OCT Versus Fluorescein Pattern for Evaluating GP Lens Fit
BY STEPHANIE L. WOO, OD, FAAO, FSLS
The conventional method of fitting GP lenses is to use diagnostic lens fitting sets; practitioners choose a lens from a fitting set and place it on the eye, instill fluorescein, then examine the lens-to-cornea fitting relationship via fluorescein pattern (Figure 1). However, one downside to this is that there is subjectivity to this method. There could be a need for precise, objective measurement of GP fittings. With a myriad of new diagnostic instruments, many practitioners want to know about new technologies that may help them with contact lens fitting. Are there instruments or machines that can assist with evaluating GP lenses? Are they vital to fitting contact lenses, or is it still acceptable to simply use a slit lamp? Will imaging equipment dramatically improve the ability to fit contact lenses?
Figure 1. Fluorescein pattern of corneal GP lens through slit lamp.
How Does OCT Compare?
Piotrowiak et al (2014) evaluated the use of anterior segment spectral optical coherence tomography (OCT) to measure the lens-to-cornea fit of GP lenses. The OCT instrument offers a non-contact, non-invasive method to capture valuable information about the tear layer between the GP lens and the cornea. The results were verified with the current criterion standard for GP fitting—fluorescein pattern analysis. Many practitioners have OCT instruments with capabilities to analyze the corneal thickness, GP lens thickness, and the tear layer between the posterior lens surface and the anterior corneal surface.
Twenty-six eyes (14 patients total) were enrolled in the study. Keratometry readings were taken to determine the starting base curve of the initial GP lenses. GP alignment fittings, along with 0.1mm base curve reductions (to give certain apical clearance), were evaluated with typical fluorescein pattern assessment and with OCT.
The number of cases detecting apical clearance was recorded comparing fluorescein pattern to OCT assessment. When the base curve of the GP lens was steepened 0.1mm (meaning the GP fit certainly had central clearance), sensitivity detecting clearance was 92.31% with fluorescein pattern, while sensitivity using the OCT was 76.92%. This means that fluorescein pattern assessment was better compared to OCT at detecting apical clearance. When the base curve was steepened by 0.2mm, fluorescein pattern sensitivity was 100%, while OCT assessment was 96.15%.
Although OCT represents a new method of assessing GP fits (Figure 2), apical clearance detection with current technology demonstrated lower sensitivity compared to fluorescein pattern assessment. The OCT method may not have performed as well because GP fitting is a dynamic process, and the lens position changes from moment to moment on the eye. The scanning of the OCT may be affected by these positional changes. CLS
Figure 2. OCT assessment of tear layer of GP lens.
For references, please visit www.clspectrum.com/references and click on document #247.
Dr. Woo currently practices at Havasu Eye Center in Lake Havasu, Ariz. She is also the treasurer for the Scleral Lens Education Society and is an Advisory Board member for the GPLI. She is a consultant or advisor to Alcon, Blanchard, Bio-Tissue, B+L, Essilor, and X-Cel.