Introduction

A cataract is opacity within the lens of the eye, and may affect either one or both eyes. The opacity changes the transparency and refractive index of the lens, resulting in the blurring of a person’s vision. According to the World Health Organisation (WHO, 2007), cataracts account for 47.9% of blindness worldwide. The reported prevalence of childhood cataracts ranges from 1-15 per 10,000 children.

Image taken from: http://en.wikipedia.org/wiki/File:Cataract_in_human_eye.png

Types of Cataract

 

 Nuclear Cataract

 

 

 

Cortical Cataract

 

 

 

Subcapsular Cataract

 

 

 

This occurs at the centre of the lens, and interferes with distance vision. It is the most common type of cataract, and is usually the result of advancing age.

 

 

This begins at the outer rim of the lens, and gradually works towards the centre of the lens. It resembles the spokes of a wheel. It is most commonly found in patients with diabetes.

 

 

This affects the back of the lens, causing glare and blurring of vision. It is the most rapidly progressing type of cataract. Risk factors for the development of a subcapsular cataract are use of steroids, diabetes, and myopia.

Aetiology

Aetiology of Cataracts

Risk Factors

The following are associated with acquired cataract in developed nations:

 

  •   Age (above 60 years of age)
  •   Smoking
  •   Physical trauma
  •   Alcohol consumption
  •   Sunlight exposure
  •   Low educational levels
  •   Poor lifestyle habits inclusive of malnutrition and physical inactivity
  •   Metabolic syndrome
  •   Diabetes mellitus
  •   Systemic corticosteroid use and possibly prolonged administration of high doses of inhaled corticosteroids

Pathogenesis

The lens of the eye is composed of specialised cells arranged in a highly ordered and complex manner. These cells are stratified epithelia and have a very high content of cytoplasmic protein; the crystallins. These proteins, along with the complex structure, impart transparency to the lens.

 

Unlike other epithelia, the lens does not shed nonviable cells. As such, it is particularly susceptible to the degenerative effects of aging on cell structure. The exact pathogenetic mechanisms of this are not known. It has, however been observed that most of the risk factors identified are environmental stressors that lead to the formation of toxins or the impairment of antioxidants.

Clinical Presentation: Symptoms and Signs

 

  •   Opacification of lens is painless, progressive, and highly variable
  • 
  •   Often bilateral but asymmetrical
  •   Common complaints include problems with night driving, reading road signs, and reading fine print
  •   "Myopic shift" (an increase in nearsightedness) happens prior to opacification of lens
  •   Cataracts may present as immature (transmits red reflex), mature (does not transmit red reflex), or hypermature (cortex of lens has liquefied and lens nucleus is mobile within capsule)
  •   Mature and hypermature cataracts can give rise to secondary glaucoma that is associated with a red and painful eye (unlike many other glaucoma's)

 

 

With regards to the presentation of congenital cataracts:

Approximately one-third of congenital cataracts in children are inherited, one third are associated with systemic diseases, and one-third are idiopathic or sporadic.

 

  •   Parent's observation of cataract
  •   Visual behaviour that deviates from normal
  •   Asymmetry of red reflex identified on Bruckner testing (simultaneous red reflex test)
  •   Leukocoria (white pupillary reflex)
  •   Nystagmus
  •   Strabismus (Squint)
  •   Photophobia
  •   Delayed development
  •   Family history of hereditary cataracts
  •   Genetic disorder associated with cataracts

 

Cataracts detected in infants and young children must be referred to a specialist as soon as possible in order to allow for normal visual development and to prevent blindness.

Differential Diagnosis

  •   Macular degeneration
  •   Presbyopia
  •   Retinal disease
  •   Retinoblastoma (in children) 

Diagnosis

This is a typical sequence of diagnosing cataracts.

