Extreme choroidal thinning in high myopia
PURPOSE: To describe the spectral domain optical coherence tomography characteristics of extreme choroidal thinning in high myopia and demonstrate its compatibility with good visual acuity. METHODS: This was a retrospective observational case review of nonconsecutive myopic patients with extreme choroidal thinning, defined as a subfoveal choroidal thickness of 20 mum or less as measured with spectral domain optical coherence tomography. Clinical features, such as visual acuity, axial length, and spectral domain optical coherence tomography characteristics including choroidal and retinal thicknesses in four quadrants were analyzed. RESULTS: Thirty-six eyes of 20 patients with extreme choroidal thinning were included. Mean subfoveal choroidal thickness was 13.9 +/- 6.0 mum, mean age was 71 years (range, 32-85 years), mean axial length was 30.7 +/- 2.2 mm, and mean follow-up duration was 44.7 +/- 15.4 months. Of these, 25 eyes (70%) had visual acuity of 20/40 or better (mean visual acuity was 20/30), whereas the remaining eyes had mean visual acuity of 20/193. All eyes with extreme choroidal thinning had prominent choroidal vessels seen under the macula documented on color fundus photography and near-infrared reflectance imaging. All eyes with visual acuity poorer than 20/40 had fovea-involving choroidal neovascularization and/or atrophy. In the 25 eyes with good visual acuity, the mean choroidal thickness was thinnest at the nasal zone, followed by inferior, superior, and temporal zones (P = 0.01); and there was no detectable decrease in choroidal thickness over time. The mean retinal thickness was thinner in the fovea and parafoveal zones when compared with highly myopic eyes without extreme choroidal thinning. CONCLUSION: Extreme choroidal thinning in myopic eyes is compatible with good visual acuity of 20/40 or better, may be present in a wide age range, and may not demonstrate any progressive decline over up to 70 months of follow-up; suggesting that choroidal thickness alone is not a reliable indicator of visual function.