Today, uveitis includes all types of intraocular inflammation. With an incidence of approximately 50/100,000 people and a prevalence of 100/100,000,1 uveitis remains one of the leading blinding disorders. All age groups can be affected.
The use of classification criteria, supported by standardisation guidelines, is very important for disorders that have a multitude of associated aetiologies. At least 150 disorders are known to be associated with intraocular inflammation. Some are caused by infectious agents; others may be of autoimmune nature, including some associated with an underlying systemic disease. In 1987, the International Uveitis Study Group (IUSG) developed criteria based on the anatomical localisation of the inflammation.2 In 2004, the Standardization of Uveitis Nomenclature (SUN) workshop analysed these criteria, found them very useful and added criteria for onset, duration and course of the disease.3 Despite being of great help in clinical practice, the IUSG criteria do not include criteria for specific uveitis entities.
The American College of Rheumatology (ACR) has developed classification criteria for many rheumatic diseases and systemic lupus erythematosus.4 These ACR criteria have been developed in a standard process and then validated against large databases, resulting in the highest achievable grade of sensitivity and specificity. Unfortunately, only provisional criteria have been developed for some uveitis-associated disorders, as they have not yet all been validated: these disorders include Vogt-Koyanagi-Harada disease,5 acute retinal necrosis,6 progressive outer retinal necrosis,7 birdshot retinopathy,8 tubulointerstitial nephritis associated uveitis,9 Behçet´s Disease10,11 and, recently, ocular sarcoidosis (submitted for publication).
Classification of Uveitis
Localisation of Uveitis
The most simple but essential criterion is the location of the uveitis. Table 1 shows the updated anatomical classification of uveitis. Important to note here is that the primary site of inflammation defines the type of uveitis. It has to be emphasised that the primary site of inflammation and the complications of the inflammation need to be differentiated. Thus, the existence of macular oedema (MO), a major complication of any type of uveitis, does not directly lead to the naming of ‘posterior uveitis’. This needs an underlying retinal or choroidal inflammation, which may then result in MO. These four anatomical types of uveitis can all be associated with or without other disorders. Illogically, the term ‘pars planitis’ is used for a subset of intermediate uveitis, characterised by snow bank formation and/or snowballs without any associated disorder.
The term ‘retinal vasculitis’ also remains unclear; this will need further work regarding classification. For ocular vasculitis it seems that the Chapel-Hill Classification for systemic vasculitis, which uses the various sizes of the inflamed vessels for their classification, is unhelpful.