Central corneal thickness (CCT)

Method

Corneal thickness at the pupil centre by ultrasound pachymetry or by Scheimpflug or OCT tomographic pachymetry, reported in micrometres. The device is recorded on the edge; ultrasound and optical pachymetry differ by roughly 10 to 20 micrometres and are not poolable.

The method is part of the endpoint identity. Studies measuring the same quantity by a different method are held as separate endpoints.

Notes

Direction is set for the keratoconus and corneal ectasia literature these papers come from, where progressive THINNING is the disease and preservation is the benefit; IN CORNEAL OEDEMA OR ENDOTHELIAL FAILURE THE SAME NUMBER IMPROVES BY FALLING, so the population must be on the edge or the sign is wrong. The near-miss is thinnest-point pachymetry, exported from the same device on the same map but at a different location: in keratoconus the thinnest point is displaced infero-temporally and differs from the pupil-centre value by tens of micrometres, larger than most treatment effects. Distinct also from endothelial cell density in the same panel.