Frequency
Five percent of the general population is affected by thyroid autoimmunity problems. [5]
United States
Bartley et al had reported a frequency of 2.9 cases per 100,000 population per year in men and 16 cases per 100,000 population per year in women. They also observed a bimodal distribution in both sexes, with women showing one peak at age 40-44 years and the other peak at age 60-64 years. In men, the bimodal occurrence was at age 45-49 years and age 65-69 years. Both peaks incidences in men were 5 years later than in women. [12]
International
Tellez et al, in another small study consisting of 155 patients who were newly diagnosed with Graves ophthalmopathy, 26% were male and 36% were female; however, the prevalence was higher in the Europeans, at a rate of 42% versus 7.7% in Asians. Analysis of the data indicated that Europeans were 6.4 times more likely to have Graves ophthalmopathy than Asians. [13] In northern India, the prevalence of Graves orbitopathy was reported as being similar to that in European patients but with less severity. [14]
Predictive
In a report from the European Group on Graves’ Orbitopathy (EUGOGO), 15% of patients who did not have orbitopathy at the time of diagnosis of Graves hyperthyroidism went on to develop orbitopathy. [15]
Mortality/Morbidity
Proptosis due to any cause can compromise visual function and the integrity of the eye.
A proptotic eye not adequately protected by the lids, as with lagophthalmos, can develop exposure punctuate keratopathy. Such disruption of the finely orchestrated homeostatic mechanism to protect the eye will result in corneal compromise, epithelial death, ulceration, and possible corneal perforation in severe cases. At a minimum, the disruption of the tear film layer and incomplete moisturizing of the eye will adversely affect vision and ocular comfort.
Proptosis secondary to a space-occupying process can result in a compressive optic neuropathy. Impeded optic nerve blood flow results in irreversible neuronal death and diminished optic nerve function. Such manifestations as depression of visual and color acuities, pupillary dysfunction, and constriction of visual field can occur.
Proptotic compressive effects are remedied initially by forward protrusion of the eye, thereby reducing the compressive effect within the orbit. However, the eye can extend only so far, and severe stretching can adversely affect the eye and compromise the optic nerve.
A difference of more than 2 mm between the 2 eyes of any given patient is considered abnormal.
Race
Epstein et al state that proptosis is a globe that protrudes 18 mm or less and exophthalmos is protrusion of greater than 18 mm. The upper limit of normal was 21 mm. [16]
In adult white males, the average distance of globe protrusion is 16.5 mm, with the upper limit of normal at 21.7 mm. [17]
In adult African American males, it averages 18.5 mm, with the upper limit of normal reported as 24.7 mm. [17] A separate study reported the average as 18.2 mm, with an upper normal limit of 24.14 mm in males and 22.74 mm in females. [18]
In Mexican adults, males averaged 15.18 mm and females averaged 14.83 mm. [19]
In Tehran, Iran, for the age group of 20-70 years, the average was 14.7 mm. [20]
In Taiwanese adults, comparing normal subjects to those with Graves disease, the normal group had an average reading of 13.91 mm versus 18.32 mm for the Graves disease group. [21]
Even within a group of people, there can be variability. Four ethnic groups in Southern Thailand had exophthalmometry measurement averages ranging from 15.4 mm to 16.6 mm. [22]
In 2477 Turkish patients, the median Hertel measurement was 13 mm, with an upper limit of 17 mm. [23]
In a Dutch study, the upper limit by Hertel measurement was 20 mm in males and 16 mm in females. [24]
Sex
Females also show racial variation. The average in white women was 15.4 mm and the average was 17.8 mm in African American women. The upper limits of normal in each group were 20.1 mm and 23 mm, respectively.
In general, adult females across all races have lower exophthalmometry readings than adult males.
Thyroid orbitopathy has a female preponderance, with a female-to-male ratio of 5:1. However, these differences diminish for the more serve cases of ophthalmopathy. The incidence of severe ophthalmopathy is 3-5%. [25] The female to male ratio in this subgroup is 1.4:1. [26, 8, 27]
Age
Proptosis occurs in both adults and children at any age. Thyroid orbitopathy and the resultant exophthalmos show a predilection for females aged 30-50 years.
Ahmadi et al showed that with increasing age occurs a "linear reduction in ocular protrusion." With advancing age, there was no asymmetries between the eyes noted. [28]
A US pediatric population showed exophthalmometry measurements that increased with increasing age, as one would expect. The results were stratified into age groups with the following corresponding averages:
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Younger than 4 years: 13.2 mm
-
Aged 5-8 years: 14.4 mm
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Aged 9-12 years: 15.2 mm
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Aged 13-17 years: 16.2 mm
Of the 673 subjects in this study, only 2 had a 2-mm difference between the eyes. [29]
In Tehran, Iran, for the age group 6-12 years, the average was 14.2 mm and for the age group 13-19 years, the average was 15.2 mm. [20]
In Chinese children and adolescents from Xiamen, in the age range from 5-17 years, the average exophthalmometry reading was 14.48 mm. [30]
Note that CT scanning and exophthalmometry yield measurements that are not identical, especially when proptosis is present. [31] In addition, parallax errors exist with most commonly used measuring devices. [32]
