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Can postlens tear thickness be measured using three-dimensional in vivo confocal microscopy?
W Matthew Petroll1, Timmy Kovoor, Patrick M Ladage
1Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9057, USA. Matthew.petroll@utsouthwestern.edu
Eye & Contact Lens
|May 30, 2003
Summary
Confocal microscopy through focusing (CMTF) cannot reliably measure postlens tear thickness (PLTT) under properly fitted contact lenses due to signal interference and limitations in resolution.
Area of Science:
- Ophthalmology
- Biomedical Optics
- Corneal Physiology
Background:
- Confocal microscopy through focusing (CMTF) provides 3D corneal structure visualization.
- Objective measurement of corneal sublayer thickness is possible with CMTF.
Purpose of the Study:
- Investigate the feasibility of using in vivo CMTF to measure postlens tear thickness (PLTT).
Main Methods:
- Evaluated rabbits and humans with rigid gas-permeable (RGP) and silicone hydrogel contact lenses.
- Performed CMTF scans after contact lens insertion, focusing through the lens, tear film, and cornea.
- Calculated PLTT by measuring the distance between the posterior lens surface and the anterior epithelium.
Main Results:
- PLTT was measurable with steep RGP lenses.
- Signal from the posterior lens surface interfered with PLTT measurement for properly fitted RGP and silicone hydrogel lenses.
- PLTT measurements were sensitive to objective lens applanation.
Conclusions:
- The tear film under properly fitted contact lenses is likely thinner than the 9-microm resolution of the CMTF microscope.
- Potential for undetected eye movement and lens contact raises concerns about measurement reliability.