The Incidence of Blindness Due to Idiopathic Intracranial Hypertension in the UK

Purpose: To determine the incidence of blindness secondary to idiopathic intracranial hypertension (IIH) in the United Kingdom. Methods: New cases of blindness occurring secondary to IIH were identified prospectively through the British Ophthalmological Surveillance Unit (BOSU) from October 2005 to November 2006. Only idiopathic cases of intracranial hypertension and those meeting the World Health Organisation's definition of blindness were included. Cases that were already blind or had already been blind registered before the study period were excluded. Results: There were 24 new cases of registerable blindness secondary to IIH reported during the 12 month period. Questionnaires were completed for 19 cases. Of these 19 cases, 3 were not truly idiopathic and 3 cases did not fulfil the strict criteria for blindness. One case was a duplicate report. There were 12 definite cases of blindness secondary to IIH giving a UK incidence of blindness secondary to IIH of 0.6-2% (assuming a UK population of 63.2 million and an incidence of IIH of 1-3/100,000). If the 5 cases reported as blind but without a completed questionnaire are assumed to be true cases then the incidence of blindness would be 1-3%. Conclusions: The results of this study suggest that approximately 1-2% of new cases of IIH are likely to become blind in a given year. This contrasts with rates of between 4-10% reported previously in hospital-based studies, but may be a more accurate figure for the population as a whole. Under-ascertainment and improving standards of care may also have contributed to the lower figure than previously reported.