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Van Herick's technique is a subjective assessment of the ratio of a corneal section width to the gap between the corneal section and iris when a beam is trained just within the limbus from 60º. Many optometrists use this technique as a guide to the potential for future angle shut down and a very narrow angle would be shown by little or no gap behind the section (so where the gap is less than a quarter of the section thickness). In some cases, no gap may be seen at all and in this case most practitioners would exercise some caution prior to dilation. Inter-practitioner variation in grading is a potential problem, as well as a tendency to over-exaggerate the size of the gap by moving the section too far on to the cornea. Having said that, large differences between the two eyes that cannot be explained by larger anisometropia or previous disease are best viewed with suspicion. Similarly, repeat readings suggesting a reduction in gap, perhaps in a maturing cataract patient, are similarly significant and should influence management.
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