Surv Ophthalmol. 1999 Sep-Oct;44(2):171-2.
Department of Ophthalmology, Hadassah University Hospital, Jerusalem, Israel.
A set of whitish rings observed before contact is made during Goldmann-type applanation tonometry can help simplify and speed the examination. The orientation and size of the rings are useful both in aligning the tonometer and in estimating the distance remaining before contact is made. Relying on these whitish rings can also avoid some of the shear-related damage exerted on the corneal epithelium from alignment movements of the tonometer tip after contact with the cornea has been made.
Figure from this article: