Ординатура / Офтальмология / Английские материалы / Relearning To See_Quackenbush_2000

Strabismus, by itself, is not an error of refraction because light rays still focus on the retina to see clearly near and far. Of course if the strabismic eye is also nearsighted or farsighted, the eye cannot see clearly at all distances.

Strabismus and related issues are covered in Chapter 18, ''Stereoscopic Vision."

A C C O M M O D A T I O N E X P L A I N E D

F U R T H E R

Optical devices, e.g. cameras, binoculars, microscopes, and telescopes, require some way of changing in order to focus images at different distances clearly. In binoculars, microscopes, and telescopes the distance between the lenses is increased and decreased. In cameras the distance between the lens and the film is increased to focus a near object, and decreased to focus afar object.

As stated above, the eye, in its normal, round, "resting" state, sees clearly in the distance. If the eye did not change in some way, a near object could not be seen clearly. This is because light rays from the near object would come to a focus in back of the retina.

Accommodation is the ability of the eye to change from the state of seeing clearly in the distance to seeing clearly up close. When the eye is in the process of changing to see clearly up close, or when it is in the state of seeing clearly up close, it is said to be "accommodating." The reverse action of accommodation returns the eye to seeing clearly in the distance, when, once again, it is said to be "at rest," and no longer accommodating. Stated more simply, the eye accommodates to see clearly up close, and then "unaccommodates" to see clearly in the distance.

How the eye accommodates has been debated for many decades—long before Bates did his research on eyesight.

T H E H E L M H O L T Z L E N S T H E O R Y

O F A C C O M M O D A T I O N

Hermann von Helmholtz (1821-1894) was a great German scientist and ophthalmologist. He developed the idea of the conservation of energy and made important contributions to the fields of optics and acoustics. The action of the ciliary muscle on the lens being the mechanism of accommodation is generally attributed to Helmholtz.

In 1943, ophthalmologist May stated the orthodox position on accommodation in his book Diseases of the Eye:

During accommodation, the ciliary muscle (especially the circular fibers) contracts, drawing forward the choroid and relaxing the suspensory Hgament;this diminishes the tension of the lens capsule and allows the inherent elasticity of the lens to increase its convexity. The change in curvature affects chiefly the anterior surface of the lens. This is Helmholtz's theory and the one usually accepted. [TQ emphasis.] Tscherning has advanced a different theory: He maintains that the ciliary muscle increases the tension of the suspensory ligament during contraction, and that this causes peripheral flattening of the lens with bulging anteriorly at its center.5

Bates writes in Perfect Sight Without Glasses,

"Marius Hans Erik Tscherning (1854-) is a Danish ophthalmologist who for twenty-five years was co-director and director of the ophthalmological laboratory of the Sorbonne. Later he became professor of ophthalmology in the University of Copenhagen."

Although both of the theories of accommodation mentioned by May involve the changing of the front side of the lens, he presents two opposite mechanisms It is interesting that as late as 1943, there were still questions

as to the actual mechanism of accommodation. So, Helmholtz's explanation was still being referred to as a "theory'* and this theory apparently was not accepted by everyone.

The 1980 edition of Webster's New Colle- giate Dictionary defines visual accommodation as: "the automatic adjustment of the eye for seeing at different distances effected chiefly [TQ emphasis] by changes in the convexity of the crystalline lens."6 The word "chiefly" seems to imply there is at least one other mechanism of automatically seeing at different distances.

In 1976 University Physics states:

To see an object distinctly, a sharp image of it must be formed on the retina. If all the elements of the eye were rigidly fixed in position, there would be but one object distance for which a sharp retinal image would be formed, while in fact the normal eye can focus sharply on an object at any distance from infinity up to about 25 cm in front of the eye. This is made possible by the action of the crystalline lens and the ciliary muscle to which it is attached. When relaxed, the normal eye is focused on objects at infinity, i.e., the second focal point is at the retina. When it is desired to view an object nearer than infinity, the ciliary muscle tenses and the crystalline lens assumes a more nearly spherical [i.e.,more convex] shape. This process is called accommodation.7

However, there seems to be some question as to whether the lens becomes rigid in presbyopia in the next paragraph in University Physics which is quoted later in this chapter.

