THE ACCOMMODATION SYSTEM
The accommodation system operates on incoming rays of light. It detects micro-blur at the surface of the retina, and changes this power of the (internal) lens of the eye, to reduce this micro-blur below a detectable level.
RAYS OF LIGHT – FROM INFINITY.
Figure 1 shows positive status, or stop position.
LIGHT RAYS FROM A 13 INCH OBJECT
Notes on the following two accommodation graphs, Figures 2 and 3.
The range of accommodation (stop-to-stop) is greater than seven diopters. To be consistent, I show a range of 7 diopters. I show this for a farsighted eye, and a nearsighted eye. But what I mean is a normal eye with a positive and negative refractive state (self-measured).
The convention I use in these graphs, is that a value of infinity, is a refractive state of 0.0 diopters. A near object will always have negative status, based on the 1/distant = Diopters equation.
Thus an object at 0.33 meters, will have a value of -3 diopters. Thus the horizontal is labeled in negative diopters (distance from the eye).
To the right, is a postive refractive environment. You can only get this by placing a +1 diopter in front of the eye.
The normal eye show linear movement between these two extremes. (Some children actually read at 4 inches, or -10 diopters.)
The accommodation system must change the eye’s total power, by an amount equal to that change to a near reading position. Thus the vertical line is labeled in positive diopters.
If you read at 13 inches (-3 diopters) your accommodation control-system must change the eye’s power by exactly +3 diopters.
The maximum and minimum stop positions are shown – as labled.
The near stop position, is seldom calculated, since few people read at 4 inches and -10 diopters. If this is and established fact, then the chart could be changed to reflect this truth.
THE EYE WITH A POSITIVE REFRACTIVE STATUS
Shows a positive status, or “stop position”
THE EYE WITH NEGATIVE REFRACTIVE STATUS
The lens of the eye moves between two “stop” positions, the distant-stop position, and the near-stop position. In the range shown, the lens maintains sharp focus on the retina of the eye.
IN THE FOLLOWING TWO FIGURES, THE EYE HAS A
REFRACTIVE STATUS OF +1 DIOPTERS.
The eye’s response to looking from the distance (infinity) to a book at 13 inches. (A change of -3 diopters. )
These drawing are a composite of infra-red measurements, to establish the true behavior of the internal lens of the eye, and its response to both a negative and positive change in its visual environment.
The accommodation response to a step-input of -3 diopters.
The internal lens response to a +1 diopter lens.
The eye’s response to a step-input of +1 diopters.
Please note – this eye has a refractive status of +1 diopter.
READING A BOOK 13 INCHES FROM THE EYE THOUGH A +3 DIOPTER LENS.
This paper contains the reference analysis and drawings taken from an infrared Optometer for your interest.
Reference 3: Theory
Reference Paper on Accommodation, with sketch of accommodation response to step-inputs. L. Stark.