Influence of corneal refractive surgery on scanning laser polarimetry

In order to improve the accuracy of glaucoma diagnostics, the use of the modern imaging technologies in routine practice has become necessary. Scanning laser polarimetry (SLP) is one of the widely-used modern imaging technologies. It was developed to measure the thickness of the retinal nerve fibre layer (RNFLT) around the optic nerve head, and to automatically compare the results with the corresponding normative database reference values. The method is based on retardation (slowing down) of the polarized illuminating laser light of the instrument along one axis (“slow axis”) by the birefringent retinal ganglion cell axons. Certain surgical interventions which involve the corneal tissue (such as LASIK) may have clinically significant influence on the corneal retardation, which may potentially lead to misinterpretation of the results. Since corneal refractive surgery has become a widely-used method to correct for ametropia, and many young people, who in future may develop glaucoma, undergo different types of refractive surgery, this issue gained great clinical significance. Following the introduction of GDx-VCC, the next generation of the GDx devices, the influence of corneal retardation became easily manageable, which helped to confirm that the virtual decrease of the post-LASIK polarimetric RNFLT was an artifact, and was not the sign of true RNFLT damage. Recently a new polarimetric software version (enhanced corneal compensation, GDx-ECC) was developed and investigated by different research groups for its ability to remove the LASlK-induced corneal retardation artifacts, proving the new method to be more accurate than GDx-VCC. It all led to a conclusion that since GDx-ECC is able to neutralize changes of corneal retardation induced by LASIK, this software may be even more suitable to long-term follow-up of eyes which undergo corneal refractive surgery.

scanning laser polarimetry, glaucoma, retardation, LASIK, GDx, сканирующая лазерная поляриметрия, глаукома, рефракционная хирургия, GDx-VCC, GDx-ECC

1. Choplin N.T., Schallhorn S.C. The effect of excimer laser photorefractive keratectomy for myopia on retinal nerve fiber layer thickness measurements as determined by scanning laser polarimetry. Ophthalmology 1999; 106: 1019-1023.

2. Choplin N.T., Schallhorn S.C., Sinai M., et al. Retinal nerve fiber layer measurements do not change after LASIK for high myopia as measured by scanning laser polarimetry with custom compensation. Ophthalmology 2005; 112: 92-97.

3. Centofani M., Oddone F., Parravano M., et al. Corneal birefringence changes after laser assisted in situ keratomileusis and their influence on retinal nerve fiber layer thickness measurement by means of scanning laser polarimetry. Br J Ophthalmol 2005; 89: 689-693.

4. Greenfield D.S., Knighton R.W., Huang X.R., et al. Effect of corneal polarization axis on assessment of retinal nerve fiber layer thickness by scanning laser poalrimetry. Am J Ophthalmol 2000; 129: 715-722.

5. Gürses-Özden R., Pons M.E., Barbieri C., et al. Scanning laser polarimetry measurements after laser-assisted in situ keratomileusis. Am J Ophthalmol 2000; 129: 461-464.

6. Holló G., Nagymihály A., Vargha P. Scanning laser polarimetry in corneal haze after excimer laser refractive surgery. J Glaucoma 1997; 6: 359-362.

7. Holló G., Nagy Z., Vargha P., et al. Influence of post-LASIK corneal healing on scanning laser polarimetric measurement of the retinal nerve fibre layer thickness. Br J Ophthalmol 2002; 86: 627-631.

8. Holló G., Katsanos A., Kóthy P., et al. Influence of LASIK on scanning laser polarimetric measurement of the retinal nerve fibre layer with fixed angle and customised corneal polarisation compensation. Br J Ophthalmol 2003; 87: 1241-1246.

9. Katsanos A., Kóthy P., Nagy Z.Z., Holló G. Scanning laser polarimetry of retinal nerve fibre layer thickness after LASIK: stability of the values after the third post-LASIK month. Acta Physiologica Hungarica 2004; 91: 119-131.

10. Lemij H.G., Reus N.J. New developments in scanning laser polarimetry for glaucoma. Curr Opin Ophthalmol 2008; 19: 136-140.

11. Tóth M., Holló G. Enhanced corneal compensation for scanning laser polarimetry on eyes with atypical polarization pattern. Br J Ophthalmology 2005; 89: 1139-1142.

12. Tóth M., Holló G. Evaluation of enhanced corneal compensation in scanning laser polarimetry: comparison with variable corneal compensation in a human LASIK model. J Glaucoma 2006; 15: 53-59.

13. Tsai Y.Y., Lin J.M. Effect of laser-assisted in situ keratomileusis on the retinal nerve fiber layer. Retina 2000; 20: 342-345.