B A T E S Q U E S T I O N S T H E A C C E P T E D T H E O R Y O F A C C O M M O D A T I O N

In Perfect Sight Without Glasses, in Chapter

III, entitled "Evidence for the Accepted Theory of Accommodation," Bates discusses research by many scientists on the role, if any, of the lens in accommodation.

Much of the research on the lens was conducted by observing possible changes in the size of reflections of images on the front and back surfaces of the lens, using reflections of images from the cornea as a reference point.

Theoretically, the corneal reflections should remain constant in size because the eyeball and cornea are said (conventionally) not to change their shapes during accommodation.

Bates discusses research by Donders, and other scientists, on the lens. In regards to Donders, Bates writes in Perfect Sight Without

Glasses, "Frans Cornells Donders (1818-1889) was professor of physiology and ophthalmology at the University of Utrecht, and is ranked as one of the greatest ophthalmologists of all time." After discussing Donders' work, he discusses the work of the great ophthalmologist Helmholtz.

From Perfect Sight Without Glasses:

Like Donders, Helmholtz found the image obtained by the ordinary methods on the front of the lens very unsatisfactory, and in his "Handbook of Physiological Optics" he describes it as being "usually so blurred that the form of the flame cannot be definitely distinguished."8 So he placed two lights, or one doubled by reflection from a mirror, behind a screen in which were two small rectangular openings, the whole being

so arranged that the lights shining through the openings of the screen formed two images on each of the reflecting surfaces. During accommodations, it seemed to Mm that the two images on the front of the lens became smaller and approached each other, while on the return of the eye to a state of rest [for distance clarityj they grew larger again and separated. This change, he said, could be seen "easily and distinctly."b The observations of Helmholtz regarding the behavior of the lens in accommodation, published about the middle of the last cen-

i tury, were soon accepted as facts, and have ever since been stated as such in every textbook dealing with the subject.

If an image reflecting from the front side of a convex lens becomes smaller, it could indicate the front side of that convex lens has increased its curvature. Helmholtz's research seemed to indicate that the images reflecting

b Ibid., vol. i, p. 122.

from the front side of the lens decreased in size when the eye accommodated to see clearly up close. An increase in the size of as image would indicate that the surface had become flatter, and vice versa.

However, the size of the images reflecting from the back side of the lens remained constant, indicating that the back side of the lens did not change in curvature during accommodation. How can a ciliary muscle change

ORTHODOX LENS THEORIES* OF ACCOMMODATION

The iift&i»flt berete'iy-yft*'—-'atp-sT Ыбмпс vision

He mholtz be leved that v/Tieo the ciliary muscle contracts,

the lens ncreases its curvature so that the eye can see clearly up close

Figure 6-5: Expected Conclusion and Conclusion from Helmholtz's Research.

only the front side of a lens, without chang­ ing the back side?

According to the Helmholtz lens theory of accommodation, when the circular ciliary muscle contracts, it moves inward toward the lens. The suspensory ligaments, which span between the ciliary body and the lens cap­ sule, relax their tension on the lens capsule. As a consequence, the front side of the lens is said to acquire more curvature. If this actu­ ally occurred, a person would then see clearly, or at least more clearly, up close; in other words, the person would be accommodating. When the ciliary muscle expands (relaxes) back to its normal state, the suspensory liga­ ments pull on the lens capsule, and the front side of the lens is said to return to its normal flatter shape for clear distant vision again.

Some contemporary books on eyesight have illustrations showing only the front side of the lens changing its curvature during accommodation, as attributed to Helmholtz. Others show both sides of the lens changing during accommodation. Helmholtz's research

did not indicate that both sides of the lens change their curvature, which is what a per­ son might expect when the ciliary muscle con­ tracts and expands around the lens.

