Lens

Age-related cataract

• Subcapsular ( Fig. 9.1 ): (a) anterior lies directly under the lens capsule, and (b) posterior lies just in front of the posterior capsule and appears black on retroillumination; the latter often has a more profound effect on vision than a comparable nuclear or cortical cataract, with glare and poor near vision.

  

• Nuclear: often associated with myopia due to an increase in the refractive index of the nucleus; when advanced, the nucleus appears brown ( Fig. 9.2 ).

  

• Cortical: starts as clefts and vacuoles between lens fibres ( Fig. 9.3 ) due to hydration of the cortex and evolves into wedge-shaped or radial spoke-like opacities ( Fig. 9.4 ).

  
  

• Christmas tree : polychromatic opacities ( Fig. 9.5 ).

  

• Cataract maturity: (a) immature (lens is partially opaque), (b) mature (lens is completely opaque), (c) hypermature (shrunken and wrinkled capsule; Fig. 9.6 ), and (d) Morgagnian cataract (inferior sinking of nucleus in a liquefied cortex; Fig. 9.7 ).

  
  

Cataract in systemic diseases

• Diabetes mellitus: hyperglycaemia leads to the overaccumulation of metabolic products in the lens, initially leading to fluctuating refraction and later to cataract, particularly accelerated age-related nuclear.

• Myotonic dystrophy: fine cortical iridescent opacities that evolve into a visually disabling stellate posterior subcapsular cataract ( Fig. 9.8 ).

  

• Atopic dermatitis: dense anterior subcapsular plaque is characteristic ( Fig. 9.9 ).

  

• NF2: cataract develops in approximately 60% of patients, often prior to the age of 30 years.

Causes of secondary cataract

A secondary (complicated) cataract develops as a result of other primary ocular disease such as the following:

• Chronic anterior uveitis: cataract may be caused both by inflammation and by the steroids; progresses more rapidly in the presence of posterior synechiae ( Fig. 9.10 ).

  

• Acute congestive angle closure: small, grey-white, anterior opacities within the pupillary area (glaukomflecken; Fig. 9.11 ).

  

• High (pathological) myopia: posterior subcapsular opacities and early onset nuclear sclerosis.

• Hereditary fundus dystrophies: retinitis pigmentosa, Leber congenital amaurosis, gyrate atrophy, and Stickler syndrome (see Chapter 15 ).

Causes of traumatic cataract

• Penetrating trauma.

• Blunt trauma may cause a characteristic flower-shaped opacity ( Fig. 9.12 ).

  

• Electric shock.

• Infrared radiation (e.g. occupational exposure).

• Ionizing radiation (e.g. for ocular tumours).