Development of a low-cost confocal instrument to measure the axial dimensions of components in the anterior section of the eye

We report on the development of a non-contact, low cost instrument based upon confocal microscopy that is capable of rapidly and accurately measuring changes in the axial dimensions of components in the anterior section of the eye. The performance of the instrument was tested by applying an oil film to a vertically mounted artificial cornea to simulate a breaking up tear film. By measuring the influence of lubricating eye drops on the thickness of the human cornea and tear film in vivo with a commercial, interferometer based instrument, we show the need for higher resolution instruments. It was found that the new instrument measured a change in thickness as small as 5 µm in the artificial system with a standard deviation of less than 1 µm. The change of thickness in the in vivo cornea was measured accurately with the interferometer based instrument, but no distinction between the thickness of the cornea and that of the tear film was possible. We therefore believe that the new confocal instrument and its further developments will play an important role in the fast and accurate measurement of tear film and corneal thickness and also in relation to glaucoma screening with applanation tonometry.