Experimental Myopia - Experiments in Myopia

SYNOPSIS

HOW AN ACCIDENTAL DISCOVERY COULD REVOLUTIONIZE MYOPIA THEORY

       An experiment designed to squeeze the eyes of a high myope improved his uncorrected visual acuity from 20/400 to 20/25.

       However, this was not the acuity as perceived by an emmetrope. It consisted of two images: a nearly clear image superimposed on a highly blurred image.

      The only logical explanation is that two distinct images could only have come from two separate focal points. Apparently, compressing the eye had created a new focal point, located behind the normal focal point.

      The method used to compress the eyes was to cause the superior oblique muscles to contract, which is known to compress the eyeball in the general area of the equator.

       It is surmised that external pressure had forced the vitreous forward, which flattened the periphery of the crystalline lens, which in turn created the new focal point.

        The dual vision remained long after the experiment was stopped, which suggests that a high degree of accommodation can be long-lasting and that in addition to axial elongation, myopia could be caused in part by the lens being permanently accommodated for near vision. This is supported by studies of NITM (Nearwork-Induced Transient Myopia).

CURRENT MYOPIA RESEARCH

      Much of myopia research in the past few years has involved attempts to prevent myopia in humans (or to slow its progression), or to produce myopia in animals.
Experiments aimed at causing myopia have centered mainly on various methods of form deprivation using animal subjects such as monkeys, rabbits and chickens.
For obvious reasons, experiments designed to elicit myopia in humans have been practically non-existent. The project described here is an anomaly: an experiment designed to produce myopia in a human subject.

      It is well established that elongation of the globe is a significant factor in myopia. Because axial length is so prominent, it has been the subject of the vast majority of myopia research; in fact it is almost universally agreed that vitreous chamber elongation is the structural change producing almost all myopia. Of the two other components of the refractive power of the eye, the cornea and the lens, the lens is considered to be the least important.
Consequently, if an emmetropic eye could be made to elongate, it should become myopic, and an experiment was devised to test this. Because the subject of this experiment was already myopic, any elongation should cause an increase in his degree of myopia.

THE EXPERIMENT

The experiment described here was designed to test the hypothesis that the extraocular muscles, specifically the superior and inferior obliques, might be a significant factor in the etiology of myopia.

Of the six extraocular muscles that control the movement of each eye, two, the superior and inferior obliques, would be the most capable of compressing the eyeball and possibly elongating it. It was decided to produce contraction of these muscles by the following means:

Because the eye muscles are not subject to individual voluntary control, it was necessary to devise some means to make only the obliques contract while maintaining relative relaxation of the others. The natural tendency of the eyes to fuse two disparate images was utilized for this purpose.

A viewing device was constructed which consisted of two identical images on a white background. When the subject looked through the device, each eye viewed one of the images; the visual cortex then fuses the two images to form a single view.

The images were then incyclorotated, i.e. as seen by the subject, the right-side image was rotated counterclockwise and the left-side image was rotated clockwise. In order to maintain fusion of the two images, each eye must then rotate in the same direction as the image it is viewing, i.e. the upper end of the vertical meridian of each eye leans nasalwards.

Although the movement of incyclorotation is effected principally by the superior oblique muscles, there is a limit as to how far the globe can rotate, since this is opposed by the check ligaments and other fascial structures of the orbit. If an effort is made to maintain fusion, the traction of the superior obliques will exert pressure on the eyeball in the general area of the equatorial meridian.

Because the compression would be exerted in the area of the equator, it would be expected that any alteration in the shape of the globe wold consist of stretching in the posterior area (or, less likely, anteriorly).

This is not to say that if the images are rotated, say, 8 degrees, each eye will also rotate exactly 8 degrees; eye rotation can be as much as 2 degrees less. This is because of Panum's fusional area, which in stereopsis allows the image to be pulled apart by some 2 degrees before being broken up into two separate images (Fender, 1967) [2] The images are actually pulled apart on the retina, but a supra-retinal function maintains perception of a single image.

The device was later modified for portable use to facilitate long-term viewing. Instead of viewing graphic images, the subject looked through a system consisting of two pairs of mirrors, one pair for each eye. By adjusting the angle of the mirrors relative to each other, the image presented to the eye can be rotated around its axis.
The mirrors were adjusted so that each set produced incyclorotation of the image, In order to eliminate any stimulus to accommodation, distance fixation of at least six meters was maintained.

The amount of tilt (incyclorotation) varied between 6 and 12 degrees. Since I was unable to find an emmetrope willing to risk becoming a myope, the subject of the experiment necessarily had to be myself.

