contact lens primer

Interpreting Fluorescein Patterns

BY TIMOTHY B. EDRINGTON, OD, MS, FAAO, & JOSEPH T. BARR, OD, MS, FAAO
September 2001

Fluorescein pattern (FP) interpretation fine-tunes the contact lens fitting relationship. Five components of the FP should be evaluated: apical (central) fitting relationship; toricity in the tear lens;  peripheral or edge clearance; lens positioning and movement; and lens wetting.

The Outcome

The apical relationship is judged as alignment, touch (flat fit) or clearance (steep fit). Alignment is is characterized by an even and minimal amount of tear fluorescence beneath the optic zone. Others define alignment as maximizing the area of lens bearing beneath the optic zone. For an apical touch fitting relationship, the smaller the area of bearing, the flatter the fitting relationship.

Figure 1. Horizontal bearing on a with-the-rule cornea.

If a non-flexing spherical base curve is applied to the cornea, the toricity in the FP will "equal" the amount and orientation of the corneal toricity. An apical touch FP will exhibit horizontal bearing if the cornea is with the rule (Figure 1) and vertical bearing if the cornea is against the rule. If a toric base curve is applied to a toric cornea, the amount of toricity viewed in the FP will decrease (the degree of ovality will decrease) by the amount of base curve toricity (Figure 2). A rigid lens with a base curve toric by the same amount as the corneal toricity will exhibit a FP pattern similar to that of a spherical lens on a spherical cornea.

	Figure 2. RGP toric lens on a with-the-rule toric cornea.

Conversely, an apical clearance FP will exhibit vertical clearance if the cornea is with the rule and horizontal clearance if the cornea is against the rule. A clearance fit will bear in the periphery of the lens ­ the peripheral bearing will be in the horizontal meridian on a with-the-rule cornea and in the vertical meridian on an against-the-rule cornea.

Peripheral clearance is usually judged to be minimal (acceptable or unacceptable), average or excessive (acceptable or unacceptable). If the peripheral clearance is minimal and unacceptable, lens seal-off with a resulting lack of tear exchange will occur. If the peripheral clearance is excessive and unacceptable, poor lens centration, excessive lens movement, poor comfort or excessive peripheral corneal staining may result.

The Process

When evaluating the FP, locate the areas of lens bearing. If you evaluate primarily the areas of clearance, you might be misled by excessive fluorescein or fluorescein on the front surface of the contact lens. When fitting an intrapalpebral design, evaluate the apical and peripheral fluorescein pattern characteristics when the lens is centered. When fitting a lid-attached design, evaluate the fitting relationship when the lens is positioned superiorly. A Burton lamp with UV lighting or slit-lamp (with the cobalt illumination filter in place) may be used to assess the pattern. The use of a yellow filter for viewing FP's behind the slit-lamp will enhance the fluorescence of the pattern and aid in interpretation.

Dr. Edrington is a professor at the Southern California College of Optometry. E-mail him at tedrington@scco.edu.

Dr. Barr is editor of Contact Lens Spectrum and assistant dean of Clinical Affairs at The Ohio State University College of Optometry.