Looking down on sperm motion: a useful added dimension?

of the object's optical wave‑front in comparison with that of a reference beam. In the paper reviewed here, 1 the DH method used for examining spermatozoa was established with suspensions of protozoa, the flagellated Giardia lamblia (~8–20 µm) and the ciliated Paramecium (~70–140 µm), that bracket the size of a human spermatozoon (~50 µm). The protozoa were placed in 80‑µm‑deep micro‑fluidic chambers (Giardia) or cm‑deep chambers (Paramecium), the light source (a laser beam of 635 nm) was passed through a ground glass screen to reduce " speckle noise " of opalescent solutions, and the software included " proximity correction " to prevent the false tracking of two adjacent motile objects as one, which was further extended to a three‑dimensional box to ensure correct tracking of objects moving in different planes. All standard CASA parameters (curvilinear velocity, straight‑line velocity, average path velocity, wobble, linearity, straightness index) can be quantified from the data, but along the cell' s unrestrained (three‑dimensional) track, rather than along a track restrained to the conventional two‑dimensional plane. Despite the ability to detect Paramecium through 2 cm of stagnant water, the technique was presumably unable to detect spermatozoa in seminal plasma, because it was removed by density gradient centrifugation. These cells were suspended at 1 × 10 6 ml −1 in Ham' s F‑10 medium with 6% (v/v) CO 2 and analyzed at 37°C. Although the chamber depth was not given, it was deep enough to distinguish sperm tracks within volumes of 100 µm × 100 µm × 60 µm over 11–37 s. It is noteworthy that tracks of five spermatozoa assessed simultaneously were parallel, but whether this is fortuitous, or reflects a limitation of the optical method or fluid drift caused by the edges of the viewing chamber was not commented upon. Whether this extension of motility assessment to the third physical dimension will bring clinical benefits remains to be proved. It will not replace routine semen analysis, which is rapidly performed T he assumed association of sperm motility with fertility has long been a preoccupation of clinicians. Whereas assessing fertility of a couple has relatively easy end‑points (time to pregnancy, number of children), assessing motility does not. The many methods developed to determine it include assessing a sperm population subjectively (by grading) and objectively (by measuring its motion‑induced movement into a light beam by spectrophotometry or nephelometry), and making measurements on individual sperm cells (by stroboscopic …