In order to determine if the device had produced any change in eyeball dimensions, I had to rely on changes in visual acuity. Thus, if in the course of the experiment I noted increased blur for distance vision, this would indicate that the eye had elongated.

After using the device for several days, I began to notice a change in my vision. However, what I saw was completely unexpected. Instead of an increase in blur that would have resulted from greater axial length, my vision had improved dramatically.

This improved acuity, however, was not the same as normal acuity but was mixed: it consisted of both sharpness and blur. For example, an object viewed at a distance was seen as sharp, yet overlaid by a larger, highly blurred image of the same object.

It could be said, then, that the experiment was a success, since it indicated that the eyeball had elongated, as evidenced by the increased degree of blur for distance vision with the subject wearing his original corrective lenses. The most significant point, however, is that these changes in acuity must have come not solely from elongation of the globe, but rather from changes in the shape and power of the crystalline lens, as visualized in Figure 1.

The monocular diplopia was so pronounced that the uncorrected acuity improved to the extent that I had become almost emmetropic--I could easily read the 20/25 line of a Snellen chart.

The only possible explanation of these dual images is that they had to come from two separate focal points. I further reasoned that what had happened was that compressing the eyeball had forced the vitreous against the back of the lens, flattening its periphery, which created a new focal point.

Spherical aberration and its relation to accommodation\

The presence of two separate focal points suggests an extreme form of spherical aberration. Spherical aberration is almost certain proof that the lens had accommodated. Many studies have demonstrated that the two go together. Ivanoff (1956) [1] and others have shown that when the eye is at rest the spherical aberration is positive, which means that the rays passing through the periphery of the lens come to a focus in front of rays passing through the axial region of the lens.

As the lens accommodates to view a near object and begins to change its shape, the spherical aberration decreases, and at around 3 diopters there is almost no aberration at all, i.e. all the rays come to a focus at the same point.

If the eye accommodates further, the aberration begins to reverse, in which case the peripheral rays come to a focus at a point behind the axial ray focal point.
Apparently this condition had reached an extreme degree, as visualized in Figure 1.

Figure 1. LENS SHAPE AND FOCAL POINTS

Rays passing through this outer region of the lens came to a focus at a point very close to the retina, which produced the secondary image (nearly clear vision), while the rays passing through the central region of the lens came to a focus in front of the retina, which produced the primary image, which was severely blurred. A subsequent eye examination revealed that my existing myopia had increased by about 5 diopters: At the start of the experiment the refraction was O.D. -7.5 -1.25 ; O.S. -5.50 -1.50. After the experiment the refraction was O.D. -11.75 -2.25 ; O.S. -9.0 -2.00.

The approximately 5 diopter increase in the degree of myopia suggests that the vitreous pressure had accommodated the lens to an extreme degree. It is important to note that the subject, who was 35 years old at the time, was far beyond the age at which myopia increases normally occur.

Because the secondary focal point had produced an almost clear image, it was thought that increasing wearing time of the device might move the focal point even closer to the retina and consequently produce a further improvement in visual acuity. The result was too successful. Apparently, further compression had moved the secondary focal point not just to the retina, but to a position behind the retina, as visualized in Figure 2.

Figure 2.

This is suggested by the fact that I was able to perceive nearly sharp images at a distance with a +4 lens. It could be said then that I had become the world’s only high myope/ hyperope.

The persistence of accommodation

It is significant that the results noted above were not momentary, but persisted after each viewing session ended: both the increased blur and dual vision remained. Eventually, after the experiment was terminated, the 5 diopter increase in myopia began to reverse, i.e. the visual acuity gradually improved over the course of a year (but never returned to its original degree). This confirms that when an eye is accommodated for long periods of time, the lens does not completely revert to its focus for distance viewing when the nearwork task is completed.

The persistence of accommodation is well documented in studies of nearwork-induced transient myopia (NITM). If, after a period of near focus, the gaze is then shifted to a distant object, the result is a temporary myopia (typically 0.25 - 0.30 D), because the eye requires a certain period of time to re-focus for distance viewing. The time required is related to the amount of time spent on the nearwork task: the longer the period of nearwork, the longer the decay time, i.e. the more time is required for the eye to relax its accommodation.
This fact forms the basis for the hypothesis that in myopia the crystalline lens is permanently accommodated for near vision.

THE CASE AGAINST THE LENS HYPOTHESIS

Study after study has shown that the principal cause of myopia is increased axial length, not increased lens power.

If, in myopic eyes, the lenses are accommodated, they would tend to be thicker than the lenses of emmetropes. Not only is this not true, but, in general, myopic eyes tend to have even thinner lenses than emmetropes.