L E N S L E SS ACCOMMODATION—

T H E " G R A N D OBJECTION"

To continue from Bates' exposition from Per­ fect Sight Without Glasses:

Yet in examining the evidence for the [Helmholtz's lens] theory we can only won­ der at the scientific credulity which could base such an important department of medical practice as the [care] of the eye upon such a mass of contradictions. Helmholtz, while apparently convinced of the correctness of his observations indi­ cating a change of form in the [front side

of the] lens during accommodation, felt himself unable to speak with certainty of the means by which the supposed change was effected,8 and strangely enough the question is still being debated. Finding, as he states, "absolutely nothing but the ciliary muscle to which accommodation could be attributed,"b Helmholtz concluded that the changes which he thought he had observed in the curvature of the [front side of the] lens must be effected by the action of this muscle; but he was unable to offer any satisfactory theory of the way it operated to produce these results, and he explicitly stated that the one he suggested possessed only the character of probability. Some of his disciples, "more loyal than the king," as Tscherning has pointed out, "have proclaimed as certain what he [Helmholtz] himself with much reserve explained as probable,"6 but there has been no such unanimity of acceptance in this case as in that of the observations regarding the behavior of the images reflected from the lens. No one except the present writer, so far as I am aware, has ventured to question that the ciliary muscle is the agent of accommodation; but as to the mode of its operation there is generally felt to be much need for more light. Since the lens is not a factor in accommodation, it is not strange that no one was able to find out how it changed its curvature. It is strange, however, that these difficulties have not in any way disturbed the universal belief that the lens does change.

aHandbuch der physiologischen Optik, vol. i, pp. 124 and 145.

bIbid., vol. i, p. 144.

e Physiologic Optics, p. 166.

Bates then presents evidence of accommodation in people who are lensless:

When the lens has been removed for cataract the person usually appears to lose his power of accommodation, and not only has to wear a glass to replace the lost part [i.e., convex glasses for distance, compensating for the loss of the lens], but has to put on a stronger [convex] glass for reading. A minority of these cases, however, after they become accustomed to the new condition, become able to see at the near point without any change in their [distance] glasses. The existence of these two classes of cases has been a great stumbling block to ophthalmology. The first and more numerous appeared to support the theory of the agency of the lens in accommodation; but the second was hard to explain away, and constituted at one time, as Dr. Thomas Young observed, the "grand objection" to this idea. A number of these cases of apparent change of focus in the lensless eye having been reported to the Royal Society by competent observers. Dr. Young, before bringing forward his theory of accommodation, took the trouble to examine some of them, and considered himself justified in concluding that an error of observation had been made. While convinced, however, that in such eyes the "actual focal distance is totally unchangeable," he characterized his own evidence in support of this view as only "tolerably satisfactory." At a later period Donders made some investigations from which he concluded that "in aphakia3 not the slightest trace of accommodative power remains."6 Helmholtz expressed similar

aAbsence of the lens.

bOn the Anomalies of Accommodation and Refraction of the Eye, p. 320.

views, and von Graefe, although he observed a "slight residuum" of accommodative power in lensless eyes, did not consider it sufficient to discredit the theory of Cramer and Helmholtz. It might be due, he said, to the accommodative action of the iris, and possibly also to a lengthening of the visual axis through the action of the external muscles.8

For nearly three-quarters of a century the opinions of these masters have echoed through ophthalmological literature. Yet it is today a perfectly well-known and undisputed fact that many persons, after the removal of the lens for cataract, are able to see perfectly at different distances without any change in their glasses. Every ophthalmologist of any experience has seen cases of this kind, and many of them have been reported in the literature.

