Friday, October 14, 2005

Spiral of Tillaux

Rectus Muscle-Insertion Distance from Limbus (mm)

  • Medial - 5.5 * (1 in figure)
  • Inferior - 6.6-6.9 (2 in figure)
  • Lateral - 6.9* (3 in figure)
  • Superior - 7.0-7.7 (4 in figure)

There is of course a range to these values. When the range is omitted in other texts, figures are usually taken from Wolff's Anatomy of the Eye and Orbit. The actual numbers have far greater variation in recent measurements. [IOVS]

The relationships of the extraocular muscles, the ora serrata and the vitreous base have implications for vitreo-retinal surgery. The ora serrata (shown in the figure as black line which is wavy on the nasal side) is approximately 8.5 mm from the temporal limbus and 7.5 mm from the nasal limbus; these numbers come from Wolf's anatomy and represent the most posterior extent of the ora. The vitreous base is 2-4 mm in width and greater generally on the nasal side. The ora bays/dentates are more pronounced on the nasal side (overemphasized by the wavy line in the figure). The extraocular muscles insert close to the ora serrata and within the borders of the vitreous except in the case of the medial rectus which often inserts well in front of the ora serrata (in my experience). The important point is that the extraocular muscle insertions generally fit within the span of vitreous base. Note that the tendon of the medial rectus (#1) is shorter than the others.


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