If accommodation of the lens were true, then myopia could be cured by simply instilling a cycloplegic. This would allow the ciliary muscle to relax and so enable the eye to re-focus for distance vision.

Of the three major determinants of refractive power, the lens is considered to be the least important. According to Hirsch (19670 [3], “Three variables, then, the axial length, the shape of the cornea, and the power of the crystalline lens, exert the greatest effect upon refraction. There is relative agreement among authors as to the relative influence which each of these exerts, the axial length being the greatest, followed by the cornea and lens in that order.”

EVIDENCE IN SUPPORT OF THE LENS HYPOTHESIS

The hypothesis presented here is based on four claims:
1. The oblique muscles can compress the globe.
2. Compression causes the eye to elongate
3. Compression moves the vitreous in the direction of the lens.
4. Pressure by the vitreous can alter lens shape and refractive power.

External Pressure on the Globe

This experiment could be significant for nearwork theory for this reason: although it involved a highly artificial situation, it was merely an extreme example of what occurs in what is undoubtedly the most common form of nearwork, reading. With the eyes converged, most people read with the gaze depressed; in this situation the continuous horizontal scanning movement of the eyes from left to right and back again produces continual rotation of the eyes, which is effected by contraction of both the superior and inferior obliques.

That the oblique muscles can exert pressure on the globe in this situation is well established. According to Curtin, (1985) [4], “With the eye converged and depressed, the SO [superior oblique] muscle is in a position to exert considerable pressure on the globe" (my emphasis).

External pressure and axial elongation

That the oblique muscle pressure on the globe could cause it to elongate is supported by an inadvertent finding from a procedure used to treat retinal detachment. Rubin (1967) [5] reported that “…when silicon bands are placed about the equator and tightened to reduce vitreous traction in retinal detachment work, the eyeball becomes longer axially and thereby increases myopia (or lessens hypermetropia). This increase in length is permanent as long as the band remains in place. It apparently does not harm the eye unless it is cinched up too tight, but I have noted up to 5 diopters of change in extreme cases; most average about 1.5 diopters over the prior existing state.”

The effect of pressure on the vitreous

That external pressure on the globe can affect the vitreous is supported by an experiment performed by von Pflugk (1935) [6] . He cut windows in the equatorial region of bovine eyes and injected a drop of dye into the anterior vitreous, midway between the ciliary body and the posterior pole of the lens. Pressing against the ciliary body from the outside in a radial direction made the dye move toward the lens capsule.

Luedde (1940) [7] in a study of subluxated lenses, reported that “The demonstration of the fact that there was a concentric impact of the periphery of the vitreous against the zonule and posterior surface of the equatorial zone of the lens when the ciliary contracted…”

Vitreous effect on the shape and refractive power of the lens

Numerous studies confirm that ciliary muscle contraction pulls the vitreous against the lens.

Araki (1965) [8] reported that in experiments on pig, dog and cat eyes, "...it is suggested that tension of the ciliary muscle/zonules stretching from the posterior surface of the lens was increased by forward movement of the ciliary body and consequently it resulted in pressure to the posterior peripheral part of the lens...the increase in pressure of the vitreous body due to contraction of the accommodative muscle is considered to be the most important factor for the transformation of the lens." (my emphasis).

Suzuki (1971) [9] performed an experiment in which he injected radiopaque material into the vitreous of a cat's eye, which during accommodation moved in a direction indicating that the vitreous was forced against the back of the lens and also somewhat toward the posterior pole of the lens.

An experiment by Koke (1942) [10] produced a similar result. He injected cat eyes with radiopaque material and took X-rays during miosis and mydriasis, which showed that during accommodation the vitreous moved toward the lens and inward toward the optic axis.

The hypothesis that the extraocular muscles play a role in the causation of myopia is certainly not new. It has been suggested by numerous investigators over the years. A major difference from this hypothesis, however, is that in none of these hypotheses has it been proposed that they have any effect on the lens. All are limited to the concept of axial elongation of the globe by elevation of the intraocular pressure, scleral weakness or other means.

Lens not spherical

The lens shape proposed by this hypothesis is supported by a number studies. The common belief that the lens becomes more spherical with accommodation is probably due to the classical experiment by Fincham (1937) [11].

An eye was made to accommodate for distance viewing by the instillation of atropine and then removed from the orbit upward after dissection of the cornea and iris. The profile of the lens can then be photographed and in this condition demonstrates the characteristic shape of the lens when the eye is looking at a distance. He then cut the fibers of the zonule all around and observed that the curvature of the anterior surface of the lens increased markedly and, as he put it, “assumed the shape that it has under maximum accommodation”, i.e. the lens becomes thicker, and this is clearly seen in the photographs taken by Fincham.

