Cataracts

Background

• A cataract is the result of a gradual thickening of the lens and loss of transparency.
• The exact mechanism behind cataracts is not known but nuclear sclerosis– which occurs when new cortical layers are added causing compression and hardening of the central nucleus of the lens.
  • A change in the fibrous content of the lens, changes in epithelial growth and death, and a decreased transfer of water and nutrients into the lens is also thought to play a role.
  • Associated with diabetes, smoking, statins, steroid use; eye surgery
• Cataracts are common (up to 20% of the population will get a cataract; and accounts for almost half of worldwide blindness)
• Can be classified by type (area of lens affected)
  • Nuclear cataracts- cause reduced contrast and colour intensity; the person has difficulty recognizing faces or car number plates. The person often retains good reading vision for many years.
  • Cortical cataracts- cause problems with glare when driving and difficulty reading; the person finds that sunlight is uncomfortable in winter (due to low sun on the horizon).
  • Subcapsular cataracts- cause difficulty in daytime driving and difficulty reading, and are visually disabling in good lighting

Presentation

• A gradual, painless, decrease in visual acuity.
• Glare is a comon complaint (disproportionate reaction to brightness( which may also manifest as a decrease in contrast sensitivity and/or colour vision.
• A risk factor for cataracts is myopic vision, and often, at the onset of cataracts, patients will require an increase of their prescription.  This is in contrast to presbyopic patients who can get temporary restoration of their near-sight.
• On examination
  • The classic sign is an absent/unclear red reflex.
  • Examination of the lens may show general opacification within the lens (nuclear type), opacification in the Posterior subcapsular space, or spoke-like opacification (cortical type).
  • Visual acuity and colour saturation may be reduced.
  • A RAPD may be present if the cataract is preventing a significant amount of light from entering the eye.

Management

• If the cataract is not causing major problems, the cataract may be left and monitored for any progression.  If the patient is having symptoms, surgical removal and ocular lens implant is the mainstay of management for patients.
  • Most patients will have Phacoemulsification + IOL implant