age, and also that the effect of
geometrico-optical and of chromatic aberrations-can reach 0.75 diopters,
an impressive agreement can be seen from the various methods of study de-
scribed. In fact, it appears that the actual relaxed position of accom-
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Ifto
1. H. von Helmholtz, "On the Accommodation of the Eye," Graefes
Archiv fur Ophthalmologie (Graefe's Archives of Ophthalmology), Volume 1
II, 1855, pages 1-74.
2. A. Meesmann, "Experimental Studies of the Antagonistic Innerva-
tion of the Ciliary Musculature," Report 57, Versuche der Deutschen Oph-
thaZmoZogischen GeseZZschaft (Experiments of the German Ophthalmological
Society), 1952, pages 236-238.
3. A. Steiger, Die Entstehung der Spharischen Refraktionen des
Menschlichen Auges (The Origin of the Spherical Refractions of the Human
Eye) (Far-Sightedness, Normal Vision, Short-Sightedness), Verlag J.
Springer, Berlin, 1913.
4. A. Betsch, "On the Human Refraction Curve," Klinische Monats-
blatt fir AugenheiZkunde (Clinical Monthly for Ophthalmology), Vol. 82,
1929, pages 365-379.
5. H. Schober, "Nocturnal Myopia and Its Causes," Graefes Archiv
fir Ophthalmologie, Volume 148, 1947, pages 171-186.
6. A. Kuhl, "The Accommodation Position and Its Influence on Night
Vision Without and With the Telescope," in Festschrift zum 25-Jahrigen
Bestehen des 0. von MiZZer PoZytechnikum, Akademie fur Angewandte Technik
(Publication in Honor of the Twenty-Fifth Anniversary of the 0. von Miller
Polytechnic Institute, Academy of Applied Technology), Munich, 1949.
7. E. Lau, "The Dioptometer," Optik (Optics), Volume 8, 1951, pages
419-425.
8. E. Lau and K. Mutze, "New Ways of Determining Ametropia," Deut-
sche Optische Wochenschrift (German Optical Weekly), Volume 69, 1952,
pages 4-9.
9. J.M. Otero and N. Aguilar, "Accommodation and Night Myopia,"
Journal of the Optical Society of America, Volume 41, 1945, pages 106
and 1062.
10. J. Cabello Gomez, "The Causes of Night Myopia," Anales de Fisica
y Qulmica (Annals of Physics and Chemistry), Vol. 41, 1945, pages 439-460.
11. J.M. Otero, M.Th. Vig6n Sanchez, and D. Galvez Armengaud, "On
the Natural Position of the Crystalline Lens and the Principal Cause of
Night Ametropia," Anales de Fisica y Quimica, Volume 46, 1950, pages 1-4.
12. A. Duran, "The Liminal Values of Nocturnal Myopia," Anales de
Fisica y Quimica, Volume 39, 1943, pages 579-585.
13. Y. LeGrand, "Concerning the Existence in Certain Subjects of a
Negative Accommodation," Compte Rendu (Transactions [of the Academy of
Sciences]), Volume 230, 1951, pages 1422-1424.
14. W.M. Morgan and J.M.D. Olmstedt, "Quantitative Measurements of
Relative Accommodation and Relative Convergence," Proceedings of the Soci-
ety for Experimental Biology and Medicine, Volume 41, 1939, pages 303-307.
15. E.F. Fincham, "The Changes in the Form of the Crystalline Lens
in Accommodation," Transactions of the Optical Society of London, Volume
- 10 -
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26, 192+-1925, pages 239-269.
16. H. Aubert and E. Forster, "Contributions to Knowledge of Indi-
rect Vision," Graefes Archiv fiir OphthaZmologie, Volume 3 II, 1857, pages
1-67.
17. P.J. Bouma, "Acuity of Vision and Rapidity of Perception Under
Street Lighting," Philips' Technischer Rundschau (Philips Technical Jour-
nal), Volume 1, 1936, pages 215-220.
18. H. von Helmholtz, Handbuch der PhysioZogischen Optik (Manual of
Physiological Optics), Volume III, Verlag Voss, Hamburg and Leipzig, 2nd
edition, 1896.
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