Documents from 1. & 2. conferences of vision educators in Italy
 
 

 

Vision and posture

by Hala Jarada et al.

 

Elliot A. Forrest's research on functional astigmatism has revealed the crucial impotence of the relationship between eye movements and head movements when scanning horizontally as opposed to scanning vertically..

His findings are as follow:

1 After about 4 months of repeated eye movements in the same direction (without head movement), astigmatism sets in along the same axis as the direction of the movements: for instance, horizontal scanning is likely to cause x180 astigmatism, while vertical scanning will trigger x90 astigmatism

2 If there is equal movement along all the axes, no astigmatism is formed.

3 If the head is still and the eyes are turned in one direction for an appreciable length of time (p. ex., at the workplace), the eye that crosses the midline of vision will be more astigmatic than the other one.

4 If the head is turned on one side and the eyes scan horizontally, oblique astigmatism will set in both eyes (along the same axes). The angle of this symmetrical oblique astigmatism will be between 30 and 60, or between 120 and 150

5 The angle of such a symmetrical oblique astigmatism depends on the position of the head: for example, a head inclined forward is likely to cause OD 45 and OS 135, while a raised chin will cause OS 45 and OD 135;

6 Asymmetrical oblique astigmatism is the result of head rotation and tilt.

7 If the lines of sight of the two eyes are on different planes (vertical and horizontal), a subject with poor binocularity may develop vertical astigmatism in one eye and horizontal astigmatism in the other one.

 

 

In 1958, Harmon (the scientist who gave his name to the standard reading distance, i.e., elbow to middle finger knuckle) noticed some postural patterns in subjects with different eye disorders:

1- myopes tend to raise their chin

2- hyperopes attack the vision field with their head

3- astigmatics tilt their head on one side

4- exophorics rotate their shoulder blades upward and outward

5- esophores rotate their shoulder blades downward and inward.

 

Translator's Note

Harmon's generalizations have repeatedly been challenged, and the author tried to respond in later articles (1966a, 1966b)

Ann Sutton Nichols, in her insightful (but scarcely appreciated) studies, remarked the presence of different styles of vision in myopes and hyperopes according to a specific plane of vision.

More precisely, a myope tends to look along a vertical plane perpendicular to the subject (in an up-and-down, judgmental attitude); a hyperope, on the other hand, tends to look along a horizontal plane, in which the subject scans the field in a typical fight-and-flight response, while at the same time feeling his/her inadequacy to face the environment. (the introspective dimension of the myope v/s. the 'dodging and escaping' attitude of the hyperope).

 

References

"Astigmatism as a Function of Visual Scan, head scan, and head posture", American Journal of Optometry and Physiological Optics, 57 (11) Nov. 844-860.

"A New Model of Functional Astigmatism" Journal of the American Optometric Association 52 (11) Nov. 1980; 889-897.

"Eye Scan Therapy for Astigmatism" Journal of the American Optometric Association 55 (12) Dec. 1984., 894-901.

"The Rationale in Developmental Vision Training" Seminar Transcript (March)

"Restrained Performance as a Contributing Cause to Visual Problems" Optometric Weekly (July 7).

Among others, see"The Pointer Method of Observing and Training Visual Skills" Part I, Optometric Weekly April 29 & May 6 1943, 359-361, 387-389; Part II ibid. May 13- & May 20, 415-417, 443-444,.

 

Historical Survey of the Theories of Accommodation in the Human Eye

(already appeared at the 17. conference of holistic vision, Paris 2002)

Bruno Feldman

 

One of the most common criticism to the Bates Method is that Bates dismissed the current theories about the accommodation of the human eye. According to Bates, accommodation depended on the axial length of the eyeball, which depends on the action of the retroocular muscles. Already in the early XIX century, the British physician Young had demonstrated the axial length does not vary during accommodation, and the conclusion that the extra ocular muscles have no role in the whole process had been drawn.

A historical survey of the theories of accommodation, however, casts some serious doubts on the commonly accepted theory, formulated by the German physician, Helmoltz in the late XIX century.

Since Greek and Roman times down the Middle Ages, the different theories of vision were based on the assumption that there exists a stream of energy, which can go either from the eye to the external objects or from the external objects to the eye.(without a clear definition of the nature of such "sensible rays"). Apparently Aristotle supported the first approach, while Euclid accepted them both.

Such a controversy came to an end in the XVII century after the optical discoveries of the laws of refraction: once the physical nature of light rays could be demonstrated, the idea of the "sensible ray" was abandoned.

