Dr. Daniel Goldberg is the first to incorporate the recent knowledge of the actual movement of the ciliary muscle during accommodation into a new theory, which he calls the Reciprocal Zonule Theory. It is well known that the lens and lens capsule in a young eye have natural elasticity. Thus, when the lens and lens capsule are removed from a young eye, the lens and capsule will round up by themselves to some extent. This is less true in older eyes. And if the lens is taken out of the capsule altogether, the lens will flatten rather than round up, so it is the capsule that is providing the elasticity.
Daniel Goldberg postulated that when the ciliary muscle moves up and in during accommodation, the anterior zonules slacken but the posterior zonules stay taught or actually tighten, This triggers or reinforces the rounding up of the lens into the accommodated position. The lens can rapidly move back into the unaccommodated, distance position when the muscle retracts back into its original position tightening the anterior zonules again. It is unclear what the purpose of the vitreous zonule might be, although Mary Ann Croft believes that it might help to stabilize the forward movement of the ciliary muscle during accommodation and also to allow for rapid return to distance vision. Like the Schachar theory, it should be noted that in the Reciprocal Zonule theory the gradual reduction in the circumlental space with age would most likely lead to presbyopia, because the tension required for the posterior zonule to trigger a rounding up of the lens would be lost over time.
A graphical depiction of a young eye demonstrating Dr. Goldberg’s Reciprocal Zonule theory, with the eye accommodated (on the right) and at distance (on the left), is shown below. The posterior zonules are in yellow. The vitreous zonules are in green. The anterior zonules are in white. In the image on the right, the ciliary muscle has moved up and in allowing the anterior zonules to relax while keeping the posterior zonules taught, which in turn allows the lens to round up into the accommodated shape (note that the anterior surface of the lens is much higher on the right than on the left).
Internally within Refocus, a similar theory has been one of the leading models to explain the potential mode of operation of the PresView Implants for several years, although when originally conceived within Refocus, it was known simply as the posterior zonule theory.
|Anterior Zonules – Taught|
|Anterior Zonules – Slack|
|Anterior lens surface – unaccommodated at distance|
|Anterior lens surface – accommodated at near|
Again, if the Reciprocal Zonule theory (or the posterior zonule theory) is true, and if the primary cause of presbyopia is the diminishing circumlental space over time, then to the extent that our implants are vaulting the sclera outwards in proximity to where the zonules are attached to the ciliary processes, the PresView implants would restore the natural tension on the zonules (assuming our implants are placed in the right position) which would allow the posterior zonules to once again trigger or reinforce the rounding up of the lens, once the anterior zonules are relaxed.
The screen shot below is from another video from Mary Ann’s presentation in Nashville taken from inside the eye of a rhesus monkey endoscopically. The vantage point is looking up from the posterior chamber through the vitreous at the bottom of the crystalline lens. The sinewy white elements sloping upwards to the left are the posterior zonules. In this video, Mary Ann has noted that posterior zonules definitely appear to be tightening and moving up during accommodation, which would support both Dan Goldburg’s Reciprocal Zonule theory and the Refocus posterior zonule theory.