This appears to be an invincible argument, conclusive proof of the relaxation theory of accommodation. However, this was a highly artificial situation; he assumed that the zonules relax uniformly, and that the consequent change in shape of the lens was the same as that which occurs in accommodation.

Even today, the belief that accommodation simply makes the lens become more spherical is widespread. According to Roorda and Glasser, writing in 2004, "The prevailing view is that the lens becomes more spherical with accommodation due to the molding force of the capsule. ‘Spherical’ does not adequately describe the shape of the accommodated lens because the peripheral area of the posterior surface of the lens is quite different from the anterior surface.”\

Fincham’s view is contradicted by subsequent studies that show that there are three sets of zonules and that they do not relax uniformly.

An experiment by Araki (1965) [12] showed that "electric recordings of the changes in tension of the ciliary zonules suggested relaxation of the zonules which was (sic) stretched to the anterior surface of the lens and on the contrary, increased tension of that stretching to the posterior surface (cat and dog eyes)”.

Schachar (2001) [13] has proposed that there are three sets of fibers: anterior, posterior and equatorial, and that when the ciliary contracts there is increased tension of the equatorial fibers which reduces the tension of the other two sets. When the eye is in the unaccommodated state, the anterior and posterior zonules are taut, and there is reduced tension on the equatorial zonules.

Instead of a lens that becomes more spherical as proposed by Fincham, the separate zonule fibers with different degrees of tension and relaxation could result in a lens that assumes a shape similar to that shown in Fig.1.

The lens shape proposed in this hypothesis evolved as follows: the presence of simultaneous blurred and sharp vision suggested strongly that there had to be two distinct focal points, and consequently one part of the lens had to be stronger than the other. A shape that would fit this requirement would be the one shown in Figure 1., a convex central region and a somewhat flat periphery.In an extensive search of the literature I found four papers (there are undoubtedly more) that describe precisely such a lens shape:

“The increasing negative spherical aberration of the accommodating lens arises from a more pronounced increase in the optical power near the central region of the lens compared to the peripheral region….this is different to the generally accepted notion that the lens simply becomes more spherical with accommodation….The increase in negative spherical aberration is likely due to the effect of the structure of the lens substance…but may also be due in part to accommodative variations in gradient refractive index of the lens”. (Roorda and Glasser, 2004) [14]

In a study of accommodation in the rhesus monkey, Bito et al [15] state that "A possible iridial contribution was also observed during carbachol-induced accommodation in young animals: development of full miosis was prevented by occlusion of the pupil by the anterior-central portion of the lens. Thus it appears that the pupillary margin and/or the sphincter muscle can apply a force to the lens which may steepen the curvature of its anterior-lenticular central portion thus increasing total dioptric power".

Lowe (1972) [16] reported that "During examination of a large series of eyes that had pupils dilated after peripheral iridectomy...I was struck by the marked curvature of the anterior lens surface within the enlarged pupil. The lens frequently appeared as though it were herniating through the enlarged pupil, with the pupillary margin of the iris seeming to grip the lens."

Jampel and Mindel (1967) [17] in a report on stimulation of the oculomotor nucleus in monkeys, observed changes "... characterized by a conspicuous forward bulging of the pupillary or central portion of the iris which produced a marked convexity of the iris diaphragm and a marked increase in the depth of the anterior chamber...On observation of the eye from the side during iris-bulge, the central portion of the lens appeared to become conoidal and to move forward into the anterior chamber."

It is highly improbable that with the vast amount of research done on the iris, such an important function as counterpressure on the lens could remain undetected. Yet these reports strongly suggest an iris/lens connection, and it is interesting that the researchers themselves seem surprised by their findings.

Spherical aberration

The fact that accommodation produces negative spherical aberration is well-established, and a number of studies, including one by Hu, et al, (2004) [18], have shown that spherical aberration is more common in high myopia Collins et al (1995) [19] report that "A high proportion of the aberroscope grids photographed in myopic eyes were too highly distorted to permit analysis. This was not the case for emmetropic subjects”.

The phenomenon of spherical aberration seems to be widely ignored. Even in basic works such as Adler's Physiology of the Eye, The Myopias (Curtin) and Visual Optics and Refraction (Michaels) and The Physiology of the Eye (Davson), the question of spherical aberration is little discussed.

The conventional wisdom that the principal changes occur in the anterior lens was challenged by Patnaik (1967) [20], who wrote that "...the often stated and commonly accepted statement, that it is the anterior lens surface which moves forward while the posterior surface remains stationary and that it is only the anterior surface which changes its curvature during accommodation seems not to be correct.”

