Port-wine vascular malformations and glaucoma risk in Sturge-Weber syndrome

Abstract

To the Editor: Sharan and colleagues1Sharan S. Swamy B. Taranath D.A. et al.Port-wine vascular malformations and glaucoma risk in Sturge-Weber syndrome.JAAPOS. 2009; 13: 374-378PubMed Scopus (45) Google Scholar highlight a controversial yet important issue. Based on the biologically plausible assumption that glaucoma might worsen after laser therapy to port-wine stain (PWS), this study looked at data to confirm or negate this hypothesis. However, the answer seems inconclusive and counterintuitive. Contrary to previous belief, the authors concluded that the incidence of glaucoma did not increase with laser treatment compared to no laser treatment for PWS.2Parsa C.F. Sturge-Weber syndrome: A unified pathophysiologic mechanism.Curr Treat Options Neurol. 2008; 10: 47-54Crossref PubMed Scopus (37) Google Scholar Actually, there was a trend toward clinically significant reduction in the incidence of glaucoma (although not statistically significant) in the laser group. Our comments and suggestions regarding this study follow. The extent of PWS would affect the amount of laser delivered and hence would have a bearing on the onset of glaucoma. It would have been nice to have a description of the total surface area affected by PWS, so that the authors' conclusions can be applied to patients with similar lesions. Mentioning the presence or absence of upper lid involvement by PWS would be informative since involvement is strongly associated with the occurrence of glaucoma.3Stevenson R.F. Morin J.D. Ocular findings in naevus flammeus.Can J Ophthalmol. 1975; 10: 136-139PubMed Google Scholar, 4Phelps C.D. The pathogenesis of glaucoma in Sturge-Weber syndrome.Ophthalmology. 1978; 85: 256-281Abstract Full Text PDF Scopus (123) Google Scholar The authors used χ2 test for comparing the children who received laser treatment for the PWS to those who did not in terms of whether or not they developed glaucoma. Fisher's exact test appears more appropriate in comparing the 2 groups (as the 2-by-2 contingency table is associated with relatively small expected cell frequencies, 1 of which is less than 5).5Conover W.J. Practical Nonparametric Statistics.3rd ed. Wiley, New York1999Google Scholar Another relevant statistical approach would have been to calculate the relative risk of developing post-laser glaucoma along with confidence intervals for the same. On performing this analysis, we found that the relative risk of developing glaucoma is 0.65 (95% CI, 0.40-1.05). This actually suggests a protective effect of laser, but it is statistically less significant since the confidence interval just crosses 1. It has been postulated that early-onset glaucoma resembles that of primary infantile glaucoma. Later-onset glaucoma is secondary to elevated episcleral venous pressure, although anomalous angle structures may play a role as well.6Cibis G. Tripayhi R. Tripayhi B. Glaucoma in Sturge-Weber syndrome.Ophthalmology. 1984; 91: 1061-1071Abstract Full Text PDF PubMed Scopus (99) Google Scholar, 7Sullivan T. Clarke M. Morin J. The ocular manifestations of the Sturge–Weber syndrome.J Pediatr Ophthalmol Strabismus. 1992; 29: 349-356PubMed Google Scholar Thus it is difficult to attribute the rise of intraocular pressure(or the lack thereof) entirely to the vascular changes that might occur following laser to the PWS. Simultaneous contribution of trabecular meshwork abnormalities should be kept in mind. Pulse dye laser therapy for cutaneous venous malformation is performed in multiple sittings spaced at 4-6 week intervals.8Léauté-Labrèze C. Boralevi F. Pedespan J.-M. Meymat Y. Taïeb A. Pulsed dye laser for Sturge-Weber syndrome.Arch Dis Child. 2002; 87: 434-435Crossref PubMed Scopus (15) Google Scholar A knowledge of that time frame is important, because with adequate inter-laser time periods, the vessels can establish new collaterals for drainage before the episcleral venous pressure can be raised substantially to cause ocular hypertension/glaucoma. The description of ocular hypertension/glaucoma is confusing. In the results, the authors mention that 24 (58.5%) patients developed ocular hypertension/glaucoma. In Table 1, however, all were considered as having glaucoma. In the discussion, incidence of glaucoma was mentioned as 65.1%, which does not match with the data mentioned previously. The incidence of new-onset glaucoma following laser therapy of PWS is indeed valuable information, and we need further multicentric pooling of data to come to a conclusion. We congratulate the authors for taking the first step in that direction.