Microscopy Primer
Light and Color
Microscope Basics
Special Techniques
Digital Imaging
Confocal Microscopy
Live-Cell Imaging
Photomicrography
Microscopy Museum
Virtual Microscopy
Fluorescence
Web Resources
License Info
Image Use
Custom Photos
Partners
Site Info
Contact Us
Publications
Home

The Galleries:

Photo Gallery
Silicon Zoo
Pharmaceuticals
Chip Shots
Phytochemicals
DNA Gallery
Microscapes
Vitamins
Amino Acids
Birthstones
Religion Collection
Pesticides
BeerShots
Cocktail Collection
Screen Savers
Win Wallpaper
Mac Wallpaper
Movie Gallery

Interactive Java Tutorials

Human Eye Accommodation

Accommodation of the eye refers to the act of physiologically adjusting crystalline lens elements to alter the refractive power and bring objects that are closer to the eye into sharp focus. This tutorial explores changes in the lens structure as objects are relocated with respect to the eye.

Interactive Java Tutorial
ATTENTION
Our servers have detected that your web browser does not have the Java Virtual Machine installed or it is not functioning properly. Please install this software in order to view our interactive Java tutorials. You may download the necessary software by clicking on the "Get It Now" button below.

 

To operate the tutorial, translate the Object Position slider and observe how the proximity of the object to the eye changes the shape of the lens. Light rays refracted at the surface of the cornea are further converged by the crystalline lens of the eye. Contraction of the ciliary muscles relaxes the tension on the lens that rounds its shape by virtue of its elasticity while also moving forward slightly. The net effect of the lens changes is to adjust the focal length of the eye to bring the image exactly into focus onto the photosensitive layer of cells residing in the retina. Accommodation relaxes the tension applied through zonule fibers to the crystalline lens, and allows the anterior surface of the lens to increase its curvature. The increased degree of refraction, coupled with a slight forward shift in the position of the lens, brings objects that are closer to the eye into focus.

Focus in the eye is controlled by a combination of elements including the iris, lens, cornea, and muscle tissue, which can alter the shape of the lens so the eye can focus on both nearby and distant objects. However, in some instances these muscles do not work properly or the eye is slightly altered in shape, and the focal point does not intersect with the retina (convergent vision). As people age, the lens becomes harder and cannot be properly focused, leading to poor vision. If the point of focus falls short of the retina, the condition is called nearsightedness or myopia, and people with this affliction cannot focus on distant objects. In cases where the focal point is behind the retina, people have trouble focusing on nearby objects, and have a condition called farsightedness or hypermetropia. These malfunctions of the eye can usually be corrected with eyeglasses (Figure 1) using a concave lens to treat myopia and a convex lens to treat hypermetropia.

Convergent vision is not totally physiological and can be influenced by training, if the eyes are not defective. Repetitive procedures can be utilized to develop strong convergent vision. Athletes, such as baseball shortstops, have well-developed convergent vision. In every movement, the two eyes have to translate in unison to preserve binocular vision, with an accurate and responsive neuromuscular apparatus that is not usually subject to fatigue, controlling their motility and coordination. Changes in ocular convergence or head motion are considered in the calculations made by the complex ocular system to produce the proper neural inputs to the eye muscles. An eye movement of 10 degrees may be completed in about 40 milliseconds, with the calculations occurring faster than the eye can reach its intended target. Small eye movements are known as saccades and the larger movements from one point to another are termed versions.

Contributing Authors

Matthew J. Parry-Hill and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


BACK TO HUMAN VISION AND COLOR PERCEPTION

Questions or comments? Send us an email.
© 1998-2013 by Michael W. Davidson and The Florida State University. All Rights Reserved. No images, graphics, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.
This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.
Last modification: Wednesday, Mar 26, 2014 at 02:23 PM
Access Count Since June 20, 1998: 175941
For more information on microscope manufacturers,
use the buttons below to navigate to their websites: