PAPERS ON PREVENTION BY OTIS BROWN AND FRANCIS YOUNG
Subject: While difficult, prevention is possible if the person has the education and motivation to take the issue seriously.
True prevention – requires a motivated person – who can still read the 20/40 line, and can rise the the challenge of the subject. Deep insight about the proven behavior of the natural eye – is crucial in the person himself – if a preventive study is to succeed.
The subject is engineering and science, and is not medical in character.
These are a series of papers written and published by the IEEE / Engineering in Medicine and Biology Society. The authors are leaders in their field of research. There are nine papers, in sequence, from 1 to 9. After they are reviewed, they will be posted on “Academia.edu”. The papers are in Microsoft Word, and must be down-loaded for review. The original papers were typewritten. These papers have been converted into an electronic file for easy reference.
“A Nearsightedness Computer”
This article is heuristic. It assumes an intimate familiarity with the problem of nearsightedness on the part of the reader.
(Heuristic: Furthering investigation, serving as an aid in the advancement of a conceptual scheme, but without necessarily being in final form or excluding alternative explanations.)
The eye is known to be a complex of feedback control elements. The subject of nearsightedness brings to fore the equation, “What controls the long-term growth of the eye”? Work done by L. Stark and others has shown that the short-term focus is by feedback control. The process by which the eye grows
and controls its focus is a closed loop system. It is impossible to model the eye’s long-term focusing ability in terms of a heredity (open-loop) control system.
“Physiological Modeling: The Long-term Growth of the Eye”
The short-term (accommodation) control system of the eye is accurate and effective. It is likely that this signal is made available to the long-term growth of the eye for correct positioning of the retina relative to the focal point of the lens. This is the thesis of this presentation. The feedback control circuit (below)
will insure that the retina is (servoed) to the focal point of the lens.
“The Response of a Servo Controlled Eye to Focal Perturbations”
Myopia is a confusing and contradictory problem. Detailed measurements made by Dr. Francis Young show major changes in the optical components of the growing human and primate eye. Paradoxically, the eye maintains a focal accuracy of better than 1.5 percent, while the individual optical components are changing in and unpredictable manner.
Dr. Lawrence Starks’s work in accommodation has demonstrated that the focal settings of the eye are determined by a feedback mechanism that servos the lens for maximum clarity of the image on the retina. With an understanding of fundamental feedback control requirements, this article develops a perturbation (growth) control equation that accurately predicts the eye’s response to step-change disturbances. The concept is then broadened to predict the eye’s expected focal setting action in the presence of noise.
“The Response of a Servo Controlled Eye to a Confined Visual Environment”
The human and primate eye maintain a high degree of focal accuracy while major optical components change in an unpredictable manner. The equation developed from a servo model capable of accounting for this degree of accuracy, also predicts that the eye’s focal status will display a time-constant effect to
a step change in its visual environment.
The predictions of this theory are compared on a qualitative and semi-quantitative basis with a heredity theory of the eye’s long-term growth.
“Measuring the Eye’s Focal Accuracy: A Heuristic Approach”
The human and primate eye maintain long-term focal accuracy in the presence of focal perturbations. It is difficult to measure the magnitude of the perturbations and the effectiveness of the consequence servo corrective action.
By making reasonable assumptions, based on a physiological model, we can obtain a preliminary numerical value for the eye’s focal tracking accuracy.
“A Predictive Mathematical Model for the Eye’s Focal Status”
Because the eye is sophisticated in its design and operational characteristics, the engineering requirement for focal accuracy suggests that the eye sets its long-term focus by a servo control process. The mechanism that establishes the eye’ focal status consists of two separate systems. The first system is a blur driven accommodation mechanism that regulates the focal power of the eye’s lens for maximum image sharpness at the surface of the retina. This control system has a time constant of 0.25 seconds.
The second system, which is responsible for controlling the eye’s long-term focus, has a time constant of 300 days. In a normal visual environment the eye’s focal status will be from 0 to +2 diopters. The focal servo system functions to overcome the inevitable perturbations that occur within the eye’s optical system.
This system has a tracking probable error of 1/10 diopters. Since the focus of a servo controlled eye is “slaved” to the average value of accommodation, shifts in the accommodation signal will result in corresponding shifts in the eye’s focal status. This predictable consequence of the design has been experimentally verified.
“A Myopia Avoidance Effort”
ABSTRACT: The Naval Academy requires unaided visual acuity of 20/20 in each eye as a basic entrance requirement. Prospective pilots are required to have normal vision on graduation. A substantial number of midshipmen, entering with 20/20 vision, become myopic during their four years at the Academy.
A reasonable assessment of the experimental evidence suggests that the eye sets its long-term focus by a servo control process. This engineering analysis of the eye’s control action predicts that a significant percentage of midshipmen could avoid the myopia problem is they wear a convex lens while reading.
“A Heuristic Model for Tonic Accommodation”
The normal eye has a competently designed lens control system. The existence of optical dead-band, or depth-of-field, causes a fundamental non-linearity in this operation of an automatically focused camera.
