8.2 Fluorescein Pattern Evaluation for RGP Lenses
Key Takeaways
Fluorescein is evaluated under cobalt blue light with a Wratten #12 (yellow barrier) filter; the tear layer between the lens and cornea fluoresces green, and more tears = brighter green
Apical clearance/pooling (bright central green) indicates a steep lens; apical touch/bearing (dark central) indicates a flat lens; alignment is uniform mild green
Midperipheral bearing (dark ring at 3–9 o'clock) signals a steep midperipheral curve; edge lift appears as a bright ring at the lens edge
Central air bubbles indicate the lens is too steep; bubbles under the edge indicate poor edge design
Three-point touch — apical touch plus midperipheral clearance plus peripheral touch — is the ideal pattern for spherical RGP fits on with-the-rule corneas
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
| Observed Pattern | Lens-Shape Cause | Adjustment |
|---|---|---|
| Bright central pooling | Base curve too steep | Flatten BC (↑ mm / ↓ D) |
| Dark central touch | Base curve too flat | Steepen BC (↓ mm / ↑ D) |
| Uniform mild green | Alignment | No change |
| Dark 3–9 ring | Steep midperipheral curve | Flatten IPC; consider aspheric |
| Bright wide edge ring | Edge lift excessive | Steepen PC |
| No edge band | Edge too tight | Flatten PC |
| Central air bubbles | Base curve too steep | Flatten BC; reduce diameter if centration is also high |
| Edge air bubbles | Poor edge design | Modify edge lift; change PC |
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:
- Light apical touch — central dark zone, small (1–2 mm)
- Midperipheral clearance — bright green paracentral ring
- 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
- Wait 20–30 min after lens insertion for settling.
- Instill fluorescein — a small drop (≤ 5 µL) at the lower cul-de-sac; high-volume drops cause false pooling.
- Examine under cobalt blue + Wratten #12 at moderate slit magnification (10–16x).
- Have the patient blink — observe how the pattern reforms after each blink; poor reform indicates poor tear exchange.
- 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.
During fluorescein evaluation of an RGP lens, you observe a bright central green pool with a thin dark ring at 3 and 9 o'clock. What does this pattern most likely indicate, and what adjustment is appropriate?
Apical alignment with good edge lift — no change needed
Lens is too flat centrally and too steep midperipherally — steepen the base curve and flatten the intermediate peripheral curve
Lens is too steep centrally and too steep midperipherally — flatten the base curve and flatten the intermediate peripheral curve
Lens has poor edge design — steepen the peripheral curve only
What filter is required for proper fluorescein pattern evaluation, and why?
A Wratten #12 yellow barrier filter, because it blocks reflected blue light so the green fluorescence is visible
A red filter, because it enhances contrast for dark bearing areas
A neutral density filter, because it reduces glare from the bright green pool
No filter is needed if cobalt blue light is used
Which observation best describes the classic three-point touch pattern for a spherical RGP lens?
Bright central pool with dark peripheral ring only
Total uniform mild green across the whole lens surface
Light central touch, midperipheral clearance, and peripheral touch
Central air bubbles with bright edge ring
Sections you finish are checked off in the contents.