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Foveolar cones and müller cells of monkeys and humans have a unique, still unknown morphology with impact for understanding the Stiles-Crawford effect

Session Details

Session Title: Imaging I

Session Date/Time: Friday 12/09/2014 | 11:00-13:00

Paper Time: 11:32

Venue: Boulevard D

First Author: : U.Schraermeyer GERMANY

Co Author(s): :                  

Abstract Details


The Stiles–Crawford (SC) effect is a property of the cone photoreceptors of the human eye and was first described 8 decades ago. It was found that foveal cones have a less pronounced directional sensitivity than parafoveal cones. It was speculated that a change in the shape or the orientation of foveal cones was responsible for the SC-effect. Until now, no morphologic evidence for this assumption has been found.


Section of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, Tuebingen, Germany


The eyes from 52 cynomolgus monkeys (Macaca fascicularis Raffles) and 2 human eye donors were fixed and embedded for electron microscopy. Semithin sections were cut from 22 foveae. Longitudinal and tangential serial sections were made from individual foveae. The image stacks were aligned and segmented using Amira® 4.0.1 (Visualization Sciences Group, SAS ) resulting in a three-dimensional model. Focused ion beam electron microscopy was also performed.


Three-dimensional reconstruction of serial sections from humans and monkeys clearly showed that in the foveola (200 – 300 µm in diameter) the inner segments of the cones were curved whereas in the fovea and parafovea they were oriented along the optical axis. Inner and outer segments together were S shaped in the foveola. The orientation of inner and outer segments from cones in the foveola in well-fixed specimens was extremely regular and nearly crystalline and not orientated parallel to the optical axis. The diameter of the Müller cells was largely enhanced in the centre of the foveola.


The shape and orientation of the foveolar cones is different to parafoveal cones in both human and monkey eyes. This orientation and the light guiding properties of the Müller cells may contribute to the directional sensitivity of the Stiles-Crawford effect.

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