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Mourits et al. [11] devised the CAS in 1989. It remains in widespread use, as it is an easy scoring system that allows the majority of patients to be classified as either active or inactive (Table 1). Patients seen for the first time are scored for 7 points, 2 symptoms and 5 soft-tissue signs. Clarifying the presence or absence of both symptoms and signs is best achieved in conjunction with the protocol and notes of the EUGOGO atlas (www.eugogo.eu). On subsequent assessments any significant change in severity is added to the score. Since its inception, it has become apparent that a significant deterioration in any ocular excursion amounts to 8° rather than 5°, and the atlas reflects this (see also the section “How Is Severity Best Classified?” below). The evidence for the value of the CAS lies in studies correlating pretreatment CAS and response to immunomodulation. Using a cut-off of at least 4 points, the positive predictive value of the CAS alone was 80% while the negative predictive value was 64% [33]. A further study showed a significant correlation between TSH receptor antibodies and the CAS [36].

The disadvantages of the CAS relate to 2 aspects. Firstly, all features are given equal weighting, and it is not clear whether this is appropriate. Secondly, it is a poor tool for monitoring change as it employs a binary score, whereby improvement of any feature does not alter the score unless it completely resolves [4].