Astigmatism

Kara Pengelly

Astigmatism Defined

Astigmatism is one of the most common vision problems, and is caused by an irregularly shaped cornea. The curved shape of the cornea affects the way images are passed onto the retina, and will cause blurred or distorted vision (Kivi & Boskey, 2015)
What Is Astigmatism? : Astigmatism of the Human Eye

The Organs Used in the Visual Process

Cornea


  • Transparent
  • First structure through which light passes when entering the eye
  • Main focusing element (Goldstein, 2014).


Retina


  • Complex network of cells
  • Located at the back of the eye
  • Receptor cells generate electrical signals in response to light
  • Other cells in the retina include horizontal, bipolar, amacrine, and ganglion cells (Goldstein, 2014).


Optic Nerve


  • Bundle of nerve fibers
  • Carry electrical impulses from the retina to the lateral geniculate nucleus and other brain structures
  • Contains approximately 1 million ganglion cell fibers (Goldstein, 2014).

How Vision Works

The visual process is initiated when visual light reflects off an object and enters a person's eye. First, the light passes through the cornea, then through the pupil, and it ends up projecting on the back portion of the eye, which is called the retina (Goldstein, 2014).


Electrical impulses are created as a result of this stimulation, and these impulses travel up the optic nerve. The impulses are then read and interpreted by the brain, and the information begins to be processed at a cognitive level (Goldstein, 2014).

Gestalt Principles

Gestalt principles state that what we perceive is affected by where it is and what surrounds it (Purdue University, 2010). When we are processing visual information, we do so in context of our experiences we have with what we are seeing.


Our experience would dictate whether what we were seeing was safe, pleasant, dangerous, abnormal, known/unknown, and would help to assess the function of what we perceived.

Correcting Astigmatism

Corrections for Astigmatism:



  1. Corrective Lenses: Work by counterbalancing the curvature of the cornea; includes both eyeglass lenses and contact lenses
  2. Surgically-Based: Refractive surgery which works by reshaping the eye; includes LASIK, Photorefractive Keratectomy, Laser-Assisted Subepithelial Keratomileusis, and Radial Keratotomy surgical options (ePainAssist, 2016).

For more information, access the following links:

References:

ePainAssist (2016). Astigmatism: Causes, types, symptoms, treatment, lenses, and refractive surgery. ePainAssist.com. Retrieved on April 6, 2016 from: http://www.epainassist.com/eye-pain/astigmatism-causes-types-symptoms-treatment-lenses-refractive-surgery


Goldstein, E. B. (2014). Sensation and perception (9th ed). Boston, MA: Wadsworth Cengage Learning.


Kivi, R., & Boskey, E. (2015). Astigmatism. healthline.com. Retrieved on April 5 from http://www.healthline.com/health/astigmatism#Overview1


Purdue University (2010). Gestalt principles and illusions. psych.perdue.edu. Retrieved on April 2, 2016 from http://www1.psych.purdue.edu/~willia55/120/Gestalt%20Perception-Spr2010.pdf