Dimensions of the ciliary muscles of Brücke, Müller and Iwanoff and their associations with axial length and glaucoma.

BACKGROUND

To assess the dimensions of Brücke's muscle, as the longitudinal portion, and of Müller's muscle and Iwanoff's muscle combined as circular and radial/reticular portions of the ciliary muscle.

METHODS

The histomorphometric study included human globes that had been enucleated due to an ocular tumor or end-stage glaucoma. After immunohistochemical staining of the ciliary muscles, the histology slides were examined under a light microscope applying a digitized image analysis system.

RESULTS

The study included 55 globes [axial length 25.6 ± 3.0 mm (range 21.0 mm-36.0 mm)] from 55 patients [mean age, 33.7 ± 18.3 years (range:1-66 years)]. Length of Brücke's muscle (mean 3.40 ± 0.76 mm) increased with longer axial length (P < 0.001; regression coefficient beta: 0.52) and was not significantly associated with age (P = 0.12), presence of glaucoma (P = 0.11) or Brücke's muscle thickness at the scleral spur (P = 0.32), at the site of the maximum thickness of the ciliary body (P = 0.84) or at the posterior end of Müller's/Iwanoff's muscle (P = 0.66), or with thickness (P = 0.29) and cross-sectional area (P = 0.85) of Müller's/Iwanoff's muscle. Mean distance between Brücke's muscle end and the ora serrata measured 1.73 ± 1.13 mm and increased with longer axial length (P < 0.001; beta: 0.46). Distance from the scleral spur to the ora serrata (mean: 4.94 ± 1.42 mm; range: 3.08-9.09 mm) increased with longer axial length (P < 0.001; beta: 0.61). Maximal thickness (mean: 245 ± 125 μm) and cross-section area (mean: 0.19 ± 0.11 mm2) of Müller's/Iwanoff's muscle decreased significantly with the diagnosis of glaucoma (P = 0.02;beta:-0.38) and longer axial length (P = 0.03; beta: -0.35).

CONCLUSIONS

Length of Brücke's muscle increased with axial length of the globe, while its cross-sectional area was independent of axial length. Müller's/Iwanoff's muscle decreased in cross-sectional area with longer axis, and in particular with the presence of glaucoma, while the dimensions of Brücke's muscle were not related to glaucoma.