Sir,
We read with interest the article by Vetrugno et al.1 The authors conducted an investigation regarding the effect that posterior capsule opacification (PCO) and subsequent Nd : YAG capsulotomy have on the results of scanning laser polarimetry (SLP) of retinal nerve fibre layer (RNFL) retardation measurements. Considering that pseudophakia in glaucoma is a relatively common condition, and that SLP has been shown to be a useful tool in the diagnosis and follow-up of glaucoma, the issue studied is clinically important.
Vetrugno et al1 found no change in GDx parameters before and after PCO removal (only Symmetry, Inferior Ratio, Superior Nasal, and Tempora-Superior-Nasal-Inferior-Temporal SD showed any modification).
Recently, a preliminary small case series (including GDx maps and PCO photographs) was published, as there was a subsequent larger study with consecutive PCO-affected patients on the same subject.2, 3 In contrast, we concluded that PCO removal is associated to remarkably significant changes in SLP measurements. Briefly, our results suggest that SLP examination with GDx VCC may overestimate RNFL retardation measurements in PCO-affected eyes.
The methods used by Vetrugno et al1 and our group were similar. Nevertheless, some questions are raised that may help to understand the surprising differences in the results, at least in part.
As it is known, anterior segment birefringence (ASB) has to be compensated to ensure accurate RNFL assessment. In the referred paper, SLP was performed on each patient using GDx ACCESS, but there was no mention of whether variable corneal compensation GDx version was used. In this case, the text adds no further details about the procedure. We are unaware whether the ASB was assessed only before capsulotomy, or before and after PCO removal. The latter strategy was chosen in our studies.
Authors can certainly enlighten us in these aspects.
References
Vetrugno M, Masselli F, Greco G, Sisto D, Maino A, Ficarelli S et al. The influence of posterior capsule opacification on scanning laser polarimetry. Eye, advance online publication, 7 April 2006. doi:10.1038/sj.eye.6702323.
Garcia-Medina JJ, Garcia-Medina M, Shahin M, Pinazo-Duran MD . Posterior capsular opacification affects scanning laser polarimetry examination. Graefes Arch Clin Exp Ophthalmol 2006; 244: 520–523.
Garcia-Medina JJ, Garcia-Medina M, Dorta SG, Pinazo-Duran MD, Gallego-Pinazo R, Zanon-Moreno VC . Effect of posterior capsular opacification removal on scanning laser polarimetry measurements. Graefes Arch Clin Exp Ophthalmol, advance online publication, 22 Mar 2006. doi:10.1007/s00417-005-0244-8.
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Garcia-Medina, J., Garcia-Medina, M. & Pinazo-Duran, M. The influence of posterior capsule opacification on scanning laser polarimetry. Eye 21, 264–265 (2007). https://doi.org/10.1038/sj.eye.6702505
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DOI: https://doi.org/10.1038/sj.eye.6702505