The mechanism of accommodation in primates

doi:10.1016/S0161-6420(99)00502-3

Ophthalmology

Volume 106, Issue 5, 1 May 1999, Pages 863-872

Presented in part at the American Academy of Ophthalmology Refractive Surgery Subspecialty Day Program, San Francisco, California, October 1997, and at the Association for Research in Vision and Ophthalmology annual meeting, Fort Lauderdale, Florida, May 1998.

https://doi.org/10.1016/S0161-6420(99)00502-3 Get rights and content

Abstract

Objective

To study the accommodative mechanism in primates using monkeys, in light of a recently proposed novel accommodative mechanism in primates and a concomitant controversial surgical procedure for the reversal of presbyopia,

Design

Experimental study.

Methods

Accommodation was induced by stimulation of an electrode surgically implanted in the midbrain and by topical ocular application of muscarinic agonists. Pharmacologic disaccommodation was achieved by topical application of a muscarinic antagonist. Movements of the lens equator and the ciliary body were imaged during accommodation and disaccommodation using ultrasound biomicroscopy and goniovideography, and the images were analyzed to determine the direction and the extent of the movements.

Results

Despite the systematic eye movements occurring with electrical stimulation and the nonsystematic eye movements occurring with pharmacologic stimulation, in all instances the ciliary body and the lens equator moved away from the sclera during accommodation.

Conclusions

Movement of the accommodative structures is consistent with the classic mechanism of accommodation described by Helmholtz, and contrary to that recently proposed by Schachar.

Section snippets

Animals

We used six cynomolgus monkeys (Macaca fascicularis, estimated ages 10 to 13 years) and eight rhesus monkeys (Macaca mulatta, ages 6 to 17 years) with centrally stimulated (described below) accommodative amplitudes ranging between 7 and 18 diopters (D). The monkeys had previously undergone complete removal of the irides bilaterally by tearing them away at the root over the entire 360° circumference,14 and surgical implantation of stimulating electrodes into the EW nucleus.11

Several other young

Results

Ultrasound biomicroscopic imaging of the ciliary muscle during central stimulation showed that the inner apex of the muscle moved anteriorly and toward the anterior-posterior axis of the eye (i.e., centripetally) and that the equatorial edge of the lens moved away from the sclera during accommodation (Fig 1). In addition, the distance along the posterior zonular fibers extending between the inner apex and the posterior insertion of the ciliary muscle increased, presumably stretching the

Discussion

Imaging of the accommodative structures during centrally or pharmacologically stimulated accommodation showed that the lens equator moves away from the sclera, in accordance with the classically described accommodative mechanism2 and contrary to Schachar’s proposed mechanism. Similarly, UBM imaging demonstrated movement of the inner apex of the ciliary muscle anteriorly and centripetally during accommodation; localized posterior or outward movement of the anterior aspect of the ciliary muscle,

Acknowledgements

The authors thank Ronald Schachar, MD, PhD, for suggesting some of the experiments and techniques and for critically evaluating the work, and Zeiss-Humphrey Instruments for the loan of the UBM.

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^☆: Supported by grants from NIH (EY10213 to P.L.K., RR00167 to Wisconsin Regional Primate Research Center), Research to Prevent Blindness, Inc., New York, New York, and Johnson & Johnson, Inc., Cincinnati, Ohio.

¹: The authors have no commercial interests or conflict of interests with anything presented in this study.

View full text

The mechanism of accommodation in primates1☆,

Abstract

Objective

Design

Methods

Results

Conclusions

Section snippets

Animals

Results

Discussion

Acknowledgements

Vision Res

Brain Res

Vision Res

Exp Eye Res

Ophthalmology

The mechanism of accommodation and presbyopia in the primate

Ann Ophthalmol

Scanning electron microscopic studies of the zonular apparatus in human and monkey eyes

Invest Ophthalmol Vis Sci

The mechanism of ciliary muscle function

Ann Ophthalmol

Cause and treatment of presbyopia with a method for increasing the amplitude of accommodation

Ann Ophthalmol

In vivo increase of the human lens equatorial diameter during accommodation

Am J Physiol

The effect of gravity on the amplitude of accommodation

Ann Ophthalmol

Age-dependent loss of accommodative amplitude in rhesus monkeysan animal model for presbyopia

Invest Ophthalmol Vis Sci

The mechanism of accommodation in primates¹☆,