Experience in clinical examination of corneal sensitivity; corneal sensitivity and the naso-lacrimal reflex after retrobulbar anaesthesia.

AN evaluation of the corneal sensitivity is an important part of many general clinical examinations and of all ophthalmological, neurological, and otological examinations. Interest in corneal sensitivity was already alive at the beginning of the 19th century, but an exact method for measuring it was not known until von Frey (1894) introduced a method, using different calibres and lengths of hair. When a hair is pressed against a surface and thereby bent, the elastic power in the hair exerts a counter pressure, which may be measured by pressing the hair on to a scale. For exact measurements of the corneal sensitivity, it is necessary to have a test-battery of hairs of different values, but, for clinical application this is often impracticable. Further, the constancy of the power of the hair varies to some extent with the moisture of the atmosphere. These disadvantages have prevented von Frey's method from becoming popular. At the present time corneal sensitivity is usually tested by means of a piece of cotton wool finely twisted in the form of a pointed brush. The cornea is lightly touched or brushed with the cotton wool, and this somewhat unequal stimulus elicits a more or less paintul sensation and a blinking reflex. The patient is asked to say whether this sensation is felt " normally ", or more on one side than the other. There is therefore a need for a practical clinical test which will give reproducible and exact results in the hands of different examiners.