Ocular and Clinical Characteristics Associated with the Extent of Posterior Lamina Cribrosa Curve in Normal Tension Glaucoma
Abstract
Although normal-tension glaucoma (NTG) is pathogenetically heterogenous, there have been few attempts to subclassify NTG patients according to the mechanism and anatomy of optic nerve damage. This cross-sectional study was performed to investigate differences in the clinical and ocular characteristics between NTG patient groups stratified according to the degree of posterior lamina cribrosa (LC) curve which was assessed by calculating LC curvature index (LCCI). A total of 101 eyes of 101 treatment naïve NTG patients were included. The optic nerve head was imaged using enhanced-depth-imaging spectral-domain optical coherence tomography in three horizontal B-scan images in each eye. The patients were divided into two groups based on the magnitude of LCCI using a cutoff of known upper 95 percentile value in healthy subjects: a steeply curved LC group (Group 1, 75 eyes, 74.3%) and a relatively flat LC group (Group 2, 26 eyes, 25.7%). NTG eyes with relatively flat LC had lower intraocular pressure, and were associated with greater parapapillary structural alternation and systemic risk factors. These data suggest that assessment of LC morphology may help clinicians seek additional risk factors and make inferences about the mechanism of optic nerve damage in individual patients. Glaucoma is a progressive optic neuropathy characterized by a typical pattern of optic nerve damage and visual field loss. Although elevated intraocular pressure (IOP) is the most important known risk factor for glaucoma onset and progression 1,2 , other factors, including vascular disorders, are considered to contribute to glaucomatous optic nerve damage individually or collectively 3,4. The role of vascular factors may be particularly important in eyes with glaucoma occurring at what are considered normal IOP (normal-tension glaucoma). These vascular risk factors may in themselves be considered diseases, such as peripheral vascular dysfunction, low nocturnal blood pressure, and obstructive sleep apnea. In addition, a group of risk factors is related to neurodegenera-tive disorders in general, such as mitochondrial dysfunction, oxidative damage, and low-grade inflammation. Currently and historically, however, treatment has been targeted only to lowering IOP in both normal-tension glaucoma and high-tension glaucoma. If patients can be stratified according to their predominant pathogenic mechanism (e.g, predominant involvement of IOP-related factors vs. non-IOP related factors), clinicians might be more able to provide a more specific targeted treatment approach to individual patients. The lamina cribrosa (LC) is a mesh-like structure which provides structural and functional support to the retinal ganglion cell (RGC) axons. It has been considered that posterior displacement, compression, and remod-eling of the LC driven by the translaminar pressure difference (TLPD) are the principal pathogenic events 5-7. The LC deformation and/or remodeling can cause blockade of axonal transport, which would ultimately lead to RGC
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