According to the theory of refraction, the focusing of an image on the retina was effected by four different factors:

n -- the curvature of the cornea

n -- the axial length of the eyeball

n -- the shape of the crystalline lens

n -- the shift of the crystalline lens along the antero-posterior axis.

 

Young had demonstrated that the cornea changes its shape during accommodation, while axial length does not vary. In 1849, Langebeck discovered that the front side of the lens changes its shape during accommodation, and shifts back and forth as well.

In 1856, Helmoltz explained that the ciliary muscle produced such a change of the lens. Although a few years later, the Danish ophthalmologist Tscherning demonstrated that the ciliary muscle has an opposite effect on the lens, the Helmoltz theory prevailed.

In 1970, the American ophthalmologist Coleman developed a hydraulic model of accommodation, based on the mutual action of humor aqueous and humor vitreous:: in addition, the tone of the extra ocular muscle changed during accommodation, without producing any detectable change. The conclusion was drown that, the humor vitreous, under the mechanical action exerted by the extra ocular muscles on the eyeball, would affect in turn the tension of the hyaloid membrane and suspensory ligaments (zonulae) of the lens, thus producing accommodation. Coleman's theory, however, remained virtually ignored, in spite of its original implications also in view of a new understanding of the Greek concept of the "sensible ray". (It is a well-established fact that the extra ocular muscles have a puzzling proprioceptive innervations. Also, Bates teachers could find an analogy between the concept of the "sensible ray" and Bates' principle of "central fixation."

 

Translator's Notes

Thomas Young (1773-1829) British Physician and scientist. "On the Mechanism of the Eye" in Philosophical Transactions of the Royal Society of London, (1801;22-88).. His theory was rebutted the following year by Everard Home Esq. in "Demonstration of Accommodation in Lensless Eyes" Cronian Lecture (1802); among his earlier works are: "Anatomical and Experimental Evidence that the Cornea Changes during the Eye's Adjustment to Different Distances; Extraocular Muscles Must Be Involved", Cronian Lecture (1795; "Further Evidence for Corneal Change during Accommodation. Theory Expanded to include Movement of Lens Elongation of Eye via Ciliary and Extraocular Muscles," Cronian Lecture (1796).

Maximilian Adolf Langenbeck (1518-1877). Professor of anatomy, Surgery and Ophthalmology at Gottingen, ( 1846-1851).

Herman- Ludwig Ferdinand von Helmholtz (1821-1894) German scientist. "Ueber die Accomodation des Augen"Albrecht von Graefes Archiv. Ophthalm. I (Abt.2) 1-74.

Marius Hans Erik Tscherning .Danish ophthalmologist who for twenty-five years was co-director and director of the Ophthalmological Laboratory of the Sorbonne., and later Professor of Ophthalmology at the University of Copenhagen. In his experiment (with ophthalmophakometer)s on the Purkinje images, he found that the center of the anterior surface of the lens increases its curvature during accommodation while the periphery is flattened.

"Unified Model for Accommodative Mechanism", American Journal of Ophthalmology 1970, Jun 69 (6)1662-79.

"On the Hydraulic Duspension Thoey of Accommodation" Transactions of the American Ophthalmological Society, 1966, 84

Coleman D. J. and S. Trokel "Direct-recoded Intraocular Pressure Variations in a Human Subject" Archives of Ophthalmology, 1969, Nov 32(5), 628-40.

"Unified Model for Accommodative Mechanism", American Journal of Ophthalmology 1970, Jun 69 (6) 1063-79.

"On the Hydraulic Duspension Thoey of Accommodation" Transactions of the American Ophthalmological Society, 1986, 84, 846-68; "Direct-recoded Intraocular Pressure Variations in a Human Subject" Archives of Ophthalmology, 1969, Nov 82 (5), 637-40.

 

SEE ALSO THE FOLLOWING STUDIES:

Greene P. R., "Mechanical considerations in Myopia: Accommodation, Accommodative Convergence, Intraocular Pressure, and Extra-ocular Muscles", American Journal of Optometry and Physiological Optics, 1980, 47, 902-914;

Paker J. W. "Changes in Corneal Astigmatism", Optical Journal and Review, April 11, 1931.

Preslan M. W. , Ciofi G. and Min Yi "Refractive Error Changes Following Strabismus Surgery " Journal of Pediatric Ophthalmology and Strabismus 1992, 29, 304.