Assessing participation bias in a sexual behaviour survey: implications for measuring HIV risk

PURPOSE: To determine risk factors for secondary hemorrhage and poor visual outcome in children with traumatic hyphemas. METHODS: We reviewed 99 eyes of 97 children younger than 18 years who had been hospitalized for hyphema within 48 hours of blunt eye trauma. Inpatient records were examined for race, age, sickle cell trait status, size of hyphema and intraocular pressure at admission, secondary hemorrhage (rebleed of hyphema), and medications while hospitalized. Fifty-five eyes of 53 children had at least 1 month of follow-up or attained best-corrected visual acuity of 20/50 or better at their last outpatient visit. RESULTS: Among 99 eyes of 97 children with traumatic hyphema, secondary hemorrhage occurred in nine eyes (9%). Among 72 eyes of 70 African-American children, secondary hemorrhage occurred in nine eyes (14%), whereas in 27 eyes of 27 white children, there were no secondary hemorrhages. However, when the 14 eyes of 13 sickle cell trait-positive children were excluded from the African-American group, the 57 eyes of sickle cell trait-negative African-American and white children did not have any secondary hemorrhages. The sickle cell trait-positive group had secondary hemorrhages in nine of 14 eyes (64%), significantly (P < .005) different from the 0% rate in the 57 eyes of African-American sickle cell trait-negative and white children. The sickle cell trait-positive group also had higher intraocular pressure and permanent visual impairment. CONCLUSION: Sickle cell trait is a significant risk factor for secondary hemorrhage, increased intraocular pressure, and permanent visual impairment in children who have traumatic hyphemas following blunt trauma.