gms | German Medical Science

Corneal birefringent properties can influence scanning laser polarimetry (SLP) with fixed compensator. Recently, a new variable cornea compensator was introduced. We investigated wether the new device allows to measure and to compensate changes of corneal polarization axis and magnitude before and after LASIK. The results are compared to scanning laser polarimetry measurements with fixed cornea compensator.

Twenty-six eyes of 16 patients were enrolled in this prospective study. Before myopic LASIK surgery all patients underwent standard ophthalmological examinations, corneal topography, corneal pachymetry, and assessment of pupil diameter. Scanning laser polarimetry was performed with a GDxVCC (LDT, San Diego, USA, software version 5.3.4) within one week before and within 9 days to 7 months after surgery.

The mean preoperative spherical equivalent was -5.4 D and the mean postoperative equivalent was -0.3 D. The mean ablation depth was 61.7 μm. The difference of main slow corneal polarization axis was 9.8° ± 12.8° and the difference of corneal retardation magnitudes was -1.1 nm ±9.0 nm. Using the same preoperative customized corneal compensation before and after LASIK, 11 of 16 SLP parameters of the RNFL changed significantly. However, SLP parameters after LASIK with new postoperative customized corneal compensation revealed no significant difference to preoperative compensated values.

Our results show that there are significant changes of corneal birefringent properties induced by LASIK and that these changes can be detected and ruled out by scanning laser polarimetry with variable but not with fixed corneal compensation. Therefore, the new variable cornea compensator may be of great clinical importance in glaucoma diagnostics because measurements are less affected by the birefringent properties of anterior eye segments.

Supported by the Alfried Krupp von Bohlen und Halbach-Stiftung, Essen, Germany