A cataract is a clouding that develops in the crystallinelens of the eye orin its envelope, varying in degree from slight to complete opacityand obstructing the passage of light. Early in the development of age-relatedcataract the power of the lens may be increased, causing near-sightedness (myopia), and thegradual yellowing and opacification of the lens may reduce the perception ofblue colours. Cataracts typically progress slowly to cause vision lossand are potentially blinding if untreated. The condition usually affects boththe eyes, but almost always one eye is affected earlier than the other.
A senile cataract, occurringin the elderly, is characterized by an initial opacity in the lens, subsequentswelling of the lens and final shrinkage with complete loss of transparency.Moreover, with time the cataract cortex liquefies to form a milky white fluidin a Morgagnian cataract, whichcan cause severe inflammation if the lens capsule ruptures and leaks.Untreated, the cataract can cause phacomorphicglaucoma. Very advanced cataracts with weak zonules areliable to dislocation anteriorly or posteriorly. Such spontaneous posteriordislocations in ancient times were regarded as a blessing from the heavens,because some perception of light was restored in the cataractous patients.
Signs and symptoms
As a cataract becomes more opaque, clear vision is compromised. A loss of visualacuity is noted. Contrast sensitivity is also lost, so thatcontours, shadows and color vision are less vivid. Veiling glare can be aproblem as light is scattered by the cataract into the eye. A contrast sensitivitytest should be performed and if a loss in contrast sensitivity isdemonstrated an eye specialist consultation is recommended.
In the developed world, particularly in high-risk groups such as diabetics,it may be advisable to seek medical opinion if a 'halo' is observed aroundstreet lights at night, especially if this phenomenon appears to be confined toone eye only.