In 1872, Professor Forster of Breslau reported15 a series of twenty-two cases of apparent accommodation in eyes from which the lens had been removed for cataract. The subjects ranged in age from eleven to seventy-four years, and the younger ones had more accommodative power than the elder. A year later Woinow of Moscow0 reported eleven cases, the subjects being from twelve to sixty years of age. In 1869 and 1870, respectively, Loring reported41 to the New York Ophthalmological Society and the American Oph-

aArchive, f Ophth., 1855, vol. ii, part 1, p. 187 et seq. Albrecht von Graefe (1828-1870) was professor of ophthalmology in the University of Berlin, and is ranked with Donders and Arlt as one of the greatest ophthalmologists of the nineteenth century.

bKlin. Montasbl. f Augenh., Erlangen, 1872, vol. x, p. 39 et seq.

cArchiv. f. Ophth., 1873, vol. xix, part 3, p. 107.

dFlint: Physiology of Man, 1875, vol. v, pp. 110-111.

thalmological Society the case of a young woman of eighteen who, without any change in her glasses, read the twenty line on the Snellen test card at twenty feet and also read diamond type at from five inches to twenty. On October 8,1894, a client of Dr. A. E. Davis who appeared to accommodate perfectly without a lens consented to go before the New York Ophthalmological Society. "The members," Dr. Davis reports,6 "were divided in their opinion as to how the person was able to accommodate for the near point with his distance glasses on"; but the fact that he could see at this point without any change in his glasses was not to be disputed.

(This person] was a chef, forty-two years old, and on January 27,1894, Dr. Davis had removed a black cataract from his right eye, supplying him at the same time with the usual outfit of glasses, one to replace the lens, for distant vision, and a stronger one for reading. In October he returned, not because his eye was not doing well, but because he was afraid he might be "straining" it. He had discarded his reading glasses after a few weeks, and had since been using only his distance glasses. Dr. Davis doubted the truth of his statements, never having seen such a case before, but found them, upon investigation, to be quite correct. With his lensless eye and a convex glass of eleven and a half diopters, the chef read the ten line on the test card at twenty feet, and with the same glass, and without any change in its position, he read fine print at from fourteen to eighteen inches. Dr. Davis then presented the case to the Ophthalmological Society but, as has been stated, he obtained

e Davis: Accommodation in the Lensless Eye, Reports of the Manhattan Eye and Ear Hospital, Jan., 1895. The article gives a review of the whole subject.

no light from that source. Four months later, February 4,1895, the chef still read 20/10 at the distance and his range at the near point had increased so that he read diamond type at from eight to twenty-two and a half inches. Dr. Davis subjected him to numerous tests, and though unable to find any explanation for his strange performances, he made some interesting observations. The results of the tests by which Donders satisfied himself that the lensless eye possessed no accommodative power were quite different from those reported by the Dutch authority [Cramer?], and Dr. Davis therefore concluded that these tests were "wholly inadequate to decide the question at issue." During accommodation the ophthalmometer3 showed that the corneal curvature was changed and that the cornea moved forward a little. Under scopolamine, a drug sometimes used instead of atropine to paralyze the ciliary muscle (1/10 percent solution every five minutes for thirty-five minutes, followed by a wait of half an hour), these changes took place as before [paralysis of the ciliary muscle rules out the possibility of the ciliary muscle being the cause of the change of the corneal curvature]; they also took place when the lids were held up. With the possible influence of lid pressure and of the ciliary muscle eliminated, therefore, Dr. Davis felt himself bound to conclude that the changes "must have been produced by the action of the external muscles."

.. .These and similar cases have been the cause of great embarrassment to those who feel called upon to reconcile them with the accepted theories. With the retinoscope the lensless eye can be seen to accommodate; but the theory of Helmholtz has dominated

* An instrument for measuring the curvature of the cornea.

the ophthalmological mind so strongly that even the evidence of objective tests was not believed. The apparent act of accommodation was said not to be real, and many theories, very curious and unscientific, have been advanced to account for it

How i s T H E H E L M H O L T Z L E N S THEORY

R E G A R D E D T O D A Y ?

The orthodox opinion remains the same

is the only mechanism of accommodation, and it becomes irreversibly rigid in middle age. After that time accommodation is not supposed to be possible.

Ironically, this position presents excellent support for the muscles being—at the very least—another mechanism of accommodation, due to the following four facts (some from above):

1.Many lensless people accommodate.