Patnaik also commented on the possibility of nuclear changes: "Our observations strongly indicate that during accommodation the increase in the thickness of the anterior cortex is minimal, and that the change in the posterior cortex is greater, and that in the nuclear thickness change is greatest".

The persistence of accommodation

Eventually, after the experiment was terminated, the 5 diopter increase in myopia began to reverse, i.e. the visual acuity gradually improved over the course of a year (but never returned to its original degree). The persistence of accommodation is well documented in studies of nearwork-induced transient myopia (NITM). If, after a period of near focus, the gaze is then shifted to a distant object, the result is a temporary myopia (typically 0.25 - 0.30 D), because the eye requires a certain period of time to re-focus for distance viewing.
The time required is related to the amount of time spent on the nearwork task: the longer the period of nearwork, the longer the decay time, i.e. the more time is required for the eye to relax its accommodation.

One of the first to study this phenomenon was Lancaster (1952) [21], who stated that “When the eye, after an intense effort of accommodation, is shifted to a distant object, although the ciliary muscle may promptly relax, it takes time (a few seconds to a few minutes depending on how long the near effort was continued) for the lens to regain its normal shape adapted to a distance”.

Ong and Ciufredda (1995) [22] in their studies of NITM state that after Lancaster "little was done in this field for the next seven decades, until computer display terminals became commonplace, and symptoms related to their use became prevalent". However, these more recent studies have attributed this slow recovery time only to the ciliary muscle in the form of changes in tonic accommodation; the possible role of the viscosity of the lens has not even been considered.

They state that "with the continuous high level of accommodative effort necessary to maintain accurate focus, the accommodative hysteresis that was reflected in the (presumed) increased level of tonic accommodation developed as a consequence of increased innervation due to gradual fatiguing of the accommodative system. This myopic increase would then be carried over to distant viewing".

In another paper, Ong and Ciufredda (1995) [23] go even further; they make the case for
the very hypothesis proposed here:

“It has been suggested that that these effects might be cumulative over time following successive periods of near tasks, with the transient myopia perhaps evolving into a more permanent form of myopia. For example, it is conceivable that prolonged and repeated periods of nearwork over extended periods of time would result in NITM that failed to decay in some susceptible individuals”.

Although the experiment described here involves a very artificial situation, compression of the globe by the obliques occurs in a very common situation: reading. With the eyes converged, most people read with the gaze depressed; in this situation the continuous horizontal scanning movement of the eyes from left to right and back again produces continual rotation of the eyes, which is effected by contraction of both the superior and inferior obliques.

It is interesting that lens viscosity is widely accepted as an explanation of presbyopia, i.e. the difficulty of seeing clearly at near for most people over the age of about 45. It is believed that lack of flexibility of the crystalline lens prevents it from changing its shape and refractive power in order to do nearwork, yet this factor is ignored in theories of myopia.

The slowness of lens changes has been studied by other investigators, not as due to ciliary fatigue, but as due to lens viscosity.

According to Kikkawa and Sato (1963) [24],"Application of an external force to the lens caused a rapid deformation followed by a second phase of slow deformation. On removal of the force, a rapid partial reversal of the deformation occurred and was followed by a gradual restoration; complete recovery was not achieved (my emphasis).

Kabe (1967) [25] reported a similar result from his investigations. He showed that when accommodation is increasing, the change in the apparent curvature of the anterior surface of the lens is slow and continuous, but when accommodation is decreasing, there is a prompt, followed by a slow phase.

Retinal defocus as a cause of elongation

The connection of nearwork with myopia is well established. However, because myopia researchers believe that of the three major determinants of refractive power, the lens is the least important, they have tried to explain the nearwork/myopia connection by claiming that nearwork causes the eye to elongate, and the mechanism they propose is retinal defocus.

It is thought that if a lag of accommodation occurs during nearwork, the amount of accommodation is less than required for a given distance and, with a reduced accommodative response, the retinal image will be defocused, i.e. the target will be focused behind the retina, and a supranuclear mechanism causes the eye to elongate.

The rationale for this theory is derived from animal studies that show that degraded retinal images produce substantial myopia in a variety of different species. For example, when negative lenses are worn by monkeys, which produce hyperopic defocus (the retinal blur from a focal point situated behind the retina), the monkeys’ eyes elongate.

