Minimum Corneal Vault Necessary To A View Fluorescein Pattern Under Gas Permeable Contact Lenses.

Background: This research study explores the minimum corneal clearance needed to view a Sodium Fluorescein (NaFl) pattern under a gas permeable (GP) contact lens. Current literature indicates the minimum tear layer thickness necessary to view a NaFl pattern is 20 microns while in ortho-keratology lenses, the apical clearance is assumed to be 5-15 microns.
Methods: By manipulating the parameters of GP contact lenses, the minimum tear layer thickness underneath the lens needed to view a NaFl pattern, can be found using the caliper function of the anterior segment Heidelberg Optical Coherence Tomographer (OCT). A Medmount E300 Corneal Topographer was used to assess corneal curvature and predict tear layer thickness under the GP lens. The NaFl pattern was viewed using a Haag-Streit slit lamp biomicroscope with a yellow wratten filter in conjunction with the cobalt blue filter.
Results: The minimum tear thickness needed to view NaFl patterns under a GP lens was determined to be seven microns. The Medmont Studio software demonstrated a high predictability of tear layer thickness under the GP lens.
Conclusions: Current research indicates a tear layer thinner than 20 microns appears dark under GP contact lenses when viewed with slit lamp biomicroscopy. Our research found tear layers as thin as seven microns can be viewed, thus indicating when no NaFl pattern is visible, the corneal clearance is smaller than previous research concludes. The Medmont software also accurately predicted tear layer thickness. The findings have a potential to change the way both GP and ortho-keratology lenses are fit in order to have the most beneficial results to the patient.