TFT #

TFT (Tear Film Thickness) are the normal tear film covering the normal ocular surface. 

PLTT #

PLTT (Post Lens Tear Thickness) are defined as the difference in sag of cornea and sag of the contact lens at the apes of the cornea of the cornea over the common cord.

Sodium Fluorescein #

Sodium Fluorescein (NaFl) instillation is the best way to clinically determine the relationship between the back surface of the lens and the cornea¹. This enables us to see a map showing the thickness of the tear layer under the lens.

The intensity of fluorescein (amount seen) varies with the relative thickness of the tear film. Bright green being increased fluorescein, thus large difference between the contact lens and the cornea, and darker, little or no fluorescein between the contact lens and the cornea². 

The absence of NaFl does not necessarily indicate touch. It just means that the tear layer under the lens is too thin to fluoresce, as the minimum TFT for visible fluorescein is 15-20 Microns².

1. Hom MM and Bruce AS. Manual of contact lens prescribing and fitting, Third Edition. 2006:167-174
2. Laäs C, Eksteen C, Booysen D. The art of contact lens fitting. 2005:23-26