Signs and Symptoms
There are three main types of age-related cataract, determined by which part of the eye they affect; they each can cause different symptoms:
- Nuclear cataracts. Nuclear cataracts affect the central part of the lens. Nuclear cataracts arise as a result of normal age-related accumulation of lens fibers in the central region of the lens. Patients with nuclear cataracts may see double or multiple images. As the cataract progresses, the lens transitions to yellow or brown, and this may lead to even more difficulties in distinguishing colors (Medline 2012; Bollinger 2008).
- Cortical cataracts. Cortical cataracts are the result of the formation of whitish opaque regions at the outer edge of the lens, or the cortex. This type of cataract is associated with diabetes (Chang 2011). Cortical cataracts may not significantly impair vision if the lens opacities remain outside the visual axis, but they can cause glare during activities such as driving (Medline 2012; Bollinger 2008).
- Posterior subcapsular cataracts. Posterior subcapsular cataracts first appear on the backside of the lens. They typically impair near vision to a greater degree than distance vision. In addition, they may affect the ability to see in bright light and cause the appearance of halos around lights during nighttime (Medline 2012; Bollinger 2008).
In addition to age-related cataracts that appear in adults, some children are either born with cataracts or develop them early in childhood. About half of congenital cataracts have genetic causes, while some of the remaining ones are caused by metabolic diseases or infections during development (Santana 2011; Medline 2012).
Early Stages of Cataract Development
Age-related cataracts cause a slow, painless loss of vision typically not associated with other signs or symptoms. The first sign of cataracts is usually a significant loss in transparency in a small region of the lens. This affects one’s ability to discern the detailed contours of objects in bright light during the day or when viewing objects near bright light at night. In addition, it leads to a loss of contrast sensitivity, which is the ability to distinguish between relative differences in light intensity (Regan 1993; Cheng 2001; Zigler 2011; Sia 2012).
Similar to a loss in contrast sensitivity is the increased incidence of glare. This occurs when cataracts begin to cause an aura around objects, and it happens most often during the daytime (Lasa 1995; Howes 2008; Mayo Clinic 2010). Glare, which can occur in all forms of cataract, can develop anywhere on the optic lens.
In many cases of nuclear cataract formation, there is also a change in how light bends, or refracts, as it moves from outside the eye through the lens. This is termed myopic shift, and is clinically defined as a hardening of the lens that causes a change from farsightedness to nearsightedness (Younan 2002; Aslam 2007; Samarawickrama 2007; Zigler 2011).
Late Stages of Cataracts
As cataracts continue to progress, the severity of these initial symptoms increases. The extent of cataract progression is defined by the degree of opacity in that part of the lens and the overall state of visual acuity. Immature cataracts are determined as those occurring in lenses with significant areas of translucency. Progression to mature cataracts is marked by significant opaque structures occurring in the lens, while hypermature cataracts are those where liquefaction of the lens structure has occurred. This final stage of cataract development results in the leakage of a milky white liquid into the lens capsule, resulting in substantial inflammation and pain (Hemalatha 2012).