2.Many older people keep excellent vision both near and far.

3.Many so-called presbyopes have improved their vision with the Bates method of re-education.

4.An eye with a paralyzed ciliary muscle, which rules out accommodation by the lens, can still accommodate.

The only rational explanation for these four facts is that the two oblique muscles accommodate the eyeball. Other physical factors have been ruled out.

These four facts indicate that whether or not the lens and/or ciliary muscle play any role in accommodation, they are not necessary for accommodation.

Chapter Six: Accommod

COULD PRESBYOPIA BE CAUSE D BY A

STRAINED OR ATROPHIED CILIARY

M U S C L E ?

Could a strained or atrophied ciliary muscle, unable to contract, be the reason a lens no longer accommodates? Could the normalization of the ciliary muscle be the reason presbyopes improve vision?

Some have taken the position that the ciliary muscle can lose its ability to change the shape of the lens as the person becomes older. The "sluggish" ciliary muscle is not functioning correctly, but after being "toned up" again, the ciliary muscle is said to regain its ability to accommodate the lens.

This position appears to require that:

1.the lens has not become rigid; or

2.the lens became semi-rigid, but kept sufficient flexibility to still accommodate; or

3.the lens became completely rigid, but regained its flexibility when the ciliary muscle was "toned up" again.

These theories are not supported by the orthodox.

The ciliary muscle "revitalization" theory still does not explain how a lensless eye, and an eye with a paralyzed ciliary muscle, can still accommodate.

In fact, Bates agreed with orthodox science that the lens becomes less flexible as a person ages. But for Bates the lens was "immaterial," because his research indicated that only the two oblique muscles are involved in accommodation.

>n and Errors of Refraction—The Orthodox View

PRESBYOPIA, A N A G E - O L D " O L D - A G E "

M Y T H

When the eye cannot see clearly up close— after the age of forty—a person is said to have presbyopia (from Greek: presby, meaning "older," and opia, meaning "eye"). Presbyopes often hear or read that their near blur is due to the inflexibility of the lens, due to the "natural aging process."

Presbyopia is said to be the result of the lens becoming rigid, in its "non-accommo- dating" flatter shape. According to the Helmholtz lens theory of accommodation, the presbyope can see clearly only in the distance, not up close. Supposedly the lens loses its flexibility and therefore the front side of the lens loses its ability to have more curvature to focus clearly on near objects. Conventional textbooks do not state that presbyopia is caused by foreshortening of the eyeball, which was Bates' position.

Quoting again from University Physics:11

The extremes of the range over which distinct vision is possible are known as the far point and the near point of the eye. The far point of a normal eye is at infinity. The position of the near point evidently [TQ emphasis] depends on the extent to which the curvature of the crystalline lens may be increased in accommodation. The range of accommodation gradually diminishes with age as the crystalline lens loses its flexibility. For this reason the near point gradually recedes as one grows older. This recession of the near point with age is called presbyopia, and should not be considered a defect of vision, since it proceeds at about the same rate in all normal eyes. The following is a table of the approximate position of the near point at various ages:

In using the word "evidently," the authors seem to suggest some doubt as to the relationship between the inflexibility of the lens' curvature and a person's near point with aging.

Bates believed presbyopia is hypermetropia occurring at middle age, and is caused by strained recti muscles foreshortening the eyeball.

Bates proved the two oblique muscles can elongate the eyeball, in which state a person sees clearly up close. When the oblique muscles release, the eye returns to the normal shape for distance vision. For Bates, accommodation occurs only by the action of the two, oblique, external eye muscles.

Bates felt there was ample evidence to support the position that the oblique muscles produce accommodation. Following is his view on presbyopia, from Chapter XX of Per- fect Sight Without Glasses. According to Bates, this condition is not inevitable, and it can be reversed when it occurs.

