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Cataract

2007 Schools Wikipedia Selection. Related subjects: Health and medicine

   CAPTION: Cataract
   Classifications and external resources

   Magnified view of cataract in human eye, seen on examination with a
   slit lamp using diffuse illumination
     ICD- 10   H 25.- H 26., H 28., Q 12.0
     ICD- 9    366
   DiseasesDB  2179
   MedlinePlus 001001
   Human eye cross-sectional view, showing position of human lens.
   Courtesy NIH National Eye Institute
   Enlarge
   Human eye cross-sectional view, showing position of human lens.
   Courtesy NIH National Eye Institute
   Human eye cross-sectional view, showing position of human lens.
   Courtesy NIH National Eye Institute
   Enlarge
   Human eye cross-sectional view, showing position of human lens.
   Courtesy NIH National Eye Institute

   A cataract is an opacity that develops in the crystalline lens of the
   eye or in its envelope. Early on in the development of senile cataract
   the power of the crystaline lens may be increased, causing myopia, and
   the gradual yellowing and opacification of the lens may reduce the
   perception of blue colours. Cataracts typically progress slowly to
   cause vision loss and are potentially blinding if untreated. Moreover,
   with time the cataract cortex liquefies to form a milky white fluid in
   a Morgagnian Cataract, and can cause severe inflammation if the lens
   capsule ruptures and leaks. Untreated, the cataract can cause
   phacomorphic glaucoma. Very advanced cataracts with weak zonules are
   liable to dislocation anteriorly or posteriorly. Such spontaneous
   posterior dislocations (akin to the earliest surgical procedure of
   couching) in ancient times were regarded as a blessing from the
   heavens, because it restored some perception of light in the
   bilaterally affected patients.

   Cataract derives from the Latin cataracta meaning "waterfall" and the
   Greek kataraktes and katarrhaktes, from katarassein meaning "to dash
   down" (kata-, "down"; arassein, "to strike, dash"). As rapidly running
   water turns white, the term may later have been used metaphorically to
   describe the similar appearance of mature ocular opacities. In Latin,
   cataracta had the alternate meaning, " portcullis", so it is also
   possible that the name came about through the sense of "obstruction".

Causes

   Normal vision. Courtesy National Institutes of Health, USA (NIH).
   Enlarge
   Normal vision. Courtesy National Institutes of Health, USA ( NIH).
   Hazy view as seen by a person with a cataract, Courtesy NIH
   Enlarge
   Hazy view as seen by a person with a cataract, Courtesy NIH

   Cataracts form for a variety of reasons, including long-term
   ultraviolet exposure, secondary effects of diseases such as diabetes,
   or simply due to advanced age; they are usually a result of
   denaturation of lens proteins. Genetic factors are often a cause of
   congenital cataracts and positive family history may also play a role
   in predisposing someone to cataracts at an earlier age, a phenomenon of
   "anticipation" in pre-senile cataracts. Cataracts can also be produced
   by eye injury or physical trauma. A study among Icelandair pilots
   showed commercial airline pilots as three times more likely to develop
   cataracts than people with non-flying jobs. This is thought to be
   caused by excessive exposure to radiation coming from outer space.
   Cataracts are also unusually common in persons exposed to infrared
   radiation, such as glassblowers who suffer from "exfoliation syndrome".
   Exposure to microwave radiation can cause cataracts.

   Cataracts may be partial or complete, stationary or progressive, hard
   or soft.

Epidemiology

   Cataracts are the leading cause of blindness in the world.

   In the United States, age-related lenticular changes have been reported
   in 42% of those between the ages of 52 to 64, 60% of those between the
   ages 65 and 74, and 91% of those between the ages of 75 and 85.

Cataract surgery

   Cataract surgery, using a temporal approach phacoemulsification probe
   (in right hand) and "chopper"(in left hand) being done under operating
   microscope at a Navy medical center
   Enlarge
   Cataract surgery, using a temporal approach phacoemulsification probe
   (in right hand) and "chopper"(in left hand) being done under operating
   microscope at a Navy medical centre

   The most effective and common treatment is to surgically remove the
   cloudy lens. There are two types of surgery that can be used to remove
   cataracts, extra-capsular and intra-capsular surgery. Extra-capsular
   surgery consists of removing the lens but leaving the majority of the
   lens capsule intact. High frequency sound waves ( phacoemulsification)
   are sometimes used to break up the lens before extraction.
   Intra-capsular surgery involves removing the entire lens of the eye,
   including the lens capsule, but it is rarely performed in modern
   practice. In either extra-capsular surgery or intra-capsular surgery,
   the cataractous lens is removed & replaced with a plastic lens (an
   intraocular lens implant) which remains permanently in the eye.

   Cataract operations are usually performed using a local anaesthetic and
   the patient will be allowed to go home the same day. Recent
   improvements in intraocular technology now allow cataract patients to
   choose a multifocal lens to create a visual environment where they are
   less dependent on glasses. Traditional intraocular lens were monofocal.
   Medicare has allowed physicians, for the first time, to bill patients
   for this advanced lens design.

