Astigmatism

A brief informational handout.

Our vision pathway.

Before we get into talking about astigmatism, we must understand the basic structures of the eye, and the pathway of our vision. The photos below show the structure of the human eye, as well as give some indication of how the eye works. Below is also a video explaining all of this, but I will include the steps for the pathway of vision here.


Pathway of vision: (Goldstein, 2014)


  1. Light refracted from environmental objects enters the eye through the pupil .
  2. The cornea and lens focus and form sharp images of the object onto the retina.
  3. The retina then uses its rods and cones, which contain visual pigments, to send electrical signals through neurons in the optic nerve.
  4. The optic nerve delivers the "message" to the occipital lobe of the brain.
  5. The brain processes the "message" allowing for identification of the object being seen.



The images we see go through two different transformations between structures in the front of the eye--cornea and lens--to the structures in the back of the eye--the receptors and neurons in the retina. These are: "(1) the transformation from light refracted from an object into an image of the object; and (2) the transformation from the image of the object into electrical signals" (Goldstein, 2014, p. 23).

Anatomy and Function of the Eye

Past perception and into the the organizing principles...

According to Gestalt psychologists, our brain has different guiding principles to organize the images we see and how to process them. Since some images are very complex, our brain needs to break down the image and organize, or group, the information for us to be able to understand exactly what it is we are perceiving and be able to identify it. Gestalt psychologists hold the belief that "whole" is not the sum of its parts (Goldstein, 2014).


The Gestalt principles of organization (or grouping) are as follows:


  • Proximity--We tend to group things together depending on how close, or far apart, they are. Things that are closer tend to be seen as being grouped (Brooks, n. d.).
  • Common Fate--The grouping of things that are moving in the same direction, and or the same way, as being "together" (Brooks, n. d.).
  • Similarity--Objects that tend to have similar characteristics are genuinely grouped together (Brooks, n. d.).
  • Good Continuation--"points when connected result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path" (Goldstein, 2014, p. 102).
  • Pragnaz (simplicity or good figure)--We see objects as being less complex and as simple as they can be (Goldstein, 2014).
  • Common Region--Objects that utilize or occupy the same area of space are seen as being grouped (Goldstein, 2014).
  • Uniform Connectedness--Objects are grouped according to the same visual characteristics being shared (Goldstein, 2014). Examples are: lightness, color, and texture.


So, why do we experience optical illusions?


We tend to depict images by what we consider to be the background and what we consider to be the image of perception (Goldstein, 2014). Optical illusions tend to rely on reversible figure-ground properties in order for us to be able to shift between two images depicted in the same picture. Just for a bit of fun, click the optical illusion link below.


http://www.grand-illusions.com/opticalillusions/



When we have vision problems these, grouping tasks can prove difficult, as we are unable to see the objects clearly and are unable to determine boundaries (border ownership) or figure-ground properties.

Big image

What is an astigmatism?

An astigmatism is an error produced in our vision due to an irregular shaping of the cornea or lens that changes the way light is refracted on the retina resulting in fuzzy, blurred, or distorted vision (Kivi & Boskey, 2015). Refraction means the bending of light, and when an astigmatism distorts this refraction within the eye, it is called a refractive error (Boyd, 2015). So, astigmatism equals refractive error. There are two types of astigmatism, as already mentioned. Lenticular astigmatism--in the lens, and corneal astigmatism--in the cornea (Nordqvist, 2015).


Astigmatisms are diagnosed, usually, by an ophthalmologist by way of eye tests and instruments such as: visual acuity test, astigmatic dial, keratometer, and keratoscope. They can affect both children and adults, but is less noticeable if a child has it. This is why routine eye exams are vital. If an astigmatism is not corrected it could lead to worse problems later on, and not just vision. It can affect work, homework, or performances (i.e. sports) (Nordqvist, 2015).


Common symptoms of an astigmatism include: blurred/fuzzy vision, sensitivity to light, headaches, squinting, constant closing of the eyes, and eye strain (Nordqvist, 2015).

Treatment Options for Astigmatism

There are a couple correction options to persons who suffer with vision distortion due to astigmatism. These include corrective lenses, such as eye glasses or contact lenses; or there is LASIK surgery.


Eye glasses and contact lenses are a more common correction to astigmatism as they are the least expensive options. The eye glass lenses and the contact lenses contain a special curvature piece to counteract the curvature of the lens or cornea of the eye that is creating the astigmatism. The links below describe how contact lenses and prescription glasses correct astigmatism.


Contact lense--https://www.youtube.com/watch?v=fDuAA-i2tZY&nohtml5=False

Eye Glasses--https://www.youtube.com/watch?v=X7RptqdvBWE



LASIK surgery on the other hand, implants this special curvature device directly into the eye. Because it is surgery, there are risks involved and may not be an option for every body. These risks include: over correction/under correction of vision, epithelial growth, dry eyes, irregular astigmatism, eye infections, and more (Wachler, 2016). There are also conditions to which may be present that would require a person looking at this correction to forego it in favor of corrective lenses.


Some items considred when determining LASIK candidate are: (Wachler, 2016)


  • thick or thin corneas
  • age
  • dry eyes
  • pregnancy
  • presence of degenerative or autoimmune disorders.
Federal Trade Commission on LASIK Eye Surgery

The FTC gives lots of advice if you are thinking about LASIK surgery to correct your vision. Please click the link and read through these helpful suggestions and important information you should know before scheduling the appointment.

About the author

My name is Deerdra, and I am a full-time student at Baker College. I will be graduating with my B. S. degree in Psychology at the end of summer (2016). These flyers created here are for class assignments.

References

Anatomy and function of the eye. (2011). [video]. Retrieved from https://www.youtube.com/watch?v=RE1MvRmWg7I.


Astigmatism explained: Easily corrected with a cylinder in your eye-wear glasses. (2011). [video]. Visio-Rx. Retrieved from https://www.youtube.com/watch?v=edYnfWFPUIw.


Boyd, K. (2015). What is astigmatism? American Academy of Ophthalmology. Retrieved from http://www.aao.org/eye-health/diseases/what-is-astigmatism.


Brooks, J. L. (n. d.). Traditional and new principles of perceptual grouping. Oxford University Press, 1-31. Retrieved from http://www.gestaltrevision.be/pdfs/oxford/Brooks-Traditional_and_new_principles_of_perceptual_grouping.pdf.


Facts about astigmatism. (2010). National Eye Institute. Retrieved from https://nei.nih.gov/health/errors/astigmatism.


Goldstein, E. B. (2014). Sensation and perception. (9th ed.). Belmont, CA: Wadsworth.


Kivi, R., & Boskey, E. (2015). Astigmatism. Healthline Media. Retrieved from http://www.healthline.com/health/astigmatism#Overview1.


Nordqvist, C. (2015). Astigmatism: Causes, symptoms, and treatments. Medical News Today. Retrieved from http://www.medicalnewstoday.com/articles/158810.php.


Wachler, B. S. B. (2016). LASIKS risks and complications. All About Vision.com. Retrieved from http://www.allaboutvision.com/visionsurgery/lasik_complication_1.htm.