Choroidal thickness and risk characteristics of eyes with myopic choroidal neovascularization (2013)

Editor, The risk factors and pathogenesis for myopic choroidal neovascularization (mCNV) are not well understood (Ohno-Matsui et al. 2003; Ikuno et al. 2008, 2010). Recently, new imaging technologies that quantify choroidal thinning and staphyloma height have suggested that these may be additional risk factors for mCNV (Ikuno & Tano 2009; Fujiwara et al. 2009). The present study aims to further examine the potential association between variation in choroidal thickness and mCNV. We conducted a prospective observational study of Asian patients with unilateral active mCNV (confirmed with fluorescein angiograph) and bilateral high myopia (spherical equivalent refractive error <-6D or axial length >26.0 mm). Myopic maculopathy was graded with colour fundus photograph according to the Avila classification (M0–M5). Lacquer crack grading was according to Ikuno et al. (2010) (L0–L2). SD-OCT scan was performed using the Heidelberg Spectralis (version 5.3.2.0; Heidelberg Engineering, Heidelberg, Germany). The baseline foveal horizontal section was used for the measurements of (i) choroidal thickness (Ikuno & Tano 2009; Fujiwara et al. 2009) subfoveally and at 1.5 mm superiorly, inferiorly, nasally and temporally; (ii) central foveal thickness; and (iii) posterior staphyloma height (Fig. 1). Averages of two independent clinicians’ measurements were used for analysis. Where measurements differed >15%, a final measurement was agreed after open arbitration. Enhanced depth imaging mode was not used, but all eyes still showed this clear interface because of choroidal thinning. Statistical analyses were performed using r version 2.14.2 (R Development Core Team, 2012). Wilcoxon’s rank-sum test or Fisher’s exact test was conducted as appropriate to assess the univariate association of ocular parameters with mCNV and fellow eyes due to small sample size. Optical coherence tomography (OCT) image and morphologic parameters measured in this study. The choroidal thickness (CT) was measured from the outer surface of the retinal pigment epithelium (RPE) complex (curved dotted line) to the inner sclera border subfoveally, and 1.5 mm nasally and temporally (illustrated). The posterior staphyloma height was measured as the vertical distance between the subfoveal RPE line and the RPE at a point 3 mm nasally and temporally from the fovea (block arrows). Fifteen patients (14 women and 1 men) aged 39–73 years (mean, 57.8; SD, 10.57) were included. The mean spherical equivalent refractive error was −9.4D (SD, 1.5) in the affected eye and −8.5D (SD, 1.1) in the fellow eye. The mean axial length was 29.00 mm (SD, 1.1) in the affected eye and 28.3 mm (SD, 1.5) in the fellow eye (Table 1). The mean presenting vision was 0.7 LogMAR (range, 0.02–1.5; SD, 0.6), and mean central retinal thickness was 374.50 μm (SD, 175.1) in the affected eye. Myopic choroidal neovascularization eyes had higher grades of myopic maculopathy (3.6 versus 2.38 p = 0.002) and higher lacquer crack grades (1.47 versus 0.62, p = 0.006) than fellow eyes. Average posterior staphyloma height was steeper in mCNV eyes (415.5 μm) than in fellow eyes (336.2 μm), although this was not statistically significant. The mean choroidal thickness was thinnest under the fovea in mCNV eyes (56.4 μm) and fellow eyes (73.1 μm). The inferior quadrant choroidal thickness and average choroidal thickness (by averaging the measurements from all five areas) were significantly reduced in mCNV eyes compared with their fellow eyes (p = 0.007 inferior quadrant, p = 0.036 average). Multiple-variable analysis showed factors associated with mCNV were maculopathy grading (OR, 3.55; 95% CI, 1.54–12.06; p = 0.001), lacquer crack grading (OR, 3.69; 95% CI, 1.45–11.59; p = 0.005) and inferior choroidal thickness (OR, 0.97; 95% CI, 0.95–0.99; p = 0.008). We demonstrated subfoveal suppression of choroidal thickness in mCNV eyes and their fellow eyes. This has not been reported in highly myopic eyes without mCNV previously (Ikuno & Tano 2009; Fujiwara et al. 2009). This study is limited by small sample size, and thus, the results should be further examined in a larger follow-up study. A follow-up study to observe the incidence of fellow eyes’ mCNV will be helpful to determine the significance of foveal suppression. The current methods of maculopathy grading and staphyloma measurement may not adequately quantify the three-dimensional structure of staphyloma and therefore contributed to the inability of demonstrating this as a significant risk factor from our results. In summary, higher myopic maculopathy grade (especially of three and above), higher lacquer crack grade, and thinner inferior and average choroidal thickness are significant ocular risk factors for mCNV. The regional variation of choroidal thickness may also be important to study in further detail.