Among people living under civilized conditions, the accommodative power of the eye gradually declines, in most cases, until at the age of sixty or seventy it appears to have been entirely lost, the subject being absolutely dependent upon his glasses for vision at the near point. As to whether the same thing happens among primitive peo-

ple or people living under primitive conditions, very little information is available. Donders3 says that the power of accommodation diminishes little, if at all, more rapidly among people who use their eyes much at the near point than among agriculturists, sailors and others who use them mainly for distant vision; and Roosa and othersb say the contrary. This is a fact, however, that people who cannot read, no matter what their age, will manifest a failure of near vision if asked to look at printed characters, although their sight for familiar objects at the near point may be perfect. The fact that such persons, at the age of forty-five or fifty, cannot differentiate between printed characters is no wanant, therefore, for the conclusion that their accommodative powers are declining. A young illiterate would do no better, and a young student who can read Roman characters at the near point without difficulty always develops symptoms of imperfect sight when he attempts to read, for the first time, old English, Greek, or Chinese characters.

When the accommodative power has declined to the point at which reading and writing become difficult, the person is said to have "presbyopia" or, more popularly, "old sight"; and the condition is generally accepted, both by the popular and the scientific mind, as one of the unavoidable inconveniences of old age. "Presbyopia," says Donders, "is the normal quality of the normal, emmetropic eye in advanced age,"'

* On the Anomalies of Accommodation and Refraction of the bye, p. 223.

bRoosa: A Clinical Manual of Diseases of the Eye, 1894, p. 537; Oliver System of Diseases of the Eye. vol. iv, p. 431.

*On the Anomalies of Accommodation ««nd Refraction of the Lye, p 2»o.

and similar statements might be multiplied endlessly. De Schweinitz calls the condition "a normal result of growing old";d according to Fuchs it is "a physiological process which every eye undergoes";' while Roosa speaks of the change as one which "ultimately affects every eye."'

The decline of accommodative power with advancing years is commonly attributed to the hardening of the lens, an influence which is believed to be augmented, in later years, by a flattening of this body and a lowering of its refractive index, together with weakness or atrophy of the ciliary muscle; and so regular is the decline, in most cases, that tables have been compiled showing the near point to be expected at various ages. From these it is said one might almost fit glasses without testing the vision of the subject; or, conversely, one might, from a man's glasses, judge his age within a year or two. The following table is quoted from Jackson's chapter on "The Dioptrics of the Eye," in Norris and Oliver's "System of Diseases of the Eye,"s and does not differ materially from the tables given by Fuchs, Donders and Duane. The first column indicates the age, the second diopters of acrommodative power, the third the near point for an emmetropic11 eye, in inches.

dDiseases of the Eye, p. 148.

eText-book of Ophthalmology, authorized translation from the twelfth German edition by Duane, 1919, p. 862. Ernst Fuchs (1851-). Professor of Ophthalmology at Vienna from 1885 to 1915. His Textbook of Ophthalmology has been translated into many languages.

fA Clinical Manual of Diseases of the Eye, p. 535.

8 Vol. i, p. 504.

hAn eye which, when it is at rest, focuses parallel rays upon the retina is said to be emmetropic or normal.

According to these depressing figures one must expect at thirty to have lost no less than half of one's original accommodative power, while at forty two-thirds of it would be gone, and at sixty it would be practically nonexistent.

There are many people, however, who do not fit this schedule. Many persons at forty can read fine print at four inches, although they ought, according to the table, to have lost that power shortly after twenty. Worse still, there are people who refuse to become presbyopic at all. Oliver Wendell Holmes mentions one of these cases in The

Autocrat of the Breakfast Table.

"There is now living in New York State," he says, "an old gentleman who, perceiving his sight to fail, immediately took to exercising it on the finest print, and in this way fairly bullied Nature out of her foolish habit of taking liberties at five-and-forty, or thereabout. [Some Natural Vision teachers would have preferred the word "coaxed" instead of "bullied," as effort is never associated with normal vision.] And now this old gentleman performs the most extraordinary feats with his pen, showing that his eyes must be a pair of microscopes. I should