Anteriorly located zonular fibres as a tool for fine regulation in accommodation.
OBJECTIVE
To describe an anteriorly located system of zonular fibres that could be involved in fine-tuning of accommodation.


METHODS
Forty-six human and 28 rhesus monkey eyes were dissected and special preparations were processed for scanning electron microscopy and reflected-light microscopy. Additional series of frontal and sagittal histological and ultrathin sections were analysed in respect to the origin and insertion of anteriorly located zonules. The presence of sensory terminals at the site of the originating zonules within the connective tissue of the ciliary body was studied by immunohistochemistry. For in-vivo visualization ultrasound biomicroscopy (UBM) was performed on 12 human subjects.


RESULTS
Fine zonular fibres originated from the valleys and lateral walls of the most anterior pars plicata that covers the anterior and inner circular ciliary muscle portion. These most anterior zonules (MAZ) showed attachments either to the anterior or posterior tines or they inserted directly onto the surface of the lens. At the site of origin, the course of the MAZ merged into the connective tissue fibres connecting the adjacent pigmented epithelium to the ciliary muscle. Numerous afferent terminals directly at the site of this MAZ-origin were connected to the intrinsic nervous network of the ciliary muscle.


CONCLUSIONS
A newly described set of zonular fibres features the capabilities to register the tensions of the zonular fork and lens capsule. The close location and neural connection towards the circular ciliary muscle portion could provide the basis for stabilization and readjustment of focusing that serves fast and fine-tuned accommodation and disaccommodation.
Institute of Anatomy II, Erlangen, Germany.
Cassandra M
CM
Flügel-Koch
Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Mary Ann
MA
Croft
Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA.|Wisconsin National Primate Research Center, University of Wisconsin, Madison, USA.
Paul L
PL
Kaufman
Institute of Anatomy II, Erlangen, Germany.
Elke
E
Lütjen-Drecoll
D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002924:Ciliary Body / Q000648:ultrastructure; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007908:Lens, Crystalline / Q000033:anatomy & histology* / Q000648:ultrastructure; D008253:Macaca mulatta; D008297:Male; D020894:Microfibrils / Q000648:ultrastructure; D033401:Microscopy, Acoustic; D064347:Microscopy, Electrochemical, Scanning / Q000379:methods; D008875:Middle Aged; D055815:Young Adult
accommodation; ciliary body; ciliary muscle; lens; zonular fibres