   Complications after cataract surgery, including posterior capsular
   opacification and retinal detachment, are possible.

Prevention

   Although cataracts have no scientifically proven prevention, it is
   sometimes said that wearing ultraviolet-protecting sunglasses may slow
   the development of cataracts. Regular intake of antioxidants (such as
   vitamin C and E) is theoretically helpful, but this is also not proven.

Recent research

   Although statins are known for their ability to lower lipids, they are
   also believed to have antioxidant qualities. It is believed that
   oxidative stress plays a role in the development of nuclear cataracts,
   which are the most common type of age-related cataract. To explore the
   relationship between nuclear cataracts and statin use, a group of
   researchers took a group of 1299 patients who were at risk of
   developing nuclear cataracts and gave some of them statins. Their
   results suggest that statin use in a general population may be
   associated with a lower risk of developing nuclear cataract.

Types of cataracts

   Bilateral cataracts in an infant due to Congenital Rubella Syndrome,
   courtesy CDC
   Enlarge
   Bilateral cataracts in an infant due to Congenital Rubella Syndrome,
   courtesy CDC

   The following is a classification of the various types of cataracts.
   This is not comprehensive and other unusual types may be noted.
     * Classified by etiology

          + Age-related cataract

               o Immature Senile Cataract (IMSC) - partially opaque lens,
                 disc view hazy
               o Mature Senile Cataract (MSC) - Completely opaque lens, no
                 disc view
               o Hypermature Senile Cataract (HMSC) - Liquefied cortical
                 matter: Morgagnian Cataract

          + Congenital cataract

               o Sutural cataract
               o Lamellar cataract
               o Zonular cataract
               o Total cataract

          + Secondary cataract

   Slit lamp photo of Anterior capsular opacification visible few months
   after implantation of Intraocular lens in eye, magnified view
   Enlarge
   Slit lamp photo of Anterior capsular opacification visible few months
   after implantation of Intraocular lens in eye, magnified view

               o Drug-induced cataract (e.g. Corticosteroids)

          + Traumatic cataract

               o Blunt trauma (capsule usually intact)
               o Penetrating trauma (capsular rupture & leakage of lens
                 material - calls for an emergency surgery for extraction
                 of lens and leaked material to minimise further damage)

     * Classified by location of opacity within lens structure (However,
       mixed morphology is quite commonly seen, e.g. PSC with nuclear
       changes & cortical spokes of cataract)

          + Anterior cortical cataract
          + Anterior polar cataract
          + Anterior subcapsular cataract

   Slit lamp photo of Posterior capsular opacification visible few months
   after implantation of Intraocular lens in eye, seen on
   retroillumination
   Enlarge
   Slit lamp photo of Posterior capsular opacification visible few months
   after implantation of Intraocular lens in eye, seen on
   retroillumination

          + Nuclear cataract - Grading correlates with hardness &
            difficulty of surgical removal

               o 1 - Grey
               o 2 - Yellow
               o 3 - Amber
               o 4 - Brown/Black (Note: "Black cataract" translated in
                 some languages (like Hindi) refers to Glaucoma, not the
                 colour of the lens nucleus)

          + Posterior cortical cataract
          + Posterior polar cataract (importance lies in higher risk of
            complication - posterior capuslar tears during surgery)
          + Posterior subcapsular cataract (PSC) (clinically common)

               o After-cataract - posterior capsular opacification
                 subsequent to a successful extracapsular cataract surgery
                 (usually within 3 months - 2 years) with or without IOL
                 implantation. Requires a quick & painless office
                 procedure with Nd:YAG laser capsulotomy to restore
                 optical clarity.

Associations with systemic conditions

     * Chromosomal disorders

          + Alport's syndrome
          + Cri-du-chat syndrome
          + Conradi's syndrome
          + Myotonia dystrophica
          + Patau's syndrome
          + Schmid-Fraccaro syndrome
          + Trisomy 18 ( Edward's syndrome)
          + Turner's syndrome

     * Disease of the skin and mucous membranes

          + Atopic dermatitis
          + Basal-cell nevus syndrome
          + Ichthyosis
          + Pemphigus

     * Metabolic and nutrition diseases

          + Aminoaciduria ( Lowe's syndrome)
          + Diabetes mellitus
          + Fabry's disease
          + Galactosemia
          + Homocystinuria
          + Hypervitaminosis D
          + Hyperparathyroidism
          + Hypothyroidism
          + Mucopolysaccharidoses
          + Wilson's disease

     * Infectious diseases

          + Congenital

               o Congential herpes simplex
               o Congenital syphilis
               o Cytomegalic inclusion disease
               o Rubella

          + Others

               o Cysticercosis
               o Leprosy
               o Onchocerciasis
               o Toxoplasmosis

     * Toxic substances introduced systemically

          + Corticosteroids
          + Haloperidol
          + Miotics
          + Triparanol

   Retrieved from " http://en.wikipedia.org/wiki/Cataract"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
