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Editors Selection IGR 20-2
Anatomical Structures: Laminar structure and field loss
Comment by Andrew Tatham on:
67171 Prelamina and Lamina Cribrosa in Glaucoma Patients With Unilateral Visual Field Loss, Kim DW; Jeoung JW; Kim YW et al., Investigative Ophthalmology and Visual Science, 2016; 57: 1662-1670
Structural changes to the optic nerve head in glaucoma can be divided into prelaminar and lamina cribrosa (LC) components. Prelaminar changes include thinning due to loss of neural tissue, whereas LC changes include posterior migration and excavation beneath the anterior scleral canal associated with connective tissue remodeling. This study investigated whether patients with a glaucomatous visual field defect in one eye, but normal visual field in the other, exhibit prelaminar or LC structural changes in the perimetrically unaffected eye.
Changes to prelaminar tissue may manifest prior to RNFL and visual changes in some individuals
Swept Source OCT was used to assess 3 parameters: (1) anterior prelaminar depth; (2) prelaminar tissue thickness; and (3) LC depth, all measured relative to a reference line at Bruch’s membrane opening. The study included patients with unilateral glaucomatous visual field loss and a similar number of age-matched healthy controls.
The results of the study confirmed that glaucomatous eyes often have significant changes to the prelaminar and LC tissues. Eyes with glaucomatous visual field loss had thinner prelaminar tissue, greater anterior prelaminar depth and greater LC depth than fellow eyes and eyes of healthy subjects. However, fellow eyes also had significantly thinner prelaminar tissue and greater prelaminar depth than controls, despite having normal visual fields and similar retinal nerve fiber layer (RNFL) thickness as the healthy eyes. This suggests that changes to prelaminar tissue may manifest prior to RNFL and visual changes in some individuals. In addition, eyes with higher initial intraocular pressure (IOP) tended to have thinner prelaminar tissue, suggesting that IOP-related stress may affect prelaminar tissue early in the disease process.
The study suggests that OCT assessment of prelaminar and LC structures may allow earlier detection of glaucoma than some currently used parameters
Of course it is important to acknowledge that this was a cross-sectional study and longitudinal studies are needed to better elucidate the temporal relationship between prelaminar, LC, RNFL and visual field changes. In addition most of the patients with glaucoma had untreated IOP of ≤ 21 mmHg. It is conceivable that the temporal relationship of glaucomatous changes may differ depending on the relative contribution of IOP-dependent and independent factors to the pathogenesis. Nevertheless, the study suggests that OCT assessment of prelaminar and LC structures may allow earlier detection of glaucoma than some currently used parameters.
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