Slit lamp examination

 

  •   The slit lamp is a binocular microscope

 

  •   Provides a three dimensional view of the eye

 

  •   A beam or "slit" of light is used as opposed to diffuse light

 

  •   Height and width can be adjusted

 

  •   Anatomic features of the eye can be accentuated

 

  •   Provides greater magnification and illumination than most handheld devices

 

  •   Is used to diagnose a number of traumatic and non-traumatic disorders, including cataract

 

 

Image taken from: http://en.wikipedia.org/wiki/Slit_lamp

Posterior capsular opacification on retroillumination with slit lamp

Image taken from: http://en.wikipedia.org/wiki/Cataract_surgery

Prevention

 

There is no proven therapy to prevent either cataract formation or its progression once it has developed. However, the following have been observed to be of benefit in decreasing risk:

  •   Eating a healthy diet
  •   Eating a diet rich in lutein and zeaxanthin
  •   Smoking cessation
  •   Postmenopausal oestrogen use (longer than 10 years)
  •   Vitamin supplementation

 

 

Management

Management options for cataracts

Phacoemulsion

 

  •   Most widely used

 

  •   Most effective

 

  •   Safest

 

  •   The hard lens nucleus is liquefied by an ultrasonic probe

 

  •   Fragments are aspirated, along with soft lens fibres

 

  •   Replacement lens (folded) is placed into empty capsular bag where it gradually unfolds

 

  •   The incision made through lens capsule heals on its own

 

 

Image taken from: http://en.wikipedia.org/wiki/Cataract_surgery

Complications that may result from surgery

      Early complications

     

    • Rupture of posterior capsule (3%)
    • 
    •   Trauma to iris
    •   Prolapsed iris
    •   Wound gape
    •   Haemorrhage in anterior chamber
    •   Rupture of lens capsule with loss of vitreous
    •   Vitreous haemorrhage
    •   Choroidal haemorrhage
    •   Post-operative endophthalmitis

        Late Complications

       

      • Opacification of posterior capsule (20%)
      • 
      •   Cystoid macular oedema
      •   Uveitis
      •   Retinal detachment
      •   Open and closed angle glaucoma
      •   Age-related macular degeneration

       

      Postoperative thickening of the lens capsule frequently occurs over time causing gradual deterioration of vision. This can be treated by splitting the capsule with a laser.

       

      Prognosis

      Postoperatively 95% of patients that have no other complications achieve a corrected acuity of 6/12.

       

      The major risk factors that affect prognosis are diabetes and diabetic retinopathy. Diabetes causes fluctuating blood glucose levels. Occasionally, high blood glucose levels cause oedema and subsequent swelling of the lens. When the blood glucose diffuses, the swelling in the lens also reduces. This repeated action causes cataracts.

       

      In paediatric cataracts, visual acuities of 20/20 to 20/40 may be achieved if cataracts are diagnosed and treated early.

      Summary

      Cataracts are lens opacities that can range in severity from unnoticed dots to total fogging of vision. Cataracts are by far the commonest cause of preventable blindness worldwide.

       

      Age-related causes are most common, although there are also familial or congenital causes. Gradual painless deterioration of vision is the most common symptom reported, with other possible co-existing symptoms such as glare and problems with night driving dependent on the type of cataract.

       

      Early symptoms can be alleviated with spectacles, but to correct vision, surgery is required. Surgery involves the insertion of an intraocular lens to replace the affected one. The exact technique used is determined by the aetiology and density of the cataracts. Phacoemulsification (a form of small incision surgery) is the most frequently used technique. Further investigations such as blood glucose, serum calcium, and liver biochemistry should be considered in order to diagnose any possible underlying metabolic disorder.

       

      It is also worth noting that cataracts may not always be bilateral, and hence, eyes may be managed and treated individually according to the severity of the cataract within each eye. 

      Useful resources

      Websites:

      http://www.cataract-doctor.com/

      Videos:

      http://www.careflash.com/video/cataracts (Cataracts explained in lay terms)

      http://www.rootatlas.com/wordpress/video/866/cartoon-cataract-surgery-video/ 

      (Cataract surgery, Phacoemulsification) My favourite!

      References

      Kumar and Clark Clinical Medicine 7th edition

      UpToDate articles "Cataract", "Cataract in children", and "Slit lamp examination"

      http://www.patient.co.uk/doctor/Cataracts-and-Cataract-Surgery.htm

      All images taken from: http://en.wikipedia.org/wiki/Cataract_surgery

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