Watch your beam angle

The angle at which the light beam hits the limbus during van Herick assessment is critical to the end result.

A study published in this month's Clinical and Experimental Optometry looked at the accuracy of the van Herick technique as the angle of incidence of the light beam trained on the limbus was varied. The researchers found that any deviation from perpendicular by 10 degrees or more resulted in significant error. Furthermore, the exact observation angle, usually set at 60° 'is not critical' and smaller angles may be used without any impact on accuracy.

? Clinical editor adds: VH is useful for monitoring changes. By setting the observation angle at 60° every time, any inter-user difference in technique that may impact on accuracy is minimised.