The lens support muscles generate a noise signal which produces a back-and-forth motion in the lens across the optical dead band. To better understand the functioning of this device, we have designed an analog computer which predicts the eye’s focal status as a function of depth-of-focus, noise in the muscles, and the diopter value of the eye’s environment.
The focal status of the lens is controlled by blur, as long as the retina can sense blur. When the eye is in darkness, the lens is driven to a “standby”, or tonic accommodation position. Experimental evidence has been presented which demonstrates that the eye’s focal status will show a servo response to a long-term change in the visual environment. It is probable that tonic accommodation will exhibit a similar response.
This heuristic model yields focal status predictions of tonic accommodation as a function of time, and the individual’s long-term environment.
Analog Computer Simulation of Accommodation
(Alternative title: A Cybernetic Model of Accommodation)
Over the past fifteen years we have evaluated numerous models of accommodation. Our task is to clarify these models by designing an automatically focused camera, with major emphasis of the capability of the retina to sense blur and feed this information back to the eye’s lens for accurate focal adjustment.
Depth-of-field, or dead-band, poses a significant obstacle for the designer of an automatically focused camera. Our approach is to use noise to provide a scanning, or dither motion so that the lens will spend 80 percent of its time in sharp focus. Retina detection of blur can be simulated by a Charge Coupled Device (CCD), designed to produce a null when sharpest focus is achieved. The nature of blank-field accommodation is judged, and a prediction made about its long-term behavior
This paper’s objective is to clarify the predictions that are implied in earlier block diagrams of the accommodation system. The diagrams do not provide active outputs which can be compared directly with the experimental data. The actual building of a working model from a block-diagram concept is challenging and will define, after review, the behavior of the normal system.
Paper by Dr. David Guyton, on getting a child to wear a +3 diopter lens for close work – and success with that process.
A listing of abstracts on preventing incipient myopia, by Otis Brown
Included – science animation of the natural eye, and abstracts of the nine previous pages.
Efforts at Prevention.
MILITARY HISTORY – AT THE NAVAL ACADEMY AND WEST POINT.
Subject: Military studies show the necessity of normal eyes having “positive status”,on entry to the Academies. This is the ability to read the 20/20 line though a +3/4 diopter lens.
Please read the “Graphics” section on this site – to understand this issue. All normal eyes have this quality or ability.
Dr. Hayden proposed a method of prevention, to reduce the number of students who would become nearsighted during their four years at the Academy.
DEVELOPMENT AND PREVENTION OF MYOPIA AT THE UNITED STATES NAVAL ACADEMY.
REYNOLDS HAYDEN, M.D.
Captain, Medical Corps, United States Navy
ABSTRACT: The visual standards for the line of the Navy, the branch which handles the naval vessels of the United States, have always been based on the fact that it is essential for navigation, watch and gunnery officers to have normal vision and not to have to wear glasses, which may become fogged in bad weather or may even be broken or lost, with consequence serious impairment of vision. For many years the high incidence of myopia which apparently developed among midshipmen after admission to the United States Naval Academy with supposedly normal vision was a cause of serious concern to all those interested.
For years every effort was made to save such men to the service by giving them extended complete rest of their eyes before reexamination of their vision, and by retaining many of them in the Naval Academy for one to three years in the hope that their vision would improve. Every effort was also made to improve the illumination of both study rooms and class rooms for midshipmen. Decisions to retain such men were largely based on the recommendations of ophthalmologists. In the vast majority of cases, however, the vision did not improve, and the midshipman was forced to leave the naval service after two to four years in the Naval Academy. Experience showed that only about 1 percent of such men had 20/20 vision on their final physical examination.
Myopia at West Point: Past and Present.
Military Med. 1976; 141(8): 542-543 .
MAJ Robert T. Gmelin, MSC, USA
ABSTRACT: In a paper presented in 1813 to the Royal Society of London, the Honorable James Ware described his observations about myopia. Most notedly, he found, “While the officers of the Queen’s Guard frequently were nearsighted, among the 10,000 foot-guards in their command, not even a half- dozen were known to be nearsighted.” In today’s volunteer Army, one out of every three enlisted men and women and two out of every three West Point graduates wear spectacles or contact lenses for the correction of myopia.
The subject of vision standards for entrance to the US Military Academy (USMA) has been and remains a controversial subject. Since 1912, these standards have been changed or amended six times, to reflect the problem of visual acuity degradation among the cadets. Since 1960, when the vision standards were last changed, new candidates have received admission to USMA within the refractive limitations of ±5.50 diopters and with waivers permitted up to —6.50 diopters (e.g., 20/800 Snellen visual acuity). Statistical records show that, since 1964, over 50 per cent of each entering class are admitted to USMA wearing spectacles, and that approximatelv 65 per cent of each graduating class depart USMA wearing spectacle or contact lenses for the correction of myopia.
This study shows a consistent “down” change in the refractive state of the natural eye, of about -1/3 diopter per year, for each year in college. Thus a student with perfect 20/20 (refractive state of exactly 0.0 diopters), has no chance of retaining 20/20, on graduation, and would be disqualified as a pilot.