Tear interferometry is increasingly used in research to observe the tear film. In clinical practice, interferometric observation can be obtained using a portable instrument designed to be used in conjunction with the slit lamp.
The Tearscope (Keeker Ltd), developed by Guillon in 1986, consists of a 90mm hemispherical cup and a handle with a 15mm diameter viewing hole. The inner surface of the cup is illuminated by a cold cathode ring light source, specifically designed to prevent the tear film from artificially drying out during the examination. The emitted light is diffuse and as such does not need to be in focus to observe the tear film.
The Tearscope allows to visualize the tear layer in a non-invasive way and to perform evaluations that will help in the adaptation of the lenses and in the treatment of dry eye. The cool light from the Tearscope provides a white background against which the tear layer can be seen, and with a range of clinically developed grids, filters and rings specifically for the Tearscope, which can be used to enrich this evaluation. The Tearscope can be used in three ways mounted on a slit lamp, handheld on a slit lamp, or handheld with its own attachable loupe. This manual contains important information on how the Tearscope works, the structure and importance of the tear film, and a series of photographs of normal and abnormal tear patterns to help you interpret what you see.
It allows the doctor to visualize the tear film and interpret the results obtained in a non-invasive way. It determines the quantity, quality and stability of the tear film, so it is necessary:
With the patient's head positioned on the chin rest, the slit lamp should be placed nasally and turned off. The Tearscope will provide the alternative lighting by itself. The tearscope should then be placed as close to the eye as possible and positioned to allow observation through the hole with one of the objectives of the biomicroscope. The closer the Tearscope is to the eye the better, so that the illuminated area can be maximized. Light reflected from the tear film can be seen as a circular white area, 10-12 mm in diameter. Initially, low magnifications are set, although they can be increased up to 20x - 40x to examine interference patterns in detail.
This instrument makes it possible to measure both the non-invasive breakdown time and the study of the lipid layer. Interpretation of the observed interference patterns takes time to refine, but excellent video material is available to serve as training.