THEORY

THEORY OF THE EYE

Subject: Long-term history and original theory of 1865 that needs a complete, thought full review and correction. (1)

This review will cover short-term change (accommodation) and long-term change (in refractive status).  This page includes a review of the history of the eye, and the original theory about about how the natural eye develops negative-status from long-term near work.

The stop-position, when positive, means excellent distant vision.  When negative, it means you will have difficulty reading the 20/40 line.  It is the purpose of this review, to develop a better understanding of the accommodation system – by building a working model of that system.

A GENERAL OVER-VIEW OF A TWO STAGE CONTROL SYSTEM.

A.  Dual Lead Screw – represents accommodation and long-term refractive control of the eye.

Section 1.  ACCOMMODATION IS SHOWN AS A CHANGE IN POSITION, BY SENSING MICRO-BLUR AT THE SURFACE OF THE RETINA. 

B:  A distant object, and the accommodation’s response.

C:  A near object, and the accommodation’s response.

D:  The effect of a plus lens on the accommodation system.

E:  A stronger plus – drives the accommodation system into the stops.

Section 2.  A REALISTIC MODEL SHOWS HOW THE RETINA CHANGES THE SHAPE OF THE LENS OF THE EYE, TO MAINTAIN ACCURATE FOCUS ON THE RETINA. 

F:  The accommodation system, is presented as a variable power plus lens, with feedback control from the retina.

G:  The change in power, caused by the lens, and a near object.

H: The plus and its additional effect on the accommodation system.

Section 3.  THE LONG-TERM REFRACTIVE STATE (LENGTH) IS UNDER CONTROL OF THE AVERAGE VALUE OF ACCOMMODATION, AS SHOWN IN THESE DRAWINGS. 

I:  Long-term change in accommodation level, always produces a change in length of the natural eye.  In this case a minus lens, produces a longer eye.

J:   When a plus changes the accommodation level, the eye changes it length to make the eye shorter.

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I believe in simplifying the original Box-Camera concept of the eye, as presented in 1865.  That concept has grown out-of-date, with respect to objective science, and repeatable objective measurements.

It very difficult to show real change in accommodation, (as a lens-power adjustment control),  as physical motion.

To see real physical action, it is necessary to show a fixed power 10 diopter lens on lead-screw, so we can intelligently understand this control system.

Conceptually it would be of educational value to build a working-model of this type of control system.

Figure A:

A. Lead Screw Model (jpg 1)The two formal published papers referenced in this drawing are, for the functioning of the accommodation system see:

Paper 9 Simulate Accommodation

“Analog Computer Simulation of Accommodation”

The refractive status of the eye is controlled by the average value of accommodation.  The paper that discusses how this works is described here:

Paper 6 Predictive Model

“A Predictive Mathematical Model for the Eye’s Refractive Status”

The accommodation system is visualized as traveling in a linear manner between two “stop” positions.  The “distant” stop position to an near stop position, will be at four inches – as shown.

A visualization of how the normal eye will change its measured refractive state, can be seen here:

https://myopiafree.wordpress.com/accommodation/

SECTION 1:  USING A FIXED FOCUS LENS TO SHOW ACTIVE RETINA CONTROL OF THE LENS POSITION. 

SCHEMATIC Design of Focal Control System for a Camera using physical motion to show the effect of a plus on the accommodation system. 

The optics of a fixed focus lens, and control of the eye’s refractive state.  This is to clarify how accommodation works.  In this case, the retina controls the lens by lead-screw adjustment.  In the eye, the power of the lens is changed by the retina.  The basic concept of feedback control is the same.  For objects at infinity, the lens will “servo” to 10 cm, or four inches, as shown in this drawing:

THE EYE LOOKING AT DISTANT OBJECTS:

Figure B:

B. Far Fixed Lens (jpg 2)When an object is moved from infinity to 40 cm (from the retina), the retinal “null seeking”, detection system, begins a raping change in the lens, by +4 inches.  (It must do this, to keep accurate focus on the retina – that is the entire purpose of this design.)

THE EYE LOOKING AT NEAR OBJECTS:

Figure C:

C. Near Fixed Lens  (jpg 5 )The next step, is to place a magnifying lens in front of this servo-controlled accommodation system – as shown.

