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a very high CAS and severe disease or conversely a very low CAS and very mild disease, as in neither circumstance would the management be influenced. For those patients who have significant but not sight-threatening disease and a low CAS, current evidence favours the use of additional tests if disease-modifying agents are to be considered. An alternative approach is simply to give a short trial of treatment provided the anticipated morbidity for that patient is acceptable.
What Signs Are Helpful for Assessing Severity?
The following features are quantified to assess severity: eyelid swelling, eyelid aperture, exophthalmos (proptosis), eye motility, visual acuity and colour vision. Pupil responses and the appearance of the cornea and optic discs are also noted.
What Value Does the Mnemonic “NOSPECS” Have?
The modified NOSPECS classification (Table 2) was devised in 1977 as a way of summarizing the severity of GO [49], with an assumed rank order attached to the various clinical features. It is now generally accepted that summary scores are of little value in assessing outcomes [4], and there are 2 further disadvantages to NOSPECS. Firstly, the order of features relates poorly to the order in which an efficient examination is performed: class I eyelid retraction, class II soft-tissue involvement, class III exophthalmos, class IV extraocular muscle involvement, class V corneal involvement, class VI visual loss. Secondly, the features are poorly defined. Without accurate definitions scoring patients remains impossible. Despite this, the mnemonic NOSPECS remains a useful reminder of the features that should be assessed.
How Are Signs of Severity Assessed?
A precise and consistent method is required when assessing the various signs of severity. One such method is described in principle below but can be found in more detail at www.eugogo.eu. The order of NOSPECS has been used.
1.Palpebral aperture (Fig. 1): The vertical height of the eyelid in the mid-pupil position is noted after first stabilizing the patient’s head position and fixation to reduce artefacts, and occluding the opposite eye if vertical strabismus is present. Both upper and lower eyelid positions are recorded relative to the respective limbus. Lateral flare is disregarded.
2.Soft-tissue involvement: Although soft-tissue involvement indicates activity, the degree of soft-tissue swelling also describes severity. The signs are assessed as described in “How Are These Signs Assessed?” and Figure 5.
Fig. 10. Measurement of exophthalmos. A Hertel exophthalmometer, ideally with a single mirror and straight foot plates, is chosen, and the fixed (left) side is positioned fairly firmly against the orbital rim (1) before sliding the other (right) side into a similar position (2). The reference points in red (3 and 4) are kept aligned while the position of the corneal surface is read off from the ruler (5).
Table 3. Scheme for subjectively scoring diplopia after Bahn and Gorman [55]
| Grade I | Intermittent diplopia, present only when patient fatigued |
| Grade II | Inconstant diplopia, present only on lateral or upward gaze |
| Grade III | Constant diplopia, present in primary gaze but correctable with prisms |
| Grade IV | Constant diplopia, not correctable by prisms |
3.Exophthalmos: This is usually measured clinically using a Hertel exophthalmometer. Unfortunately the numerous models available give significantly different readings, and accuracy will depend on using the same instrument, and ideally the same observer [50]. An intercanthal distance is chosen to fit the instrument snugly against the lateral orbital margins at the level of the lateral canthi and prevent horizontal rotation, and the patient looks at the examiner’s eye being used to record the position of the corneal apex, i.e., the examiner’s right eye for the patient’s left eye, etc. The measurement is taken after aligning the reference points on the instrument (Fig. 10). Exophthalmos is defined as a reading 2 mm greater than the upper limit of normal for that patient’s gender, age, and race; however, despite many publications reporting normal ranges, the instruments on which they are based are not always described, and meaningful calibration has yet to be achieved [51–53]. It appears true that women have lower measurements than men, and children have lower measurements than adults, although these decline again with age. Asians have lower measurements than Caucasians who have lower measurements than Black people. Until normal ranges are reported for specified and calibrated instruments, the measured change in exophthalmometry is of the greatest relevance to monitoring [54].
4.Extraocular muscle dysfunction: There are numerous ways of assessing the extraocular muscles; indeed, the lack of a standardized system makes for real difficulties when comparing patient cohorts and surgical outcomes. Some assessments are more relevant to quantifying the severity of GO than others. Subjective diplopia scores [55] are simple and reasonably helpful (Table 3); however, significant changes in limitation of motility will go unrecorded. Additionally, it could be argued that grade II may be less severe than grade I. For example, a patient may have severe but asymmetrical bilateral inferior rectus restriction to which they have adapted well owing to a good prism fusion range, but their fusion may break down daily when tired, leading to intermittent diplopia. By contrast a car driver may be very aware of a much smaller restriction in one medial rectus which is evident daily on lateral gaze. Hence, objective assessments are required to assess therapeutic interventions, and these should include assessment of the capacity for fusion.
The extraocular muscles may behave quite differently over the course of GO. Hence, uniocular fields of fixation (UFOFs) are of value as they independently assess the limitation of excursions of each eye [32, 56–58]. The prism cover test and the field of binocular single vision (BSV) reflect changes in both eyes; however, each retains a valuable place in assessment, the first in planning for strabismus surgery and the second as a useful way to monitor change. They remain useful when both eyes are abnormal, unlike the Hess-Lees screen [4]. BSV has been shown to be quantifiable and reproducible [59], and to correlate well with the functional deficit from the patient’s perspective [60]. UFOFs are quantified in either 4 or 6 directions of gaze [56,