It is difficult to understand belief in this theory because the only direct evidence that retinal defocus produces myopia in humans comes from cases of severe image degradation caused by conditions such as vitreous hemorrhage, corneal opacity and traumatic cataract.
In addition, contrary evidence is found in cases of ocular pathology such as albinism and maculopathies, which impair foveal vision in children and is frequently associated with hyperopia.

In any case, even the animal studies are not entirely consistent. In studies of kittens, Ni and Smith (1989) [26] showed that minus lenses did produce axial elongation, but so did plus lenses.

A more recent view by Hung, G.K. and Ciufredda, K. J. (2002) [27] is that the detection mechanism does not depend on the sign of the blur, but rather on the change in blur magnitude during genetically-programmed ocular growth.. In any case, the retinal defocus hypothesis refers to the period of ocular growth of the eye, which ends at about the age of 17. Consequently, it does nothing to explain adult-onset myopia.

Many investigators have attempted to link myopia to ciliary muscle tonus, i.e. pseudomyopia, in which after the gaze is shifted away from the nearwork situation the ciliary muscle maintains its contraction. There is a major problem with this idea: in general, myopes have the lowest level of tonic accommodation and their ciliary muscles are poorly developed compared to those of emmetropes.

It is almost inconceivable that thousands of studies in physiological optics could have missed the significance of the lens in myopia.

There are three possible reasons:

1) The difficulty of determining internal changes in the lens.

2) Excessive trust in the reliability of many of the most basic assumptions about the eye.

3) Researchers have apparently assumed that a thin lens must necessarily be of low power.

Otsuka (1970) [28] commented on the difficulty of studying the posterior surface of the lens: "...the exact radius of the posterior lens surface is impossible to determine because of the lack of knowledge regarding the internal change of the lens substances."
He also suggested the possibility of a thin, yet high power, lens: "the thicker the lens became during accommodation, the thinner the lens became annually." This is intriguing, but unfortunately he did not elaborate.

Smith, G. (2003) [29] confirms the difficulty of such measurements: “It is now possible to accurately measure the aberrations of the whole eye using the Hartrnann-Shack aberrometer and the corneal aberrations via the anterior surface shape. Missing are the shapes of the posterior corneal surface and the anterior and posteriorlenticular surfaces’.

Faulty Data

Textbooks of ophthalmology give the impression of a solid edifice of knowledge built on firm foundations. Yet at least one researcher, Ludlam, (1967) [30] suggests that some of the most basic facts about the eye are based on faulty data and should be re-evaluated:
These include invalid mathematical assumptions, mixed sampling, inadequate experimental technique, and oversimplified models of the refractive system, some of these dating from the nineteenth century:

Nevertheless, the analyses and conclusions drawn from such studies can be no better than either the methods of acquisition of the basic data or the validity of the assumptions underlying the mathematical formulation of the ocular model. It is well to note that in all of these studies the model of the ocular system utilized has consisted of:

Spherical refracting surfaces (my emphasis), causing a systematic under-estimation of the paraxial refracting power of each surface.

Schematic refractive indices, invariant in the population--which assumes that all variability in the ocular refracting system derives only from differences in curvature and spacing of the ocular elements, thus again underestimating both the number of variables in a given eye and the true variability for each component actually existing in the population

A homogeneous monoindicial lens (my emphasis).This places a high order of importance on the accuracy and precision of the measures of curvature of both the anterior and posterior surfaces of the lens and concomitantly increases the potential effects of spherical assumption.

In addition, in none of these studies have all the refractive components of any given eye been measured. There has always been at least one component whose value was calculated from the other measured elements, so that the measurement errors would all tend to accumulate in the non-measured element.

Since the measurement errors have not always been stated with sufficient clarity to enable the effects of these errors to be assessed, the probability exists that measurement errors have contributed substantially to spurious correlations of measured and calculated elements, as for example between the lens and axial length.

Further evidence for the lens hypothesis

A device was constructed for the purpose of applying vibration to the eye in order to see if it had any effect on the lens. Application was through a soft rubber tip placed on the upper eyelid and vibrated at a rate of 60 Hz and amplitude of 1 mm. The vibrated eye was abducted as far as possible and the other eye was occluded

he result was that initially the visual acuity improved significantly. This suggests that the lens had been accommodated, and that vibration had "softened" the lens, allowing it to revert to a less accommodated state. However, since the subject, the author, was then in the early stages of presbyopia, it was assumed that further improvement was prevented by the lack of flexibility of the lens substance.\

It could be argued that a different mechanism was operating, e.g. that vibration shortened the globe. However, the evidence that it was the lens is provided by a phenomenon that appeared early in the experiment: increased color brightness and the perception of blackness. It never occurred to me to question what black looks like, but with vibration of the eye there was a marked intensification in the appearance of black objects.

