Extrapolation of Central Corneal Topography Into the Periphery

The effect of sodium fluorescein on anterior eye surface measurements

PURPOSE

During image acquisition, certain topographers require the addition of sodium fluorescein (NaFl) dye to the tear film. This study investigates the effect of NaFl dye on corneal topography and tear surface quality.

METHOD

The E300 corneal topographer (Medmont International Pty Ltd., Victoria, Australia) was used to measure ocular surface topography and quality of 57 eyes of 57 healthy individuals without dry eye symptoms, age 35.1 ± 15.2 years (mean ± standard deviation) ranging between 19 and 65 years. The mean of three simulated keratometry values, a variety of corneal shape descriptors, and Tear Film Surface Quality (TFSQ) were measured under three different conditions; without NaFl (baseline), with the addition of a single dose NaFl, and using a double dose of NaFl.

RESULTS

Compared to baseline, the Inferior-Superior (IS) index decreased significantly after a single dose (P = 0.034) or double dose of NaFl (P = 0.030). The corneal surface was significantly more regular without NaFl (P = 0.003) or one insertion of NaFl (P = 0.024) when compared to two doses of NaFl. There was no association with age, or dry eye signs or symptoms on the variance observed in any of the indices between baseline, intervention I, and intervention II (P > 0.05). Agreement between corneal surface indices reduced following the addition of NaFl.

CONCLUSION

In comparison to measurements taken without an ocular dye, one dose of NaFl resulted in increased reliability and consistency in corneal topography measurements using the E300 topographer, but 2 doses decreased reliability and consistency. Practitioners ought to be aware that tear film surface regularity and inferior-superior corneal power changed significantly following the addition of NaFl in those with healthy corneas. Its effect in diseased corneas is unknown.