Contact lens types:
Hard contact lenses were introduced in 1948. Made of polymethyl-methacrylate (PMMA), they were impermeable to oxygen. These lenses have been superseded by various gas permeable materials. Modern hard lenses are generally known as rigid gas permeable lenses (RGPs).
Soft contact lenses are made from polyhydroxyethylmethacrylate (poly-HEMA). They contain some water making them relatively gas permeable. They are marketed as daily or extended wear lenses for up to 30 day use, disposed of after one day to some months.
Clinical features and diagnostic considerations:
• Acuity assessment is mandatory whenever examining the eyes.
• Examine the eye properly with the use of a high power magnifier with a good light – ideally a slit lamp.
• Use fluorescein sodium in every case to highlight areas of epithelial loss or irregularity.
• Rule out any foreign body on the superior tarsal surface by everting the upper lid, using a cotton bud as a fulcrum.
• Note the movement of the pupils and the clarity or otherwise, of the cornea.
• General physicians should at minimum perform these simple manoeuvres.