Fluorescent imaging of single helicene molecules is applied to study the optical activity of chiral fluorophores. In contrast to the previous report by Hassey et al. (Science 2006, 314, 1437), the dissymmetry factors of single chiral fluorophores are found not to differ significantly from the bulk value of |g| < 10(-4) at 457 nm. Linear dichroism and birefringence of the dichroic mirror inside the fluorescence microscope change the polarization state of the incoming laser beam significantly; i.e., circular polarized light sent into the microscope becomes highly elliptically polarized after reflection from the dichroic mirror. Compensation for this effect should be made to avoid artifacts brought by linear dichroism in single immobilized molecules.

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Third-degree tear occurs in association with less than 1 per cent of vaginal deliveries, but occult sphincter injury occurs at one-third of deliveries and may be significant in later life. Incontinence may result from sphincter damage or nerve injury, or both. Risk factors for these injuries can be identified. Clinical evaluation, anorectal physiology and endoanal ultrasonography allow accurate planning of subsequent surgery. Overlapping anterior anal sphincter repair provides symptomatic control of continence in 80 per cent of patients. Repair of an acute anal sphincter injury after a third-degree tear is controversial and a defined policy should be agreed between obstetric and colorectal teams.

Oral nifedipine reduces resting anal pressure. It is well tolerated and offers an alternative treatment for chronic anal fissure.