ANDREW MCCLENAGHAN / SCIENCE PHOTO LIBRARY ANDREW MCCLENAGHAN / SCIENCE PHOTO LIBRARY
Optician using a keratometer to measure the radius of curvature of the patient's cornea. A reading is taken by superimposing two patterns projected onto the cornea. Accurate measurements of the curvature are needed when fitting contact lenses, and when investigating disorders such as astigmatism (ab- normal curvature: surface resembles an egg rather than a sphere) and glaucoma (excessive pressure of internal fluid).
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