The explanation may be that because in a high myope, light rays are dispersed on the retina in the form of blur circles; as lens power decreases, the blur circles shrink, and the rays are concentrated in a progressively smaller area, resulting in increased density of color or blackness. This phenomenon suggests strongly that vibration produced a decrease in lens power.

Replication

It would be difficult to replicate the experiment because of the ethical problem of potential harm, e.g. causing a subject to become myopic.
A possible alternative would be to replicate the vibration experiment, not with a human subject, but by using the enucleated lens of a myope, subjecting it to vibration and measuring changes in shape or structure of the lens and/or globe that might mimic the changes that occur with relaxation of accommodation in a living eye.

Another possibility is to apply external pressure to an enucleated eye and then use x-rays, computerized tomography or ultrasound to look for any alteration in lens shape or power. Implications

The persistence of accommodation shown in this experiment lends support to the recommendation of some ophthalmologists and optometrists that the development of myopia, especially in the young, can be mitigated by avoiding continuous long periods of nearwork. At present, this is not widely advocated, but is consistent with the idea of avoiding NITM by frequent rest periods from nearwork by looking at a distance of 9.

The Failure of Therapeutic Measures

The lens/vitreous hypothesis provides a possible explanation for the failure, or at least disappointing results, of therapeutic measures aimed at preventing or slowing the progress of myopia, such as cycloplegics, and progressive addition spectacle lenses. In both cases, they undoubtedly reduce ciliary muscle contraction, but for only a few hours at a time, while the lens may require far more time for a significant reduction in the degree of accommodation.

More importantly, in both these regimens the subjects are permitted to continue doing nearwork, so that even if complete relaxation of the ciliary muscle were achieved, accommodation could still have been maintained, at least partly: reading, with continuous back-and-forth scanning movements with depressed gaze, requires a constant contraction/relaxation of the superior obliques, and this could compress the globe sufficiently to force the vitreous against the lens.

CONCLUSION

Needless to say, acceptance of the hypothesis proposed here would require an almost complete reversal of opinion.

Actually there are a few cases in which a universally accepted theory has been overturned. An example is the theory of nervous system plasticity:

According to Sperry (1959) [31],"During the past 15 years, however,
scientific and medical opinion has undergone a major shift,
amounting to an almost complete about-face ... The evidence for
this view, which comes from new experiments and exacting clinical
observations, is so persuasive that it is difficult to understand
how the opposite view could have prevailed for so long. It appears
that most of the earlier reports of the high functional plasticity
of the nervous system will go down in the record as unfortunate
examples of how an erroneous medical or scientific opinion, once
implanted can snowball until it biases experimental observations
and crushes dissenting opinions...Hundreds of experiments (my emphasis) seemed
to support the now-discounted opinion..."

One of the objections might be that this hypothesis is too speculative, but some papers are even more so, as shown in this example by a proponent of defocus theory (words in italics are my emphasis, with one exception):

"…late onset myopia may result from a progressive sequence. Firstly, there is diminished augmentation of sympathetic inhibition of ciliary smooth muscle which would normally accompany sustained near vision; the deficit may have an hereditary basis and be exacerbated by high levels of cognitive demand. Secondly, the sympathetic deficit alters the near oculomotor autonomic response profile and triggers a series of latent [original author’s emphasis] within-task micro-adaptational processes; these processes could be driven by subperceptual retinal blur processes linked to enhanced accommodative lag at near or to uncoupling of normal accommodative-vergence interactions. Thirdly, the adaptational process accumulates to a critical level (perhaps via an iterative ratchet-type response with regard to accommodative gain) where structural recalibration takes place, that is, elongation of the vitreous chamber".

Another objection: my lack of credentials. However, this can be a positive. As James Surowiecki (in The Wisdom of Crowds), and researcher James G. March) put it, there are advantages of allowing outsiders to take part in experts’ deliberations:

"The development of knowledge may depend on maintaining an influx of the naive and the ignorant,…The reason, March suggested, is that groups that are too much alike find it harder to keep learning, because each member is bringing less and less new information to the table.

“Bringing new members into the organization, even if they’re less experienced and less capable, actually makes the group smarter simply because what little the new members do know is not redundant with what everyone else knows”.

I’m not dogmatic about the lens hypothesis. If it can be shown, with solid, experiment-based evidence, that the lens hypothesis is wrong, I will retract it in a heartbeat. It would be painful and embarrassing, but so what? The only thing that counts in science are facts.

