Fig. 7.

Hypothetical mechanisms of the formation and regeneration of outer lamellar and full-thickness macular holes. a Normal fovea. The Müller cell cone in the foveola is shown in pink. The black lines indicate the main and side processes of the z-shaped Müller cells of the foveal walls and parafovea. The arrows indicate traction vectors which are effective in the normal fovea. The fovea externa is formed by the elongated photoreceptor outer segments and is visible by the inclined courses of the external limiting membrane (ELM) and ellipsoid zone (EZ) lines. The horizontal layer of the Müller cell cone keeps the inner layers of the foveal walls together, and the vertical stalk of the Müller cell cone prevents an elevation of the inner layers of the foveal walls. The outer processes of the Müller cells of the foveal walls provide the structural stability of the outer layers, by tight-like junctions between these processes and photoreceptor cells, especially in the outer part of the outer nuclear layer (ONL), and by constitution of the ELM. Müller cells of the foveal walls may also regulate the slope of the ELM in the fovea externa. The side processes of the cells in the outer plexiform layer (OPL) are connected; horizontal contraction of these processes produces a centrifugal displacement of Henle fibers resulting in a steeper slope of the ELM in the fovea externa. b–d Formation (b) and closure (c) of outer lamellar holes, and regeneration of the foveal shape (d). The presumed Müller cell-mediated tissue movements are indicated by red arrows. Blue arrows indicate traction exerted by the posterior hyaloid. e–g Formation (e) and closure (f) of full-thickness macular holes, and regeneration of the foveal shape (g). GCL, ganglion cell layer; HFL, Henle fiber layer; INL, inner nuclear layer; IPL, inner plexiform layer; IZ, interdigitation zone; NFL, nerve fiber layer; RPE, retinal pigment epithelium