Evaluation of enhanced corneal compensation in scanning laser polarimetry: comparison with variable corneal compensation on human eyes undergoing LASIK.

PURPOSE

To investigate the potential advantages of an enhanced corneal compensation algorithm (ECC) compared with variable corneal compensation (VCC), in scanning laser polarimetry.

METHODS

One eye of 15 healthy ametropic subjects was imaged immediately before and 7 days after uncomplicated LASIK surgery. Anterior segment birefringence was assessed at each measurement session. For post-LASIK calculations, either actual post-LASIK corneal retardation (VCC and ECC groups), or the pre-LASIK corneal retardation (VCC* and ECC* groups) was used.

RESULTS

The typical scan score-value was higher for ECC both before and after LASIK (P < 0.01), and it was not influenced by LASIK in either compensation method. Both the axis and the magnitude of corneal birefringence altered after LASIK (P < 0.01). After LASIK, with VCC* all eyes showed uncompensated birefringence, but with ECC* none did. LASIK had no effect on retinal nerve fiber layer measurements in VCC and ECC methods. In VCC* the LASIK-induced retinal nerve fiber layer thickness change was significant (P < 0.01) in the temporal, superior, and nasal quadrants. After LASIK, the number of significantly altered sectors along the TSNIT plot showed no difference when comparing VCC and ECC, VCC and ECC*, or ECC and ECC*. In contrast, significantly more sectors were altered in VCC* than in either VCC or ECC* (P < 0.001).

CONCLUSIONS

The new ECC software is more effective than VCC in neutralization of atypical polarization pattern and the uncompensated corneal retardation.