REFERENCES

[1] Ivanoff, A. Au Sujet de l'Aberration spherique de l'oeil (1956) Optica Acta 3, 47-48.
[2] Fender, D. (1967) Extension of Panum's fusional area in binocularly stabilized vision. Journal of the Optical Society of America, 57, 819-830.
[3] Hirsch, M. (1967) In Refractive Anomalies of the Eye. Public Health Service Publication No. 1687, National Institute of Neurological Diseases and Blindness, Monograph No. 5, U.S. Department of Health, Education and Welfare.
[4] Curtin, B. The Myopias. Philadelphia. Harper and Row, (1985). p.104
[5] Rubin, M. (1967) In Refractive Anomalies of the Eye. Public Health Service Publication No. 1687, National Institute of Neurological Diseases and Blindness, Monograph No. 5, U.S. Department of Health, Education and Welfare.
[6] von Pflugk (1935). New ways in the study of accommodation V. The vitreous in the accommodating eye, Graefes Archive for Clinical and Experimental Ophthalmology, 133, 545-558.
[7] Luedde, W.H. What subluxated lenses reveal about the mechanism of accommodation. Department of Ophthalmology, Saint Louis University School of Medicine. Presented at the Sectional Meeting of the American College of Surgeons, Detroit, Michigan, April 2, 1940.
[8] Araki, M. Changes of the ciliary region and the ciliary zonule in accommodation. (1965) Japanese Journal of Ophthalmology, 9 50-58.
[9] Suzuki, H. Observations on the intraocular changes associated with accommodation. (1971) Japanese Journal of Ophthalmology, 15, 47-58.
[10] Koke, M. Mechanism of accommodation (1942). Archives of Ophthalmology, 27, 950-968.
[11] Fincham, E F. (1937) The Mechanism of Accommodation. British Journal of Ophthalmology, 8 (Supplement).
[12] Araki, M. Changes of the ciliary region and the ciliary zonule in accommodation. (1965) Japanese Journal of Ophthalmology, 9, 50-58.
[13] Schachar, R. (2001). The mechanism of human accommodation as analyzed by nonlinear finite element analysis. Comparative Therapies, 27, 22-132.
[14] Roorda and Glasser. Wave aberrations of the isolated crystalline lens, Journal of Vision (2004) 4, 250-261.
[15] Bito, L.Z., Kaufman, P.L., Neider, M.W. and Miranda, C.O. The Rhesus Monkey Eye as a Model for the Mechanism of Accommodation, and the Etiology of Presbyopia and Other Aspects of Ocular Aging. Proceedings of the International Society for Eye Research, Volume III.
[16] Lowe, R F. (1972) Anterior lens curvature. Comparison between normal eyes and those with primary angle-closure glaucoma. British Journal of Ophthalmology, 56, 409-413.
[17] Jampel, R S. and Mindel, J. (1967) The nucleus for accommodation in the midbrain of the macaque. Investigative Ophthalmology & Visual Science, 6, 40-50.
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[20] Patnaik, B. (1967). A photographic study of accommodative mechanisms, changes in the lens nucleus during accommodation. Investigative Ophthalmology & Visual Science, 6, 601-611.
[21Lancaster,W. (1952) Refraction and Motility. Springfield, Charles C. Thomas.
[22] Ong, E, Ciufredda, KJ (1995) Nearwork-induced transient myopia. Documenta Ophthalmologica, 91, 57-85.
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[24] Kikkawa, Y. and Sato, T. (1963). Elastic properties of the lens. Experimental Eye Research, 2, 210-215.
[25] Kabe, S. (1967) Dynamic aspects of accommodation. Photographic records of the 3rd Purkinje-image showing changes in size associated with accommodation. Rincho Ganka (Japanese Journal of Clinical Ophthalmology), 21, 341-352.
[26] Ni, J. and Smith, E.L. (1989) Effect of chronic optical defocus on the kitten’s refractive status. Vis. Res. 29, 929-938.]
[27] Hung, G.K. and Ciufredda, K.J. A Unifying theory of Refractive Error Development. Bulletin of Mathamatical Biology (2002) 62, 1087-1108] [28] Otsuka, J, Hirano, S, Suzuki, K, and Imagawa, N. (1970). A new approach to the theory of accommodation. Excerpta Medica International Congress Series No. 222.
[29] Smith, G. The optical properties of the crystalline lens and their
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[30] Ludlam, W. (1967) Refractive Anomalies of the Eye. Public Health Service Publication No. 1687, National Institute of Neurological Diseases and Blindness, Monograph No. 5, U.S. Department of Health, Education and Welfare.
[31] . Sperry R. W. The Growth of Nerve Circuits. Sci Am. 68-75, Nov. 1959.