University of Iowa Health Care

Ophthalmology and Visual Sciences


From One Medical Student to Another

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A cataract is any opacity or discoloration of the usually clear crystalline lens. This opacity or discoloration prevents light from passing properly through the lens to focus on the retina. Symptoms appear slowly and painlessly. They include any one or all of the following:

  • cloudy/blurry vision
  • glare
  • halos
  • perception of faded colors
  • yellowing/browning of vision
  • decreased night vision
  • frequent eyeglass prescription changes


The different types of cataracts are generally described by their position within the lens, as noted below.

Nuclear Nuclear Cataract the innermost, oldest layer of the lens. Nuclear cataracts are the most common cataracts. The patient may notice progressive loss of vision and decreased perception of certain colors, particularly blues. Although mostly age-related, studies have linked these types of cataracts to smoking, diet, and gender (Congdo et al 2003).
Cortical Cortical Cataract the outermost, youngest layer of the lens. Cortical cataracts are four-fold more common in African Americans and linked to diabetes mellitus, trauma, smoking, and excessive sunlight exposure (Solomon and Donnenfeld 2003). Patients can have vision loss, halos and glare that are especially noticeable while driving at night. This cataract has a wedge shaped or "cortical spoke" appearance that commonly appears inferiorly and nasally
Posterior Subcapsular Posterior Subcapsular cataract just under the candy shell. Posterior subcapsular cataracts are associated with diabetes mellitus, radiation, smoking and long term corticosteroid use (Solomon and Donnenfeld 2003). The symptoms associated with this cataract (glare, halos, image blur and distortion) are usually more rapidly progressive compared to other types of cataracts and are therefore usually more noticeable to the patient.

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last updated: 07-05-2010

Boeke P, Oetting T.
Cataracts: from one medical student to another. July 5, 2010; Available from: tutorials/cataract-for-med-students/

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