8.2 Fluorescein Pattern Evaluation for RGP Lenses

8.2 Fluorescein Pattern Evaluation for RGP Lenses

Quick Answer: Instill fluorescein, view under cobalt blue + Wratten #12 yellow barrier filter, and read the green tear pattern. Bright central = steep (pooling); dark central = flat (touch); uniform mild green = alignment; dark 3–9 ring = steep midperiphery; bright edge ring = edge lift; central bubbles = too steep; edge bubbles = poor edge. Three-point touch is the classic ideal for a spherical RGP.

How the Pattern Forms

Sodium fluorescein dye pools in the tear layer between the RGP lens and the cornea. Under cobalt blue illumination, fluorescein fluoresces green. The Wratten #12 (yellow barrier) filter blocks reflected blue light so only the green fluorescence is visible.

Rule of thumb:

• More tears between lens and cornea → brighter green (clearance/pooling)
• Less tears (lens touches cornea) → dark areas (bearing/touch)
• No tears (direct contact) → black

The RGP lens itself does not fluoresce. You are reading the tear lens thickness map that the back-surface geometry creates.

The Six Core Patterns

1. Apical Clearance / Pooling

• Appearance: Bright central green pooling under the lens
• Meaning: The lens is too steep for the cornea — it lifts off the central cornea and traps tears
• Symptoms: Good comfort but poor tear exchange; potential corneal edema with long wear
• Adjustment: Flatten the base curve (increase radius in mm, decrease in diopters); consider a larger diameter if centration is also poor

2. Apical Touch / Bearing

• Appearance: Dark central area where the lens contacts the cornea
• Meaning: The lens is too flat — central cornea bears the lens weight
• Symptoms: Comfort may be reduced; central staining visible after removal
• Adjustment: Steepen the base curve (decrease radius in mm, increase in diopters); if area is small and peripheral fit is good, may accept with monitoring

3. Alignment

• Appearance: Uniform mild green across the central and paracentral zones, with a thin bright band at the edge
• Meaning: Lens back surface matches the corneal shape — ideal central relationship
• Adjustment: None — this is the target for aspheric and some spherical designs

4. Midperipheral Bearing

• Appearance: Dark ring at approximately the 3 and 9 o'clock positions (midperiphery)
• Meaning: The midperipheral curve is too steep relative to the cornea — the lens bears in the midperiphery while possibly clearing centrally
• Symptoms: 3 and 9 o'clock staining after wear; awareness on lateral gaze
• Adjustment: Flatten the intermediate peripheral curve (IPC) or use an aspheric design; reduce lens diameter if bearing is at the very edge

5. Edge Lift

• Appearance: Bright green ring at the lens edge
• Meaning: Tears pool under the edge. Excessive edge lift = edge curve too flat → lens rocks, debris enters, comfort poor. Minimal edge lift (thin bright band) = good — allows tear exchange
• Adjustment: If excessive, steepen the peripheral curve (PC); if none, flatten the PC slightly to allow tear pump

6. Air Bubbles

• Location matters:
  • Central bubbles → lens is too steep (excess central clearance traps air); flatten base curve
  • Under edge bubbles → poor edge design; modify edge lift or PC
• Bubbles never indicate a good fit; they cause staining where they sit

Pattern → Adjustment Reference Table

Three-Point Touch — The Classic Spherical RGP Ideal

For a spherical RGP on a regular with-the-rule cornea, the three-point touch pattern is the traditional ideal:

1. Light apical touch — central dark zone, small (1–2 mm)
2. Midperipheral clearance — bright green paracentral ring
3. Peripheral touch — thin dark ring near the edge where the peripheral curve contacts the cornea

This distributes weight across three zones, minimizes central bearing, and allows a tear pump through the midperipheral clearance. Excess of any one zone (heavy central touch, no midperipheral clearance, or heavy peripheral seal) signals a parameter change.

Evaluation Technique

1. Wait 20–30 min after lens insertion for settling.
2. Instill fluorescein — a small drop (≤ 5 µL) at the lower cul-de-sac; high-volume drops cause false pooling.
3. Examine under cobalt blue + Wratten #12 at moderate slit magnification (10–16x).
4. Have the patient blink — observe how the pattern reforms after each blink; poor reform indicates poor tear exchange.
5. Assess in primary, lateral, and up/down gaze to check for lens decentration and lid interaction effects.

Key Takeaways

• Fluorescein reading requires cobalt blue + Wratten #12; without the yellow barrier filter, blue reflected light obscures the green.
• Bright = tears (clearance); dark = touch (bearing) — that single rule explains most patterns.
• Three-point touch is the classic spherical RGP ideal: apical touch, midperipheral clearance, peripheral touch.
• Bubbles always indicate a problem — central bubbles mean too steep; edge bubbles mean poor edge design.
• Wait 20–30 min after insertion before judging an RGP fit.