THE EYE LOOKING AT NEAR OBJECT THROUGH A PLUS LENS:

Figure D:

D. Plus and Fixed Lens (jpg 6)Placing the “plus lens” causes an instant blur at the surface of the retina.  The retina, (in combination with dead-band) senses this out-of-focus condition, and moves its lens towards the retina, stopping at 10 cm from the lens.

The plus optically moves the near object, into the distance.

WHAT IS THE FAR “STOP” POSITION OF THIS AUTO-FOCUSED CAMERA.

Figure E:

E. Strong Plus and Fixed (jpg 7)The +2 diopter, placed the +10 diopters (original lens) creates a power of 12 diopters, and a focal length of 8.3 cm.

The retina, sensing micro-blur, will move the lens towards, and into the stops in this drawing.  A stronger plus lens will cause blur on the retina, because the lens can move no further to the right.

SECTION 2:  ACCOMMODATION BY CHANGING THE SHAPE OF THE LENS UNDER RETINA CONTROL

The design of a full range (variable focus) lens for the natural eye.

This model will reproduce this experimental data – exactly, when completed.

This data suggest that prevention is possible, for a person who has the long-term motivation to do what is necessary to prevent entry into myopia.  This is a science-based, not medical-based explanation.

Drawing are:

F) Distant objects.

G) Near object,

H) Object, though a plus lens.

When those drawings are complete, I will show the position of the retina changing in both directions, which is required in the normal eye.

Figure F:

F. Far Var. Lens (jpg 2 )The first stage is to present the accommodation system.  i.e., power change of 13 diopters, stop-to-stop.  The lens is rotated to change its power, though that range.  The control signal comes from the retina.

Figure G:

G. Near Var. Lens  (jpg 2 )

The target is at 10 cm.  The retina must change the power of the lens by plus 10 diopters.

Figure H:

H. Plus & Var. Lens (jpg 2 )

SECTION 3:  THE PREVIOUS DRAWINGS WERE ABOUT SHORT TERM  ACCOMMODATION.  THIS SECTIONS SHOWS THAT THE EYE WILL CHANGE ITS REFRACTIVE LENGTH IN BOTH DIRECTIONS, OVER A PERIOD OF 12 WEEKS. 

The previous drawings show the behavior of the accommodation system for short periods of time.  Here is the data that shows long-term length-change, when you change the average value of accommodation.

http://myopiafree.i-see.org/FundEye.html

I like to be very accurate – to objective science and fact, when modeling this length change – in both directions. 

These drawing will show the change of refractive state, or eye-length over a period of four months.  This are normal changes, and are tragically, not accepted by standard medical practice.

Figure: I:

I. Minus Induced Change (jpg 4 )The natural eye changes its length/power from the forced wearing of a strong minus lens.

Figure J:

J. Positve Induced Change (jpg 4 )

A positive lens, worn for 12 weeks, results in the natural eye becoming shorter.

THE DRAWINGS WERE CREATED TO EXPLAIN

1) SIMPLE ACCOMMODATION AS LENS MOVEMENT,

2) ACCOMMODATION AS LENS POWER CHANGE, AND

3)  CHANGE OF THE EYE’S LENGTH – IN BOTH DIRECTIONS.

Please reference this concept of accommodation, on this site, when evaluating this analogy of normal accommodation:

https://myopiafree.wordpress.com/accommodation/

This shows how the refractive state of the eye is measured, as positive and negative by one diopters

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(1)  THE OBSOLETE SCHEMATIC EYE OF HELMHOLTZ.

THE PURPOSE OF THESE DRAWINGS IS TO ENHANCE YOUR ABILITY TO VISUALIZE OF HOW ACCOMMODATION WORKS – BY USING A FIXED-FOCUS LENS, AND THEN A VARIABLE FOCUS LENS. 

This presentation is a proposal to clarify the, Schematic-Eye, as presented in the book, “Introduction to Physiological Optics”, by James P. C. Southall.

The schematic eye was first proposed by Listing in 1851, and was finalized by Helmholtz in 1865.  Since then – the basic concept has not changed.

As per the book by Southall,  we know that the lens is controlled by sphincter muscles, that change the power of the lens, typically though a range of 7 to 13 diopters.

I believe in simplifying the original Box-Camera concept of the eye, as presented in 1865.  That concept of a box-camera eye has grown out-of-date, with respect to objective science, and repeatable objective measurements.

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