Cataract (dull red reflex). Minor opacifications of the crystalline lens are best seen by examining the red reflex through ophthalmoscopy. The pupillary aperture is viewed through an ophthalmoscope by using a lens of + 10 dioptres (the examiner's own refractive error should be added to the + 10 dioptres). The viewing distance is about 5 to 10 cm.
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